path: root/common/content/completion.js

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/** @scope modules */

/**
 * Creates a new completion context.
 *
 * @class A class to provide contexts for command completion.
 * Manages the filtering and formatting of completions, and keeps
 * track of the positions and quoting of replacement text. Allows for
 * the creation of sub-contexts with different headers and quoting
 * rules.
 *
 * @param {nsIEditor} editor The editor for which completion is
 *     intended. May be a {CompletionContext} when forking a context,
 *     or a {string} when creating a new one.
 * @param {string} name The name of this context. Used when the
 *     context is forked.
 * @param {number} offset The offset from the parent context.
 * @author Kris Maglione <maglione.k@gmail.com>
 * @constructor
 */
function CompletionContext(editor, name, offset) //{{{
{
    if (!(this instanceof arguments.callee))
        return new arguments.callee(editor, name, offset);
    if (!name)
        name = "";

    let self = this;
    if (editor instanceof arguments.callee)
    {
        let parent = editor;
        name = parent.name + "/" + name;
        this.contexts = parent.contexts;
        if (name in this.contexts)
            self = this.contexts[name];
        else
            self.contexts[name] = this;

        /**
         * @property {CompletionContext} This context's parent. {null} when
         *     this is a top-level context.
         */
        self.parent = parent;

        ["filters", "keys", "title", "quote"].forEach(function (key)
            self[key] = parent[key] && util.cloneObject(parent[key]));
        ["anchored", "compare", "editor", "_filter", "filterFunc", "keys", "_process", "top"].forEach(function (key)
            self[key] = parent[key]);

        self.__defineGetter__("value", function () this.top.value);

        self.offset = parent.offset;
        self.advance(offset);

        /**
         * @property {boolean} Specifies that this context is not finished
         *     generating results.
         * @default false
         */
        self.incomplete = false;
        self.message = null;
        /**
         * @property {boolean} Specifies that this context is waiting for the
         *     user to press <Tab>. Useful when fetching completions could be
         *     dangerous or slow, and the user has enabled autocomplete.
         */
        self.waitingForTab = false;

        delete self._generate;
        delete self._ignoreCase;
        if (self != this)
            return self;
        ["_caret", "contextList", "maxItems", "onUpdate", "selectionTypes", "tabPressed", "updateAsync", "value"].forEach(function (key) {
            self.__defineGetter__(key, function () this.top[key]);
            self.__defineSetter__(key, function (val) this.top[key] = val);
        });
    }
    else
    {
        if (typeof editor == "string")
            this._value = editor;
        else
            this.editor = editor;
        this.compare = function (a, b) String.localeCompare(a.text, b.text);

        /**
         * @property {function} This function is called when we close
         *     a completion window with Esc or Ctrl-c. Usually this callback
         *     is only needed for long, asynchronous completions
         */
        this.cancel = null;
        /**
         * @property {function} The function used to filter the results.
         * @default Selects all results which match every predicate in the
         *     {@link #filters} array.
         */
        this.filterFunc = function (items)
        {
                let self = this;
                return this.filters.
                    reduce(function (res, filter) res.filter(function (item) filter.call(self, item)),
                            items);
        }
        /**
         * @property {Array} An array of predicates on which to filter the
         *     results.
         */
        this.filters = [function (item) {
            let text = Array.concat(item.text);
            for (let [i, str] in Iterator(text))
            {
                if (this.match(String(str)))
                {
                    item.text = String(text[i]);
                    return true;
                }
            }
            return false;
        }];
        /**
         * @property {boolean} Specifies whether this context results must
         *     match the filter at the beginning of the string.
         * @default true
         */
        this.anchored = true;
        /**
         * @property {Object} A map of all contexts, keyed on their names.
         *    Names are assigned when a context is forked, with its specified
         *    name appended, after a '/', to its parent's name. May
         *    contain inactive contexts. For active contexts, see
         *    {@link #contextList}.
         */
        this.contexts = { "": this };
        /**
         * @property {Object} A mapping of keys, for {@link #getKey}. Given
         *      { key: value }, getKey(item, key) will return values as such:
         *      if value is a string, it will return item.item[value]. If it's a
         *      function, it will return value(item.item).
         */
        this.keys = { text: 0, description: 1, icon: "icon" };
        /**
         * @property {number} This context's offset from the beginning of
         *     {@link #editor}'s value.
         */
        this.offset = offset || 0;
        /**
         * @property {function} A function which is called when any subcontext
         *     changes its completion list. Only called when
         *     {@link #updateAsync} is true.
         */
        this.onUpdate = function () true;
        /**
         * @property {CompletionContext} The top-level completion context.
         */
        this.top = this;
        this.__defineGetter__("incomplete", function () this.contextList.some(function (c) c.parent && c.incomplete));
        this.__defineGetter__("waitingForTab", function () this.contextList.some(function (c) c.parent && c.waitingForTab));
        this.reset();
    }
    /**
     * @property {Object} A general-purpose store for functions which need to
     *     cache data between calls.
     */
    this.cache = {};
    /**
     * @private
     * @property {Object} A cache for return values of {@link #generate}.
     */
    this.itemCache = {};
    /**
     * @property {string} A key detailing when the cached value of
     *     {@link #generate} may be used. Every call to
     *     {@link #generate} stores its result in {@link #itemCache}.
     *     When itemCache[key] exists, its value is returned, and
     *     {@link #generate} is not called again.
     */
    this.key = "";
    /**
     * @property {string} A message to be shown before any results.
     */
    this.message = null;
    this.name = name || "";
    /** @private */
    this._completions = []; // FIXME
    /**
     * Returns a key, as detailed in {@link #keys}.
     * @function
     */
    this.getKey = function (item, key) (typeof self.keys[key] == "function") ? self.keys[key].call(this, item.item) :
            key in self.keys ? item.item[self.keys[key]]
                             : item.item[key];
}

CompletionContext.Sort = {
    number: function (a, b) parseInt(b) - parseInt(a) || String.localeCompare(a, b),

    unsorted: null
};

CompletionContext.prototype = {
    // Temporary
    /**
     * @property {Object}
     *
     * An object describing the results from all sub-contexts. Results are
     * adjusted so that all have the same starting offset.
     *
     * @deprecated
     */
    get allItems()
    {
        try
        {
            let self = this;
            let minStart = Math.min.apply(Math, [context.offset for ([k, context] in Iterator(this.contexts)) if (context.items.length && context.hasItems)]);
            if (minStart == Infinity)
                minStart = 0;
            let items = this.contextList.map(function (context) {
                if (!context.hasItems)
                    return [];
                let prefix = self.value.substring(minStart, context.offset);
                return context.items.map(function makeItem(item) ({ text: prefix + item.text, item: item.item }));
            });
            return { start: minStart, items: util.Array.flatten(items), longestSubstring: this.longestAllSubstring }
        }
        catch (e)
        {
            liberator.reportError(e);
            return { start: 0, items: [], longestAllSubstring: "" }
        }
    },
    // Temporary
    get allSubstrings()
    {
        let contexts = this.contextList.filter(function (c) c.hasItems && c.items.length);
        let minStart = Math.min.apply(Math, contexts.map(function (c) c.offset));
        let lists = contexts.map(function (context) {
            let prefix = context.value.substring(minStart, context.offset);
            return context.substrings.map(function (s) prefix + s);
        });

        let substrings = lists.reduce(
                function (res, list) res.filter(function (str) list.some(function (s) s.substr(0, str.length) == str)),
                lists.pop());
        if (!substrings) // FIXME: How is this undefined?
            return [];
        return util.Array.uniq(substrings);
    },
    // Temporary
    get longestAllSubstring()
    {
        return this.allSubstrings.reduce(function (a, b) a.length > b.length ? a : b, "");
    },

    get caret() this._caret - this.offset,
    set caret(val) this._caret = val + this.offset,

    get compare() this._compare || function () 0,
    set compare(val) this._compare = val,

    get completions() this._completions || [],
    set completions(items)
    {
        // Accept a generator
        if ({}.toString.call(items) != '[object Array]')
            items = [x for (x in Iterator(items))];
        delete this.cache.filtered;
        delete this.cache.filter;
        this.cache.rows = [];
        this.hasItems = items.length > 0;
        this._completions = items;
        let self = this;
        if (this.updateAsync && !this.noUpdate)
            liberator.callInMainThread(function () { self.onUpdate.call(self) });
    },

    get createRow() this._createRow || template.completionRow, // XXX
    set createRow(createRow) this._createRow = createRow,

    get filterFunc() this._filterFunc || util.identity,
    set filterFunc(val) this._filterFunc = val,

    get filter() this._filter != null ? this._filter : this.value.substr(this.offset, this.caret),
    set filter(val)
    {
        delete this._ignoreCase;
        return this._filter = val
    },

    get format() ({
        anchored: this.anchored,
        title: this.title,
        keys: this.keys,
        process: this.process
    }),
    set format(format)
    {
        this.anchored = format.anchored,
        this.title = format.title || this.title;
        this.keys = format.keys || this.keys;
        this.process = format.process || this.process;
    },

    get message() this._message || (this.waitingForTab ? "Waiting for <Tab>" : null),
    set message(val) this._message = val,

    get proto()
    {
        let res = {};
        for (let i in Iterator(this.keys))
        {
            let [k, v] = i;
            let _k = "_" + k;
            if (typeof v == "string" && /^[.[]/.test(v))
                v = eval("(function (i) i" + v + ")")
            if (typeof v == "function")
                res.__defineGetter__(k, function () _k in this ? this[_k] : (this[_k] = v(this.item)));
            else
                res.__defineGetter__(k, function () _k in this ? this[_k] : (this[_k] = this.item[v]));
            res.__defineSetter__(k, function (val) this[_k] = val);
        }
        return res;
    },

    get regenerate() this._generate && (!this.completions || !this.itemCache[this.key] || this.cache.offset != this.offset),
    set regenerate(val) { if (val) delete this.itemCache[this.key] },

    get generate() !this._generate ? null : function ()
    {
        if (this.offset != this.cache.offset)
            this.itemCache = {};
        this.cache.offset = this.offset;
        if (!this.itemCache[this.key])
            this.itemCache[this.key] = this._generate.call(this) || [];
        return this.itemCache[this.key];
    },
    set generate(arg)
    {
        this.hasItems = true;
        this._generate = arg;
        //**/ liberator.dump(this.name + ": set generate()");
        if (this.background && this.regenerate)
        {
            //**/ this.__i = (this.__i || 0) + 1;
            //**/ let self = this;
            //**/ function dump(msg) liberator.callInMainThread(function () liberator.dump(self.name + ":" + self.__i + ": " + msg));
            //**/ dump("set generate() regenerating");

            let lock = {};
            this.cache.backgroundLock = lock;
            this.incomplete = true;
            let thread = this.getCache("backgroundThread", liberator.newThread);
            //**/ dump(thread);
            liberator.callAsync(thread, this, function () {
                //**/ dump("In async");
                if (this.cache.backgroundLock != lock)
                {
                    //**/ dump("Lock !ok");
                    return;
                }
                let items = this.generate();
                //**/ dump("Generated");
                if (this.cache.backgroundLock != lock)
                {
                    //**/ dump("Lock !ok");
                    return;
                }
                this.incomplete = false;
                //**/ dump("completions=");
                this.completions = items;
                //**/ dump("completions==");
            });
        }
    },

    get ignoreCase()
    {
        if ("_ignoreCase" in this)
            return this._ignoreCase;
        let mode = options["wildcase"];
        if (mode == "match")
            return this._ignoreCase = false;
        if (mode == "ignore")
            return this._ignoreCase = true;
        return this._ignoreCase = !/[A-Z]/.test(this.filter);
    },
    set ignoreCase(val) this._ignoreCase = val,

    get items()
    {
        if (!this.hasItems || this.backgroundLock)
            return [];
        if (this.cache.filtered && this.cache.filter == this.filter)
            return this.cache.filtered;
        this.cache.rows = [];
        let items = this.completions;
        if (this.generate && !this.background)
        {
            // XXX
            this.noUpdate = true;
            this.completions = items = this.generate();
            this.noUpdate = false;
        }
        this.cache.filter = this.filter;
        if (items == null)
            return items;

        let self = this;
        delete this._substrings;

        let proto = this.proto;
        let filtered = this.filterFunc(items.map(function (item) ({ __proto__: proto, item: item })));
        if (this.maxItems)
            filtered = filtered.slice(0, this.maxItems);

        if (options.get("wildoptions").has("sort") && this.compare)
            filtered.sort(this.compare);
        let quote = this.quote;
        if (quote)
            filtered.forEach(function (item) {
                item.unquoted = item.text;
                item.text = quote[0] + quote[1](item.text) + quote[2];
            })
        return this.cache.filtered = filtered;
    },

    get process() // FIXME
    {
        let self = this;
        let process = this._process;
        process = [process[0] || template.icon, process[1] || function (item, k) k];
        let first = process[0];
        let filter = this.filter;
        if (!this.anchored)
            process[0] = function (item, text) first.call(self, item, template.highlightFilter(item.text, filter));
        return process;
    },
    set process(process)
    {
        this._process = process;
    },

    get substrings()
    {
        let items = this.items;
        if (items.length == 0 || !this.hasItems)
            return [];
        if (this._substrings)
            return this._substrings;

        let fixCase = this.ignoreCase ? String.toLowerCase : util.identity;
        let text = fixCase(items[0].unquoted || items[0].text);
        let filter = fixCase(this.filter);
        if (this.anchored)
        {
            function compare (text, s) text.substr(0, s.length) == s;
            substrings = util.map(util.range(filter.length, text.length + 1),
                function (end) text.substring(0, end));
        }
        else
        {
            function compare (text, s) text.indexOf(s) >= 0;
            substrings = [];
            let start = 0;
            let idx;
            let length = filter.length;
            while ((idx = text.indexOf(filter, start)) > -1 && idx < text.length)
            {
                for (let end in util.range(idx + length, text.length + 1))
                    substrings.push(text.substring(idx, end));
                start = idx + 1;
            }
        }
        substrings = items.reduce(
                function (res, item) res.filter(function (str) compare(fixCase(item.unquoted || item.text), str)),
                substrings);
        let quote = this.quote;
        if (quote)
            substrings = substrings.map(function (str) quote[0] + quote[1](str));
        return this._substrings = substrings;
    },

    /**
     * Advances the context <b>count</b> characters. {@link #filter} is
     * advanced to match. If {@link #quote} is non-null, its prefix and suffix
     * are set to the null-string.
     *
     * This function is still imperfect for quoted strings. When
     * {@link #quote} is non-null, it adjusts the count based on the quoted
     * size of the <b>count</b>-character substring of the filter, which is
     * accurate so long as unquoting and quoting a string will always map to
     * the original quoted string, which is often not the case.
     *
     * @param {number} count The number of characters to advance the context.
     */
    advance: function advance(count)
    {
        delete this._ignoreCase;
        if (this.quote)
        {
            count = this.quote[0].length + this.quote[1](this.filter.substr(0, count)).length;
            this.quote[0] = "";
            this.quote[2] = "";
        }
        this.offset += count;
        if (this._filter)
            this._filter = this._filter.substr(count);
    },

    cancelAll: function ()
    {
        for (let [,context] in Iterator(this.contextList))
        {
            if (context.cancel)
                context.cancel();
        }
    },

    /**
     * Gets a key from {@link #cache}, setting it to <b>defVal</b> if it
     * doesn't already exists.
     * @param {string} key
     * @param defVal
     */
    getCache: function (key, defVal)
    {
        if (!(key in this.cache))
            this.cache[key] = defVal();
        return this.cache[key];
    },

    getItems: function getItems(start, end)
    {
        let self = this;
        let items = this.items;
        let step = start > end ? -1 : 1;
        start = Math.max(0, start || 0);
        end = Math.min(items.length, end ? end : items.length);
        return util.map(util.range(start, end, step), function (i) items[i]);
    },

    getRows: function getRows(start, end, doc)
    {
        let self = this;
        let items = this.items;
        let cache = this.cache.rows;
        let step = start > end ? -1 : 1;
        start = Math.max(0, start || 0);
        end = Math.min(items.length, end != null ? end : items.length);
        for (let i in util.range(start, end, step))
            yield [i, cache[i] = cache[i] || util.xmlToDom(self.createRow(items[i]), doc)];
    },

    fork: function fork(name, offset, self, completer)
    {
        if (typeof completer == "string")
            completer = self[completer]
        let context = new CompletionContext(this, name, offset);
        this.contextList.push(context);
        if (completer)
            return completer.apply(self || this, [context].concat(Array.slice(arguments, arguments.callee.length)));
        return context;
    },

    getText: function getText(item)
    {
        let text = item[self.keys["text"]];
        if (self.quote)
            return self.quote(text);
        return text;
    },

    highlight: function highlight(start, length, type)
    {
        try // Firefox <3.1 doesn't have repaintSelection
        {
            this.selectionTypes[type] = null;
            const selType = Ci.nsISelectionController["SELECTION_" + type];
            const editor = this.editor;
            let sel = editor.selectionController.getSelection(selType);
            if (length == 0)
                sel.removeAllRanges();
            else
            {
                let range = editor.selection.getRangeAt(0).cloneRange();
                range.setStart(range.startContainer, this.offset + start);
                range.setEnd(range.startContainer, this.offset + start + length);
                sel.addRange(range);
            }
            editor.selectionController.repaintSelection(selType);
        }
        catch (e) {}
    },

    // FIXME
    _match: function _match(filter, str)
    {
        if (this.ignoreCase)
        {
            filter = filter.toLowerCase();
            str = str.toLowerCase();
        }
        if (this.anchored)
            return str.substr(0, filter.length) == filter;
        return str.indexOf(filter) > -1;
    },

    match: function match(str)
    {
        return this._match(this.filter, str);
    },

    reset: function reset()
    {
        let self = this;
        if (this.parent)
            throw Error();
        // Not ideal.
        for (let type in this.selectionTypes)
            this.highlight(0, 0, type);

        /**
         * @property {[CompletionContext]} A list of active
         *     completion contexts, in the order in which they were
         *     instantiated.
         */
        this.contextList = [];
        this.offset = 0;
        this.process = [];
        this.selectionTypes = {};
        this.tabPressed = false;
        this.title = ["Completions"];
        this.updateAsync = false;
        try
        {
            this.waitingForTab = false;
        }
        catch (e) {}

        this.cancelAll();

        if (this.editor)
        {
            this.value = this.editor.selection.focusNode.textContent;
            this._caret = this.editor.selection.focusOffset;
        }
        else
        {
            this.value = this._value;
            this._caret = this.value.length;
        }
        //for (let key in (k for ([k, v] in Iterator(self.contexts)) if (v.offset > this.caret)))
        //    delete this.contexts[key];
        for each (let context in this.contexts)
        {
            context.hasItems = false;
            try
            {
                context.incomplete = false;
            }
            catch (e) {}
        }
    },

    /**
     * Wait for all subcontexts to complete.
     *
     * @param {boolean} interruptible When true, the call may be interrupted
     *    via <C-c>, in which case, "Interrupted" may be thrown.
     * @param {number} timeout The maximum time, in milliseconds, to wait.
     *    If 0 or null, wait indefinately.
     */
    wait: function wait(interruptable, timeout)
    {
        let end = Date.now() + timeout;
        while (this.incomplete && (!timeout || Date.now() > end))
            liberator.threadYield(false, interruptable);
        return this.incomplete;
    }
}; //}}}

/**
 * @instance completion
 */
function Completion() //{{{
{
    ////////////////////////////////////////////////////////////////////////////////
    ////////////////////// PRIVATE SECTION /////////////////////////////////////////
    /////////////////////////////////////////////////////////////////////////////{{{

    const EVAL_TMP = "__liberator_eval_tmp";

    function Javascript()
    {
        const OFFSET = 0, CHAR = 1, STATEMENTS = 2, DOTS = 3, FULL_STATEMENTS = 4, COMMA = 5, FUNCTIONS = 6;
        let stack = [];
        let functions = [];
        let top = [];  // The element on the top of the stack.
        let last = ""; // The last opening char pushed onto the stack.
        let lastNonwhite = ""; // Last non-whitespace character we saw.
        let lastChar = "";     // Last character we saw, used for \ escaping quotes.
        let compl = [];
        let str = "";

        let lastIdx = 0;

        let cacheKey = null;

        this.completers = {};

        // Some object members are only accessible as function calls
        function getKey(obj, key)
        {
            try
            {
                return obj[key];
            }
            catch (e)
            {
                return undefined;
            }
        }

        this.iter = function iter(obj)
        {
            let iterator = ([k, getKey(obj, k)] for (k in obj));
            try
            {
                // The point of 'for k in obj' is to get keys
                // that are accessible via . or [] notation.
                // Iterators quite often return values of no
                // use whatsoever for this purpose, so, we try
                // this rather dirty hack of getting a standard
                // object iterator for any object that defines its
                // own.
                if ("__iterator__" in obj)
                {
                    let oldIter = obj.__iterator__;
                    delete obj.__iterator__;
                    iterator = Iterator(obj);
                    obj.__iterator__ = oldIter;
                }
            }
            catch (e) {}
            return iterator;
        }

        // Search the object for strings starting with @key.
        // If @last is defined, key is a quoted string, it's
        // wrapped in @last after @offset characters are sliced
        // off of it and it's quoted.
        this.objectKeys = function objectKeys(obj)
        {
            // Things we can dereference
            if (["object", "string", "function"].indexOf(typeof obj) == -1)
                return [];
            if (!obj)
                return [];

            // XPCNativeWrappers, etc, don't show all accessible
            // members until they're accessed, so, we look at
            // the wrappedJSObject instead, and return any keys
            // available in the object itself.
            let orig = obj;

            if (modules.isPrototypeOf(obj))
                compl = [v for (v in Iterator(obj))];
            else
            {
                if (getKey(obj, 'wrappedJSObject'))
                    obj = obj.wrappedJSObject;
                // v[0] in orig and orig[v[0]] catch different cases. XPCOM
                // objects are problematic, to say the least.
                compl = [v for (v in this.iter(obj))
                    if ((typeof orig == "object" && v[0] in orig) || getKey(orig, v[0]) !== undefined)];
            }

            // And if wrappedJSObject happens to be available,
            // return that, too.
            if (getKey(orig, 'wrappedJSObject'))
                compl.push(["wrappedJSObject", obj]);

            // Add keys for sorting later.
            // Numbers are parsed to ints.
            // Constants, which should be unsorted, are found and marked null.
            compl.forEach(function (item) {
                let key = item[0];
                if (!isNaN(key))
                    key = parseInt(key);
                else if (/^[A-Z_][A-Z0-9_]*$/.test(key))
                    key = "";
                item.key = key;
            });

            return compl;
        }

        this.eval = function eval(arg, key, tmp)
        {
            let cache = this.context.cache.eval;
            let context = this.context.cache.evalContext;

            if (!key)
                key = arg;
            if (key in cache)
                return cache[key];

            context[EVAL_TMP] = tmp;
            try
            {
                return cache[key] = liberator.eval(arg, context);
            }
            catch (e)
            {
                return null;
            }
            finally
            {
                delete context[EVAL_TMP];
            }
        }

        // Get an element from the stack. If @n is negative,
        // count from the top of the stack, otherwise, the bottom.
        // If @m is provided, return the @mth value of element @o
        // of the stack entry at @n.
        let get = function get(n, m, o)
        {
            let a = stack[n >= 0 ? n : stack.length + n];
            if (o != null)
                a = a[o];
            if (m == null)
                return a;
            return a[a.length - m - 1];
        }

        function buildStack(filter)
        {
            let self = this;
            // Push and pop the stack, maintaining references to 'top' and 'last'.
            let push = function push(arg)
            {
                top = [i, arg, [i], [], [], [], []];
                last = top[CHAR];
                stack.push(top);
            }
            let pop = function pop(arg)
            {
                if (top[CHAR] != arg)
                {
                    self.context.highlight(top[OFFSET], i - top[OFFSET], "SPELLCHECK");
                    self.context.highlight(top[OFFSET], 1, "FIND");
                    throw new Error("Invalid JS");
                }
                if (i == self.context.caret - 1)
                    self.context.highlight(top[OFFSET], 1, "FIND");
                // The closing character of this stack frame will have pushed a new
                // statement, leaving us with an empty statement. This doesn't matter,
                // now, as we simply throw away the frame when we pop it, but it may later.
                if (top[STATEMENTS][top[STATEMENTS].length - 1] == i)
                    top[STATEMENTS].pop();
                top = get(-2);
                last = top[CHAR];
                let ret = stack.pop();
                return ret;
            }

            let i = 0, c = "";     // Current index and character, respectively.

            // Reuse the old stack.
            if (str && filter.substr(0, str.length) == str)
            {
                i = str.length;
                if (this.popStatement)
                    top[STATEMENTS].pop();
            }
            else
            {
                stack = [];
                functions = [];
                push("#root");
            }

            // Build a parse stack, discarding entries as opening characters
            // match closing characters. The stack is walked from the top entry
            // and down as many levels as it takes us to figure out what it is
            // that we're completing.
            str = filter;
            let length = str.length;
            for (; i < length; lastChar = c, i++)
            {
                c = str[i];
                if (last == '"' || last == "'" || last == "/")
                {
                    if (lastChar == "\\") // Escape. Skip the next char, whatever it may be.
                    {
                        c = "";
                        i++;
                    }
                    else if (c == last)
                        pop(c);
                }
                else
                {
                    // A word character following a non-word character, or simply a non-word
                    // character. Start a new statement.
                    if (/[a-zA-Z_$]/.test(c) && !/[\w$]/.test(lastChar) || !/[\w\s$]/.test(c))
                        top[STATEMENTS].push(i);

                    // A "." or a "[" dereferences the last "statement" and effectively
                    // joins it to this logical statement.
                    if ((c == "." || c == "[") && /[\w$\])"']/.test(lastNonwhite)
                    ||  lastNonwhite == "." && /[a-zA-Z_$]/.test(c))
                            top[STATEMENTS].pop();

                    switch (c)
                    {
                        case "(":
                            // Function call, or if/while/for/...
                            if (/[\w$]/.test(lastNonwhite))
                            {
                                functions.push(i);
                                top[FUNCTIONS].push(i);
                                top[STATEMENTS].pop();
                            }
                        case '"':
                        case "'":
                        case "/":
                        case "{":
                            push(c);
                            break;
                        case "[":
                            push(c);
                            break;
                        case ".":
                            top[DOTS].push(i);
                            break;
                        case ")": pop("("); break;
                        case "]": pop("["); break;
                        case "}": pop("{"); // Fallthrough
                        case ";":
                            top[FULL_STATEMENTS].push(i);
                            break;
                        case ",":
                            top[COMMA].push(i);
                            break;
                    }

                    if (/\S/.test(c))
                        lastNonwhite = c;
                }
            }

            this.popStatement = false;
            if (!/[\w$]/.test(lastChar) && lastNonwhite != ".")
            {
                this.popStatement = true;
                top[STATEMENTS].push(i);
            }

            lastIdx = i;
        }

        this.complete = function _complete(context)
        {
            this.context = context;

            let self = this;
            try
            {
                buildStack.call(this, context.filter);
            }
            catch (e)
            {
                if (e.message != "Invalid JS")
                    liberator.reportError(e);
                lastIdx = 0;
                return;
            }

            let cache = this.context.cache;
            this.context.getCache("eval", Object);
            this.context.getCache("evalContext", function () ({ __proto__: userContext }));

            // Okay, have parse stack. Figure out what we're completing.

            // Find any complete statements that we can eval before we eval our object.
            // This allows for things like: let doc = window.content.document; let elem = doc.createElement...; elem.<Tab>
            let prev = 0;
            for (let [,v] in Iterator(get(0)[FULL_STATEMENTS]))
            {
                let key = str.substring(prev, v + 1);
                if (checkFunction(prev, v, key))
                    return;
                this.eval(key);
                prev = v + 1;
            }

            // Don't eval any function calls unless the user presses tab.
            function checkFunction(start, end, key)
            {
                let res = functions.some(function (idx) idx >= start && idx < end);
                if (!res || self.context.tabPressed || key in cache.eval)
                    return false;
                self.context.waitingForTab = true;
                return true;
            }

            // For each DOT in a statement, prefix it with TMP, eval it,
            // and save the result back to TMP. The point of this is to
            // cache the entire path through an object chain, mainly in
            // the presence of function calls. There are drawbacks. For
            // instance, if the value of a variable changes in the course
            // of inputting a command (let foo=bar; frob(foo); foo=foo.bar; ...),
            // we'll still use the old value. But, it's worth it.
            function getObj(frame, stop)
            {
                let statement = get(frame, 0, STATEMENTS) || 0; // Current statement.
                let prev = statement;
                let obj;
                let cacheKey;
                for (let [i, dot] in Iterator(get(frame)[DOTS].concat(stop)))
                {
                    if (dot < statement)
                        continue;
                    if (dot > stop || dot <= prev)
                        break;
                    let s = str.substring(prev, dot);

                    if (prev != statement)
                        s = EVAL_TMP + "." + s;
                    cacheKey = str.substring(statement, dot);

                    if (checkFunction(prev, dot, cacheKey))
                        return [];

                    prev = dot + 1;
                    obj = self.eval(s, cacheKey, obj);
                }
                return [[obj, cacheKey]]
            }

            function getObjKey(frame)
            {
                let dot = get(frame, 0, DOTS) || -1; // Last dot in frame.
                let statement = get(frame, 0, STATEMENTS) || 0; // Current statement.
                let end = (frame == -1 ? lastIdx : get(frame + 1)[OFFSET]);

                cacheKey = null;
                let obj = [[cache.evalContext, "Local Variables"], [userContext, "Global Variables"],
                           [modules, "modules"], [window, "window"]]; // Default objects;
                // Is this an object dereference?
                if (dot < statement) // No.
                    dot = statement - 1;
                else // Yes. Set the object to the string before the dot.
                    obj = getObj(frame, dot);

                let [, space, key] = str.substring(dot + 1, end).match(/^(\s*)(.*)/);
                return [dot + 1 + space.length, obj, key];
            }

            function fill(context, obj, name, compl, anchored, key, last, offset)
            {
                context.title = [name];
                context.anchored = anchored;
                context.filter = key;
                context.itemCache = context.parent.itemCache;
                context.key = name;

                if (last != null)
                    context.quote = [last, function (text) util.escapeString(text.substr(offset), ""), last];
                else // We're not looking for a quoted string, so filter out anything that's not a valid identifier
                    context.filters.push(function (item) /^[a-zA-Z_$][\w$]*$/.test(item.text));

                compl.call(self, context, obj);
            }

            function complete(objects, key, compl, string, last)
            {
                let orig = compl;
                if (!compl)
                {
                    compl = function (context, obj)
                    {
                        context.process = [null, function highlight(item, v) template.highlight(v, true)];
                        // Sort in a logical fashion for object keys:
                        //  Numbers are sorted as numbers, rather than strings, and appear first.
                        //  Constants are unsorted, and appear before other non-null strings.
                        //  Other strings are sorted in the default manner.
                        let compare = context.compare;
                        context.compare = function (a, b)
                        {
                            if (!isNaN(a.item.key) && !isNaN(b.item.key))
                                return a.item.key - b.item.key;
                            return isNaN(b.item.key) - isNaN(a.item.key) || compare(a.item.key, b.item.key);
                        }
                        if (!context.anchored) // We've already listed anchored matches, so don't list them again here.
                            context.filters.push(function (item) util.compareIgnoreCase(item.text.substr(0, this.filter.length), this.filter));
                        if (obj == cache.evalContext)
                            context.regenerate = true;
                        context.generate = function () self.objectKeys(obj);
                    }
                }
                // TODO: Make this a generic completion helper function.
                let filter = key + (string || "");
                for (let [,obj] in Iterator(objects))
                {
                    this.context.fork(obj[1], top[OFFSET], this, fill,
                        obj[0], obj[1], compl, compl != orig, filter, last, key.length);
                }
                if (orig)
                    return;
                for (let [,obj] in Iterator(objects))
                {
                    obj[1] += " (substrings)";
                    this.context.fork(obj[1], top[OFFSET], this, fill,
                        obj[0], obj[1], compl, false, filter, last, key.length);
                }
            }

            // In a string. Check if we're dereferencing an object.
            // Otherwise, do nothing.
            if (last == "'" || last == '"')
            {
                //
                // str = "foo[bar + 'baz"
                // obj = "foo"
                // key = "bar + ''"
                //

                // The top of the stack is the sting we're completing.
                // Wrap it in its delimiters and eval it to process escape sequences.
                let string = str.substring(get(-1)[OFFSET] + 1, lastIdx);
                string = eval(last + string + last);

                function getKey()
                {
                    if (last == "")
                        return "";
                    // After the opening [ upto the opening ", plus '' to take care of any operators before it
                    let key = str.substring(get(-2, 0, STATEMENTS), get(-1, null, OFFSET)) + "''";
                    // Now eval the key, to process any referenced variables.
                    return this.eval(key);
                }

                // Is this an object accessor?
                if (get(-2)[CHAR] == "[") // Are we inside of []?
                {
                    // Stack:
                    //  [-1]: "...
                    //  [-2]: [...
                    //  [-3]: base statement

                    // Yes. If the [ starts at the beginning of a logical
                    // statement, we're in an array literal, and we're done.
                     if (get(-3, 0, STATEMENTS) == get(-2)[OFFSET])
                        return;

                    // Beginning of the statement upto the opening [
                    let obj = getObj(-3, get(-2)[OFFSET]);

                    return complete.call(this, obj, getKey(), null, string, last);
                }

                // Is this a function call?
                if (get(-2)[CHAR] == "(")
                {
                    // Stack:
                    //  [-1]: "...
                    //  [-2]: (...
                    //  [-3]: base statement

                    // Does the opening "(" mark a function call?
                    if (get(-3, 0, FUNCTIONS) != get(-2)[OFFSET])
                        return; // No. We're done.

                    let [offset, obj, func] = getObjKey(-3);
                    if (!obj.length)
                        return;
                    obj = obj.slice(0, 1);

                    try
                    {
                        var completer = obj[0][0][func].liberatorCompleter;
                    }
                    catch (e) {}
                    if (!completer)
                        completer = this.completers[func];
                    if (!completer)
                        return;

                    // Split up the arguments
                    let prev = get(-2)[OFFSET];
                    let args = [];
                    for (let [i, idx] in Iterator(get(-2)[COMMA]))
                    {
                        let arg = str.substring(prev + 1, idx);
                        prev = idx;
                        args.__defineGetter__(i, function () self.eval(arg));
                    }
                    let key = getKey();
                    args.push(key + string);

                    compl = function (context, obj)
                    {
                        let res = completer.call(self, context, func, obj, args);
                        if (res)
                            context.completions = res;
                    }

                    obj[0][1] += "." + func + "(... [" + args.length + "]";
                    return complete.call(this, obj, key, compl, string, last);
                }

                // In a string that's not an obj key or a function arg.
                // Nothing to do.
                return;
            }

            //
            // str = "foo.bar.baz"
            // obj = "foo.bar"
            // key = "baz"
            //
            // str = "foo"
            // obj = [modules, window]
            // key = "foo"
            //

            let [offset, obj, key] = getObjKey(-1);

            // Wait for a keypress before completing the default objects.
            if (!this.context.tabPressed && key == "" && obj.length > 1)
            {
                this.context.waitingForTab = true;
                this.context.message = "Waiting for key press";
                return;
            }

            if (!/^(?:[a-zA-Z_$][\w$]*)?$/.test(key))
                return; // Not a word. Forget it. Can this even happen?

            try
            { // FIXME
                var o = top[OFFSET];
                top[OFFSET] = offset;
                return complete.call(this, obj, key);
            }
            finally
            {
                top[OFFSET] = o;
            }
        }
    };
    let javascript = new Javascript();

    /////////////////////////////////////////////////////////////////////////////}}}
    ////////////////////// PUBLIC SECTION //////////////////////////////////////////
    /////////////////////////////////////////////////////////////////////////////{{{

    const self = {

        setFunctionCompleter: function setFunctionCompleter(funcs, completers)
        {
            funcs = Array.concat(funcs);
            for (let [,func] in Iterator(funcs))
            {
                func.liberatorCompleter = function liberatorCompleter(context, func, obj, args) {
                    let completer = completers[args.length - 1];
                    if (!completer)
                        return [];
                    return completer.call(this, context, obj, args);
                };
            }
        },

        // FIXME
        _runCompleter: function _runCompleter(name, filter, maxItems)
        {
            let context = CompletionContext(filter);
            context.maxItems = maxItems;
            let res = context.fork.apply(context, ["run", 0, this, name].concat(Array.slice(arguments, 3)));
            if (res) // FIXME
                return { items: res.map(function (i) ({ item: i })) };
            context.wait(true);
            return context.allItems;
        },

        runCompleter: function runCompleter(name, filter, maxItems)
        {
            return this._runCompleter.apply(this, Array.slice(arguments))
                       .items.map(function (i) i.item);
        },

        listCompleter: function listCompleter(name, filter, maxItems)
        {
            let context = CompletionContext(filter || "");
            context.maxItems = maxItems;
            context.fork.apply(context, ["list", 0, completion, name].concat(Array.slice(arguments, 3)));
            context = context.contexts["/list"];
            context.wait();

            let list = template.commandOutput(
                <div highlight="Completions">
                    { template.completionRow(context.title, "CompTitle") }
                    { template.map(context.items, function (item) context.createRow(item), null, 100) }
                </div>);
            commandline.echo(list, commandline.HL_NORMAL, commandline.FORCE_MULTILINE);
        },

        ////////////////////////////////////////////////////////////////////////////////
        ////////////////////// COMPLETION TYPES ////////////////////////////////////////
        /////////////////////////////////////////////////////////////////////////////{{{

        // TODO: shouldn't all of these have a standard signature (context, args, ...)? --djk
        abbreviation: function abbreviation(context, args, mode)
        {
            mode = mode || "!";

            if (args.completeArg == 0)
            {
                let abbreviations = editor.getAbbreviations(mode);
                context.completions = [[lhs, ""] for ([, [, lhs,]] in Iterator(abbreviations))];
            }
        },

        alternateStyleSheet: function alternateStylesheet(context)
        {
            context.title = ["Stylesheet", "Location"];

            // unify split style sheets
            let styles = {};

            buffer.alternateStyleSheets.forEach(function (style) {
                if (!(style.title in styles))
                    styles[style.title] = [];

                styles[style.title].push(style.href || "inline");
            });

            context.completions = [[s, styles[s].join(", ")] for (s in styles)];
        },

        autocmdEvent: function autocmdEvent(context)
        {
            context.completions = config.autocommands;
        },

        // TODO: shouldn't these app-specific completers be moved to config.js? --djk
        bookmark: function bookmark(context, tags, extra)
        {
            context.title = ["Bookmark", "Title"];
            context.format = bookmarks.format;
            for (let val in Iterator(extra || []))
            {
                let [k, v] = val; // Need block scope here for the closure
                if (v)
                    context.filters.push(function (item) this._match(v, item[k]));
            }
            // Need to make a copy because set completions() checks instanceof Array,
            // and this may be an Array from another window.
            context.completions = Array.slice(storage["bookmark-cache"].bookmarks);
            completion.urls(context, tags);
        },

        song: function song(context, args)
        {
            // TODO: useful descriptions?
            function map(list) list.map(function (i) [i, ""]);
            let [artist, album] = [args[0], args[1]];

            if (args.completeArg == 0)
            {
                context.title = ["Artists"];
                context.completions = map(library.getArtists());
            }
            else if (args.completeArg == 1)
            {
                context.title = ["Albums by " + artist];
                context.completions = map(library.getAlbums(artist));
            }
            else if (args.completeArg == 2)
            {
                context.title = ["Tracks from " + album + " by " + artist];
                context.completions = map(library.getTracks(artist, album));
            }
        },

        playlist: function playlist(context, args)
        {
            context.title = ["Playlist", "Type"];
            context.keys = { text: "name", description: "type" };
            context.completions = player.getPlaylists();
        },

        buffer: function buffer(context)
        {
            filter = context.filter.toLowerCase();
            context.anchored = false;
            context.title = ["Buffer", "URL"];
            context.keys = { text: "text", description: "url", icon: "icon" };
            context.compare = CompletionContext.Sort.number;
            let process = context.process[0];
            context.process = [function (item, text)
                    <>
                        <span highlight="Indicator" style="display: inline-block; width: 1.5em; text-align: center">{item.item.indicator}</span>
                        { process.call(this, item, text) }
                    </>];

            context.completions = util.map(tabs.browsers, function ([i, browser]) {
                let indicator = " ";
                if (i == tabs.index())
                   indicator = "%"
                else if (i == tabs.index(tabs.alternate))
                   indicator = "#";

                let tab = tabs.getTab(i);
                let url = browser.contentDocument.location.href;
                i = i + 1;

                return {
                    text: [i + ": " + (tab.label || "(Untitled)"), i + ": " + url],
                    url:  template.highlightURL(url),
                    indicator: indicator,
                    icon: tab.image || DEFAULT_FAVICON
                };
            });
        },

        charset: function (context)
        {
            context.anchored = false;
            context.generate = function () {
                let names = util.Array(
                    'more1 more2 more3 more4 more5 unicode'.split(' ').map(function (key)
                        options.getPref('intl.charsetmenu.browser.' + key).split(', ')))
                    .flatten().uniq();
                let bundle = document.getElementById('liberator-charset-bundle');
                return names.map(function (name) [name, bundle.getString(name.toLowerCase() + '.title')]);
            };
        },

        colorScheme: function colorScheme(context)
        {
            let colors = [];

            io.getRuntimeDirectories("colors").forEach(function (dir) {
                io.readDirectory(dir).forEach(function (file) {
                    if (/\.vimp$/.test(file.leafName) && !colors.some(function (c) c.leafName == file.leafName))
                        colors.push(file);
                });
            });

            context.title = ["Color Scheme", "Runtime Path"];
            context.completions = [[c.leafName.replace(/\.vimp$/, ""), c.parent.path] for ([,c] in Iterator(colors))]
        },

        command: function command(context)
        {
            context.title = ["Command"];
            context.keys = { text: "longNames", description: "description" };
            context.completions = [k for (k in commands)];
        },

        dialog: function dialog(context)
        {
            context.title = ["Dialog"];
            context.completions = config.dialogs;
        },

        directory: function directory(context, full)
        {
            this.file(context, full);
            context.filters.push(function ({ item: f }) f.isDirectory());
        },

        environment: function environment(context)
        {
            let command = liberator.has("Win32") ? "set" : "env";
            let lines = io.system(command).split("\n");
            lines.pop();

            context.title = ["Environment Variable", "Value"];
            context.generate = function () lines.map(function (line) (line.match(/([^=]+)=(.+)/) || []).slice(1));
        },

        // provides completions for ex commands, including their arguments
        ex: function ex(context)
        {
            // if there is no space between the command name and the cursor
            // then get completions of the command name
            let [count, cmd, bang, args] = commands.parseCommand(context.filter);
            let [, prefix, junk] = context.filter.match(/^(:*\d*)\w*(.?)/) || [];
            context.advance(prefix.length)
            if (!junk)
                return context.fork("", 0, this, "command");

            // dynamically get completions as specified with the command's completer function
            let command = commands.get(cmd);
            if (!command)
            {
                context.highlight(0, cmd.length, "SPELLCHECK");
                return;
            }

            [prefix] = context.filter.match(/^(?:\w*[\s!]|!)\s*/);
            let cmdContext = context.fork(cmd, prefix.length);
            let argContext = context.fork("args", prefix.length);
            args = command.parseArgs(cmdContext.filter, argContext, { count: count, bang: bang });
            if (args)
            {
                // FIXME: Move to parseCommand
                args.count = count;
                args.bang = bang;
                if (!args.completeOpt && command.completer)
                {
                    cmdContext.advance(args.completeStart);
                    cmdContext.quote = args.quote;
                    cmdContext.filter = args.completeFilter;
                    try
                    {
                        let compObject = command.completer.call(command, cmdContext, args);
                        if (compObject instanceof Array) // for now at least, let completion functions return arrays instead of objects
                            compObject = { start: compObject[0], items: compObject[1] };
                        if (compObject != null)
                        {
                            cmdContext.advance(compObject.start);
                            cmdContext.filterFunc = null;
                            cmdContext.completions = compObject.items;
                        }
                    }
                    catch (e)
                    {
                        liberator.reportError(e);
                    }
                }
            }
        },

        // TODO: support file:// and \ or / path separators on both platforms
        // if "tail" is true, only return names without any directory components
        file: function file(context, full)
        {
            // dir == "" is expanded inside readDirectory to the current dir
            let [dir] = context.filter.match(/^(?:.*[\/\\])?/);

            if (!full)
                context.advance(dir.length);

            context.title = [full ? "Path" : "Filename", "Type"];
            context.keys = {
                text: !full ? "leafName" : function (f) dir + f.leafName,
                description: function (f) f.isDirectory() ? "Directory" : "File",
                isdir: function (f) f.isDirectory(),
                icon: function (f) f.isDirectory() ? "resource://gre/res/html/folder.png"
                                                             : "moz-icon://" + f.leafName
            };
            context.compare = function (a, b)
                        b.isdir - a.isdir || String.localeCompare(a.text, b.text);

            if (options["wildignore"])
            {
                let wigRegexp = RegExp("(^" + options.get("wildignore").values.join("|") + ")$");
                context.filters.push(function ({item: f}) f.isDirectory() || !wigRegexp.test(f.leafName));
            }

            // context.background = true;
            context.key = dir;
            context.generate = function generate_file()
            {
                try
                {
                    return io.readDirectory(dir);
                }
                catch (e) {}
            };
        },

        help: function help(context)
        {
            context.title = ["Help"];
            context.anchored = false;
            context.generate = function ()
            {
                let res = config.helpFiles.map(function (file) {
                    let resp = util.httpGet("chrome://liberator/locale/" + file);
                    if (!resp)
                        return [];
                    let doc = resp.responseXML;
                    return Array.map(doc.getElementsByClassName("tag"),
                            function (elem) [elem.textContent, file]);
                });
                return util.Array.flatten(res);
            }
        },

        // XXX
        highlightGroup: function highlightGroup(context, args) commands.get("highlight").completer(context, args),

        history: function _history(context, maxItems)
        {
            context.format = history.format;
            context.title = ["History"]
            context.compare = CompletionContext.Sort.unsorted;
            //context.background = true;
            if (context.maxItems == null)
                context.maxItems = 100;
            context.regenerate = true;
            context.generate = function () history.get(context.filter, this.maxItems);
        },

        get javascriptCompleter() javascript,

        javascript: function _javascript(context) javascript.complete(context),

        location: function location(context)
        {
            if (!services.get("autoCompleteSearch"))
                return;

            context.anchored = false;
            context.title = ["Smart Completions"];
            context.keys.icon = 2;
            context.incomplete = true;
            context.hasItems = context.completions.length > 0; // XXX
            context.filterFunc = null;
            context.cancel = function () services.get("autoCompleteSearch").stopSearch();
            context.compare = CompletionContext.Sort.unsorted;
            let timer = new Timer(50, 100, function (result) {
                context.incomplete = result.searchResult >= result.RESULT_NOMATCH_ONGOING;
                context.completions = [
                    [result.getValueAt(i), result.getCommentAt(i), result.getImageAt(i)]
                        for (i in util.range(0, result.matchCount))
                ];
            });
            services.get("autoCompleteSearch").stopSearch();
            services.get("autoCompleteSearch").startSearch(context.filter, "", context.result, {
                onSearchResult: function onSearchResult(search, result)
                {
                    context.result = result;
                    timer.tell(result);
                    if (result.searchResult <= result.RESULT_SUCCESS)
                        timer.flush();
                }
            });
        },

        macro: function macro(context)
        {
            context.title = ["Macro", "Keys"];
            context.completions = [item for (item in events.getMacros())];
        },

        mark: function mark(context)
        {
            function percent(i) Math.round(i * 100);

            // FIXME: Line/Column doesn't make sense with %
            context.title = ["Mark", "Line Column File"];
            context.keys.description = function ([,m]) percent(m.position.y) + "% " + percent(m.position.x) + "% " + m.location;
            context.completions = marks.all;
        },

        mediaView: function mediaView(context)
        {
            context.title = ["Media View", "URL"];
            context.anchored = false;
            context.keys = { text: "contentTitle", description: "contentUrl" };
            context.completions = player.getMediaPages();
        },

        menuItem: function menuItem(context)
        {
            context.title = ["Menu Path", "Label"];
            context.anchored = false;
            context.keys = { text: "fullMenuPath", description: function (item) item.getAttribute("label") };
            context.completions = liberator.menuItems;
        },

        option: function option(context, scope)
        {
            context.title = ["Option"];
            context.keys = { text: "names", description: "description" };
            context.completions = options;
            if (scope)
                context.filters.push(function ({ item: opt }) opt.scope & scope);
        },

        optionValue: function (context, name, op, curValue)
        {
            let opt = options.get(name);
            let completer = opt.completer;
            if (!completer)
                return;

            let curValues = curValue != null ? opt.parseValues(curValue) : opt.values;
            let newValues = opt.parseValues(context.filter);

            let len = context.filter.length;
            switch (opt.type)
            {
                case "boolean":
                    if (!completer)
                        completer = function () [["true", ""], ["false", ""]];
                    break;
                case "stringlist":
                    let target = newValues.pop();
                    len = target ? target.length : 0;
                    break;
                case "charlist":
                    len = 0;
                    break;
            }
            // TODO: Highlight when invalid
            context.advance(context.filter.length - len);

            context.title = ["Option Value"];
            let completions = completer(context);
            if (!completions)
                return;
            // Not Vim compatible, but is a significant enough improvement
            // that it's worth breaking compatibility.
            if (newValues instanceof Array)
            {
                completions = completions.filter(function (val) newValues.indexOf(val[0]) == -1);
                switch (op)
                {
                    case "+":
                        completions = completions.filter(function (val) curValues.indexOf(val[0]) == -1);
                        break;
                    case "-":
                        completions = completions.filter(function (val) curValues.indexOf(val[0]) > -1);
                        break;
                }
            }
            context.completions = completions;
        },

        preference: function preference(context)
        {
            context.anchored = false;
            context.title = ["Firefox Preference", "Value"];
            context.keys = { text: function (item) item, description: function (item) options.getPref(item) };
            context.completions = services.get("pref").getChildList("", { value: 0 });
        },

        search: function search(context, noSuggest)
        {
            let [, keyword, space, args] = context.filter.match(/^\s*(\S*)(\s*)(.*)$/);
            let keywords = bookmarks.getKeywords();
            let engines = bookmarks.getSearchEngines();

            context.title = ["Search Keywords"];
            context.completions = keywords.concat(engines);
            context.keys = { text: 0, description: 1, icon: 2 };

            if (!space || noSuggest)
                return;

            context.fork("suggest", keyword.length + space.length, this, "searchEngineSuggest",
                    keyword, true);

            let item = keywords.filter(function (k) k.keyword == keyword)[0];
            if (item && item.url.indexOf("%s") > -1)
                context.fork("keyword/" + keyword, keyword.length + space.length, null, function (context) {
                    context.format = history.format;
                    context.title = [keyword + " Quick Search"];
                    // context.background = true;
                    context.compare = CompletionContext.Sort.unsorted;
                    context.generate = function () {
                        let [begin, end] = item.url.split("%s");

                        return history.get({ uri: window.makeURI(begin), uriIsPrefix: true }).map(function (item) {
                            let rest = item.url.length - end.length;
                            let query = item.url.substring(begin.length, rest);
                            if (item.url.substr(rest) == end && query.indexOf("&") == -1)
                            {
                                item.url = decodeURIComponent(query);
                                return item;
                            }
                        }).filter(util.identity);
                    };
                });
        },

        searchEngineSuggest: function searchEngineSuggest(context, engineAliases, kludge)
        {
            if (!context.filter)
                return;

            let engineList = (engineAliases || options["suggestengines"] || "google").split(",");

            let completions = [];
            engineList.forEach(function (name) {
                let engine = services.get("browserSearch").getEngineByAlias(name);
                if (!engine)
                    return;
                let [,word] = /^\s*(\S+)/.exec(context.filter) || [];
                if (!kludge && word == name) // FIXME: Check for matching keywords
                    return;
                let ctxt = context.fork(name, 0);

                ctxt.title = [engine.description + " Suggestions"];
                ctxt.compare = CompletionContext.Sort.unsorted;
                ctxt.incomplete = true;
                bookmarks.getSuggestions(name, ctxt.filter, function (compl) {
                    ctxt.incomplete = false;
                    ctxt.completions = compl;
                });
            });
        },

        shellCommand: function shellCommand(context)
        {
            context.title = ["Shell Command", "Path"];
            context.generate = function ()
            {
                let dirNames = services.get("environment").get("PATH").split(RegExp(liberator.has("Win32") ? ";" : ":"));
                let commands = [];

                for (let [,dirName] in Iterator(dirNames))
                {
                    let dir = io.getFile(dirName);
                    if (dir.exists() && dir.isDirectory())
                    {
                        commands.push([[file.leafName, dir.path] for ([i, file] in Iterator(io.readDirectory(dir)))
                                            if (file.isFile() && file.isExecutable())]);
                    }
                }

                return util.Array.flatten(commands);
            }
        },

        sidebar: function sidebar(context)
        {
            let menu = document.getElementById("viewSidebarMenu");
            context.title = ["Sidebar Panel"];
            context.completions = Array.map(menu.childNodes, function (n) [n.label, ""]);
        },

        // filter a list of urls
        //
        // may consist of search engines, filenames, bookmarks and history,
        // depending on the 'complete' option
        // if the 'complete' argument is passed like "h", it temporarily overrides the complete option
        url: function url(context, complete)
        {
            let numLocationCompletions = 0; // how many async completions did we already return to the caller?
            let start = 0;
            let skip = context.filter.match("^.*" + options["urlseparator"]); // start after the last 'urlseparator'
            if (skip)
                context.advance(skip[0].length);

            // Will, and should, throw an error if !(c in opts)
            Array.forEach(complete || options["complete"], function (c) {
                let completer = completion.urlCompleters[c];
                context.fork.apply(context, [c, 0, completion, completer.completer].concat(completer.args));
            });
        },

        urlCompleters: {},

        addUrlCompleter: function addUrlCompleter(opt)
        {
            let completer = UrlCompleter.apply(null, Array.slice(arguments));
            completer.args = Array.slice(arguments, completer.length);
            this.urlCompleters[opt] = completer;
        },

        urls: function (context, tags)
        {
            let compare = String.localeCompare;
            let contains = String.indexOf
            if (context.ignoreCase)
            {
                compare = util.compareIgnoreCase;
                contains = function (a, b) a && a.toLowerCase().indexOf(b.toLowerCase()) > -1;
            }

            if (tags)
                context.filters.push(function (item) tags.
                    every(function (tag) (item.tags || []).
                        some(function (t) !compare(tag, t))));

            context.anchored = false;
            if (!context.title)
                context.title = ["URL", "Title"];

            context.fork("additional", 0, this, function (context) {
                context.title[0] += " (additional)";
                context.filter = context.parent.filter; // FIXME
                context.completions = context.parent.completions;
                // For items whose URL doesn't exactly match the filter,
                // accept them if all tokens match either the URL or the title.
                // Filter out all directly matching strings.
                let match = context.filters[0];
                context.filters[0] = function (item) !match.call(this, item);
                // and all that don't match the tokens.
                let tokens = context.filter.split(/\s+/);
                context.filters.push(function (item) tokens.every(
                        function (tok) contains(item.url, tok) ||
                                       contains(item.title, tok)));

                let re = RegExp(tokens.filter(util.identity).map(util.escapeRegex).join("|"), "g");
                function highlight(item, text, i) process[i].call(this, item, template.highlightRegexp(text, re));
                let process = [template.icon, function (item, k) k];
                context.process = [
                    function (item, text) highlight.call(this, item, item.text, 0),
                    function (item, text) highlight.call(this, item, text, 1)
                ];
            });
        },

        userCommand: function userCommand(context)
        {
            context.title = ["User Command", "Definition"];
            context.keys = { text: "name", description: "replacementText" };
            context.completions = commands.getUserCommands();
        },

        userMapping: function userMapping(context, args, modes)
        {
            // FIXME: have we decided on a 'standard' way to handle this clash? --djk
            modes = modes || [modules.modes.NORMAL];

            if (args.completeArg == 0)
            {
                let maps = [[m.names[0], ""] for (m in mappings.getUserIterator(modes))];
                context.completions = maps;
            }
        }
        //}}}
    };

    const UrlCompleter = new Struct("name", "description", "completer");
    self.addUrlCompleter("S", "Suggest engines", self.searchEngineSuggest);
    self.addUrlCompleter("b", "Bookmarks", self.bookmark);
    self.addUrlCompleter("h", "History", self.history);
    self.addUrlCompleter("f", "Local files", self.file);
    self.addUrlCompleter("l", "Firefox location bar entries (bookmarks and history sorted in an intelligent way)", self.location);
    self.addUrlCompleter("s", "Search engines and keyword URLs", self.search);

    return self;
    //}}}
}; //}}}

// vim: set fdm=marker sw=4 ts=4 et: