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Filename : microhistory.js
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/* vim: set expandtab sw=4 ts=4 sts=4: */
/**
 * An implementation of a client-side page cache.
 * This object also uses the cache to provide a simple microhistory,
 * that is the ability to use the back and forward buttons in the browser
 */
PMA_MicroHistory = {
    /**
     * @var int The maximum number of pages to keep in the cache
     */
    MAX: 6,
    /**
     * @var object A hash used to prime the cache with data about the initially
     *             loaded page. This is set in the footer, and then loaded
     *             by a double-queued event further down this file.
     */
    primer: {},
    /**
     * @var array Stores the content of the cached pages
     */
    pages: [],
    /**
     * @var int The index of the currently loaded page
     *          This is used to know at which point in the history we are
     */
    current: 0,
    /**
     * Saves a new page in the cache
     *
     * @param string hash    The hash part of the url that is being loaded
     * @param array  scripts A list of scripts that is required for the page
     * @param string menu    A hash that links to a menu stored
     *                       in a dedicated menu cache
     * @param array  params  A list of parameters used by PMA_commonParams()
     * @param string rel     A relationship to the current page:
     *                       'samepage': Forces the response to be treated as
     *                                   the same page as the current one
     *                       'newpage':  Forces the response to be treated as
     *                                   a new page
     *                       undefined:  Default behaviour, 'samepage' if the
     *                                   selflinks of the two pages are the same.
     *                                   'newpage' otherwise
     *
     * @return void
     */
    add: function (hash, scripts, menu, params, rel) {
        if (this.pages.length > PMA_MicroHistory.MAX) {
            // Trim the cache, to the maximum number of allowed entries
            // This way we will have a cached menu for every page
            for (var i = 0; i < this.pages.length - this.MAX; i++) {
                delete this.pages[i];
            }
        }
        while (this.current < this.pages.length) {
            // trim the cache if we went back in the history
            // and are now going forward again
            this.pages.pop();
        }
        if (rel === 'newpage' ||
            (
                typeof rel === 'undefined' && (
                    typeof this.pages[this.current - 1] === 'undefined' ||
                    this.pages[this.current - 1].hash !== hash
                )
            )
        ) {
            this.pages.push({
                hash: hash,
                content: $('#page_content').html(),
                scripts: scripts,
                selflink: $('#selflink').html(),
                menu: menu,
                params: params
            });
            PMA_SetUrlHash(this.current, hash);
            this.current++;
        }
    },
    /**
     * Restores a page from the cache. This is called when the hash
     * part of the url changes and it's structure appears to be valid
     *
     * @param string index Which page from the history to load
     *
     * @return void
     */
    navigate: function (index) {
        if (typeof this.pages[index] === 'undefined' ||
            typeof this.pages[index].content === 'undefined' ||
            typeof this.pages[index].menu === 'undefined' ||
            ! PMA_MicroHistory.menus.get(this.pages[index].menu)
        ) {
            PMA_ajaxShowMessage(
                '<div class="error">' + PMA_messages.strInvalidPage + '</div>',
                false
            );
        } else {
            AJAX.active = true;
            var record = this.pages[index];
            AJAX.scriptHandler.reset(function () {
                $('#page_content').html(record.content);
                $('#selflink').html(record.selflink);
                PMA_MicroHistory.menus.replace(PMA_MicroHistory.menus.get(record.menu));
                PMA_commonParams.setAll(record.params);
                AJAX.scriptHandler.load(record.scripts);
                PMA_MicroHistory.current = ++index;
            });
        }
    },
    /**
     * Resaves the content of the current page in the cache.
     * Necessary in order not to show the user some outdated version of the page
     *
     * @return void
     */
    update: function () {
        var page = this.pages[this.current - 1];
        if (page) {
            page.content = $('#page_content').html();
        }
    },
    /**
     * @var object Dedicated menu cache
     */
    menus: {
        /**
         * Returns the number of items in an associative array
         *
         * @return int
         */
        size: function (obj) {
            var size = 0;
            var key;
            for (key in obj) {
                if (obj.hasOwnProperty(key)) {
                    size++;
                }
            }
            return size;
        },
        /**
         * @var hash Stores the content of the cached menus
         */
        data: {},
        /**
         * Saves a new menu in the cache
         *
         * @param string hash    The hash (trimmed md5) of the menu to be saved
         * @param string content The HTML code of the menu to be saved
         *
         * @return void
         */
        add: function (hash, content) {
            if (this.size(this.data) > PMA_MicroHistory.MAX) {
                // when the cache grows, we remove the oldest entry
                var oldest;
                var key;
                var init = 0;
                for (var i in this.data) {
                    if (this.data[i]) {
                        if (! init || this.data[i].timestamp.getTime() < oldest.getTime()) {
                            oldest = this.data[i].timestamp;
                            key = i;
                            init = 1;
                        }
                    }
                }
                delete this.data[key];
            }
            this.data[hash] = {
                content: content,
                timestamp: new Date()
            };
        },
        /**
         * Retrieves a menu given its hash
         *
         * @param string hash The hash of the menu to be retrieved
         *
         * @return string
         */
        get: function (hash) {
            if (this.data[hash]) {
                return this.data[hash].content;
            } else {
                // This should never happen as long as the number of stored menus
                // is larger or equal to the number of pages in the page cache
                return '';
            }
        },
        /**
         * Prepares part of the parameter string used during page requests,
         * this is necessary to tell the server which menus we have in the cache
         *
         * @return string
         */
        getRequestParam: function () {
            var param = '';
            var menuHashes = [];
            for (var i in this.data) {
                menuHashes.push(i);
            }
            var menuHashesParam = menuHashes.join('-');
            if (menuHashesParam) {
                param = PMA_commonParams.get('arg_separator') + 'menuHashes=' + menuHashesParam;
            }
            return param;
        },
        /**
         * Replaces the menu with new content
         *
         * @return void
         */
        replace: function (content) {
            $('#floating_menubar').html(content)
                // Remove duplicate wrapper
                // TODO: don't send it in the response
                .children().first().remove();
            $('#topmenu').menuResizer(PMA_mainMenuResizerCallback);
        }
    }
};

/**
 * URL hash management module.
 * Allows direct bookmarking and microhistory.
 */
PMA_SetUrlHash = (function (jQuery, window) {
    'use strict';
    /**
     * Indictaes whether we have already completed
     * the initialisation of the hash
     *
     * @access private
     */
    var ready = false;
    /**
     * Stores a hash that needed to be set when we were not ready
     *
     * @access private
     */
    var savedHash = '';
    /**
     * Flag to indicate if the change of hash was triggered
     * by a user pressing the back/forward button or if
     * the change was triggered internally
     *
     * @access private
     */
    var userChange = true;

    // Fix favicon disappearing in Firefox when setting location.hash
    function resetFavicon () {
        if (navigator.userAgent.indexOf('Firefox') > -1) {
            // Move the link tags for the favicon to the bottom
            // of the head element to force a reload of the favicon
            $('head > link[href="favicon\\.ico"]').appendTo('head');
        }
    }

    /**
     * Sets the hash part of the URL
     *
     * @access public
     */
    function setUrlHash (index, hash) {
        /*
         * Known problem:
         * Setting hash leads to reload in webkit:
         * http://www.quirksmode.org/bugreports/archives/2005/05/Safari_13_visual_anomaly_with_windowlocationhref.html
         *
         * so we expect that users are not running an ancient Safari version
         */

        userChange = false;
        if (ready) {
            window.location.hash = 'PMAURL-' + index + ':' + hash;
            resetFavicon();
        } else {
            savedHash = 'PMAURL-' + index + ':' + hash;
        }
    }
    /**
     * Start initialisation
     */
    var urlhash = window.location.hash;
    if (urlhash.substring(0, 8) === '#PMAURL-') {
        // We have a valid hash, let's redirect the user
        // to the page that it's pointing to
        var colon_position = urlhash.indexOf(':');
        var questionmark_position = urlhash.indexOf('?');
        if (colon_position !== -1 && questionmark_position !== -1 && colon_position < questionmark_position) {
            var hash_url = urlhash.substring(colon_position + 1, questionmark_position);
            if (PMA_gotoWhitelist.indexOf(hash_url) !== -1) {
                window.location = urlhash.substring(
                    colon_position + 1
                );
            }
        }
    } else {
        // We don't have a valid hash, so we'll set it up
        // when the page finishes loading
        jQuery(function () {
            /* Check if we should set URL */
            if (savedHash !== '') {
                window.location.hash = savedHash;
                savedHash = '';
                resetFavicon();
            }
            // Indicate that we're done initialising
            ready = true;
        });
    }
    /**
     * Register an event handler for when the url hash changes
     */
    jQuery(function () {
        jQuery(window).hashchange(function () {
            if (userChange === false) {
                // Ignore internally triggered hash changes
                userChange = true;
            } else if (/^#PMAURL-\d+:/.test(window.location.hash)) {
                // Change page if the hash changed was triggered by a user action
                var index = window.location.hash.substring(
                    8, window.location.hash.indexOf(':')
                );
                PMA_MicroHistory.navigate(index);
            }
        });
    });
    /**
     * Publicly exposes a reference to the otherwise private setUrlHash function
     */
    return setUrlHash;
}(jQuery, window));