/*
 * This script is provided for inclusion in HTML activities that wish to access
 * VLE features such as parameters, attachments, and server-side data.
 *
 * This is a stub. If running on the VLE, the actual version of these functions
 * will automatically be applied using a script from the server that overwrites
 * the definitions here.
 *
 * For new projects, the current version of this file is available on the VLE
 * as /mod/oucontent/api/vleapi.js (this file is not actually used by the VLE).
 * We will try to ensure that old versions of this file keep working.
 */

var VLE = {
    /**
     * API version of this file (integer changed only when API has
     * non-compatible change).
     */
    apiversion : 1,

    /**
     * Point version of this file. Changed for information when there is an
     * update to the file version that does not break API.
     */
    pointversion : 0,

    /**
     * Marked true if sent from server.
     */
    serverversion : false,

    /**
     * Obtains value of a named parameter or attachment. For attachments, this
     * will return the URL of the attachment. If you want to retrieve the
     * content of the attachment, use get_attachment function.
     *
     * Parameter names are restricted to these characters: [A-Za-z0-9_-.] and
     * can only be up to 20 characters long.
     *
     * Because parameters are provided in the URL to index.html, this function
     * will not work if the user has clicked a link to a different file within
     * your activity, unless you previously ensured that all parameters were
     * included in the link.
     *
     * When not running in the VLE, this code still works to retrieve parameter
     * values from the URL.
     *
     * The following special parameter names are available when running in the
     * VLE. They have short names to avoid taking up too much space in the URL.
     *
     * _c : Course id (number); not set for previews
     * _i : Document item id (text; from id= on Item; not set for previews
     *      or if document item id does not match character restriction)
     * _p : Preview id (number); only set for previews
     * _a : Activity id (text; from id= on MediaContent); may or may not be set
     * _s : Moodle session key for user (text)
     * _u : Moodle user id (number)
     *
     * @param name Parameter name
     * @return Value of parameter or null if not set
     */
    get_param : function(name) {
        // Check valid param name
        this.check_key(name, 'Invalid param name: ' + name);

        // Find in query
        var search = String(location.search);
        var matches = new RegExp('[?&]' + name + '=([^&]+)').exec(search);
        if (matches && matches[1]) {
            return decodeURIComponent(matches[1].replace(/\+/g, ' '));
        } else {
            return null;
        }
    },

    /**
     * Gets the content of an attachment. (If you only want to retrieve the
     * URL, use get_param function.) The attachment is assumed to be an XML
     * or text file.
     *
     * You must pass two functions as parameters. Here is an example:
     * VLE.get_attachment('frog', function ok(text, xmldocument) { ... },
     *   function error(message) {...});
     *
     * In this example the xmldocument parameter is a DOM document object
     * containing the XML file result (if any), and the text parameter is a
     * string containing the result as plain text (if any). The error parameter
     * is a string.
     *
     * When not running in the VLE, this function may still work but should
     * be used for testing purposes only. Specifically, it only works fully
     * on Firefox (tested on Firefox 12) and while testing, the attachment must
     * be placed in the same folder as the HTML file. It doesn't work in Chrome
     * due to browser security restrictions (Chromium issue 47416) and works
     * only partially on IE9.
     *
     * @param name Attachment name
     * @param ok Function that is called if the attachment is retrieved OK.
     * @param error Function that is called if there is an error.
     */
    get_attachment : function(name, ok, error) {
        var url = this.get_param(name);
        if (!url) {
            error('Parameter not found: ' + name);
            return;
        }

        this.ajax_get(url, function(req) {
            ok(req.responseText, req.responseXML);
        }, error);
    },

    /**
     * Gets data that was stored on the server.
     *
     * Note that you should not normally use the last three parameters.
     * These are for special cases where you want to access the same
     * data across different activities.
     *
     * You can retrieve data either for the current user (each user has
     * independent data) or for all users (so that all users have different
     * data).
     *
     * You must pass two functions as parameters. Here is an example:
     * VLE.get_user_data(true, ['frog'], function ok(values) { ... },
     *   function error(message) { ...});
     *
     * In this example the 'values' parameter is a JavaScript object containing
     * fields with the same names as you passed (so in this case, values.frog
     * would be the value of the data named 'frog' for this user, or null if
     * no such data had been set). The 'message' parameter is a string.
     *
     * When not running in the VLE, always calls the 'error' function with the
     * message set to null.
     *
     * @param user If true, stores data for current user
     * @param names Array of names
     * @param ok Function that is called if the data is retrieved OK.
     * @param error Function that is called if there is an error.
     * @param activityid Activity id (Optional: omit to use current activity)
     * @param itemid Document item id (Optional; omit to use current document)
     * @param courseid Course numeric id (Optional; omit to use current course)
     */
    get_server_data : function(user, names, ok, error, activityid, itemid, courseid) {
        window.setTimeout(function() { error(null); }, 0);
    },

    /**
     * Stores data on the server for the current user.
     *
     * Note that you should not normally use the last three parameters.
     * These are for special cases where you want to access the same
     * data across different activities.
     *
     * You can set data either for the current user (each user has
     * independent data) or for all users (so that all users have different
     * data).
     *
     * The value of each key-value pair is limited to 65,536 characters but
     * can contain any Unicode. Keys may be up to 20 characters and must contain
     * only [A-Za-z0-9_-.]. Activity IDs and item IDs have the same restriction.
     * (Only when using them for HTML activities - this isn't enforced by the
     * schema as a whole.)
     *
     * You must pass two functions as parameters. Here is an example:
     * VLE.set_user_data(true, {'frog' : 'Ribbit!'}, function ok() { ... },
     *   function error(message) { ...});
     *
     * In this example the 'message' parameter is a string.
     *
     * Especially when storing data for all users, you may wish to consider
     * race conditions. For example, if you are storing a count value, you may
     * use a pattern where based on a user action, you retrieve the current
     * value (say, 4) and then set a new one (say, 5). If two users do this at
     * a similar time, you will end up setting it to 5 twice. To avoid this
     * possibility, you can use the optional previousvalues and retry
     * parameters. If you specify previousvalues, this should be the object
     * containing the old values of the data, as retrieved by get_server_data.
     * The system will only apply the update if the data is the same as this.
     * If it is different, then the retry function will be called, passing the
     * actual current server data as its single parameter.
     *
     * When not running in the VLE, always calls the 'error' function with the
     * message set to null.
     *
     * @param user If true, stores data for current user
     * @param values JavaScript object containing the key/value pairs to set
     * @param ok Function that is called if the data is set OK.
     * @param error Function that is called if there is an error.
     * @param previousvalues Previous values (optional)
     * @param retry Function that is called if previous values changed (optional)
     * @param activityid Activity id (optional: omit to use current activity)
     * @param itemid Document item id (optional; omit to use current document)
     * @param courseid Course numeric id (optional; omit to use current course)
     */
    set_server_data : function(user, values, ok, error, previousvalues, retry,
                               activityid, itemid, courseid) {
        window.setTimeout(function() { error(null); }, 0);
    },

    /**
     * (Internal function, not recommended for other use.)
     * Makes an AJAX GET request and calls the ok function if it succeeds or the
     * error function if it fails.
     */
    ajax_get : function(url, ok, error) {
        // Get the XMLHttpRequest object. On IE we prefer the ActiveX version
        // even though it now supports the standard way too, because the ActiveX
        // one can access files if run locally.
        var req;
        if (window.ActiveXObject) {
            req = new ActiveXObject("Microsoft.XMLHTTP");
        } else {
            req = new XMLHttpRequest();
        }
        req.open('GET', url, true);
        req.onreadystatechange = function(e) {
            if (req.readyState == 4) {
                // Status 0 is for local files (testing use only).
                if (req.status == 200 || req.status == 0) {
                    ok(req);
                } else {
                    error('Error ' + req.status + ' loading ' + url);
                }
            }
        };
        req.send(null);
    },

    /**
     * Internal use only: Various keys are restricted to a certain regular
     * expression. This checks it and throws exception if it doesn't match.
     * @param key Key to test
     * @param message Message to throw if it fails test
     */
    check_key : function(key, message) {
        if (key===null || !key.match(/^[A-Za-z0-9._-]{1,20}$/)) {
            throw message;
        }
    }
};
