var FORMCHANGECHECKERNAME = 'core-formchangechecker',

    FORMCHANGECHECKER = function() {
        FORMCHANGECHECKER.superclass.constructor.apply(this, arguments);
    };

Y.extend(FORMCHANGECHECKER, Y.Base, {

        // The delegated listeners we need to detach after the initial value has been stored once
        initialvaluelisteners : [],

        /**
          * Initialize the module
          */
        initializer : function() {
            var formid = 'form#' + this.get('formid'),
                currentform = Y.one(formid);

            if (!currentform) {
                // If the form was not found, then we can't check for changes.
                return;
            }

            // Add change events to the form elements
            currentform.delegate('change', M.core_formchangechecker.set_form_changed, 'input', this);
            currentform.delegate('change', M.core_formchangechecker.set_form_changed, 'textarea', this);
            currentform.delegate('change', M.core_formchangechecker.set_form_changed, 'select', this);

            // Add a focus event to check for changes which are made without triggering a change event
            this.initialvaluelisteners.push(currentform.delegate('focus', this.store_initial_value, 'input', this));
            this.initialvaluelisteners.push(currentform.delegate('focus', this.store_initial_value, 'textarea', this));
            this.initialvaluelisteners.push(currentform.delegate('focus', this.store_initial_value, 'select', this));

            // We need any submit buttons on the form to set the submitted flag
            Y.one(formid).on('submit', M.core_formchangechecker.set_form_submitted, this);

            // YUI doesn't support onbeforeunload properly so we must use the DOM to set the onbeforeunload. As
            // a result, the has_changed must stay in the DOM too
            window.onbeforeunload = M.core_formchangechecker.report_form_dirty_state;
        },

        /**
          * Store the initial value of the currently focussed element
          *
          * If an element has been focussed and changed but not yet blurred, the on change
          * event won't be fired. We need to store it's initial value to compare it in the
          * get_form_dirty_state function later.
          */
        store_initial_value : function(e) {
            var thisevent;
            if (e.target.hasClass('ignoredirty')) {
                // Don't warn on elements with the ignoredirty class
                return;
            }
            if (M.core_formchangechecker.get_form_dirty_state()) {
                // Detach all listen events to prevent duplicate initial value setting
                while (this.initialvaluelisteners.length) {
                    thisevent = this.initialvaluelisteners.shift();
                    thisevent.detach();
                }

                return;
            }

            // Make a note of the current element so that it can be interrogated and
            // compared in the get_form_dirty_state function
            M.core_formchangechecker.stateinformation.focused_element = {
                element : e.target,
                initial_value : e.target.get('value')
            };
        }
    },
    {
        NAME : FORMCHANGECHECKERNAME,
        ATTRS : {
            formid : {
                'value' : ''
            }
        }
    }
);

M.core_formchangechecker = M.core_formchangechecker || {};

// We might have multiple instances of the form change protector
M.core_formchangechecker.instances = M.core_formchangechecker.instances || [];
M.core_formchangechecker.init = function(config) {
    var formchangechecker = new FORMCHANGECHECKER(config);
    M.core_formchangechecker.instances.push(formchangechecker);
    return formchangechecker;
};

// Store state information
M.core_formchangechecker.stateinformation = [];

/**
  * Set the form changed state to true
  */
M.core_formchangechecker.set_form_changed = function(e) {
    if (e && e.target && e.target.hasClass('ignoredirty')) {
        // Don't warn on elements with the ignoredirty class
        return;
    }
    M.core_formchangechecker.stateinformation.formchanged = 1;

    // Once the form has been marked as dirty, we no longer need to keep track of form elements
    // which haven't yet blurred
    delete M.core_formchangechecker.stateinformation.focused_element;
};

/**
  * Set the form submitted state to true
  */
M.core_formchangechecker.set_form_submitted = function() {
    M.core_formchangechecker.stateinformation.formsubmitted = 1;
};

/**
  * Attempt to determine whether the form has been modified in any way and
  * is thus 'dirty'
  *
  * @return Integer 1 is the form is dirty; 0 if not
  */
M.core_formchangechecker.get_form_dirty_state = function() {
    var state = M.core_formchangechecker.stateinformation,
        editor;

    // If the form was submitted, then return a non-dirty state
    if (state.formsubmitted) {
        return 0;
    }

    // If any fields have been marked dirty, return a dirty state
    if (state.formchanged) {
        return 1;
    }

    // If a field has been focused and changed, but still has focus then the browser won't fire the
    // onChange event. We check for this eventuality here
    if (state.focused_element) {
        if (state.focused_element.element.get('value') !== state.focused_element.initial_value) {
            return 1;
        }
    }

    // Handle TinyMCE editor instances
    // We can't add a listener in the initializer as the editors may not have been created by that point
    // so we do so here instead
    if (typeof tinyMCE !== 'undefined') {
        for (editor in tinyMCE.editors) {
            if (tinyMCE.editors[editor].isDirty()) {
                return 1;
            }
        }
    }

    // If we reached here, then the form hasn't met any of the dirty conditions
    return 0;
};

/**
  * Return a suitable message if changes have been made to a form
  */
M.core_formchangechecker.report_form_dirty_state = function(e) {
    if (!M.core_formchangechecker.get_form_dirty_state()) {
        // the form is not dirty, so don't display any message
        return;
    }

    // This is the error message that we'll show to browsers which support it
    var warningmessage = M.util.get_string('changesmadereallygoaway', 'moodle');

    if (M.cfg.behatsiterunning) {
        // If the behat site is running we don't want browser alerts.
        return;
    }

    // Most browsers are happy with the returnValue being set on the event
    // But some browsers do not consistently pass the event
    if (e) {
        e.returnValue = warningmessage;
    }

    // But some require it to be returned instead
    return warningmessage;
};