ko.bindingHandlers['value'] = {
    'after': ['options', 'foreach'],
    'init': function (element, valueAccessor, allBindings) {
        // If the value binding is placed on a radio/checkbox, then just pass through to checkedValue and quit
        if (element.tagName.toLowerCase() == "input" && (element.type == "checkbox" || element.type == "radio")) {
            ko.applyBindingAccessorsToNode(element, { 'checkedValue': valueAccessor });
            return;
        }

        // Always catch "change" event; possibly other events too if asked
        var eventsToCatch = ["change"];
        var requestedEventsToCatch = allBindings.get("valueUpdate");
        var propertyChangedFired = false;
        var elementValueBeforeEvent = null;

        if (requestedEventsToCatch) {
            if (typeof requestedEventsToCatch == "string") // Allow both individual event names, and arrays of event names
                requestedEventsToCatch = [requestedEventsToCatch];
            ko.utils.arrayPushAll(eventsToCatch, requestedEventsToCatch);
            eventsToCatch = ko.utils.arrayGetDistinctValues(eventsToCatch);
        }

        var valueUpdateHandler = function() {
            elementValueBeforeEvent = null;
            propertyChangedFired = false;
            var modelValue = valueAccessor();
            var elementValue = ko.selectExtensions.readValue(element);
            ko.expressionRewriting.writeValueToProperty(modelValue, allBindings, 'value', elementValue);
        }

        // Workaround for https://github.com/SteveSanderson/knockout/issues/122
        // IE doesn't fire "change" events on textboxes if the user selects a value from its autocomplete list
        var ieAutoCompleteHackNeeded = ko.utils.ieVersion && element.tagName.toLowerCase() == "input" && element.type == "text"
                                       && element.autocomplete != "off" && (!element.form || element.form.autocomplete != "off");
        if (ieAutoCompleteHackNeeded && ko.utils.arrayIndexOf(eventsToCatch, "propertychange") == -1) {
            ko.utils.registerEventHandler(element, "propertychange", function () { propertyChangedFired = true });
            ko.utils.registerEventHandler(element, "focus", function () { propertyChangedFired = false });
            ko.utils.registerEventHandler(element, "blur", function() {
                if (propertyChangedFired) {
                    valueUpdateHandler();
                }
            });
        }

        ko.utils.arrayForEach(eventsToCatch, function(eventName) {
            // The syntax "after<eventname>" means "run the handler asynchronously after the event"
            // This is useful, for example, to catch "keydown" events after the browser has updated the control
            // (otherwise, ko.selectExtensions.readValue(this) will receive the control's value *before* the key event)
            var handler = valueUpdateHandler;
            if (ko.utils.stringStartsWith(eventName, "after")) {
                handler = function() {
                    // The elementValueBeforeEvent variable is non-null *only* during the brief gap between
                    // a keyX event firing and the valueUpdateHandler running, which is scheduled to happen
                    // at the earliest asynchronous opportunity. We store this temporary information so that
                    // if, between keyX and valueUpdateHandler, the underlying model value changes separately,
                    // we can overwrite that model value change with the value the user just typed. Otherwise,
                    // techniques like rateLimit can trigger model changes at critical moments that will
                    // override the user's inputs, causing keystrokes to be lost.
                    elementValueBeforeEvent = ko.selectExtensions.readValue(element);
                    setTimeout(valueUpdateHandler, 0);
                };
                eventName = eventName.substring("after".length);
            }
            ko.utils.registerEventHandler(element, eventName, handler);
        });

        var updateFromModel = function () {
            var newValue = ko.utils.unwrapObservable(valueAccessor());
            var elementValue = ko.selectExtensions.readValue(element);

            if (elementValueBeforeEvent !== null && newValue === elementValueBeforeEvent) {
                setTimeout(updateFromModel, 0);
                return;
            }

            var valueHasChanged = (newValue !== elementValue);

            if (valueHasChanged) {
                if (ko.utils.tagNameLower(element) === "select") {
                    var allowUnset = allBindings.get('valueAllowUnset');
                    var applyValueAction = function () {
                        ko.selectExtensions.writeValue(element, newValue, allowUnset);
                    };
                    applyValueAction();

                    if (!allowUnset && newValue !== ko.selectExtensions.readValue(element)) {
                        // If you try to set a model value that can't be represented in an already-populated dropdown, reject that change,
                        // because you're not allowed to have a model value that disagrees with a visible UI selection.
                        ko.dependencyDetection.ignore(ko.utils.triggerEvent, null, [element, "change"]);
                    } else {
                        // Workaround for IE6 bug: It won't reliably apply values to SELECT nodes during the same execution thread
                        // right after you've changed the set of OPTION nodes on it. So for that node type, we'll schedule a second thread
                        // to apply the value as well.
                        setTimeout(applyValueAction, 0);
                    }
                } else {
                    ko.selectExtensions.writeValue(element, newValue);
                }
            }
        };

        ko.computed(updateFromModel, null, { disposeWhenNodeIsRemoved: element });
    },
    'update': function() {} // Keep for backwards compatibility with code that may have wrapped value binding
};
ko.expressionRewriting.twoWayBindings['value'] = true;
