/* angularjs Scroll Glue
 * version 2.1.0
 * https://github.com/Luegg/angularjs-scroll-glue
 * An AngularJs directive that automatically scrolls to the bottom of an element on changes in it's scope.
*/

// Allow module to be loaded via require when using common js. e.g. npm
if(typeof module === "object" && module.exports){
    module.exports = 'luegg.directives';
}

(function(angular, undefined){
    'use strict';

    function createActivationState($parse, attr, scope){
        function unboundState(initValue){
            var activated = initValue;
            return {
                getValue: function(){
                    return activated;
                },
                setValue: function(value){
                    activated = value;
                }
            };
        }

        function oneWayBindingState(getter, scope){
            return {
                getValue: function(){
                    return getter(scope);
                },
                setValue: function(){}
            };
        }

        function twoWayBindingState(getter, setter, scope){
            return {
                getValue: function(){
                    return getter(scope);
                },
                setValue: function(value){
                    if(value !== getter(scope)){
                        scope.$apply(function(){
                            setter(scope, value);
                        });
                    }
                }
            };
        }

        if(attr !== ""){
            var getter = $parse(attr);
            if(getter.assign !== undefined){
                return twoWayBindingState(getter, getter.assign, scope);
            } else {
                return oneWayBindingState(getter, scope);
            }
        } else {
            return unboundState(true);
        }
    }

    function createDirective(module, attrName, direction){
        module.directive(attrName, ['$parse', '$window', '$timeout', function($parse, $window, $timeout){
            return {
                priority: 1,
                restrict: 'A',
                link: function(scope, $el, attrs){
                    var el = $el[0],
                        activationState = createActivationState($parse, attrs[attrName], scope);

                    function scrollIfGlued() {
                        if(activationState.getValue() && !direction.isAttached(el)){
                            direction.scroll(el);
                        }
                    }

                    function onScroll() {
                        activationState.setValue(direction.isAttached(el));
                    }

                    scope.$watch(scrollIfGlued);

                    $timeout(scrollIfGlued, 0, false);

                    $window.addEventListener('resize', scrollIfGlued, false);

                    $el.on('scroll', onScroll);


                    // Remove listeners on directive destroy
                    $el.on('$destroy', function() {
                        $el.unbind('scroll', onScroll);
                    });

                    scope.$on('$destroy', function() {
                        $window.removeEventListener('resize', scrollIfGlued, false);
                    });
                }
            };
        }]);
    }

    var bottom = {
        isAttached: function(el){
            // + 1 catches off by one errors in chrome
            return el.scrollTop + el.clientHeight + 1 >= el.scrollHeight;
        },
        scroll: function(el){
            el.scrollTop = el.scrollHeight;
        }
    };

    var top = {
        isAttached: function(el){
            return el.scrollTop <= 1;
        },
        scroll: function(el){
            el.scrollTop = 0;
        }
    };

    var right = {
        isAttached: function(el){
            return el.scrollLeft + el.clientWidth + 1 >= el.scrollWidth;
        },
        scroll: function(el){
            el.scrollLeft = el.scrollWidth;
        }
    };

    var left = {
        isAttached: function(el){
            return el.scrollLeft <= 1;
        },
        scroll: function(el){
            el.scrollLeft = 0;
        }
    };

    var module = angular.module('luegg.directives', []);

    createDirective(module, 'scrollGlue', bottom);
    createDirective(module, 'scrollGlueTop', top);
    createDirective(module, 'scrollGlueBottom', bottom);
    createDirective(module, 'scrollGlueLeft', left);
    createDirective(module, 'scrollGlueRight', right);
}(angular));
