/**
 * Checklist-model
 * AngularJS directive for list of checkboxes
 * https://github.com/vitalets/checklist-model
 * License: MIT http://opensource.org/licenses/MIT
 */

angular.module('checklist-model', [])
.directive('checklistModel', ['$parse', '$compile', function($parse, $compile) {
  // contains
  function contains(arr, item, comparator) {
    if (angular.isArray(arr)) {
      for (var i = arr.length; i--;) {
        if (comparator(arr[i], item)) {
          return true;
        }
      }
    }
    return false;
  }

  // add
  function add(arr, item, comparator) {
    arr = angular.isArray(arr) ? arr : [];
      if(!contains(arr, item, comparator)) {
          arr.push(item);
      }
    return arr;
  }  

  // remove
  function remove(arr, item, comparator) {
    if (angular.isArray(arr)) {
      for (var i = arr.length; i--;) {
        if (comparator(arr[i], item)) {
          arr.splice(i, 1);
          break;
        }
      }
    }
    return arr;
  }

  // http://stackoverflow.com/a/19228302/1458162
  function postLinkFn(scope, elem, attrs) {
     // exclude recursion, but still keep the model
    var checklistModel = attrs.checklistModel;
    attrs.$set("checklistModel", null);
    // compile with `ng-model` pointing to `checked`
    $compile(elem)(scope);
    attrs.$set("checklistModel", checklistModel);

    // getter for original model
    var checklistModelGetter = $parse(checklistModel);
    var checklistChange = $parse(attrs.checklistChange);
    var checklistBeforeChange = $parse(attrs.checklistBeforeChange);
    var ngModelGetter = $parse(attrs.ngModel);



    var comparator = angular.equals;

    if (attrs.hasOwnProperty('checklistComparator')){
      if (attrs.checklistComparator[0] == '.') {
        var comparatorExpression = attrs.checklistComparator.substring(1);
        comparator = function (a, b) {
          return a[comparatorExpression] === b[comparatorExpression];
        };
        
      } else {
        comparator = $parse(attrs.checklistComparator)(scope.$parent);
      }
    }

    // watch UI checked change
    scope.$watch(attrs.ngModel, function(newValue, oldValue) {
      if (newValue === oldValue) { 
        return;
      }

      if (checklistBeforeChange && (checklistBeforeChange(scope) === false)) {
        ngModelGetter.assign(scope, contains(checklistModelGetter(scope.$parent), getChecklistValue(), comparator));
        return;
      }

      setValueInChecklistModel(getChecklistValue(), newValue);

      if (checklistChange) {
        checklistChange(scope);
      }
    });

    // watches for value change of checklistValue (Credit to @blingerson)
    scope.$watch(getChecklistValue, function(newValue, oldValue) {
      if( newValue != oldValue && angular.isDefined(oldValue) && scope[attrs.ngModel] === true ) {
        var current = checklistModelGetter(scope.$parent);
        checklistModelGetter.assign(scope.$parent, remove(current, oldValue, comparator));
        checklistModelGetter.assign(scope.$parent, add(current, newValue, comparator));
      }
    });

    function getChecklistValue() {
      return attrs.checklistValue ? $parse(attrs.checklistValue)(scope.$parent) : attrs.value;
    }
    
    function setValueInChecklistModel(value, checked) {
      var current = checklistModelGetter(scope.$parent);
      if (angular.isFunction(checklistModelGetter.assign)) {
        if (checked === true) {
          checklistModelGetter.assign(scope.$parent, add(current, value, comparator));
        } else {
          checklistModelGetter.assign(scope.$parent, remove(current, value, comparator));
        }
      }
      
    }

    // declare one function to be used for both $watch functions
    function setChecked(newArr, oldArr) {
      if (checklistBeforeChange && (checklistBeforeChange(scope) === false)) {
        setValueInChecklistModel(getChecklistValue(), ngModelGetter(scope));
        return;
      }
      ngModelGetter.assign(scope, contains(newArr, getChecklistValue(), comparator));
    }

    // watch original model change
    // use the faster $watchCollection method if it's available
    if (angular.isFunction(scope.$parent.$watchCollection)) {
        scope.$parent.$watchCollection(checklistModel, setChecked);
    } else {
        scope.$parent.$watch(checklistModel, setChecked, true);
    }
  }

  return {
    restrict: 'A',
    priority: 1000,
    terminal: true,
    scope: true,
    compile: function(tElement, tAttrs) {

      if (!tAttrs.checklistValue && !tAttrs.value) {
        throw 'You should provide `value` or `checklist-value`.';
      }

      // by default ngModel is 'checked', so we set it if not specified
      if (!tAttrs.ngModel) {
        // local scope var storing individual checkbox model
        tAttrs.$set("ngModel", "checked");
      }

      return postLinkFn;
    }
  };
}]);

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Use object equality for watching checklist value