var optionsCache = {},
    // Used for splitting on whitespace
    core_rnotwhite = /\S+/g;

// Convert String-formatted options into Object-formatted ones and store in cache
function createOptions( options ) {
    // 多個變數指向同一物件(或陣列)引用時，其中一個變數修改了被引用物件的內部結構，其他引用變數也會表現出來
    var object = optionsCache[ options ] = {};
    jQuery.each( options.match( core_rnotwhite ) 
 
|| [], function( _, flag ) {
        object[ flag ] = true; // optionsCache[ options ][ flag ] = true;
    });
    return object;
}

jQuery.Callbacks = function( options ) {

    // Convert options from String-formatted to Object-formatted if needed
    // (we check in cache first)
    options = typeof
 
 options === "string" ?
        // 快取所有的引數標誌，當再次傳遞已傳遞過的引數標誌，則使用快取值optionsCache[ options ]        
        ( optionsCache[ options ] || createOptions( options ) ) :

        // 說明也可以這樣$.Callbacks({once:true, memory:true})使用
        jQuery.extend( {}, options );

    var // Flag to know if list is currently firing
 

        firing,
        // Last fire value (for non-forgettable lists)
        memory,
        // Flag to know if list was already fired
        fired,
        // End of the loop when firing
        firingLength,
        // Index of currently firing callback (modified by remove if needed)
        firingIndex,
        // First callback to fire (used internally by add and fireWith)
        firingStart,
        // Actual callback list
        list = [],
        // Stack of fire calls for repeatable lists
        stack = !options.once && [],

        // Fire callbacks
        // data為fireWith內部整理的args陣列
        fire = function( data ) {
            memory = options.memory && data;
            fired = true;

            // 處理在add中，options.memory = true;的情況
            firingIndex = firingStart || 0;
            firingStart = 0;

            firingLength = list.length;
            firing = true;
            for ( ; list && firingIndex < firingLength; firingIndex++ ) {
                // 正在執行的回撥返回值為false 且 options.stopOnFalse為true，則終止回撥佇列的執行
                if ( list[ firingIndex ].apply( data[ 0 ], data[ 1 ] ) === false && options.stopOnFalse ) {
                    memory = false; // To prevent further calls using add
                    break;
                }
            }
            firing = false;
            if ( list ) {
                // 處理正在執行的回撥中執行fireWith的操作;
                if ( stack ) {
                    if ( stack.length ) {
                        fire( stack.shift() );
                    }
                }
                // 上一分支狀態為回撥執行過，且可以執行多次
                // 此時 options.once = true; 這裡將list設定為[]，只是確保下次執行fire時，無回撥執行
                // 但是如果 options.memory = true; 仍然會執行add中的fire操作，因為此時回撥列表中已有回撥
                else if ( memory ) {
                    list = [];
                }
                else {
                    self.disable();
                }
            }
        },
        // Actual Callbacks object
        self = {
            // Add a callback or a collection of callbacks to the list
            add: function() {
                if ( list ) {
                    // First, we save the current length
                    var start = list.length;
                    (function add( args ) {
                        jQuery.each( args, function( _, arg ) {
                            var type = jQuery.type( arg );
                            if ( type === "function" ) {
                                // 回撥不唯一 或 唯一且不存在，則push
                                if ( !options.unique || !self.has( arg ) ) {
                                    list.push( arg );
                                }
                            }
                            // 遞迴檢查
                            else if ( arg && arg.length && type !== "string" ) {
                                // Inspect recursively
                                add( arg );
                            }
                        });
                    })( arguments );
                    // Do we need to add the callbacks to the
                    // current firing batch?
                    // 正在執行的回撥執行了add操作，則更新firingLength
                    if ( firing ) {
                        firingLength = list.length;

                    // With memory, if we're not firing then
                    // we should call right away
                    // 如果options.memory為true，則再次執行fire，且引數相同，fire中的firingIndex為此時的firingStart
                    }
                    else if ( memory ) {
                        firingStart = start;
                        fire( memory );
                    }
                }
                return this;
            },
            // Remove a callback from the list
            remove: function() {
                if ( list ) {
                    jQuery.each( arguments, function( _, arg ) {
                        var index;                
                        while( ( index = jQuery.inArray( arg, list, index ) ) > -1 ) {
                            // 查詢到所對應的索引，則移除索引項
                            list.splice( index, 1 );

                            // Handle firing indexes
                            // 正在執行的回撥執行了remvoe操作，則更新firingLength和firingIndex的值
                            if ( firing ) {
                                if ( index <= firingLength ) {
                                    firingLength--;
                                }
                                if ( index <= firingIndex ) {
                                    firingIndex--;
                                }
                            }
                        }
                    });
                }
                return this;
            },
            // Check if a given callback is in the list.
            // If no argument is given, return whether or not list has callbacks attached.
            has: function( fn ) {
                return fn ? jQuery.inArray( fn, list ) > -1 : !!( list && list.length );
            },
            // Remove all callbacks from the list
            empty: function() {
                list = [];
                return this;
            },
            // Have the list do nothing anymore
            // 禁用add,remove,fire主要方法的工作
            disable: function() {
                list = stack = memory = undefined;
                return this;
            },
            // Is it disabled?
            disabled: function() {
                return !list;
            },
            // Lock the list in its current state
            lock: function() {
                // 如果回撥執行過，則將阻止self.fire操作
                // 但如果 options.memory = true，則仍然會執行fire操作
                stack = undefined;
                
                // 回撥未執行，則禁用
                if ( !memory ) {
                    self.disable();
                }
                return this;
            },
            // Is it locked?
            locked: function() {
                return !stack;
            },
            // Call all callbacks with the given context and arguments
            fireWith: function( context, args ) {
                args = args || [];
                args = [ context, args.slice ? args.slice() : args ];
                
                // 回撥未執行 或 已執行且可以執行多次
                if ( list && ( !fired || stack ) ) {

                    // 正在執行的回撥函式執行了fireWith操作( 暗指回撥列表已執行過，且可以執行多次，stack = []; )
                    // 該函式需要條件執行，或有移除該函式的操作，否則陷入死迴圈，詳見例2
                    if ( firing ) {
                        stack.push( args );
                    }
                    // 正在執行的回撥函式沒有執行fireWith操作
                    else {
                        fire( args );
                    }
                }
                return this;
            },
            // Call all the callbacks with the given arguments
            fire: function() {
                self.fireWith( this, arguments );
                return this;
            },
            // To know if the callbacks have already been called at least once
            fired: function() {
                return !!fired;
            }
        };
    return self;
};