/*global setTimeout: false, console: false */
(function () {

    var async = {};

    // global on the server, window in the browser
    var root = this,
        previous_async = root.async;

    if (typeof module !== 'undefined' && module.exports) {
        module.exports = async;
    }
    else {
        root.async = async;
    }

    async.noConflict = function () {
        root.async = previous_async;
        return async;
    };

    //// cross-browser compatiblity functions ////

    var _forEach = function (arr, iterator) {
        if (arr.forEach) {
            return arr.forEach(iterator);
        }
        for (var i = 0; i < arr.length; i += 1) {
            iterator(arr[i], i, arr);
        }
    };

    var _map = function (arr, iterator) {
        if (arr.map) {
            return arr.map(iterator);
        }
        var results = [];
        _forEach(arr, function (x, i, a) {
            results.push(iterator(x, i, a));
        });
        return results;
    };

    var _reduce = function (arr, iterator, memo) {
        if (arr.reduce) {
            return arr.reduce(iterator, memo);
        }
        _forEach(arr, function (x, i, a) {
            memo = iterator(memo, x, i, a);
        });
        return memo;
    };

    var _keys = function (obj) {
        if (Object.keys) {
            return Object.keys(obj);
        }
        var keys = [];
        for (var k in obj) {
            if (obj.hasOwnProperty(k)) {
                keys.push(k);
            }
        }
        return keys;
    };

    var _indexOf = function (arr, item) {
        if (arr.indexOf) {
            return arr.indexOf(item);
        }
        for (var i = 0; i < arr.length; i += 1) {
            if (arr[i] === item) {
                return i;
            }
        }
        return -1;
    };

    //// exported async module functions ////

    //// nextTick implementation with browser-compatible fallback ////
    if (typeof process === 'undefined' || !(process.nextTick)) {
        async.nextTick = function (fn) {
            setTimeout(fn, 0);
        };
    }
    else {
        async.nextTick = process.nextTick;
    }

    async.forEach = function (arr, iterator, callback) {
        if (!arr.length) {
            return callback();
        }
        var completed = 0;
        _forEach(arr, function (x) {
            iterator(x, function (err) {
                if (err) {
                    callback(err);
                    callback = function () {};
                }
                else {
                    completed += 1;
                    if (completed === arr.length) {
                        callback();
                    }
                }
            });
        });
    };

    async.forEachSeries = function (arr, iterator, callback) {
        if (!arr.length) {
            return callback();
        }
        var completed = 0;
        var iterate = function () {
            iterator(arr[completed], function (err) {
                if (err) {
                    callback(err);
                    callback = function () {};
                }
                else {
                    completed += 1;
                    if (completed === arr.length) {
                        callback();
                    }
                    else {
                        iterate();
                    }
                }
            });
        };
        iterate();
    };


    var doParallel = function (fn) {
        return function () {
            var args = Array.prototype.slice.call(arguments);
            return fn.apply(null, [async.forEach].concat(args));
        };
    };
    var doSeries = function (fn) {
        return function () {
            var args = Array.prototype.slice.call(arguments);
            return fn.apply(null, [async.forEachSeries].concat(args));
        };
    };


    var _asyncMap = function (eachfn, arr, iterator, callback) {
        var results = [];
        arr = _map(arr, function (x, i) {
            return {index: i, value: x};
        });
        eachfn(arr, function (x, callback) {
            iterator(x.value, function (err, v) {
                results[x.index] = v;
                callback(err);
            });
        }, function (err) {
            callback(err, results);
        });
    };
    async.map = doParallel(_asyncMap);
    async.mapSeries = doSeries(_asyncMap);


    // reduce only has a series version, as doing reduce in parallel won't
    // work in many situations.
    async.reduce = function (arr, memo, iterator, callback) {
        async.forEachSeries(arr, function (x, callback) {
            iterator(memo, x, function (err, v) {
                memo = v;
                callback(err);
            });
        }, function (err) {
            callback(err, memo);
        });
    };
    // inject alias
    async.inject = async.reduce;
    // foldl alias
    async.foldl = async.reduce;

    async.reduceRight = function (arr, memo, iterator, callback) {
        var reversed = _map(arr, function (x) {
            return x;
        }).reverse();
        async.reduce(reversed, memo, iterator, callback);
    };
    // foldr alias
    async.foldr = async.reduceRight;

    var _filter = function (eachfn, arr, iterator, callback) {
        var results = [];
        arr = _map(arr, function (x, i) {
            return {index: i, value: x};
        });
        eachfn(arr, function (x, callback) {
            iterator(x.value, function (v) {
                if (v) {
                    results.push(x);
                }
                callback();
            });
        }, function (err) {
            callback(_map(results.sort(function (a, b) {
                return a.index - b.index;
            }), function (x) {
                return x.value;
            }));
        });
    };
    async.filter = doParallel(_filter);
    async.filterSeries = doSeries(_filter);
    // select alias
    async.select = async.filter;
    async.selectSeries = async.filterSeries;

    var _reject = function (eachfn, arr, iterator, callback) {
        var results = [];
        arr = _map(arr, function (x, i) {
            return {index: i, value: x};
        });
        eachfn(arr, function (x, callback) {
            iterator(x.value, function (v) {
                if (!v) {
                    results.push(x);
                }
                callback();
            });
        }, function (err) {
            callback(_map(results.sort(function (a, b) {
                return a.index - b.index;
            }), function (x) {
                return x.value;
            }));
        });
    };
    async.reject = doParallel(_reject);
    async.rejectSeries = doSeries(_reject);

    var _detect = function (eachfn, arr, iterator, main_callback) {
        eachfn(arr, function (x, callback) {
            iterator(x, function (result) {
                if (result) {
                    main_callback(x);
                }
                else {
                    callback();
                }
            });
        }, function (err) {
            main_callback();
        });
    };
    async.detect = doParallel(_detect);
    async.detectSeries = doSeries(_detect);

    async.some = function (arr, iterator, main_callback) {
        async.forEach(arr, function (x, callback) {
            iterator(x, function (v) {
                if (v) {
                    main_callback(true);
                    main_callback = function () {};
                }
                callback();
            });
        }, function (err) {
            main_callback(false);
        });
    };
    // any alias
    async.any = async.some;

    async.every = function (arr, iterator, main_callback) {
        async.forEach(arr, function (x, callback) {
            iterator(x, function (v) {
                if (!v) {
                    main_callback(false);
                    main_callback = function () {};
                }
                callback();
            });
        }, function (err) {
            main_callback(true);
        });
    };
    // all alias
    async.all = async.every;

    async.sortBy = function (arr, iterator, callback) {
        async.map(arr, function (x, callback) {
            iterator(x, function (err, criteria) {
                if (err) {
                    callback(err);
                }
                else {
                    callback(null, {value: x, criteria: criteria});
                }
            });
        }, function (err, results) {
            if (err) {
                return callback(err);
            }
            else {
                var fn = function (left, right) {
                    var a = left.criteria, b = right.criteria;
                    return a < b ? -1 : a > b ? 1 : 0;
                };
                callback(null, _map(results.sort(fn), function (x) {
                    return x.value;
                }));
            }
        });
    };

    async.auto = function (tasks, callback) {
        callback = callback || function () {};
        var keys = _keys(tasks);
        if (!keys.length) {
            return callback(null);
        }

        var completed = [];

        var listeners = [];
        var addListener = function (fn) {
            listeners.unshift(fn);
        };
        var removeListener = function (fn) {
            for (var i = 0; i < listeners.length; i += 1) {
                if (listeners[i] === fn) {
                    listeners.splice(i, 1);
                    return;
                }
            }
        };
        var taskComplete = function () {
            _forEach(listeners, function (fn) {
                fn();
            });
        };

        addListener(function () {
            if (completed.length === keys.length) {
                callback(null);
            }
        });

        _forEach(keys, function (k) {
            var task = (tasks[k] instanceof Function) ? [tasks[k]]: tasks[k];
            var taskCallback = function (err) {
                if (err) {
                    callback(err);
                    // stop subsequent errors hitting callback multiple times
                    callback = function () {};
                }
                else {
                    completed.push(k);
                    taskComplete();
                }
            };
            var requires = task.slice(0, Math.abs(task.length - 1)) || [];
            var ready = function () {
                return _reduce(requires, function (a, x) {
                    return (a && _indexOf(completed, x) !== -1);
                }, true);
            };
            if (ready()) {
                task[task.length - 1](taskCallback);
            }
            else {
                var listener = function () {
                    if (ready()) {
                        removeListener(listener);
                        task[task.length - 1](taskCallback);
                    }
                };
                addListener(listener);
            }
        });
    };

    async.waterfall = function (tasks, callback) {
        if (!tasks.length) {
            return callback();
        }
        callback = callback || function () {};
        var wrapIterator = function (iterator) {
            return function (err) {
                if (err) {
                    callback(err);
                    callback = function () {};
                }
                else {
                    var args = Array.prototype.slice.call(arguments, 1);
                    var next = iterator.next();
                    if (next) {
                        args.push(wrapIterator(next));
                    }
                    else {
                        args.push(callback);
                    }
                    async.nextTick(function () {
                        iterator.apply(null, args);
                    });
                }
            };
        };
        wrapIterator(async.iterator(tasks))();
    };

    async.parallel = function (tasks, callback) {
        callback = callback || function () {};
        if (tasks.constructor === Array) {
            async.map(tasks, function (fn, callback) {
                if (fn) {
                    fn(function (err) {
                        var args = Array.prototype.slice.call(arguments, 1);
                        if (args.length <= 1) {
                            args = args[0];
                        }
                        callback.call(null, err, args || null);
                    });
                }
            }, callback);
        }
        else {
            var results = {};
            async.forEach(_keys(tasks), function (k, callback) {
                tasks[k](function (err) {
                    var args = Array.prototype.slice.call(arguments, 1);
                    if (args.length <= 1) {
                        args = args[0];
                    }
                    results[k] = args;
                    callback(err);
                });
            }, function (err) {
                callback(err, results);
            });
        }
    };

    async.series = function (tasks, callback) {
        callback = callback || function () {};
        if (tasks.constructor === Array) {
            async.mapSeries(tasks, function (fn, callback) {
                if (fn) {
                    fn(function (err) {
                        var args = Array.prototype.slice.call(arguments, 1);
                        if (args.length <= 1) {
                            args = args[0];
                        }
                        callback.call(null, err, args || null);
                    });
                }
            }, callback);
        }
        else {
            var results = {};
            async.forEachSeries(_keys(tasks), function (k, callback) {
                tasks[k](function (err) {
                    var args = Array.prototype.slice.call(arguments, 1);
                    if (args.length <= 1) {
                        args = args[0];
                    }
                    results[k] = args;
                    callback(err);
                });
            }, function (err) {
                callback(err, results);
            });
        }
    };

    async.iterator = function (tasks) {
        var makeCallback = function (index) {
            var fn = function () {
                if (tasks.length) {
                    tasks[index].apply(null, arguments);
                }
                return fn.next();
            };
            fn.next = function () {
                return (index < tasks.length - 1) ? makeCallback(index + 1): null;
            };
            return fn;
        };
        return makeCallback(0);
    };

    async.apply = function (fn) {
        var args = Array.prototype.slice.call(arguments, 1);
        return function () {
            return fn.apply(
                null, args.concat(Array.prototype.slice.call(arguments))
            );
        };
    };

    var _concat = function (eachfn, arr, fn, callback) {
        var r = [];
        eachfn(arr, function (x, cb) {
            fn(x, function (err, y) {
                r = r.concat(y || []);
                cb(err);
            });
        }, function (err) {
            callback(err, r);
        });
    };
    async.concat = doParallel(_concat);
    async.concatSeries = doSeries(_concat);

    async.whilst = function (test, iterator, callback) {
        if (test()) {
            iterator(function (err) {
                if (err) {
                    return callback(err);
                }
                async.whilst(test, iterator, callback);
            });
        }
        else {
            callback();
        }
    };

    async.until = function (test, iterator, callback) {
        if (!test()) {
            iterator(function (err) {
                if (err) {
                    return callback(err);
                }
                async.until(test, iterator, callback);
            });
        }
        else {
            callback();
        }
    };

    async.queue = function (worker, concurrency) {
        var workers = 0;
        var tasks = [];
        var q = {
            concurrency: concurrency,
            push: function (data, callback) {
                tasks.push({data: data, callback: callback});
                async.nextTick(q.process);
            },
            process: function () {
                if (workers < q.concurrency && tasks.length) {
                    var task = tasks.splice(0, 1)[0];
                    workers += 1;
                    worker(task.data, function () {
                        workers -= 1;
                        if (task.callback) {
                            task.callback.apply(task, arguments);
                        }
                        q.process();
                    });
                }
            },
            length: function () {
                return tasks.length;
            }
        };
        return q;
    };

    var _console_fn = function (name) {
        return function (fn) {
            var args = Array.prototype.slice.call(arguments, 1);
            fn.apply(null, args.concat([function (err) {
                var args = Array.prototype.slice.call(arguments, 1);
                if (typeof console !== 'undefined') {
                    if (err) {
                        if (console.error) {
                            console.error(err);
                        }
                    }
                    else if (console[name]) {
                        _forEach(args, function (x) {
                            console[name](x);
                        });
                    }
                }
            }]));
        };
    };
    async.log = _console_fn('log');
    async.dir = _console_fn('dir');
    /*async.info = _console_fn('info');
    async.warn = _console_fn('warn');
    async.error = _console_fn('error');*/

    async.memoize = function (fn, hasher) {
        var memo = {};
        hasher = hasher || function (x) {
            return x;
        };
        return function () {
            var args = Array.prototype.slice.call(arguments);
            var callback = args.pop();
            var key = hasher.apply(null, args);
            if (key in memo) {
                callback.apply(null, memo[key]);
            }
            else {
                fn.apply(null, args.concat([function () {
                    memo[key] = arguments;
                    callback.apply(null, arguments);
                }]));
            }
        };
    };

}());