# Underscore.js
# (c) 2009 Jeremy Ashkenas, DocumentCloud Inc.
# Underscore is freely distributable under the terms of the MIT license.
# Portions of Underscore are inspired by or borrowed from Prototype.js,
# Oliver Steele's Functional, and John Resig's Micro-Templating.
# For all details and documentation:
# http://documentcloud.github.com/underscore/

=>

  # ------------------------- Baseline setup ---------------------------------

  # Establish the root object, "window" in the browser, or "global" on the server.
  root = this

  # Save the previous value of the "_" variable.
  previousUnderscore = root._

  # If Underscore is called as a function, it returns a wrapped object that
  # can be used OO-style. This wrapper holds altered versions of all the
  # underscore functions. Wrapped objects may be chained.
  wrapper = (obj => this._wrapped = obj)

  # Establish the object that gets thrown to break out of a loop iteration.
  breaker = typeof StopIteration !== 'undefined' ? StopIteration : '__break__'

  # Create a safe reference to the Underscore object for reference below.
  _ = root._ = obj => new wrapper(obj)

  # Export the Underscore object for CommonJS.
  exports._ = _ if typeof exports !== 'undefined'

  # Create quick reference variables for speed access to core prototypes.
  slice                 = Array.prototype.slice
  unshift               = Array.prototype.unshift
  toString              = Object.prototype.toString
  hasOwnProperty        = Object.prototype.hasOwnProperty
  propertyIsEnumerable  = Object.prototype.propertyIsEnumerable

  # Current version.
  _.VERSION = '0.5.1'

  # ------------------------ Collection Functions: ---------------------------

  # The cornerstone, an each implementation.
  # Handles objects implementing forEach, arrays, and raw objects.
  _.each = obj, iterator, context =>
    index = 0
    try
      return obj.forEach(iterator, context) if obj.forEach
      canLoop = _.isArray(obj) or _.isArguments(obj)
      return for (i=0, l=obj.length; i<l; i++) iterator.call(context, obj[i], i, obj) if canLoop
      keys = _.keys(obj)
      l    = keys.length
      for (var i=0; i<l; i++) iterator.call(context, obj[keys[i]], keys[i], obj)
    catch(e)
      throw e if (e != breaker)
    return obj;

  # Return the results of applying the iterator to each element. Use JavaScript
  # 1.6's version of map, if possible.
  _.map = obj, iterator, context =>
    return obj.map(iterator, context) if (obj and _.isFunction(obj.map))
    results = []
    _.each(obj, (value, index, list =>
      results.push(iterator.call(context, value, index, list))
    ))
    results

  # Reduce builds up a single result from a list of values. Also known as
  # inject, or foldl. Uses JavaScript 1.8's version of reduce, if possible.
  _.reduce = obj, memo, iterator, context =>
    return obj.reduce(_.bind(iterator, context), memo) if (obj and _.isFunction(obj.reduce))
    _.each(obj, (value, index, list =>
      memo = iterator.call(context, memo, value, index, list)
    ))
    memo

  # The right-associative version of reduce, also known as foldr. Uses
  # JavaScript 1.8's version of reduceRight, if available.
  _.reduceRight = function(obj, memo, iterator, context) {
    if (obj && _.isFunction(obj.reduceRight)) return obj.reduceRight(_.bind(iterator, context), memo);
    var reversed = _.clone(_.toArray(obj)).reverse();
    _.each(reversed, function(value, index) {
      memo = iterator.call(context, memo, value, index, obj);
    });
    return memo;
  };

  # Return the first value which passes a truth test.
  _.detect = function(obj, iterator, context) {
    var result;
    _.each(obj, function(value, index, list) {
      if (iterator.call(context, value, index, list)) {
        result = value;
        _.breakLoop();
      }
    });
    return result;
  };

  # Return all the elements that pass a truth test. Use JavaScript 1.6's
  # filter(), if it exists.
  _.select = function(obj, iterator, context) {
    if (obj && _.isFunction(obj.filter)) return obj.filter(iterator, context);
    var results = [];
    _.each(obj, function(value, index, list) {
      iterator.call(context, value, index, list) && results.push(value);
    });
    return results;
  };

  # Return all the elements for which a truth test fails.
  _.reject = function(obj, iterator, context) {
    var results = [];
    _.each(obj, function(value, index, list) {
      !iterator.call(context, value, index, list) && results.push(value);
    });
    return results;
  };

  # Determine whether all of the elements match a truth test. Delegate to
  # JavaScript 1.6's every(), if it is present.
  _.all = function(obj, iterator, context) {
    iterator = iterator || _.identity;
    if (obj && _.isFunction(obj.every)) return obj.every(iterator, context);
    var result = true;
    _.each(obj, function(value, index, list) {
      if (!(result = result && iterator.call(context, value, index, list))) _.breakLoop();
    });
    return result;
  };

  # Determine if at least one element in the object matches a truth test. Use
  # JavaScript 1.6's some(), if it exists.
  _.any = function(obj, iterator, context) {
    iterator = iterator || _.identity;
    if (obj && _.isFunction(obj.some)) return obj.some(iterator, context);
    var result = false;
    _.each(obj, function(value, index, list) {
      if (result = iterator.call(context, value, index, list)) _.breakLoop();
    });
    return result;
  };

  # Determine if a given value is included in the array or object,
  # based on '==='.
  _.include = function(obj, target) {
    if (_.isArray(obj)) return _.indexOf(obj, target) != -1;
    var found = false;
    _.each(obj, function(value) {
      if (found = value === target) _.breakLoop();
    });
    return found;
  };

  # Invoke a method with arguments on every item in a collection.
  _.invoke = function(obj, method) {
    var args = _.rest(arguments, 2);
    return _.map(obj, function(value) {
      return (method ? value[method] : value).apply(value, args);
    });
  };

  # Convenience version of a common use case of map: fetching a property.
  _.pluck = function(obj, key) {
    return _.map(obj, function(value){ return value[key]; });
  };

  # Return the maximum item or (item-based computation).
  _.max = function(obj, iterator, context) {
    if (!iterator && _.isArray(obj)) return Math.max.apply(Math, obj);
    var result = {computed : -Infinity};
    _.each(obj, function(value, index, list) {
      var computed = iterator ? iterator.call(context, value, index, list) : value;
      computed >= result.computed && (result = {value : value, computed : computed});
    });
    return result.value;
  };

  # Return the minimum element (or element-based computation).
  _.min = function(obj, iterator, context) {
    if (!iterator && _.isArray(obj)) return Math.min.apply(Math, obj);
    var result = {computed : Infinity};
    _.each(obj, function(value, index, list) {
      var computed = iterator ? iterator.call(context, value, index, list) : value;
      computed < result.computed && (result = {value : value, computed : computed});
    });
    return result.value;
  };

  # Sort the object's values by a criteria produced by an iterator.
  _.sortBy = function(obj, iterator, context) {
    return _.pluck(_.map(obj, function(value, index, list) {
      return {
        value : value,
        criteria : iterator.call(context, value, index, list)
      };
    }).sort(function(left, right) {
      var a = left.criteria, b = right.criteria;
      return a < b ? -1 : a > b ? 1 : 0;
    }), 'value');
  };

  # Use a comparator function to figure out at what index an object should
  # be inserted so as to maintain order. Uses binary search.
  _.sortedIndex = function(array, obj, iterator) {
    iterator = iterator || _.identity;
    var low = 0, high = array.length;
    while (low < high) {
      var mid = (low + high) >> 1;
      iterator(array[mid]) < iterator(obj) ? low = mid + 1 : high = mid;
    }
    return low;
  };

  # Convert anything iterable into a real, live array.
  _.toArray = function(iterable) {
    if (!iterable)                return [];
    if (iterable.toArray)         return iterable.toArray();
    if (_.isArray(iterable))      return iterable;
    if (_.isArguments(iterable))  return slice.call(iterable);
    return _.map(iterable, function(val){ return val; });
  };

  # Return the number of elements in an object.
  _.size = function(obj) {
    return _.toArray(obj).length;
  };

  /*-------------------------- Array Functions: ------------------------------*/

  # Get the first element of an array. Passing "n" will return the first N
  # values in the array. Aliased as "head". The "guard" check allows it to work
  # with _.map.
  _.first = function(array, n, guard) {
    return n && !guard ? slice.call(array, 0, n) : array[0];
  };

  # Returns everything but the first entry of the array. Aliased as "tail".
  # Especially useful on the arguments object. Passing an "index" will return
  # the rest of the values in the array from that index onward. The "guard"
   //check allows it to work with _.map.
  _.rest = function(array, index, guard) {
    return slice.call(array, _.isUndefined(index) || guard ? 1 : index);
  };

  # Get the last element of an array.
  _.last = function(array) {
    return array[array.length - 1];
  };

  # Trim out all falsy values from an array.
  _.compact = function(array) {
    return _.select(array, function(value){ return !!value; });
  };

  # Return a completely flattened version of an array.
  _.flatten = function(array) {
    return _.reduce(array, [], function(memo, value) {
      if (_.isArray(value)) return memo.concat(_.flatten(value));
      memo.push(value);
      return memo;
    });
  };

  # Return a version of the array that does not contain the specified value(s).
  _.without = function(array) {
    var values = _.rest(arguments);
    return _.select(array, function(value){ return !_.include(values, value); });
  };

  # Produce a duplicate-free version of the array. If the array has already
  # been sorted, you have the option of using a faster algorithm.
  _.uniq = function(array, isSorted) {
    return _.reduce(array, [], function(memo, el, i) {
      if (0 == i || (isSorted === true ? _.last(memo) != el : !_.include(memo, el))) memo.push(el);
      return memo;
    });
  };

  # Produce an array that contains every item shared between all the
  # passed-in arrays.
  _.intersect = function(array) {
    var rest = _.rest(arguments);
    return _.select(_.uniq(array), function(item) {
      return _.all(rest, function(other) {
        return _.indexOf(other, item) >= 0;
      });
    });
  };

  # Zip together multiple lists into a single array -- elements that share
  # an index go together.
  _.zip = function() {
    var args = _.toArray(arguments);
    var length = _.max(_.pluck(args, 'length'));
    var results = new Array(length);
    for (var i=0; i<length; i++) results[i] = _.pluck(args, String(i));
    return results;
  };

  # If the browser doesn't supply us with indexOf (I'm looking at you, MSIE),
  # we need this function. Return the position of the first occurence of an
  # item in an array, or -1 if the item is not included in the array.
  _.indexOf = function(array, item) {
    if (array.indexOf) return array.indexOf(item);
    for (var i=0, l=array.length; i<l; i++) if (array[i] === item) return i;
    return -1;
  };

  # Provide JavaScript 1.6's lastIndexOf, delegating to the native function,
  # if possible.
  _.lastIndexOf = function(array, item) {
    if (array.lastIndexOf) return array.lastIndexOf(item);
    var i = array.length;
    while (i--) if (array[i] === item) return i;
    return -1;
  };

  # Generate an integer Array containing an arithmetic progression. A port of
  # the native Python range() function. See:
  # http://docs.python.org/library/functions.html#range
  _.range = function(start, stop, step) {
    var a     = _.toArray(arguments);
    var solo  = a.length <= 1;
    var start = solo ? 0 : a[0], stop = solo ? a[0] : a[1], step = a[2] || 1;
    var len   = Math.ceil((stop - start) / step);
    if (len <= 0) return [];
    var range = new Array(len);
    for (var i = start, idx = 0; true; i += step) {
      if ((step > 0 ? i - stop : stop - i) >= 0) return range;
      range[idx++] = i;
    }
  };

  /* ----------------------- Function Functions: -----------------------------*/

  # Create a function bound to a given object (assigning 'this', and arguments,
  # optionally). Binding with arguments is also known as 'curry'.
  _.bind = function(func, obj) {
    var args = _.rest(arguments, 2);
    return function() {
      return func.apply(obj || root, args.concat(_.toArray(arguments)));
    };
  };

  # Bind all of an object's methods to that object. Useful for ensuring that
  # all callbacks defined on an object belong to it.
  _.bindAll = function(obj) {
    var funcs = _.rest(arguments);
    if (funcs.length == 0) funcs = _.functions(obj);
    _.each(funcs, function(f) { obj[f] = _.bind(obj[f], obj); });
    return obj;
  };

  # Delays a function for the given number of milliseconds, and then calls
  # it with the arguments supplied.
  _.delay = function(func, wait) {
    var args = _.rest(arguments, 2);
    return setTimeout(function(){ return func.apply(func, args); }, wait);
  };

  # Defers a function, scheduling it to run after the current call stack has
  # cleared.
  _.defer = function(func) {
    return _.delay.apply(_, [func, 1].concat(_.rest(arguments)));
  };

  # Returns the first function passed as an argument to the second,
  # allowing you to adjust arguments, run code before and after, and
  # conditionally execute the original function.
  _.wrap = function(func, wrapper) {
    return function() {
      var args = [func].concat(_.toArray(arguments));
      return wrapper.apply(wrapper, args);
    };
  };

  # Returns a function that is the composition of a list of functions, each
  # consuming the return value of the function that follows.
  _.compose = function() {
    var funcs = _.toArray(arguments);
    return function() {
      var args = _.toArray(arguments);
      for (var i=funcs.length-1; i >= 0; i--) {
        args = [funcs[i].apply(this, args)];
      }
      return args[0];
    };
  };

  /* ------------------------- Object Functions: ---------------------------- */

  # Retrieve the names of an object's properties.
  _.keys = function(obj) {
    if(_.isArray(obj)) return _.range(0, obj.length);
    var keys = [];
    for (var key in obj) if (hasOwnProperty.call(obj, key)) keys.push(key);
    return keys;
  };

  # Retrieve the values of an object's properties.
  _.values = function(obj) {
    return _.map(obj, _.identity);
  };

  # Return a sorted list of the function names available in Underscore.
  _.functions = function(obj) {
    return _.select(_.keys(obj), function(key){ return _.isFunction(obj[key]); }).sort();
  };

  # Extend a given object with all of the properties in a source object.
  _.extend = function(destination, source) {
    for (var property in source) destination[property] = source[property];
    return destination;
  };

  # Create a (shallow-cloned) duplicate of an object.
  _.clone = function(obj) {
    if (_.isArray(obj)) return obj.slice(0);
    return _.extend({}, obj);
  };

  # Perform a deep comparison to check if two objects are equal.
  _.isEqual = function(a, b) {
    # Check object identity.
    if (a === b) return true;
    # Different types?
    var atype = typeof(a), btype = typeof(b);
    if (atype != btype) return false;
    # Basic equality test (watch out for coercions).
    if (a == b) return true;
    # One is falsy and the other truthy.
    if ((!a && b) || (a && !b)) return false;
    # One of them implements an isEqual()?
    if (a.isEqual) return a.isEqual(b);
    # Check dates' integer values.
    if (_.isDate(a) && _.isDate(b)) return a.getTime() === b.getTime();
    # Both are NaN?
    if (_.isNaN(a) && _.isNaN(b)) return true;
    # Compare regular expressions.
    if (_.isRegExp(a) && _.isRegExp(b))
      return a.source     === b.source &&
             a.global     === b.global &&
             a.ignoreCase === b.ignoreCase &&
             a.multiline  === b.multiline;
    # If a is not an object by this point, we can't handle it.
    if (atype !== 'object') return false;
    # Check for different array lengths before comparing contents.
    if (a.length && (a.length !== b.length)) return false;
    # Nothing else worked, deep compare the contents.
    var aKeys = _.keys(a), bKeys = _.keys(b);
    # Different object sizes?
    if (aKeys.length != bKeys.length) return false;
    # Recursive comparison of contents.
    for (var key in a) if (!_.isEqual(a[key], b[key])) return false;
    return true;
  };

  # Is a given array or object empty?
  _.isEmpty = function(obj) {
    return _.keys(obj).length == 0;
  };

  # Is a given value a DOM element?
  _.isElement = function(obj) {
    return !!(obj && obj.nodeType == 1);
  };

  # Is a given variable an arguments object?
  _.isArguments = function(obj) {
    return obj && _.isNumber(obj.length) && !_.isArray(obj) && !propertyIsEnumerable.call(obj, 'length');
  };

  # Is the given value NaN -- this one is interesting. NaN != NaN, and
  # isNaN(undefined) == true, so we make sure it's a number first.
  _.isNaN = function(obj) {
    return _.isNumber(obj) && isNaN(obj);
  };

  # Is a given value equal to null?
  _.isNull = function(obj) {
    return obj === null;
  };

  # Is a given variable undefined?
  _.isUndefined = function(obj) {
    return typeof obj == 'undefined';
  };

  # Invokes interceptor with the obj, and then returns obj.
  # The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain.
  _.tap = function(obj, interceptor) {
    interceptor(obj);
    return obj;
  }

  # Define the isArray, isDate, isFunction, isNumber, isRegExp, and isString
  # functions based on their toString identifiers.
  var types = ['Array', 'Date', 'Function', 'Number', 'RegExp', 'String'];
  for (var i=0, l=types.length; i<l; i++) {
    (function() {
      var identifier = '[object ' + types[i] + ']';
      _['is' + types[i]] = function(obj) { return toString.call(obj) == identifier; };
    })();
  }

  /* -------------------------- Utility Functions: -------------------------- */

  # Run Underscore.js in noConflict mode, returning the '_' variable to its
  # previous owner. Returns a reference to the Underscore object.
  _.noConflict = function() {
    root._ = previousUnderscore;
    return this;
  };

  # Keep the identity function around for default iterators.
  _.identity = function(value) {
    return value;
  };

  # Break out of the middle of an iteration.
  _.breakLoop = function() {
    throw breaker;
  };

  # Generate a unique integer id (unique within the entire client session).
  # Useful for temporary DOM ids.
  var idCounter = 0;
  _.uniqueId = function(prefix) {
    var id = idCounter++;
    return prefix ? prefix + id : id;
  };

  # JavaScript templating a-la ERB, pilfered from John Resig's
  # "Secrets of the JavaScript Ninja", page 83.
  _.template = function(str, data) {
    var fn = new Function('obj',
      'var p=[],print=function(){p.push.apply(p,arguments);};' +
      'with(obj){p.push(\'' +
      str
        .replace(/[\r\t\n]/g, " ")
        .split("<%").join("\t")
        .replace(/((^|%>)[^\t]*)'/g, "$1\r")
        .replace(/\t=(.*?)%>/g, "',$1,'")
        .split("\t").join("');")
        .split("%>").join("p.push('")
        .split("\r").join("\\'")
    + "');}return p.join('');");
    return data ? fn(data) : fn;
  };

  /*------------------------------- Aliases ----------------------------------*/

  _.forEach  = _.each;
  _.foldl    = _.inject       = _.reduce;
  _.foldr    = _.reduceRight;
  _.filter   = _.select;
  _.every    = _.all;
  _.some     = _.any;
  _.head     = _.first;
  _.tail     = _.rest;
  _.methods  = _.functions;

  /*------------------------ Setup the OOP Wrapper: --------------------------*/

  # Helper function to continue chaining intermediate results.
  var result = function(obj, chain) {
    return chain ? _(obj).chain() : obj;
  };

  # Add all of the Underscore functions to the wrapper object.
  _.each(_.functions(_), function(name) {
    var method = _[name];
    wrapper.prototype[name] = function() {
      unshift.call(arguments, this._wrapped);
      return result(method.apply(_, arguments), this._chain);
    };
  });

  # Add all mutator Array functions to the wrapper.
  _.each(['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'], function(name) {
    var method = Array.prototype[name];
    wrapper.prototype[name] = function() {
      method.apply(this._wrapped, arguments);
      return result(this._wrapped, this._chain);
    };
  });

  # Add all accessor Array functions to the wrapper.
  _.each(['concat', 'join', 'slice'], function(name) {
    var method = Array.prototype[name];
    wrapper.prototype[name] = function() {
      return result(method.apply(this._wrapped, arguments), this._chain);
    };
  });

  # Start chaining a wrapped Underscore object.
  wrapper.prototype.chain = function() {
    this._chain = true;
    return this;
  };

  # Extracts the result from a wrapped and chained object.
  wrapper.prototype.value = function() {
    return this._wrapped;
  };

()