/**
 * Determines if the provided value has been defined.
 *
 * @param {mixed} object
 * @returns {boolean}
 */
var isset = function(object) {
	return typeof object !== 'undefined';
};

/**
 * Converts a scalar to its best string representation
 * for hash keys and HTML attribute values.
 *
 * Transformations:
 *   'str'     -> 'str'
 *   null      -> ''
 *   undefined -> ''
 *   true      -> '1'
 *   false     -> '0'
 *   0         -> '0'
 *   1         -> '1'
 *
 * @param {string} value
 * @returns {string|null}
 */
var hash_key = function(value) {
	if (typeof value === 'undefined' || value === null) return null;
	if (typeof value === 'boolean') return value ? '1' : '0';
	return value + '';
};

/**
 * Escapes a string for use within HTML.
 *
 * @param {string} str
 * @returns {string}
 */
var escape_html = function(str) {
	return (str + '')
		.replace(/&/g, '&')
		.replace(/</g, '&lt;')
		.replace(/>/g, '&gt;')
		.replace(/"/g, '&quot;');
};

/**
 * Escapes "$" characters in replacement strings.
 *
 * @param {string} str
 * @returns {string}
 */
var escape_replace = function(str) {
	return (str + '').replace(/\$/g, '$$$$');
};

var hook = {};

/**
 * Wraps `method` on `self` so that `fn`
 * is invoked before the original method.
 *
 * @param {object} self
 * @param {string} method
 * @param {function} fn
 */
hook.before = function(self, method, fn) {
	var original = self[method];
	self[method] = function() {
		fn.apply(self, arguments);
		return original.apply(self, arguments);
	};
};

/**
 * Wraps `method` on `self` so that `fn`
 * is invoked after the original method.
 *
 * @param {object} self
 * @param {string} method
 * @param {function} fn
 */
hook.after = function(self, method, fn) {
	var original = self[method];
	self[method] = function() {
		var result = original.apply(self, arguments);
		fn.apply(self, arguments);
		return result;
	};
};

/**
 * Wraps `fn` so that it can only be invoked once.
 *
 * @param {function} fn
 * @returns {function}
 */
var once = function(fn) {
	var called = false;
	return function() {
		if (called) return;
		called = true;
		fn.apply(this, arguments);
	};
};

/**
 * Wraps `fn` so that it can only be called once
 * every `delay` milliseconds (invoked on the falling edge).
 *
 * @param {function} fn
 * @param {int} delay
 * @returns {function}
 */
var debounce = function(fn, delay) {
	var timeout;
	return function() {
		var self = this;
		var args = arguments;
		window.clearTimeout(timeout);
		timeout = window.setTimeout(function() {
			fn.apply(self, args);
		}, delay);
	};
};

/**
 * Debounce all fired events types listed in `types`
 * while executing the provided `fn`.
 *
 * @param {object} self
 * @param {array} types
 * @param {function} fn
 */
var debounce_events = function(self, types, fn) {
	var type;
	var trigger = self.trigger;
	var event_args = {};

	// override trigger method
	self.trigger = function() {
		var type = arguments[0];
		if (types.indexOf(type) !== -1) {
			event_args[type] = arguments;
		} else {
			return trigger.apply(self, arguments);
		}
	};

	// invoke provided function
	fn.apply(self, []);
	self.trigger = trigger;

	// trigger queued events
	for (type in event_args) {
		if (event_args.hasOwnProperty(type)) {
			trigger.apply(self, event_args[type]);
		}
	}
};

/**
 * A workaround for http://bugs.jquery.com/ticket/6696
 *
 * @param {object} $parent - Parent element to listen on.
 * @param {string} event - Event name.
 * @param {string} selector - Descendant selector to filter by.
 * @param {function} fn - Event handler.
 */
var watchChildEvent = function($parent, event, selector, fn) {
	$parent.on(event, selector, function(e) {
		var child = e.target;
		while (child && child.parentNode !== $parent[0]) {
			child = child.parentNode;
		}
		e.currentTarget = child;
		return fn.apply(this, [e]);
	});
};

/**
 * Determines the current selection within a text input control.
 * Returns an object containing:
 *   - start
 *   - length
 *
 * @param {object} input
 * @returns {object}
 */
var getSelection = function(input) {
	var result = {};
	if ('selectionStart' in input) {
		result.start = input.selectionStart;
		result.length = input.selectionEnd - result.start;
	} else if (document.selection) {
		input.focus();
		var sel = document.selection.createRange();
		var selLen = document.selection.createRange().text.length;
		sel.moveStart('character', -input.value.length);
		result.start = sel.text.length - selLen;
		result.length = selLen;
	}
	return result;
};

/**
 * Copies CSS properties from one element to another.
 *
 * @param {object} $from
 * @param {object} $to
 * @param {array} properties
 */
var transferStyles = function($from, $to, properties) {
	var i, n, styles = {};
	if (properties) {
		for (i = 0, n = properties.length; i < n; i++) {
			styles[properties[i]] = $from.css(properties[i]);
		}
	} else {
		styles = $from.css();
	}
	$to.css(styles);
};

/**
 * Measures the width of a string within a
 * parent element (in pixels).
 *
 * @param {string} str
 * @param {object} $parent
 * @returns {int}
 */
var measureString = function(str, $parent) {
	if (!str) {
		return 0;
	}

	var $test = $('<test>').css({
		position: 'absolute',
		top: -99999,
		left: -99999,
		width: 'auto',
		padding: 0,
		whiteSpace: 'pre'
	}).text(str).appendTo('body');

	transferStyles($parent, $test, [
		'letterSpacing',
		'fontSize',
		'fontFamily',
		'fontWeight',
		'textTransform'
	]);

	var width = $test.width();
	$test.remove();

	return width;
};

/**
 * Sets up an input to grow horizontally as the user
 * types. If the value is changed manually, you can
 * trigger the "update" handler to resize:
 *
 * $input.trigger('update');
 *
 * @param {object} $input
 */
var autoGrow = function($input) {
	var currentWidth = null;

	var update = function(e, options) {
		var value, keyCode, printable, placeholder, width;
		var shift, character, selection;
		e = e || window.event || {};
		options = options || {};

		if (e.metaKey || e.altKey) return;
		if (!options.force && $input.data('grow') === false) return;

		value = $input.val();
		if (e.type && e.type.toLowerCase() === 'keydown') {
			keyCode = e.keyCode;
			printable = (
				(keyCode >= 97 && keyCode <= 122) || // a-z
				(keyCode >= 65 && keyCode <= 90)  || // A-Z
				(keyCode >= 48 && keyCode <= 57)  || // 0-9
				keyCode === 32 // space
			);

			if (keyCode === KEY_DELETE || keyCode === KEY_BACKSPACE) {
				selection = getSelection($input[0]);
				if (selection.length) {
					value = value.substring(0, selection.start) + value.substring(selection.start + selection.length);
				} else if (keyCode === KEY_BACKSPACE && selection.start) {
					value = value.substring(0, selection.start - 1) + value.substring(selection.start + 1);
				} else if (keyCode === KEY_DELETE && typeof selection.start !== 'undefined') {
					value = value.substring(0, selection.start) + value.substring(selection.start + 1);
				}
			} else if (printable) {
				shift = e.shiftKey;
				character = String.fromCharCode(e.keyCode);
				if (shift) character = character.toUpperCase();
				else character = character.toLowerCase();
				value += character;
			}
		}

		placeholder = $input.attr('placeholder');
		if (!value && placeholder) {
			value = placeholder;
		}

		width = measureString(value, $input) + 4;
		if (width !== currentWidth) {
			currentWidth = width;
			$input.width(width);
			$input.triggerHandler('resize');
		}
	};

	$input.on('keydown keyup update blur', update);
	update();
};