/*
 * Lexical analysis and token construction.
 */

"use strict";

var _      = require("underscore");
var events = require("events");
var reg    = require("./reg.js");
var state  = require("./state.js").state;

// Some of these token types are from JavaScript Parser API
// while others are specific to JSHint parser.
// JS Parser API: https://developer.mozilla.org/en-US/docs/SpiderMonkey/Parser_API

var Token = {
	Identifier: 1,
	Punctuator: 2,
	NumericLiteral: 3,
	StringLiteral: 4,
	Comment: 5,
	Keyword: 6,
	NullLiteral: 7,
	BooleanLiteral: 8,
	RegExp: 9
};

// This is auto generated from the unicode tables.
// The tables are at:
// http://www.fileformat.info/info/unicode/category/Lu/list.htm
// http://www.fileformat.info/info/unicode/category/Ll/list.htm
// http://www.fileformat.info/info/unicode/category/Lt/list.htm
// http://www.fileformat.info/info/unicode/category/Lm/list.htm
// http://www.fileformat.info/info/unicode/category/Lo/list.htm
// http://www.fileformat.info/info/unicode/category/Nl/list.htm

var unicodeLetterTable = [
	170, 170, 181, 181, 186, 186, 192, 214,
	216, 246, 248, 705, 710, 721, 736, 740, 748, 748, 750, 750,
	880, 884, 886, 887, 890, 893, 902, 902, 904, 906, 908, 908,
	910, 929, 931, 1013, 1015, 1153, 1162, 1319, 1329, 1366,
	1369, 1369, 1377, 1415, 1488, 1514, 1520, 1522, 1568, 1610,
	1646, 1647, 1649, 1747, 1749, 1749, 1765, 1766, 1774, 1775,
	1786, 1788, 1791, 1791, 1808, 1808, 1810, 1839, 1869, 1957,
	1969, 1969, 1994, 2026, 2036, 2037, 2042, 2042, 2048, 2069,
	2074, 2074, 2084, 2084, 2088, 2088, 2112, 2136, 2308, 2361,
	2365, 2365, 2384, 2384, 2392, 2401, 2417, 2423, 2425, 2431,
	2437, 2444, 2447, 2448, 2451, 2472, 2474, 2480, 2482, 2482,
	2486, 2489, 2493, 2493, 2510, 2510, 2524, 2525, 2527, 2529,
	2544, 2545, 2565, 2570, 2575, 2576, 2579, 2600, 2602, 2608,
	2610, 2611, 2613, 2614, 2616, 2617, 2649, 2652, 2654, 2654,
	2674, 2676, 2693, 2701, 2703, 2705, 2707, 2728, 2730, 2736,
	2738, 2739, 2741, 2745, 2749, 2749, 2768, 2768, 2784, 2785,
	2821, 2828, 2831, 2832, 2835, 2856, 2858, 2864, 2866, 2867,
	2869, 2873, 2877, 2877, 2908, 2909, 2911, 2913, 2929, 2929,
	2947, 2947, 2949, 2954, 2958, 2960, 2962, 2965, 2969, 2970,
	2972, 2972, 2974, 2975, 2979, 2980, 2984, 2986, 2990, 3001,
	3024, 3024, 3077, 3084, 3086, 3088, 3090, 3112, 3114, 3123,
	3125, 3129, 3133, 3133, 3160, 3161, 3168, 3169, 3205, 3212,
	3214, 3216, 3218, 3240, 3242, 3251, 3253, 3257, 3261, 3261,
	3294, 3294, 3296, 3297, 3313, 3314, 3333, 3340, 3342, 3344,
	3346, 3386, 3389, 3389, 3406, 3406, 3424, 3425, 3450, 3455,
	3461, 3478, 3482, 3505, 3507, 3515, 3517, 3517, 3520, 3526,
	3585, 3632, 3634, 3635, 3648, 3654, 3713, 3714, 3716, 3716,
	3719, 3720, 3722, 3722, 3725, 3725, 3732, 3735, 3737, 3743,
	3745, 3747, 3749, 3749, 3751, 3751, 3754, 3755, 3757, 3760,
	3762, 3763, 3773, 3773, 3776, 3780, 3782, 3782, 3804, 3805,
	3840, 3840, 3904, 3911, 3913, 3948, 3976, 3980, 4096, 4138,
	4159, 4159, 4176, 4181, 4186, 4189, 4193, 4193, 4197, 4198,
	4206, 4208, 4213, 4225, 4238, 4238, 4256, 4293, 4304, 4346,
	4348, 4348, 4352, 4680, 4682, 4685, 4688, 4694, 4696, 4696,
	4698, 4701, 4704, 4744, 4746, 4749, 4752, 4784, 4786, 4789,
	4792, 4798, 4800, 4800, 4802, 4805, 4808, 4822, 4824, 4880,
	4882, 4885, 4888, 4954, 4992, 5007, 5024, 5108, 5121, 5740,
	5743, 5759, 5761, 5786, 5792, 5866, 5870, 5872, 5888, 5900,
	5902, 5905, 5920, 5937, 5952, 5969, 5984, 5996, 5998, 6000,
	6016, 6067, 6103, 6103, 6108, 6108, 6176, 6263, 6272, 6312,
	6314, 6314, 6320, 6389, 6400, 6428, 6480, 6509, 6512, 6516,
	6528, 6571, 6593, 6599, 6656, 6678, 6688, 6740, 6823, 6823,
	6917, 6963, 6981, 6987, 7043, 7072, 7086, 7087, 7104, 7141,
	7168, 7203, 7245, 7247, 7258, 7293, 7401, 7404, 7406, 7409,
	7424, 7615, 7680, 7957, 7960, 7965, 7968, 8005, 8008, 8013,
	8016, 8023, 8025, 8025, 8027, 8027, 8029, 8029, 8031, 8061,
	8064, 8116, 8118, 8124, 8126, 8126, 8130, 8132, 8134, 8140,
	8144, 8147, 8150, 8155, 8160, 8172, 8178, 8180, 8182, 8188,
	8305, 8305, 8319, 8319, 8336, 8348, 8450, 8450, 8455, 8455,
	8458, 8467, 8469, 8469, 8473, 8477, 8484, 8484, 8486, 8486,
	8488, 8488, 8490, 8493, 8495, 8505, 8508, 8511, 8517, 8521,
	8526, 8526, 8544, 8584, 11264, 11310, 11312, 11358,
	11360, 11492, 11499, 11502, 11520, 11557, 11568, 11621,
	11631, 11631, 11648, 11670, 11680, 11686, 11688, 11694,
	11696, 11702, 11704, 11710, 11712, 11718, 11720, 11726,
	11728, 11734, 11736, 11742, 11823, 11823, 12293, 12295,
	12321, 12329, 12337, 12341, 12344, 12348, 12353, 12438,
	12445, 12447, 12449, 12538, 12540, 12543, 12549, 12589,
	12593, 12686, 12704, 12730, 12784, 12799, 13312, 13312,
	19893, 19893, 19968, 19968, 40907, 40907, 40960, 42124,
	42192, 42237, 42240, 42508, 42512, 42527, 42538, 42539,
	42560, 42606, 42623, 42647, 42656, 42735, 42775, 42783,
	42786, 42888, 42891, 42894, 42896, 42897, 42912, 42921,
	43002, 43009, 43011, 43013, 43015, 43018, 43020, 43042,
	43072, 43123, 43138, 43187, 43250, 43255, 43259, 43259,
	43274, 43301, 43312, 43334, 43360, 43388, 43396, 43442,
	43471, 43471, 43520, 43560, 43584, 43586, 43588, 43595,
	43616, 43638, 43642, 43642, 43648, 43695, 43697, 43697,
	43701, 43702, 43705, 43709, 43712, 43712, 43714, 43714,
	43739, 43741, 43777, 43782, 43785, 43790, 43793, 43798,
	43808, 43814, 43816, 43822, 43968, 44002, 44032, 44032,
	55203, 55203, 55216, 55238, 55243, 55291, 63744, 64045,
	64048, 64109, 64112, 64217, 64256, 64262, 64275, 64279,
	64285, 64285, 64287, 64296, 64298, 64310, 64312, 64316,
	64318, 64318, 64320, 64321, 64323, 64324, 64326, 64433,
	64467, 64829, 64848, 64911, 64914, 64967, 65008, 65019,
	65136, 65140, 65142, 65276, 65313, 65338, 65345, 65370,
	65382, 65470, 65474, 65479, 65482, 65487, 65490, 65495,
	65498, 65500, 65536, 65547, 65549, 65574, 65576, 65594,
	65596, 65597, 65599, 65613, 65616, 65629, 65664, 65786,
	65856, 65908, 66176, 66204, 66208, 66256, 66304, 66334,
	66352, 66378, 66432, 66461, 66464, 66499, 66504, 66511,
	66513, 66517, 66560, 66717, 67584, 67589, 67592, 67592,
	67594, 67637, 67639, 67640, 67644, 67644, 67647, 67669,
	67840, 67861, 67872, 67897, 68096, 68096, 68112, 68115,
	68117, 68119, 68121, 68147, 68192, 68220, 68352, 68405,
	68416, 68437, 68448, 68466, 68608, 68680, 69635, 69687,
	69763, 69807, 73728, 74606, 74752, 74850, 77824, 78894,
	92160, 92728, 110592, 110593, 119808, 119892, 119894, 119964,
	119966, 119967, 119970, 119970, 119973, 119974, 119977, 119980,
	119982, 119993, 119995, 119995, 119997, 120003, 120005, 120069,
	120071, 120074, 120077, 120084, 120086, 120092, 120094, 120121,
	120123, 120126, 120128, 120132, 120134, 120134, 120138, 120144,
	120146, 120485, 120488, 120512, 120514, 120538, 120540, 120570,
	120572, 120596, 120598, 120628, 120630, 120654, 120656, 120686,
	120688, 120712, 120714, 120744, 120746, 120770, 120772, 120779,
	131072, 131072, 173782, 173782, 173824, 173824, 177972, 177972,
	177984, 177984, 178205, 178205, 194560, 195101
];

var identifierStartTable = [];

for (var i = 0; i < 128; i++) {
	identifierStartTable[i] =
		i === 36 ||           // $
		i >= 65 && i <= 90 || // A-Z
		i === 95 ||           // _
		i >= 97 && i <= 122;  // a-z
}

var identifierPartTable = [];

for (var i = 0; i < 128; i++) {
	identifierPartTable[i] =
		identifierStartTable[i] || // $, _, A-Z, a-z
		i >= 48 && i <= 57;        // 0-9
}

// Object that handles postponed lexing verifications that checks the parsed
// environment state.

function asyncTrigger() {
	var _checks = [];

	return {
		push: function (fn) {
			_checks.push(fn);
		},

		check: function () {
			for (var check = 0; check < _checks.length; ++check) {
				_checks[check]();
			}

			_checks.splice(0, _checks.length);
		}
	};
}

/*
 * Lexer for JSHint.
 *
 * This object does a char-by-char scan of the provided source code
 * and produces a sequence of tokens.
 *
 *   var lex = new Lexer("var i = 0;");
 *   lex.start();
 *   lex.token(); // returns the next token
 *
 * You have to use the token() method to move the lexer forward
 * but you don't have to use its return value to get tokens. In addition
 * to token() method returning the next token, the Lexer object also
 * emits events.
 *
 *   lex.on("Identifier", function (data) {
 *     if (data.name.indexOf("_") >= 0) {
 *       // Produce a warning.
 *     }
 *   });
 *
 * Note that the token() method returns tokens in a JSLint-compatible
 * format while the event emitter uses a slightly modified version of
 * Mozilla's JavaScript Parser API. Eventually, we will move away from
 * JSLint format.
 */
function Lexer(source) {
	var lines = source;

	if (typeof lines === "string") {
		lines = lines
			.replace(/\r\n/g, "\n")
			.replace(/\r/g, "\n")
			.split("\n");
	}

	// If the first line is a shebang (#!), make it a blank and move on.
	// Shebangs are used by Node scripts.

	if (lines[0] && lines[0].substr(0, 2) === "#!") {
		lines[0] = "";
	}

	this.emitter = new events.EventEmitter();
	this.source = source;
	this.setLines(lines);
	this.prereg = true;

	this.line = 0;
	this.char = 1;
	this.from = 1;
	this.input = "";

	for (var i = 0; i < state.option.indent; i += 1) {
		state.tab += " ";
	}
}

Lexer.prototype = {
	_lines: [],

	getLines: function () {
		this._lines = state.lines;
		return this._lines;
	},

	setLines: function (val) {
		this._lines = val;
		state.lines = this._lines;
	},

	/*
	 * Return the next i character without actually moving the
	 * char pointer.
	 */
	peek: function (i) {
		return this.input.charAt(i || 0);
	},

	/*
	 * Move the char pointer forward i times.
	 */
	skip: function (i) {
		i = i || 1;
		this.char += i;
		this.input = this.input.slice(i);
	},

	/*
	 * Subscribe to a token event. The API for this method is similar
	 * Underscore.js i.e. you can subscribe to multiple events with
	 * one call:
	 *
	 *   lex.on("Identifier Number", function (data) {
	 *     // ...
	 *   });
	 */
	on: function (names, listener) {
		names.split(" ").forEach(function (name) {
			this.emitter.on(name, listener);
		}.bind(this));
	},

	/*
	 * Trigger a token event. All arguments will be passed to each
	 * listener.
	 */
	trigger: function () {
		this.emitter.emit.apply(this.emitter, Array.prototype.slice.call(arguments));
	},

	/*
	 * Postpone a token event. the checking condition is set as
	 * last parameter, and the trigger function is called in a
	 * stored callback. To be later called using the check() function
	 * by the parser. This avoids parser's peek() to give the lexer
	 * a false context.
	 */
	triggerAsync: function (type, args, checks, fn) {
		checks.push(function () {
			if (fn()) {
				this.trigger(type, args);
			}
		}.bind(this));
	},

	/*
	 * Extract a punctuator out of the next sequence of characters
	 * or return 'null' if its not possible.
	 *
	 * This method's implementation was heavily influenced by the
	 * scanPunctuator function in the Esprima parser's source code.
	 */
	scanPunctuator: function () {
		var ch1 = this.peek();
		var ch2, ch3, ch4;

		switch (ch1) {
		// Most common single-character punctuators
		case ".":
			if ((/^[0-9]$/).test(this.peek(1))) {
				return null;
			}
			if (this.peek(1) === "." && this.peek(2) === ".") {
				return {
					type: Token.Punctuator,
					value: "..."
				};
			}
			/* falls through */
		case "(":
		case ")":
		case ";":
		case ",":
		case "{":
		case "}":
		case "[":
		case "]":
		case ":":
		case "~":
		case "?":
			return {
				type: Token.Punctuator,
				value: ch1
			};

		// A pound sign (for Node shebangs)
		case "#":
			return {
				type: Token.Punctuator,
				value: ch1
			};

		// We're at the end of input
		case "":
			return null;
		}

		// Peek more characters

		ch2 = this.peek(1);
		ch3 = this.peek(2);
		ch4 = this.peek(3);

		// 4-character punctuator: >>>=

		if (ch1 === ">" && ch2 === ">" && ch3 === ">" && ch4 === "=") {
			return {
				type: Token.Punctuator,
				value: ">>>="
			};
		}

		// 3-character punctuators: === !== >>> <<= >>=

		if (ch1 === "=" && ch2 === "=" && ch3 === "=") {
			return {
				type: Token.Punctuator,
				value: "==="
			};
		}

		if (ch1 === "!" && ch2 === "=" && ch3 === "=") {
			return {
				type: Token.Punctuator,
				value: "!=="
			};
		}

		if (ch1 === ">" && ch2 === ">" && ch3 === ">") {
			return {
				type: Token.Punctuator,
				value: ">>>"
			};
		}

		if (ch1 === "<" && ch2 === "<" && ch3 === "=") {
			return {
				type: Token.Punctuator,
				value: "<<="
			};
		}

		if (ch1 === ">" && ch2 === ">" && ch3 === "=") {
			return {
				type: Token.Punctuator,
				value: ">>="
			};
		}

		// Fat arrow punctuator
		if (ch1 === "=" && ch2 === ">") {
			return {
				type: Token.Punctuator,
				value: ch1 + ch2
			};
		}

		// 2-character punctuators: <= >= == != ++ -- << >> && ||
		// += -= *= %= &= |= ^= (but not /=, see below)
		if (ch1 === ch2 && ("+-<>&|".indexOf(ch1) >= 0)) {
			return {
				type: Token.Punctuator,
				value: ch1 + ch2
			};
		}

		if ("<>=!+-*%&|^".indexOf(ch1) >= 0) {
			if (ch2 === "=") {
				return {
					type: Token.Punctuator,
					value: ch1 + ch2
				};
			}

			return {
				type: Token.Punctuator,
				value: ch1
			};
		}

		// Special case: /=. We need to make sure that this is an
		// operator and not a regular expression.

		if (ch1 === "/") {
			if (ch2 === "=" && /\/=(?!(\S*\/[gim]?))/.test(this.input)) {
				// /= is not a part of a regular expression, return it as a
				// punctuator.
				return {
					type: Token.Punctuator,
					value: "/="
				};
			}

			return {
				type: Token.Punctuator,
				value: "/"
			};
		}

		return null;
	},

	/*
	 * Extract a comment out of the next sequence of characters and/or
	 * lines or return 'null' if its not possible. Since comments can
	 * span across multiple lines this method has to move the char
	 * pointer.
	 *
	 * In addition to normal JavaScript comments (// and /*) this method
	 * also recognizes JSHint- and JSLint-specific comments such as
	 * /*jshint, /*jslint, /*globals and so on.
	 */
	scanComments: function () {
		var ch1 = this.peek();
		var ch2 = this.peek(1);
		var rest = this.input.substr(2);
		var startLine = this.line;
		var startChar = this.char;

		// Create a comment token object and make sure it
		// has all the data JSHint needs to work with special
		// comments.

		function commentToken(label, body, opt) {
			var special = ["jshint", "jslint", "members", "member", "globals", "global", "exported"];
			var isSpecial = false;
			var value = label + body;
			var commentType = "plain";
			opt = opt || {};

			if (opt.isMultiline) {
				value += "*/";
			}

			special.forEach(function (str) {
				if (isSpecial) {
					return;
				}

				// Don't recognize any special comments other than jshint for single-line
				// comments. This introduced many problems with legit comments.
				if (label === "//" && str !== "jshint") {
					return;
				}

				if (body.substr(0, str.length) === str) {
					isSpecial = true;
					label = label + str;
					body = body.substr(str.length);
				}

				if (!isSpecial && body.charAt(0) === " " && body.substr(1, str.length) === str) {
					isSpecial = true;
					label = label + " " + str;
					body = body.substr(str.length + 1);
				}

				if (!isSpecial) {
					return;
				}

				switch (str) {
				case "member":
					commentType = "members";
					break;
				case "global":
					commentType = "globals";
					break;
				default:
					commentType = str;
				}
			});

			return {
				type: Token.Comment,
				commentType: commentType,
				value: value,
				body: body,
				isSpecial: isSpecial,
				isMultiline: opt.isMultiline || false,
				isMalformed: opt.isMalformed || false
			};
		}

		// End of unbegun comment. Raise an error and skip that input.
		if (ch1 === "*" && ch2 === "/") {
			this.trigger("error", {
				code: "E018",
				line: startLine,
				character: startChar
			});

			this.skip(2);
			return null;
		}

		// Comments must start either with // or /*
		if (ch1 !== "/" || (ch2 !== "*" && ch2 !== "/")) {
			return null;
		}

		// One-line comment
		if (ch2 === "/") {
			this.skip(this.input.length); // Skip to the EOL.
			return commentToken("//", rest);
		}

		var body = "";

		/* Multi-line comment */
		if (ch2 === "*") {
			this.skip(2);

			while (this.peek() !== "*" || this.peek(1) !== "/") {
				if (this.peek() === "") { // End of Line
					body += "\n";

					// If we hit EOF and our comment is still unclosed,
					// trigger an error and end the comment implicitly.
					if (!this.nextLine()) {
						this.trigger("error", {
							code: "E017",
							line: startLine,
							character: startChar
						});

						return commentToken("/*", body, {
							isMultiline: true,
							isMalformed: true
						});
					}
				} else {
					body += this.peek();
					this.skip();
				}
			}

			this.skip(2);
			return commentToken("/*", body, { isMultiline: true });
		}
	},

	/*
	 * Extract a keyword out of the next sequence of characters or
	 * return 'null' if its not possible.
	 */
	scanKeyword: function () {
		var result = /^[a-zA-Z_$][a-zA-Z0-9_$]*/.exec(this.input);
		var keywords = [
			"if", "in", "do", "var", "for", "new",
			"try", "let", "this", "else", "case",
			"void", "with", "enum", "while", "break",
			"catch", "throw", "const", "yield", "class",
			"super", "return", "typeof", "delete",
			"switch", "export", "import", "default",
			"finally", "extends", "function", "continue",
			"debugger", "instanceof"
		];

		if (result && keywords.indexOf(result[0]) >= 0) {
			return {
				type: Token.Keyword,
				value: result[0]
			};
		}

		return null;
	},

	/*
	 * Extract a JavaScript identifier out of the next sequence of
	 * characters or return 'null' if its not possible. In addition,
	 * to Identifier this method can also produce BooleanLiteral
	 * (true/false) and NullLiteral (null).
	 */
	scanIdentifier: function () {
		var id = "";
		var index = 0;
		var type, char;

		// Detects any character in the Unicode categories "Uppercase
		// letter (Lu)", "Lowercase letter (Ll)", "Titlecase letter
		// (Lt)", "Modifier letter (Lm)", "Other letter (Lo)", or
		// "Letter number (Nl)".
		//
		// Both approach and unicodeLetterTable were borrowed from
		// Google's Traceur.

		function isUnicodeLetter(code) {
			for (var i = 0; i < unicodeLetterTable.length;) {
				if (code < unicodeLetterTable[i++]) {
					return false;
				}

				if (code <= unicodeLetterTable[i++]) {
					return true;
				}
			}

			return false;
		}

		function isHexDigit(str) {
			return (/^[0-9a-fA-F]$/).test(str);
		}

		var readUnicodeEscapeSequence = function () {
			/*jshint validthis:true */
			index += 1;

			if (this.peek(index) !== "u") {
				return null;
			}

			var ch1 = this.peek(index + 1);
			var ch2 = this.peek(index + 2);
			var ch3 = this.peek(index + 3);
			var ch4 = this.peek(index + 4);
			var code;

			if (isHexDigit(ch1) && isHexDigit(ch2) && isHexDigit(ch3) && isHexDigit(ch4)) {
				code = parseInt(ch1 + ch2 + ch3 + ch4, 16);

				if (isUnicodeLetter(code)) {
					index += 5;
					return "\\u" + ch1 + ch2 + ch3 + ch4;
				}

				return null;
			}

			return null;
		}.bind(this);

		var getIdentifierStart = function () {
			/*jshint validthis:true */
			var chr = this.peek(index);
			var code = chr.charCodeAt(0);

			if (code === 92) {
				return readUnicodeEscapeSequence();
			}

			if (code < 128) {
				if (identifierStartTable[code]) {
					index += 1;
					return chr;
				}

				return null;
			}

			if (isUnicodeLetter(code)) {
				index += 1;
				return chr;
			}

			return null;
		}.bind(this);

		var getIdentifierPart = function () {
			/*jshint validthis:true */
			var chr = this.peek(index);
			var code = chr.charCodeAt(0);

			if (code === 92) {
				return readUnicodeEscapeSequence();
			}

			if (code < 128) {
				if (identifierPartTable[code]) {
					index += 1;
					return chr;
				}

				return null;
			}

			if (isUnicodeLetter(code)) {
				index += 1;
				return chr;
			}

			return null;
		}.bind(this);

		char = getIdentifierStart();
		if (char === null) {
			return null;
		}

		id = char;
		for (;;) {
			char = getIdentifierPart();

			if (char === null) {
				break;
			}

			id += char;
		}

		switch (id) {
		case "true":
		case "false":
			type = Token.BooleanLiteral;
			break;
		case "null":
			type = Token.NullLiteral;
			break;
		default:
			type = Token.Identifier;
		}

		return {
			type: type,
			value: id
		};
	},

	/*
	 * Extract a numeric literal out of the next sequence of
	 * characters or return 'null' if its not possible. This method
	 * supports all numeric literals described in section 7.8.3
	 * of the EcmaScript 5 specification.
	 *
	 * This method's implementation was heavily influenced by the
	 * scanNumericLiteral function in the Esprima parser's source code.
	 */
	scanNumericLiteral: function () {
		var index = 0;
		var value = "";
		var length = this.input.length;
		var char = this.peek(index);
		var bad;

		function isDecimalDigit(str) {
			return (/^[0-9]$/).test(str);
		}

		function isOctalDigit(str) {
			return (/^[0-7]$/).test(str);
		}

		function isHexDigit(str) {
			return (/^[0-9a-fA-F]$/).test(str);
		}

		function isIdentifierStart(ch) {
			return (ch === "$") || (ch === "_") || (ch === "\\") ||
				(ch >= "a" && ch <= "z") || (ch >= "A" && ch <= "Z");
		}

		// Numbers must start either with a decimal digit or a point.

		if (char !== "." && !isDecimalDigit(char)) {
			return null;
		}

		if (char !== ".") {
			value = this.peek(index);
			index += 1;
			char = this.peek(index);

			if (value === "0") {
				// Base-16 numbers.
				if (char === "x" || char === "X") {
					index += 1;
					value += char;

					while (index < length) {
						char = this.peek(index);
						if (!isHexDigit(char)) {
							break;
						}
						value += char;
						index += 1;
					}

					if (value.length <= 2) { // 0x
						return {
							type: Token.NumericLiteral,
							value: value,
							isMalformed: true
						};
					}

					if (index < length) {
						char = this.peek(index);
						if (isIdentifierStart(char)) {
							return null;
						}
					}

					return {
						type: Token.NumericLiteral,
						value: value,
						base: 16,
						isMalformed: false
					};
				}

				// Base-8 numbers.
				if (isOctalDigit(char)) {
					index += 1;
					value += char;
					bad = false;

					while (index < length) {
						char = this.peek(index);

						// Numbers like '019' (note the 9) are not valid octals
						// but we still parse them and mark as malformed.

						if (isDecimalDigit(char)) {
							bad = true;
						} else if (!isOctalDigit(char)) {
							break;
						}
						value += char;
						index += 1;
					}

					if (index < length) {
						char = this.peek(index);
						if (isIdentifierStart(char)) {
							return null;
						}
					}

					return {
						type: Token.NumericLiteral,
						value: value,
						base: 8,
						isMalformed: false
					};
				}

				// Decimal numbers that start with '0' such as '09' are illegal
				// but we still parse them and return as malformed.

				if (isDecimalDigit(char)) {
					index += 1;
					value += char;
				}
			}

			while (index < length) {
				char = this.peek(index);
				if (!isDecimalDigit(char)) {
					break;
				}
				value += char;
				index += 1;
			}
		}

		// Decimal digits.

		if (char === ".") {
			value += char;
			index += 1;

			while (index < length) {
				char = this.peek(index);
				if (!isDecimalDigit(char)) {
					break;
				}
				value += char;
				index += 1;
			}
		}

		// Exponent part.

		if (char === "e" || char === "E") {
			value += char;
			index += 1;
			char = this.peek(index);

			if (char === "+" || char === "-") {
				value += this.peek(index);
				index += 1;
			}

			char = this.peek(index);
			if (isDecimalDigit(char)) {
				value += char;
				index += 1;

				while (index < length) {
					char = this.peek(index);
					if (!isDecimalDigit(char)) {
						break;
					}
					value += char;
					index += 1;
				}
			} else {
				return null;
			}
		}

		if (index < length) {
			char = this.peek(index);
			if (isIdentifierStart(char)) {
				return null;
			}
		}

		return {
			type: Token.NumericLiteral,
			value: value,
			base: 10,
			isMalformed: !isFinite(value)
		};
	},

	/*
	 * Extract a string out of the next sequence of characters and/or
	 * lines or return 'null' if its not possible. Since strings can
	 * span across multiple lines this method has to move the char
	 * pointer.
	 *
	 * This method recognizes pseudo-multiline JavaScript strings:
	 *
	 *   var str = "hello\
	 *   world";
	 */
	scanStringLiteral: function (checks) {
		/*jshint loopfunc:true */
		var quote = this.peek();

		// String must start with a quote.
		if (quote !== "\"" && quote !== "'") {
			return null;
		}

		// In JSON strings must always use double quotes.
		this.triggerAsync("warning", {
			code: "W108",
			line: this.line,
			character: this.char // +1?
		}, checks, function () { return state.jsonMode && quote !== "\""; });

		var value = "";
		var startLine = this.line;
		var startChar = this.char;
		var allowNewLine = false;

		this.skip();

		while (this.peek() !== quote) {
			while (this.peek() === "") { // End Of Line

				// If an EOL is not preceded by a backslash, show a warning
				// and proceed like it was a legit multi-line string where
				// author simply forgot to escape the newline symbol.
				//
				// Another approach is to implicitly close a string on EOL
				// but it generates too many false positives.

				if (!allowNewLine) {
					this.trigger("warning", {
						code: "W112",
						line: this.line,
						character: this.char
					});
				} else {
					allowNewLine = false;

					// Otherwise show a warning if multistr option was not set.
					// For JSON, show warning no matter what.

					this.triggerAsync("warning", {
						code: "W043",
						line: this.line,
						character: this.char
					}, checks, function () { return !state.option.multistr; });

					this.triggerAsync("warning", {
						code: "W042",
						line: this.line,
						character: this.char
					}, checks, function () { return state.jsonMode && state.option.multistr; });
				}

				// If we get an EOF inside of an unclosed string, show an
				// error and implicitly close it at the EOF point.

				if (!this.nextLine()) {
					this.trigger("error", {
						code: "E029",
						line: startLine,
						character: startChar
					});

					return {
						type: Token.StringLiteral,
						value: value,
						isUnclosed: true,
						quote: quote
					};
				}
			}

			allowNewLine = false;
			var char = this.peek();
			var jump = 1; // A length of a jump, after we're done
			              // parsing this character.

			if (char < " ") {
				// Warn about a control character in a string.
				this.trigger("warning", {
					code: "W113",
					line: this.line,
					character: this.char,
					data: [ "<non-printable>" ]
				});
			}

			// Special treatment for some escaped characters.

			if (char === "\\") {
				this.skip();
				char = this.peek();

				switch (char) {
				case "'":
					this.triggerAsync("warning", {
						code: "W114",
						line: this.line,
						character: this.char,
						data: [ "\\'" ]
					}, checks, function () {return state.jsonMode; });
					break;
				case "b":
					char = "\b";
					break;
				case "f":
					char = "\f";
					break;
				case "n":
					char = "\n";
					break;
				case "r":
					char = "\r";
					break;
				case "t":
					char = "\t";
					break;
				case "0":
					char = "\0";

					// Octal literals fail in strict mode.
					// Check if the number is between 00 and 07.
					var n = parseInt(this.peek(1), 10);
					this.triggerAsync("warning", {
						code: "W115",
						line: this.line,
						character: this.char
					}, checks,
					function () { return n >= 0 && n <= 7 && state.directive["use strict"]; });
					break;
				case "u":
					char = String.fromCharCode(parseInt(this.input.substr(1, 4), 16));
					jump = 5;
					break;
				case "v":
					this.triggerAsync("warning", {
						code: "W114",
						line: this.line,
						character: this.char,
						data: [ "\\v" ]
					}, checks, function () { return state.jsonMode; });

					char = "\v";
					break;
				case "x":
					var	x = parseInt(this.input.substr(1, 2), 16);

					this.triggerAsync("warning", {
						code: "W114",
						line: this.line,
						character: this.char,
						data: [ "\\x-" ]
					}, checks, function () { return state.jsonMode; });

					char = String.fromCharCode(x);
					jump = 3;
					break;
				case "\\":
				case "\"":
				case "/":
					break;
				case "":
					allowNewLine = true;
					char = "";
					break;
				case "!":
					if (value.slice(value.length - 2) === "<") {
						break;
					}

					/*falls through */
				default:
					// Weird escaping.
					this.trigger("warning", {
						code: "W044",
						line: this.line,
						character: this.char
					});
				}
			}

			value += char;
			this.skip(jump);
		}

		this.skip();
		return {
			type: Token.StringLiteral,
			value: value,
			isUnclosed: false,
			quote: quote
		};
	},

	/*
	 * Extract a regular expression out of the next sequence of
	 * characters and/or lines or return 'null' if its not possible.
	 *
	 * This method is platform dependent: it accepts almost any
	 * regular expression values but then tries to compile and run
	 * them using system's RegExp object. This means that there are
	 * rare edge cases where one JavaScript engine complains about
	 * your regular expression while others don't.
	 */
	scanRegExp: function () {
		var index = 0;
		var length = this.input.length;
		var char = this.peek();
		var value = char;
		var body = "";
		var flags = [];
		var malformed = false;
		var isCharSet = false;
		var terminated;

		var scanUnexpectedChars = function () {
			// Unexpected control character
			if (char < " ") {
				malformed = true;
				this.trigger("warning", {
					code: "W048",
					line: this.line,
					character: this.char
				});
			}

			// Unexpected escaped character
			if (char === "<") {
				malformed = true;
				this.trigger("warning", {
					code: "W049",
					line: this.line,
					character: this.char,
					data: [ char ]
				});
			}
		}.bind(this);

		// Regular expressions must start with '/'
		if (!this.prereg || char !== "/") {
			return null;
		}

		index += 1;
		terminated = false;

		// Try to get everything in between slashes. A couple of
		// cases aside (see scanUnexpectedChars) we don't really
		// care whether the resulting expression is valid or not.
		// We will check that later using the RegExp object.

		while (index < length) {
			char = this.peek(index);
			value += char;
			body += char;

			if (isCharSet) {
				if (char === "]") {
					if (this.peek(index - 1) !== "\\" || this.peek(index - 2) === "\\") {
						isCharSet = false;
					}
				}

				if (char === "\\") {
					index += 1;
					char = this.peek(index);
					body += char;
					value += char;

					scanUnexpectedChars();
				}

				index += 1;
				continue;
			}

			if (char === "\\") {
				index += 1;
				char = this.peek(index);
				body += char;
				value += char;

				scanUnexpectedChars();

				if (char === "/") {
					index += 1;
					continue;
				}

				if (char === "[") {
					index += 1;
					continue;
				}
			}

			if (char === "[") {
				isCharSet = true;
				index += 1;
				continue;
			}

			if (char === "/") {
				body = body.substr(0, body.length - 1);
				terminated = true;
				index += 1;
				break;
			}

			index += 1;
		}

		// A regular expression that was never closed is an
		// error from which we cannot recover.

		if (!terminated) {
			this.trigger("error", {
				code: "E015",
				line: this.line,
				character: this.from
			});

			return void this.trigger("fatal", {
				line: this.line,
				from: this.from
			});
		}

		// Parse flags (if any).

		while (index < length) {
			char = this.peek(index);
			if (!/[gim]/.test(char)) {
				break;
			}
			flags.push(char);
			value += char;
			index += 1;
		}

		// Check regular expression for correctness.

		try {
			new RegExp(body, flags.join(""));
		} catch (err) {
			malformed = true;
			this.trigger("error", {
				code: "E016",
				line: this.line,
				character: this.char,
				data: [ err.message ] // Platform dependent!
			});
		}

		return {
			type: Token.RegExp,
			value: value,
			flags: flags,
			isMalformed: malformed
		};
	},

	/*
	 * Scan for any occurence of mixed tabs and spaces. If smarttabs option
	 * is on, ignore tabs followed by spaces.
	 *
	 * Tabs followed by one space followed by a block comment are allowed.
	 */
	scanMixedSpacesAndTabs: function () {
		var at, match;

		if (state.option.smarttabs) {
			// Negative look-behind for "//"
			match = this.input.match(/(\/\/|^\s?\*)? \t/);
			at = match && !match[1] ? 0 : -1;
		} else {
			at = this.input.search(/ \t|\t [^\*]/);
		}

		return at;
	},

	/*
	 * Scan for characters that get silently deleted by one or more browsers.
	 */
	scanUnsafeChars: function () {
		return this.input.search(reg.unsafeChars);
	},

	/*
	 * Produce the next raw token or return 'null' if no tokens can be matched.
	 * This method skips over all space characters.
	 */
	next: function (checks) {
		this.from = this.char;

		// Move to the next non-space character.
		var start;
		if (/\s/.test(this.peek())) {
			start = this.char;

			while (/\s/.test(this.peek())) {
				this.from += 1;
				this.skip();
			}

			if (this.peek() === "") { // EOL
				if (!/^\s*$/.test(this.getLines()[this.line - 1]) && state.option.trailing) {
					this.trigger("warning", { code: "W102", line: this.line, character: start });
				}
			}
		}

		// Methods that work with multi-line structures and move the
		// character pointer.

		var match = this.scanComments() ||
			this.scanStringLiteral(checks);

		if (match) {
			return match;
		}

		// Methods that don't move the character pointer.

		match =
			this.scanRegExp() ||
			this.scanPunctuator() ||
			this.scanKeyword() ||
			this.scanIdentifier() ||
			this.scanNumericLiteral();

		if (match) {
			this.skip(match.value.length);
			return match;
		}

		// No token could be matched, give up.

		return null;
	},

	/*
	 * Switch to the next line and reset all char pointers. Once
	 * switched, this method also checks for mixed spaces and tabs
	 * and other minor warnings.
	 */
	nextLine: function () {
		var char;

		if (this.line >= this.getLines().length) {
			return false;
		}

		this.input = this.getLines()[this.line];
		this.line += 1;
		this.char = 1;
		this.from = 1;

		char = this.scanMixedSpacesAndTabs();
		if (char >= 0) {
			this.trigger("warning", { code: "W099", line: this.line, character: char + 1 });
		}

		this.input = this.input.replace(/\t/g, state.tab);
		char = this.scanUnsafeChars();

		if (char >= 0) {
			this.trigger("warning", { code: "W100", line: this.line, character: char });
		}

		// If there is a limit on line length, warn when lines get too
		// long.

		if (state.option.maxlen && state.option.maxlen < this.input.length) {
			this.trigger("warning", { code: "W101", line: this.line, character: this.input.length });
		}

		return true;
	},

	/*
	 * This is simply a synonym for nextLine() method with a friendlier
	 * public name.
	 */
	start: function () {
		this.nextLine();
	},

	/*
	 * Produce the next token. This function is called by advance() to get
	 * the next token. It retuns a token in a JSLint-compatible format.
	 */
	token: function () {
		/*jshint loopfunc:true */
		var checks = asyncTrigger();
		var token;


		function isReserved(token, isProperty) {
			if (!token.reserved) {
				return false;
			}
			var meta = token.meta;

			if (meta && meta.isFutureReservedWord && state.option.inES5()) {
				// ES3 FutureReservedWord in an ES5 environment.
				if (!meta.es5) {
					return false;
				}

				// Some ES5 FutureReservedWord identifiers are active only
				// within a strict mode environment.
				if (meta.strictOnly) {
					if (!state.option.strict && !state.directive["use strict"]) {
						return false;
					}
				}

				if (isProperty) {
					return false;
				}
			}

			return true;
		}

		// Produce a token object.
		var create = function (type, value, isProperty) {
			/*jshint validthis:true */
			var obj;

			if (type !== "(endline)" && type !== "(end)") {
				this.prereg = false;
			}

			if (type === "(punctuator)") {
				switch (value) {
				case ".":
				case ")":
				case "~":
				case "#":
				case "]":
					this.prereg = false;
					break;
				default:
					this.prereg = true;
				}

				obj = Object.create(state.syntax[value] || state.syntax["(error)"]);
			}

			if (type === "(identifier)") {
				if (value === "return" || value === "case" || value === "typeof") {
					this.prereg = true;
				}

				if (_.has(state.syntax, value)) {
					obj = Object.create(state.syntax[value] || state.syntax["(error)"]);

					// If this can't be a reserved keyword, reset the object.
					if (!isReserved(obj, isProperty && type === "(identifier)")) {
						obj = null;
					}
				}
			}

			if (!obj) {
				obj = Object.create(state.syntax[type]);
			}

			obj.identifier = (type === "(identifier)");
			obj.type = obj.type || type;
			obj.value = value;
			obj.line = this.line;
			obj.character = this.char;
			obj.from = this.from;

			if (isProperty && obj.identifier) {
				obj.isProperty = isProperty;
			}

			obj.check = checks.check;

			return obj;
		}.bind(this);

		for (;;) {
			if (!this.input.length) {
				return create(this.nextLine() ? "(endline)" : "(end)", "");
			}

			token = this.next(checks);

			if (!token) {
				if (this.input.length) {
					// Unexpected character.
					this.trigger("error", {
						code: "E024",
						line: this.line,
						character: this.char,
						data: [ this.peek() ]
					});

					this.input = "";
				}

				continue;
			}

			switch (token.type) {
			case Token.StringLiteral:
				this.triggerAsync("String", {
					line: this.line,
					char: this.char,
					from: this.from,
					value: token.value,
					quote: token.quote
				}, checks, function () { return true; });

				return create("(string)", token.value);
			case Token.Identifier:
				this.trigger("Identifier", {
					line: this.line,
					char: this.char,
					from: this.form,
					name: token.value,
					isProperty: state.tokens.curr.id === "."
				});

				/* falls through */
			case Token.Keyword:
			case Token.NullLiteral:
			case Token.BooleanLiteral:
				return create("(identifier)", token.value, state.tokens.curr.id === ".");

			case Token.NumericLiteral:
				if (token.isMalformed) {
					this.trigger("warning", {
						code: "W045",
						line: this.line,
						character: this.char,
						data: [ token.value ]
					});
				}

				this.triggerAsync("warning", {
					code: "W114",
					line: this.line,
					character: this.char,
					data: [ "0x-" ]
				}, checks, function () { return token.base === 16 && state.jsonMode; });

				this.triggerAsync("warning", {
					code: "W115",
					line: this.line,
					character: this.char
				}, checks, function () {
					return state.directive["use strict"] && token.base === 8;
				});

				this.trigger("Number", {
					line: this.line,
					char: this.char,
					from: this.from,
					value: token.value,
					base: token.base,
					isMalformed: token.malformed
				});

				return create("(number)", token.value);

			case Token.RegExp:
				return create("(regexp)", token.value);

			case Token.Comment:
				state.tokens.curr.comment = true;

				if (token.isSpecial) {
					return {
						id: '(comment)',
						value: token.value,
						body: token.body,
						type: token.commentType,
						isSpecial: token.isSpecial,
						line: this.line,
						character: this.char,
						from: this.from
					};
				}

				break;

			case "":
				break;

			default:
				return create("(punctuator)", token.value);
			}
		}
	}
};

exports.Lexer = Lexer;
