var generate = require('regjsgen').generate;
var parse = require('regjsparser').parse;
var regenerate = require('regenerate');
var iuMappings = require('./data/iu-mappings.json');
var ESCAPE_SETS = require('./data/character-class-escape-sets.js');

function getCharacterClassEscapeSet(character) {
	if (unicode) {
		if (ignoreCase) {
			return ESCAPE_SETS.UNICODE_IGNORE_CASE[character];
		}
		return ESCAPE_SETS.UNICODE[character];
	}
	return ESCAPE_SETS.REGULAR[character];
}

var object = {};
var hasOwnProperty = object.hasOwnProperty;
function has(object, property) {
	return hasOwnProperty.call(object, property);
}

// Prepare a Regenerate set containing all code points, used for negative
// character classes (if any).
var UNICODE_SET = regenerate().addRange(0x0, 0x10FFFF);
// Without the `u` flag, the range stops at 0xFFFF.
// https://mths.be/es6#sec-pattern-semantics
var BMP_SET = regenerate().addRange(0x0, 0xFFFF);

// Prepare a Regenerate set containing all code points that are supposed to be
// matched by `/./u`. https://mths.be/es6#sec-atom
var DOT_SET_UNICODE = UNICODE_SET.clone() // all Unicode code points
	.remove(
		// minus `LineTerminator`s (https://mths.be/es6#sec-line-terminators):
		0x000A, // Line Feed <LF>
		0x000D, // Carriage Return <CR>
		0x2028, // Line Separator <LS>
		0x2029  // Paragraph Separator <PS>
	);
// Prepare a Regenerate set containing all code points that are supposed to be
// matched by `/./` (only BMP code points).
var DOT_SET = DOT_SET_UNICODE.clone()
	.intersection(BMP_SET);

// Add a range of code points + any case-folded code points in that range to a
// set.
regenerate.prototype.iuAddRange = function(min, max) {
	var $this = this;
	do {
		var folded = caseFold(min);
		if (folded) {
			$this.add(folded);
		}
	} while (++min <= max);
	return $this;
};

function assign(target, source) {
	for (var key in source) {
		// Note: `hasOwnProperty` is not needed here.
		target[key] = source[key];
	}
}

function update(item, pattern) {
	// TODO: Test if memoizing `pattern` here is worth the effort.
	if (!pattern) {
		return;
	}
	var tree = parse(pattern, '');
	switch (tree.type) {
		case 'characterClass':
		case 'group':
		case 'value':
			// No wrapping needed.
			break;
		default:
			// Wrap the pattern in a non-capturing group.
			tree = wrap(tree, pattern);
	}
	assign(item, tree);
}

function wrap(tree, pattern) {
	// Wrap the pattern in a non-capturing group.
	return {
		'type': 'group',
		'behavior': 'ignore',
		'body': [tree],
		'raw': '(?:' + pattern + ')'
	};
}

function caseFold(codePoint) {
	return has(iuMappings, codePoint) ? iuMappings[codePoint] : false;
}

var ignoreCase = false;
var unicode = false;
function processCharacterClass(characterClassItem) {
	var set = regenerate();
	var body = characterClassItem.body.forEach(function(item) {
		switch (item.type) {
			case 'value':
				set.add(item.codePoint);
				if (ignoreCase && unicode) {
					var folded = caseFold(item.codePoint);
					if (folded) {
						set.add(folded);
					}
				}
				break;
			case 'characterClassRange':
				var min = item.min.codePoint;
				var max = item.max.codePoint;
				set.addRange(min, max);
				if (ignoreCase && unicode) {
					set.iuAddRange(min, max);
				}
				break;
			case 'characterClassEscape':
				set.add(getCharacterClassEscapeSet(item.value));
				break;
			// The `default` clause is only here as a safeguard; it should never be
			// reached. Code coverage tools should ignore it.
			/* istanbul ignore next */
			default:
				throw Error('Unknown term type: ' + item.type);
		}
	});
	if (characterClassItem.negative) {
		set = (unicode ? UNICODE_SET : BMP_SET).clone().remove(set);
	}
	update(characterClassItem, set.toString());
	return characterClassItem;
}

function processTerm(item) {
	switch (item.type) {
		case 'dot':
			update(
				item,
				(unicode ? DOT_SET_UNICODE : DOT_SET).toString()
			);
			break;
		case 'characterClass':
			item = processCharacterClass(item);
			break;
		case 'characterClassEscape':
			update(
				item,
				getCharacterClassEscapeSet(item.value).toString()
			);
			break;
		case 'alternative':
		case 'disjunction':
		case 'group':
		case 'quantifier':
			item.body = item.body.map(processTerm);
			break;
		case 'value':
			var codePoint = item.codePoint;
			var set = regenerate(codePoint);
			if (ignoreCase && unicode) {
				var folded = caseFold(codePoint);
				if (folded) {
					set.add(folded);
				}
			}
			update(item, set.toString());
			break;
		case 'anchor':
		case 'empty':
		case 'group':
		case 'reference':
			// Nothing to do here.
			break;
		// The `default` clause is only here as a safeguard; it should never be
		// reached. Code coverage tools should ignore it.
		/* istanbul ignore next */
		default:
			throw Error('Unknown term type: ' + item.type);
	}
	return item;
};

module.exports = function(pattern, flags) {
	var tree = parse(pattern, flags);
	ignoreCase = flags ? flags.indexOf('i') > -1 : false;
	unicode = flags ? flags.indexOf('u') > -1 : false;
	assign(tree, processTerm(tree));
	return generate(tree);
};