/*
	compiles a selector to an executable function
*/

module.exports = compileFactory;

var parse          = require("css-what"),
	BaseFuncs      = require("boolbase"),
	sortRules      = require("./sort.js"),
	procedure      = require("./procedure.json"),
	rulesFactory   = require("./general.js"),
	pseudosFactory = require("./pseudos.js"),
	trueFunc       = BaseFuncs.trueFunc,
	falseFunc      = BaseFuncs.falseFunc;

function compileFactory(adapter){
	var Pseudos     = pseudosFactory(adapter),
		filters     = Pseudos.filters,
		Rules 			= rulesFactory(adapter, Pseudos);

	function compile(selector, options, context){
		var next = compileUnsafe(selector, options, context);
		return wrap(next);
	}

	function wrap(next){
		return function base(elem){
			return adapter.isTag(elem) && next(elem);
		};
	}

	function compileUnsafe(selector, options, context){
		var token = parse(selector, options);
		return compileToken(token, options, context);
	}

	function includesScopePseudo(t){
		return t.type === "pseudo" && (
			t.name === "scope" || (
				Array.isArray(t.data) &&
				t.data.some(function(data){
					return data.some(includesScopePseudo);
				})
			)
		);
	}

	var DESCENDANT_TOKEN = {type: "descendant"},
		FLEXIBLE_DESCENDANT_TOKEN = {type: "_flexibleDescendant"},
		SCOPE_TOKEN = {type: "pseudo", name: "scope"},
		PLACEHOLDER_ELEMENT = {};

	//CSS 4 Spec (Draft): 3.3.1. Absolutizing a Scope-relative Selector
	//http://www.w3.org/TR/selectors4/#absolutizing
	function absolutize(token, context){
		//TODO better check if context is document
		var hasContext = !!context && !!context.length && context.every(function(e){
			return e === PLACEHOLDER_ELEMENT || !!adapter.getParent(e);
		});


		token.forEach(function(t){
			if(t.length > 0 && isTraversal(t[0]) && t[0].type !== "descendant"){
				//don't return in else branch
			} else if(hasContext && !includesScopePseudo(t)){
				t.unshift(DESCENDANT_TOKEN);
			} else {
				return;
			}

			t.unshift(SCOPE_TOKEN);
		});
	}

	function compileToken(token, options, context){
		token = token.filter(function(t){ return t.length > 0; });

		token.forEach(sortRules);

		var isArrayContext = Array.isArray(context);

		context = (options && options.context) || context;

		if(context && !isArrayContext) context = [context];

		absolutize(token, context);

		var shouldTestNextSiblings = false;

		var query = token
			.map(function(rules){
				if(rules[0] && rules[1] && rules[0].name === "scope"){
					var ruleType = rules[1].type;
					if(isArrayContext && ruleType === "descendant") rules[1] = FLEXIBLE_DESCENDANT_TOKEN;
					else if(ruleType === "adjacent" || ruleType === "sibling") shouldTestNextSiblings = true;
				}
				return compileRules(rules, options, context);
			})
			.reduce(reduceRules, falseFunc);

		query.shouldTestNextSiblings = shouldTestNextSiblings;

		return query;
	}

	function isTraversal(t){
		return procedure[t.type] < 0;
	}

	function compileRules(rules, options, context){
		return rules.reduce(function(func, rule){
			if(func === falseFunc) return func;
			return Rules[rule.type](func, rule, options, context);
		}, options && options.rootFunc || trueFunc);
	}

	function reduceRules(a, b){
		if(b === falseFunc || a === trueFunc){
			return a;
		}
		if(a === falseFunc || b === trueFunc){
			return b;
		}

		return function combine(elem){
			return a(elem) || b(elem);
		};
	}

	function containsTraversal(t){
		return t.some(isTraversal);
	}

	//:not, :has and :matches have to compile selectors
	//doing this in lib/pseudos.js would lead to circular dependencies,
	//so we add them here
	filters.not = function(next, token, options, context){
		var opts = {
			xmlMode: !!(options && options.xmlMode),
			strict: !!(options && options.strict)
		};

		if(opts.strict){
			if(token.length > 1 || token.some(containsTraversal)){
				throw new Error("complex selectors in :not aren't allowed in strict mode");
			}
		}

		var func = compileToken(token, opts, context);

		if(func === falseFunc) return next;
		if(func === trueFunc)  return falseFunc;

		return function(elem){
			return !func(elem) && next(elem);
		};
	};

	filters.has = function(next, token, options){
		var opts = {
			xmlMode: !!(options && options.xmlMode),
			strict: !!(options && options.strict)
		};

		//FIXME: Uses an array as a pointer to the current element (side effects)
		var context = token.some(containsTraversal) ? [PLACEHOLDER_ELEMENT] : null;

		var func = compileToken(token, opts, context);

		if(func === falseFunc) return falseFunc;
		if(func === trueFunc){
			return function(elem){
				return adapter.getChildren(elem).some(adapter.isTag) && next(elem);
			};
		}

		func = wrap(func);

		if(context){
			return function has(elem){
				return next(elem) && (
					(context[0] = elem), adapter.existsOne(func, adapter.getChildren(elem))
				);
			};
		}

		return function has(elem){
			return next(elem) && adapter.existsOne(func, adapter.getChildren(elem));
		};
	};

	filters.matches = function(next, token, options, context){
		var opts = {
			xmlMode: !!(options && options.xmlMode),
			strict: !!(options && options.strict),
			rootFunc: next
		};

		return compileToken(token, opts, context);
	};

	compile.compileToken = compileToken;
	compile.compileUnsafe = compileUnsafe;
	compile.Pseudos = Pseudos;

	return compile;
}