"use strict";

const Promise = require("bluebird");
const pegRedux = require("peg-redux");
const moduleEval = require("eval");
const vm = require("vm");
const asExpression = require("as-expression");
const { chain } = require("error-chain");
const textParser = require("../text-parser");

const { validateOptions } = require("@validatem/core");
const isString = require("@validatem/is-string");
const isPlainObject = require("@validatem/is-plain-object");
const requireEither = require("@validatem/require-either");

module.exports = function createPegParser(_options) {
	let { grammar, grammarFile, options } = validateOptions(arguments, [
		{
			grammar: [ isString ],
			grammarFile: [ isString ],
			options: [ isPlainObject ]
		}, requireEither([ "grammar", "grammarFile" ])
	]);

	let parserOptions = {
		... options,
		output: "source",
		format: "commonjs"
	};

	return Promise.try(() => {
		return (grammarFile != null)
			? pegRedux.generateFromFile(grammarFile, parserOptions)
			: pegRedux.generate(grammar, parserOptions);
	}).then((parserCode) => {
		let parser = asExpression(() => {
			if (grammarFile != null) {
				return moduleEval(parserCode, grammarFile, {}, true);
			} else {
				let exports_ = {};
	
				let sandbox = {
					exports: exports_,
					module: {
						exports: exports_,
					},
					require: function () {
						throw new Error("You cannot use require() when loading a grammar as a string; use the `grammarFile` option instead");
					}
				};
				
				let script = new vm.Script(parserCode.replace(/^\#\!.*/, ''));
				script.runInNewContext(sandbox);
	
				return sandbox.module.exports;
			}
		});
		
		return {
			supportsStreams: false,
			parse: function (text) {
				try {
					return parser.parse(text);
				} catch (error) {
					if (error.name === "SyntaxError") {
						throw chain(error, textParser.NoResult, "Parsing output failed");
					} else {
						throw error;
					}
				}
			}
		};
	});
};