"use strict";

const pegjs = require("pegjs");
const { validateOptions, either, required, isString, isPlainObject, allowExtraProperties } = require("validatem");
const fs = require("fs");
const moduleEval = require("eval");
const vm = require("vm");
const asExpression = require("as-expression");
const textParser = require("../text-parser");

module.exports = function createPegParser({ grammar, grammarFile, options }) {
	validateOptions(arguments, [
		{
			grammar: [ isString ],
			grammarFile: [ isString ],
			options: [ isPlainObject ]
		},
		// FIXME: require-either
		either(
			allowExtraProperties({ grammar: [ required ] }),
			allowExtraProperties({ grammarFile: [ required ] })
		)
	]);

	if (grammarFile != null) {
		// FIXME: cache
		grammar = fs.readFileSync(grammarFile, "utf8");
	}

	let parserCode = pegjs.generate(grammar, {
		... options,
		output: "source",
		format: "commonjs"
	});

	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 textParser.NoResult.chain(error, "Parsing output failed");
				} else {
					throw error;
				}
			}
		}
	};
};