"use strict";

const measureTime = require("./astformer/util/measure-time");
const transpile = require("./transpile");

module.exports = function evaluate(nixCode) {
	let transpiled = transpile(nixCode);

	const api = {
		builtins: {},
		$memoize: function (func) {
			let isCalled = false;
			let storedResult;

			return function (arg) {
				if (isCalled === false) {
					storedResult = func(arg);
					isCalled = true;
				}

				return storedResult;
			};
		},
		$handleArgument: function (name, _arg, defaultValue) {
			// We need to evaluate the lazy wrapper for `arg`, as it is passed in as an attribute set; and since that is a value, it will have been wrapped.
			const arg = _arg();

			// FIXME: Improve this check, check for a (translated) attrset specifically
			if (typeof arg === "object") {
				// NOTE: We do *not* evaluate the actual attributes, nor the default value; them merely being present is enough for our case.
				const value = arg[name];

				if (value !== undefined) {
					return value;
				} else if (defaultValue !== undefined) {
					return defaultValue;
				} else {
					throw new Error(`Missing required argument '${name}'`);
				}
			} else {
				// FIXME: Improve error
				throw new Error(`Must pass an attribute set to function that expects one`);
			}
		},
		$assertUniqueKeys: function (keys) {
			let seen = new Set();

			for (let key of keys) {
				if (seen.has(key)) {
					throw new Error(`Attempted to define duplicate attribute '${key}'`);
				} else {
					seen.add(key);
				}
			}
		}
	};

	// TODO: Switch to Node `vm` API instead, and check whether there's a polyfill for it for non-Node environments, build a custom one if not
	const context = { module: {}, exports: {} };
	context.module.exports = exports;

	new Function("module", transpiled)(context.module);

	// Warm-up for hot VM performance testing
	// for (let i = 0; i < 10000; i++) {
	// 	context.module.exports(api);
	// }

	let result = measureTime(() => context.module.exports(api));

	if (process.env.DEBUG_NIX) {
		console.log("-- EVALUATION RESULT:");
		console.log(result);
	}

	return result;
};