/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

import { isErrnoException } from "./error";

const resolveModulePath = (importPath: string): string | undefined => {
	try {
		return require.resolve(importPath);
	} catch (error) {
		if (
			error instanceof Error &&
			isErrnoException(error) &&
			error.code === "MODULE_NOT_FOUND"
		) {
			return;
		}
		throw error;
	}
};

const removeParentModuleRef = (mod: NodeModule): void => {
	const parent = mod.parent;
	if (parent == null) {
		return;
	}

	const siblings = parent.children;
	const nSiblings = siblings.length;
	for (let i = nSiblings - 1; i >= 0; i--) {
		const sibling = siblings[i];
		if (sibling.id === mod.id) {
			siblings.splice(i, 1);
			return;
		}
	}
};

/**
 * Clear a module and its dependencies from node's module cache, ensuring that
 * requiring the module again will reload the code from disk.
 *
 * @param importPath Path or name of the module to resolve (same as
 *        {@see require}).
 *
 * @throws Error if the module could not be resolved due to filesystem error.
 */
export const decacheModule = (importPath: string): void => {
	const modulePath = resolveModulePath(importPath);
	if (modulePath == null) {
		return;
	}

	// DFS the module dependency tree, using iteration to avoid stack size
	// exceeded exceptions.
	const modsToCheck: NodeModule[] = [];
	const visited: Set<string> = new Set();
	let currentMod: NodeModule | undefined = require.cache[modulePath];
	while (currentMod != null) {
		if (visited.has(currentMod.id)) {
			currentMod = modsToCheck.pop();
			continue;
		}

		removeParentModuleRef(currentMod);
		delete require.cache[currentMod.id];
		for (const childMod of currentMod.children) {
			modsToCheck.push(childMod);
		}

		visited.add(currentMod.id);
		currentMod = modsToCheck.pop();
	}
};