/* eslint-disable no-undef */
"use strict";

const Promise = require("bluebird");
const fs = require("fs").promises;
const path = require("path");
const unreachable = require("@joepie91/unreachable")("@promistream/walk-folder");

const pipe = require("@promistream/pipe");
const simpleQueue = require("@promistream/simple-queue");
const parallelize = require("@promistream/parallelize");
const mapFilter = require("@promistream/map-filter");

const { validateArguments } = require("@validatem/core");
const required = require("@validatem/required");
const isBoolean = require("@validatem/is-boolean");
const isString = require("@validatem/is-string");
const defaultTo = require("@validatem/default-to");

// TODO: Change API to also provide access to the corresponding stat object, not just the path?

module.exports = function createWalkFolderStream(_rootPath, _options) {
	let [ rootPath, options ] = validateArguments(arguments, {
		rootPath: [ required, isString ],
		options: [ defaultTo({}), {
			linear: [ defaultTo(false), isBoolean ],
			followSymlinks: [ defaultTo(true), isBoolean ],
			throughStream: [ defaultTo(null) ] // FIXME: either null or isPromistream, take implementation from `pipe`
		}]
	});

	// linear: Whether to walk the tree linearly (breadth-first) instead of randomly. This will make output deterministic, usually at the cost of being slower. On some filesystems that deal poorly with concurrent I/O, this may actually be a little faster.
	// 		linear -> sort + no parallelize, random -> parallelize infinity unordered
	let queue = simpleQueue([ rootPath ]);
	let seenInodes = new Set(); // NOTE: Used for detecting and avoiding infinite loops through eg. symlinks

	function queueDirectoryContents(targetPath) {
		return Promise.try(() => {
			return fs.readdir(targetPath);
		}).then((entries) => {
			if (options.linear === true) {
				entries.sort(); // To make the output deterministic
			}

			return entries;
		}).map((item) => {
			return queue.push(path.join(targetPath, item));
		});
	}

	let statStream = mapFilter((targetPath) => {
		return Promise.try(() => {
			if (options.followSymlinks === true) {
				return fs.stat(targetPath);
			} else {
				return fs.lstat(targetPath);
			}
		}).then((stats) => {
			if (stats.ino == null) {
				throw new unreachable("Stats without inode encountered");
			} else if (!seenInodes.has(stats.ino)) {
				seenInodes.add(stats.ino);

				return Promise.try(() => {
					if (stats.isDirectory()) {
						return queueDirectoryContents(targetPath);
					}
				}).then(() => {
					return { path: targetPath, stats: stats };
				});
			} else {
				return mapFilter.NoValue;
			}
		}).catch((error) => {
			console.error(targetPath, error);
		});
	});

	return pipe([
		queue.stream,
		options.throughStream,
		statStream,
		(options.linear !== false)
			? parallelize(Infinity, { ordered: false })
			: null
	]);
};