import {statSync, createReadStream, promises as fs} from 'fs';
import {basename} from 'path';
import {MessageChannel} from 'worker_threads';

import File from './file.js';
import Blob from './index.js';

const {stat} = fs;

const DOMException = globalThis.DOMException || (() => {
	const port = new MessageChannel().port1
	const ab = new ArrayBuffer(0)
	try { port.postMessage(ab, [ab, ab]) }
	catch (err) { return err.constructor }
})()

/**
 * @param {string} path filepath on the disk
 * @param {string} [type] mimetype to use
 */
const blobFromSync = (path, type) => fromBlob(statSync(path), path, type);

/**
 * @param {string} path filepath on the disk
 * @param {string} [type] mimetype to use
 */
const blobFrom = (path, type) => stat(path).then(stat => fromBlob(stat, path, type));

/**
 * @param {string} path filepath on the disk
 * @param {string} [type] mimetype to use
 */
const fileFrom = (path, type) => stat(path).then(stat => fromFile(stat, path, type));

/**
 * @param {string} path filepath on the disk
 * @param {string} [type] mimetype to use
 */
const fileFromSync = (path, type) => fromFile(statSync(path), path, type);

// @ts-ignore
const fromBlob = (stat, path, type = '') => new Blob([new BlobDataItem({
	path,
	size: stat.size,
	lastModified: stat.mtimeMs,
	start: 0
})], {type});

// @ts-ignore
const fromFile = (stat, path, type = '') => new File([new BlobDataItem({
	path,
	size: stat.size,
	lastModified: stat.mtimeMs,
	start: 0
})], basename(path), { type, lastModified: stat.mtimeMs });

/**
 * This is a blob backed up by a file on the disk
 * with minium requirement. Its wrapped around a Blob as a blobPart
 * so you have no direct access to this.
 *
 * @private
 */
class BlobDataItem {
	#path;
	#start;

	constructor(options) {
		this.#path = options.path;
		this.#start = options.start;
		this.size = options.size;
		this.lastModified = options.lastModified
	}

	/**
	 * Slicing arguments is first validated and formatted
	 * to not be out of range by Blob.prototype.slice
	 */
	slice(start, end) {
		return new BlobDataItem({
			path: this.#path,
			lastModified: this.lastModified,
			size: end - start,
			start
		});
	}

	async * stream() {
		const {mtimeMs} = await stat(this.#path)
		if (mtimeMs > this.lastModified) {
			throw new DOMException('The requested file could not be read, typically due to permission problems that have occurred after a reference to a file was acquired.', 'NotReadableError');
		}
		yield * createReadStream(this.#path, {
			start: this.#start,
			end: this.#start + this.size - 1
		});
	}

	get [Symbol.toStringTag]() {
		return 'Blob';
	}
}

export default blobFromSync;
export {File, Blob, blobFrom, blobFromSync, fileFrom, fileFromSync};