import { Dirent, readdir as _readdir } from 'fs'
import mv from 'mv'
import { join } from 'path'
import { rimraf } from 'rimraf'
import { promisify } from 'util'

import { getSettings } from '../SettingsHandler.ipc'
import { DownloadError } from './ChartDownload'

const readdir = promisify(_readdir)

interface EventCallback {
	'start': (destinationFolder: string) => void
	'error': (err: DownloadError, retry: () => void | Promise<void>) => void
	'complete': () => void
}
type Callbacks = { [E in keyof EventCallback]: EventCallback[E] }

const transferErrors = {
	readError: (err: NodeJS.ErrnoException) => fsError(err, 'Failed to read file.'),
	deleteError: (err: NodeJS.ErrnoException) => fsError(err, 'Failed to delete file.'),
	rimrafError: (err: NodeJS.ErrnoException) => fsError(err, 'Failed to delete folder.'),
	mvError: (err: NodeJS.ErrnoException) => fsError(
		err,
		`Failed to move folder to library.${err.code == 'EPERM' ? ' (does the chart already exist?)' : ''}`,
	),
}

function fsError(err: NodeJS.ErrnoException, description: string) {
	return { header: description, body: `${err.name}: ${err.message}` }
}

export class FileTransfer {

	private callbacks = {} as Callbacks
	private wasCanceled = false
	private destinationFolder: string
	private nestedSourceFolder: string // The top-level folder that is copied to the library folder
	constructor(private sourceFolder: string, destinationFolderName: string) {
		this.destinationFolder = join(getSettings().libraryPath, destinationFolderName)
		this.nestedSourceFolder = sourceFolder
	}

	/**
	 * Calls `callback` when `event` fires. (no events will be fired after `this.cancelTransfer()` is called)
	 */
	on<E extends keyof EventCallback>(event: E, callback: EventCallback[E]) {
		this.callbacks[event] = callback
	}

	async beginTransfer() {
		this.callbacks.start(this.destinationFolder)
		await this.cleanFolder()
		if (this.wasCanceled) { return }
		this.moveFolder()
	}

	/**
	 * Fixes common problems with the download chart folder.
	 */
	private async cleanFolder() {
		let files: Dirent[]
		try {
			files = await readdir(this.nestedSourceFolder, { withFileTypes: true })
		} catch (err) {
			this.callbacks.error(transferErrors.readError(err), () => this.cleanFolder())
			return
		}

		// Remove nested folders
		if (files.length == 1 && !files[0].isFile()) {
			this.nestedSourceFolder = join(this.nestedSourceFolder, files[0].name)
			await this.cleanFolder()
			return
		}

		// Delete '__MACOSX' folder
		for (const file of files) {
			if (!file.isFile() && file.name == '__MACOSX') {
				try {
					await rimraf(join(this.nestedSourceFolder, file.name))
				} catch (err) {
					this.callbacks.error(transferErrors.rimrafError(err), () => this.cleanFolder())
					return
				}
			} else {
				// TODO: handle other common problems, like chart/audio files not named correctly
			}
		}
	}

	/**
	 * Moves the downloaded chart to the library path.
	 */
	private moveFolder() {
		mv(this.nestedSourceFolder, this.destinationFolder, { mkdirp: true }, err => {
			if (err) {
				this.callbacks.error(transferErrors.mvError(err), () => this.moveFolder())
			} else {
				rimraf(this.sourceFolder) // Delete temp folder
				this.callbacks.complete()
			}
		})
	}

	/**
	 * Stop the process of transfering the file. (no more events will be fired after this is called)
	 */
	cancelTransfer() {
		this.wasCanceled = true
	}
}