Restructure

src-electron/ipc/download/FilesystemChecker.ts

@@ -0,0 +1,122 @@
+import { randomBytes as _randomBytes } from 'crypto'
+import { access, constants, mkdir } from 'fs'
+import { join } from 'path'
+import { promisify } from 'util'
+
+import { devLog } from '../../shared/ElectronUtilFunctions'
+import { tempPath } from '../../shared/Paths'
+import { AnyFunction } from '../../shared/UtilFunctions'
+import { getSettings } from '../SettingsHandler.ipc'
+import { DownloadError } from './ChartDownload'
+
+const randomBytes = promisify(_randomBytes)
+
+interface EventCallback {
+	'start': () => void
+	'error': (err: DownloadError, retry: () => void | Promise<void>) => void
+	'complete': (tempPath: string) => void
+}
+type Callbacks = { [E in keyof EventCallback]: EventCallback[E] }
+
+const filesystemErrors = {
+	libraryFolder: () => ({ header: 'Library folder not specified', body: 'Please go to the settings to set your library folder.' }),
+	libraryAccess: (err: NodeJS.ErrnoException) => fsError(err, 'Failed to access library folder.'),
+	destinationFolderExists: (destinationPath: string) => {
+		return { header: 'This chart already exists in your library folder.', body: destinationPath, isLink: true }
+	},
+	mkdirError: (err: NodeJS.ErrnoException) => fsError(err, 'Failed to create temporary folder.'),
+}
+
+function fsError(err: NodeJS.ErrnoException, description: string) {
+	return { header: description, body: `${err.name}: ${err.message}` }
+}
+
+export class FilesystemChecker {
+
+	private callbacks = {} as Callbacks
+	private wasCanceled = false
+	constructor(private destinationFolderName: string) { }
+
+	/**
+	 * Calls `callback` when `event` fires. (no events will be fired after `this.cancelDownload()` is called)
+	 */
+	on<E extends keyof EventCallback>(event: E, callback: EventCallback[E]) {
+		this.callbacks[event] = callback
+	}
+
+	/**
+	 * Check that the filesystem is set up for the download.
+	 */
+	beginCheck() {
+		this.callbacks.start()
+		this.checkLibraryFolder()
+	}
+
+	/**
+	 * Verifies that the user has specified a library folder.
+	 */
+	private checkLibraryFolder() {
+		if (getSettings().libraryPath == undefined) {
+			this.callbacks.error(filesystemErrors.libraryFolder(), () => this.beginCheck())
+		} else {
+			access(getSettings().libraryPath, constants.W_OK, this.cancelable(err => {
+				if (err) {
+					this.callbacks.error(filesystemErrors.libraryAccess(err), () => this.beginCheck())
+				} else {
+					this.checkDestinationFolder()
+				}
+			}))
+		}
+	}
+
+	/**
+	 * Checks that the destination folder doesn't already exist.
+	 */
+	private checkDestinationFolder() {
+		const destinationPath = join(getSettings().libraryPath, this.destinationFolderName)
+		access(destinationPath, constants.F_OK, this.cancelable(err => {
+			if (err) { // File does not exist
+				this.createDownloadFolder()
+			} else {
+				this.callbacks.error(filesystemErrors.destinationFolderExists(destinationPath), () => this.beginCheck())
+			}
+		}))
+	}
+
+	/**
+	 * Attempts to create a unique folder in Bridge's data paths.
+	 */
+	private async createDownloadFolder(retryCount = 0) {
+		const tempChartPath = join(tempPath, `chart_${(await randomBytes(5)).toString('hex')}`)
+
+		mkdir(tempChartPath, this.cancelable(err => {
+			if (err) {
+				if (retryCount < 5) {
+					devLog(`Error creating folder [${tempChartPath}], retrying with a different folder...`)
+					this.createDownloadFolder(retryCount + 1)
+				} else {
+					this.callbacks.error(filesystemErrors.mkdirError(err), () => this.createDownloadFolder())
+				}
+			} else {
+				this.callbacks.complete(tempChartPath)
+			}
+		}))
+	}
+
+	/**
+	 * Stop the process of checking the filesystem permissions. (no more events will be fired after this is called)
+	 */
+	cancelCheck() {
+		this.wasCanceled = true
+	}
+
+	/**
+	 * Wraps a function that is able to be prevented if `this.cancelCheck()` was called.
+	 */
+	private cancelable<F extends AnyFunction>(fn: F) {
+		return (...args: Parameters<F>): ReturnType<F> => {
+			if (this.wasCanceled) { return }
+			return fn(...Array.from(args))
+		}
+	}
+}