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program.ts
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program.ts
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import { EventEmitter } from 'events'
import os from 'os'
import path from 'path'
import TypedEventEmitter from 'typed-emitter'
import { Argv, ParserConfigurationOptions } from 'yargs'
import createYargs from 'yargs/yargs'
import { command, Command } from './command.js'
import { history, History } from './history.js'
import { Repl, repl } from './repl.js'
import { isPromise } from './utils.js'
const DEFAULT_PROMPT = '> '
const DEFAULT_HISTORY_FILE = '.bandersnatch_history'
type Events = {
run: (command: string | readonly string[]) => void
}
type ProgramOptions = {
/**
* Program description. Can also be set by calling
* `program().description(...)`.
*
* Defaults to `undefined`.
*/
description?: string
/**
* Sets a custom REPL prompt. Can also be set by calling
* `program().prompt(...)`.
*
* Defaults to `> `.
*/
prompt?: string
/**
* Whether or not to add a global help command that displays an overview of
* commands.
*
* Defaults to `true`.
*/
help?: boolean
/**
* Whether or not to add a global version command that displays the version as
* specified in the package.json file.
*
* Defaults to `true`.
*/
version?: boolean
/**
* Use this history file. Set to NULL to disable history file.
*
* Defaults to `{homedir}/.bandersnatch_history`.
*/
historyFile?: string | null
/**
* Specifies whether to add a default behaviour for an `exit` command.
*
* Takes a boolean or a function argument:
* - `false` installs no handler
* - `true` will install the default handler
* - a given function will be installed as the handler
*
* Defaults to `() => process.exit()`.
*/
exit?: boolean | (() => void)
/**
* Pass Yargs parser configuration, for available options, see
* https://github.com/yargs/yargs/blob/main/docs/advanced.md#customizing-yargs-parser.
*
* Defaults to `undefined`.
*/
parserConfiguration?: Partial<ParserConfigurationOptions>
}
/**
* Creates a new bandersnatch program.
*/
export function program(options: ProgramOptions = {}) {
return new Program(options)
}
function extractCommandFromProcess() {
return process.argv.slice(2)
}
export class Program extends (EventEmitter as new () => TypedEventEmitter<Events>) {
private commands: Command<any>[] = []
private history?: History
private replInstance?: Repl
constructor(public options: ProgramOptions = {}) {
super()
// Set default prompt
if (typeof this.options.prompt === 'undefined') {
this.options.prompt = DEFAULT_PROMPT
}
// Set default historyFile
if (typeof this.options.historyFile === 'undefined') {
this.options.historyFile = path.join(os.homedir(), DEFAULT_HISTORY_FILE)
}
// Set default exit handler
if (
this.options.exit === true ||
typeof this.options.exit === 'undefined'
) {
this.options.exit = () => process.exit()
}
if (this.options.historyFile !== null) {
this.history = history(this)
}
}
/**
* Set the program description.
*/
public description(description: string) {
this.options.description = description
return this
}
/**
* Sets a custom REPL prompt.
*/
public prompt(prompt: string) {
this.options.prompt = prompt
return this
}
/**
* Create a new yargs instance. This method may change at any time, not
* intended for public use.
*
* @private
*/
public createYargsInstance(
overrideParserConfiguration?: Partial<ParserConfigurationOptions>
) {
let yargs = createYargs()
this.options.description && yargs.usage(this.options.description)
// Help accepts boolean
yargs.help(this.options.help !== false)
// Version must be false or undefined
this.options.version !== false ? yargs.version() : yargs.version(false)
// Pass yargs parser options if defined
if (typeof this.options.parserConfiguration !== 'undefined') {
yargs = yargs.parserConfiguration({
...this.options.parserConfiguration,
...overrideParserConfiguration,
})
}
// Non-configurable options
yargs.recommendCommands()
yargs.strict()
yargs.demandCommand()
// Hidden completion command
yargs.completion('completion', false)
// Custom fail function.
yargs.fail(this.failHandler.bind(this))
// In case we're in a REPL session, do not exit on errors.
yargs.exitProcess(!this.isRepl())
// Add commands
this.commands.forEach((command) => {
command.toYargs(yargs, (command: string) => {
return this.run(command)
})
})
return yargs
}
/**
* Adds a new command to the program.
*/
public add<T>(command: Command<T>) {
this.commands.push(command)
return this
}
/**
* Adds a new command to the program and marks it as the default command.
*/
public default<T>(command: Command<T>) {
this.commands.push(command.default())
return this
}
/**
* Evaluate command (or process.argv) and return promise.
*/
public run(command?: string | readonly string[]) {
const cmd = command || extractCommandFromProcess()
this.emit('run', cmd)
// Return promise resolving to the return value of the command
// handler.
return new Promise((resolve, reject) => {
// @ts-ignore Not sure why this is needed?
this.createYargsInstance()
.parse(cmd, {}, (err, argv, output) => {
// We don't use yargs 17 promise style argv
if (isPromise(argv)) {
throw new Error('argv is of unexpected type')
}
/**
* From the yargs docs:
* > any text that would have been output by yargs to the terminal,
* > had a callback not been provided.
* http://yargs.js.org/docs/#api-parseargs-context-parsecallback
*
* Seems that this is primarily used for built-in commands like
* --version and --help.
*/
if (output) {
console.log(output)
}
/**
* From the yargs docs:
* > Populated if any validation errors raised while parsing.
* http://yargs.js.org/docs/#api-parseargs-context-parsecallback
* This seems to be incorrect though, and err is populated when any
* error is thrown inside the command handler.
*/
if (err) {
// Ignore err value, which encourages users to deliberately handle
// error conditions in their programs.
}
if (isPromise(argv.__promise)) {
// Delegate resolve/reject to promise returned from handler
argv.__promise.then(resolve).catch(reject)
} else {
// Resolve with undefined if promise is not available, which is the
// case with e.g. --version and --help. It should be noted that
// this might need to be filtered when e.g. printing resolved values
// from command handlers in a .then() function.
resolve(undefined)
}
})
.catch(() => {})
})
}
/**
* Run event loop which reads command from stdin.
*/
public repl() {
this.replInstance = repl(this)
// Add exit command
if (typeof this.options.exit === 'function') {
this.add(
command('exit')
.description('Exit the application')
.action(this.options.exit)
)
}
if (this.history) {
this.replInstance.attachHistory(this.history)
}
this.replInstance.start()
return this.replInstance
}
/**
* When argv is set, run the program, otherwise start repl loop.
*/
public runOrRepl() {
return extractCommandFromProcess().length ? this.run() : this.repl()
}
/**
* Returns `true` if program is running a repl loop, `false` otherwise.
*/
public isRepl() {
return !!this.replInstance
}
/**
* Method to execute when a failure occurs, rather than printing the failure
* message.
*
* Called with the failure message that would have been printed, the Error
* instance originally thrown and yargs state when the failure occured.
*/
private failHandler(msg: string, err: Error, yargs: Argv) {
if (msg) {
// Simply throw validation messages to reject runner promise
throw new Error(msg)
}
}
}