Added watch option to re-run the linters when a file changes ⌚️ (#2)

* Added `watch` option to re-run the linters when a file changes ⌚️

* Added watch events for adding/removing a file 🗳️

* Updated test text to increase clarity of functionality 🆑

* Set ignoreInitial on the watcher now that `add` has been added 🪨

package.json

@@ -24,6 +24,7 @@
   },
   "dependencies": {
     "chalk": "5.3.0",
+    "chokidar": "3.6.0",
     "commander": "12.1.0",
     "eslint": "9.4.0",
     "glob": "10.4.1",

src/__tests__/watchFiles.spec.ts

@@ -0,0 +1,162 @@
+import { readFile } from 'fs'
+
+import chokidar from 'chokidar'
+
+import { Events } from '@Types'
+
+import { fileChangeEvent, watchFiles } from '../watchFiles'
+
+jest.mock('fs')
+jest.mock('chokidar')
+
+describe('watchFiles', () => {
+  let mockWatcher: chokidar.FSWatcher
+
+  const mockReadFile = (content: string) => {
+    jest.mocked(readFile).mockImplementationOnce((_path: any, _encoding: any, callback?: (error: any, data: any) => void): void => {
+      if (callback) {
+        callback(null, content)
+      }
+    })
+  }
+
+  beforeEach(() => {
+    mockWatcher = {
+      add: jest.fn(),
+      close: jest.fn(),
+      on: jest.fn(),
+      unwatch: jest.fn(),
+    } as unknown as chokidar.FSWatcher
+
+    jest.mocked(chokidar.watch).mockReturnValue(mockWatcher)
+  })
+
+  afterEach(() => {
+    fileChangeEvent.removeAllListeners()
+  })
+
+  it('initialises chokidar with the correct file and ignore patterns', () => {
+    const filePatterns = ['**/*.ts']
+    const ignorePatterns = ['node_modules']
+
+    watchFiles({ filePatterns, ignorePatterns })
+
+    expect(chokidar.watch).toHaveBeenCalledWith(filePatterns, {
+      ignored: ignorePatterns,
+      ignoreInitial: true,
+      persistent: true,
+    })
+  })
+
+  it('emits a "FILE_CHANGED" event when saving an existing file (because there is no hash map yet)', done => {
+    expect.assertions(1)
+
+    const mockPath = 'mock/existing-file.ts'
+    mockReadFile('open-and-save')
+
+    fileChangeEvent.on(Events.FILE_CHANGED, params => {
+      expect(params).toStrictEqual({
+        message: `File \`${mockPath}\` has been changed.`,
+        path: mockPath,
+      })
+      done()
+    })
+
+    watchFiles({ filePatterns: [mockPath], ignorePatterns: [] })
+
+    const changeHandler = (mockWatcher.on as jest.Mock).mock.calls.find(call => call[0] === 'change')[1]
+    changeHandler(mockPath)
+  })
+
+  it('emits a "FILE_CHANGED" event if the file content changes', done => {
+    expect.assertions(2)
+
+    const mockPath = 'mock/old-file.ts'
+    mockReadFile('old-content')
+
+    fileChangeEvent.on(Events.FILE_CHANGED, params => {
+      expect(params).toStrictEqual({
+        message: `File \`${mockPath}\` has been changed.`,
+        path: mockPath,
+      })
+    })
+
+    watchFiles({ filePatterns: [mockPath], ignorePatterns: [] })
+
+    const changeHandler = (mockWatcher.on as jest.Mock).mock.calls.find(call => call[0] === 'change')[1]
+    changeHandler(mockPath)
+
+    mockReadFile('new-content')
+    changeHandler(mockPath)
+
+    setTimeout(() => {
+      done()
+    }, 100)
+  })
+
+  it('does not emit a "FILE_CHANGED" event if the file content did not change', done => {
+    expect.assertions(1)
+
+    const mockPath = 'mock/old-file.ts'
+    mockReadFile('old-content')
+
+    fileChangeEvent.on(Events.FILE_CHANGED, params => {
+      expect(params).toStrictEqual({
+        message: `File \`${mockPath}\` has been changed.`,
+        path: mockPath,
+      })
+    })
+
+    watchFiles({ filePatterns: [mockPath], ignorePatterns: [] })
+
+    const changeHandler = (mockWatcher.on as jest.Mock).mock.calls.find(call => call[0] === 'change')[1]
+    changeHandler(mockPath)
+    changeHandler(mockPath)
+    changeHandler(mockPath)
+
+    setTimeout(() => {
+      done()
+    }, 100)
+  })
+
+  it('emits a "FILE_CHANGED" event if a file is added', done => {
+    expect.assertions(1)
+
+    const mockPath = 'mock/new-file.ts'
+    mockReadFile('new-content')
+
+    fileChangeEvent.on(Events.FILE_CHANGED, params => {
+      expect(params).toStrictEqual({
+        message: `File \`${mockPath}\` has been added.`,
+        path: mockPath,
+      })
+      done()
+    })
+
+    watchFiles({ filePatterns: [mockPath], ignorePatterns: [] })
+
+    const changeHandler = (mockWatcher.on as jest.Mock).mock.calls.find(call => call[0] === 'add')[1]
+    changeHandler(mockPath)
+  })
+
+  it('emits a "FILE_CHANGED" event if a file is removed', done => {
+    expect.assertions(1)
+
+    const mockPath = 'mock/legacy-file.ts'
+    mockReadFile('legacy-content')
+
+    fileChangeEvent.on(Events.FILE_CHANGED, params => {
+      expect(params).toStrictEqual({
+        message: `File \`${mockPath}\` has been removed.`,
+        path: mockPath,
+      })
+      done()
+    })
+
+    watchFiles({ filePatterns: [mockPath], ignorePatterns: [] })
+
+    const changeHandler = (mockWatcher.on as jest.Mock).mock.calls.find(call => call[0] === 'unlink')[1]
+    changeHandler(mockPath)
+  })
+
+})

src/index.ts

@@ -1,12 +1,14 @@
 #!/usr/bin/env node
 import { Command } from 'commander'
 
-import { Linter, type LinterResult } from '@Types'
+import { Events, Linter, type LinterResult } from '@Types'
 import colourLog from '@Utils/colourLog'
 import { notifyResults } from '@Utils/notifier'
+import { clearTerminal } from '@Utils/terminal'
 
 import linters from './linters/index'
 import sourceFiles from './sourceFiles'
+import { fileChangeEvent, watchFiles } from './watchFiles'
 
 const program = new Command()
 
@@ -21,7 +23,14 @@ interface RunLinter {
   linter: Linter
 }
 
+interface RunLintPilot {
+  debug: boolean
+  title: string
+  watch: boolean
+}
+
 const runLinter = async ({ debug, filePattern, linter }: RunLinter) => {
+  // TODO: Handle case where no files are sourced
   const startTime = new Date().getTime()
   colourLog.info(`Running ${linter.toLowerCase()}...`)
 
@@ -39,42 +48,69 @@ const runLinter = async ({ debug, filePattern, linter }: RunLinter) => {
   return result
 }
 
+const runLintPilot = ({ debug, title, watch }: RunLintPilot) => {
+  Promise.all([
+    runLinter({
+      debug,
+      filePattern: '**/*.{cjs,js,jsx,mjs,ts,tsx}',
+      linter: Linter.ESLint,
+    }),
+    runLinter({
+      debug,
+      filePattern: '**/*.{md,mdx}',
+      linter: Linter.Markdownlint,
+    }),
+    runLinter({
+      debug,
+      filePattern: '**/*.{css,scss,less,sass,styl,stylus}',
+      linter: Linter.Stylelint,
+    }),
+  ]).then((results) => {
+    console.log()
+
+    results.forEach(({ processedResult }) => {
+      colourLog.resultBlock(processedResult)
+    })
+
+    const exitCode = notifyResults(results, title)
+
+    if (watch) {
+      colourLog.info('Watching for changes...')
+    } else {
+      process.exit(exitCode)
+    }
+  })
+}
+
 program
   .option('-e, --emoji <string>', 'customise the emoji displayed when running lint-pilot', '✈️')
   .option('-t, --title <string>', 'customise the title displayed when running lint-pilot', 'Lint Pilot')
+  .option('-w, --watch', 'watch for file changes and re-run the linters', false)
   .option('--debug', 'output additional debug information including the list of files being linted', false)
-  .action(({ debug, emoji, title }) => {
-    console.clear()
+  .action(({ debug, emoji, title, watch }) => {
+    clearTerminal()
     colourLog.title(`${emoji} ${title} ${emoji}`)
     console.log()
 
-    Promise.all([
-      runLinter({
-        debug,
-        filePattern: '**/*.{cjs,js,jsx,mjs,ts,tsx}',
-        linter: Linter.ESLint,
-      }),
-      runLinter({
-        debug,
-        filePattern: '**/*.{md,mdx}',
-        linter: Linter.Markdownlint,
-      }),
-      runLinter({
-        debug,
-        filePattern: '**/*.{css,scss,less,sass,styl,stylus}',
-        linter: Linter.Stylelint,
-      }),
-    ]).then((results) => {
-      console.log()
-
-      results.forEach(({ processedResult }) => {
-        colourLog.resultBlock(processedResult)
-      })
+    runLintPilot({ debug, title, watch })
 
-      const exitCode = notifyResults(results, title)
+    if (watch) {
+      watchFiles({
+        filePatterns: [
+          '**/*.{cjs,js,jsx,mjs,ts,tsx}',
+          '**/*.{md,mdx}',
+          '**/*.{css,scss,less,sass,styl,stylus}',
+        ],
+        ignorePatterns: ['**/+(coverage|node_modules)/**'],
+      })
 
-      process.exit(exitCode)
-    })
+      fileChangeEvent.on(Events.FILE_CHANGED, ({ message }) => {
+        clearTerminal()
+        colourLog.info(message)
+        console.log()
+        runLintPilot({ debug, title, watch })
+      })
+    }
   })
 
 program.parse(process.argv)

src/types/index.ts

@@ -1,3 +1,7 @@
+enum Events {
+  FILE_CHANGED = 'FILE_CHANGED',
+}
+
 enum Linter {
   ESLint = 'ESLint',
   Markdownlint = 'MarkdownLint',
@@ -24,5 +28,6 @@ export type {
 }
 
 export {
+  Events,
   Linter,
 }

src/utils/__tests__/terminal.spec.ts

@@ -0,0 +1,14 @@
+import { clearTerminal } from '../terminal'
+
+describe('clearTerminal', () => {
+
+  it('calls process.stdout.write to clear the terminal', () => {
+    const mockWrite = jest.spyOn(process.stdout, 'write').mockImplementation(() => true)
+
+    clearTerminal()
+
+    expect(mockWrite).toHaveBeenCalledWith('\x1Bc\x1B[3J\x1B[2J\x1B[H')
+    mockWrite.mockRestore()
+  })
+
+})

src/utils/terminal.ts

@@ -0,0 +1,5 @@
+const clearTerminal = () => process.stdout.write('\x1Bc\x1B[3J\x1B[2J\x1B[H')
+
+export {
+  clearTerminal,
+}

src/watchFiles.ts

@@ -0,0 +1,58 @@
+import { createHash } from 'crypto'
+import { EventEmitter } from 'events'
+import { readFile } from 'fs'
+
+import chokidar from 'chokidar'
+
+import { Events } from '@Types'
+
+interface WatchFiles {
+  filePatterns: Array<string>
+  ignorePatterns: Array<string>
+}
+
+const fileChangeEvent = new EventEmitter()
+
+const fileHashes = new Map<string, string>()
+
+const getHash = (data: string) => createHash('md5').update(data).digest('hex')
+
+const watchFiles = ({ filePatterns, ignorePatterns }: WatchFiles) => {
+  const watcher = chokidar.watch(filePatterns, {
+    ignored: ignorePatterns,
+    ignoreInitial: true,
+    persistent: true,
+  })
+
+  watcher.on('add', (path, _stats) => {
+    fileChangeEvent.emit(Events.FILE_CHANGED, {
+      message: `File \`${path}\` has been added.`,
+      path,
+    })
+  })
+
+  watcher.on('change', (path, _stats) => {
+    readFile(path, 'utf8', (_error, data) => {
+      const newHash = getHash(data)
+      if (fileHashes.get(path) !== newHash) {
+        fileHashes.set(path, newHash)
+        fileChangeEvent.emit(Events.FILE_CHANGED, {
+          message: `File \`${path}\` has been changed.`,
+          path,
+        })
+      }
+    })
+  })
+
+  watcher.on('unlink', path => {
+    fileChangeEvent.emit(Events.FILE_CHANGED, {
+      message: `File \`${path}\` has been removed.`,
+      path,
+    })
+  })
+}
+
+export {
+  fileChangeEvent,
+  watchFiles,
+}