gulp-function/readme.md

# @push.rocks/gulp-function

`@push.rocks/gulp-function` is a tiny, typed Gulp plugin for running your own sync or async functions inside a Gulp object stream without changing the files that flow through it. Use it when a pipeline needs custom side effects: logging, validation, deployment calls, metrics, cache invalidation, or any project-specific action that does not deserve a full custom Gulp plugin.

## Issue Reporting and Security

For reporting bugs, issues, or security vulnerabilities, please visit [community.foss.global/](https://community.foss.global/). This is the central community hub for all issue reporting. Developers who sign and comply with our contribution agreement and go through identification can also get a [code.foss.global/](https://code.foss.global/) account to submit Pull Requests directly.

## Install

```bash
pnpm add -D @push.rocks/gulp-function
```

## What It Does

Gulp streams are great at moving Vinyl files through transforms. Sometimes you need to run code at a specific point in that stream while leaving every file untouched. `@push.rocks/gulp-function` gives you three small helpers for that:

- `forEach(fn)`: run `fn(file, enc)` for every file and pass the file on after the function resolves.
- `forFirst(fn)`: run `fn(file, enc)` only for the first file and pass all files through.
- `atEnd(fn)`: pass all files through immediately, then run `fn(null, null)` once when the stream flushes.

The default export exposes the same behavior as `gulpFunction(fnOrFns, mode)`, where `mode` is `'forEach'`, `'forFirst'`, or `'atEnd'`. The default export also accepts an array of functions and runs them in parallel for the selected mode.

## Quick Start

```ts
import gulp from 'gulp';
import { forEach } from '@push.rocks/gulp-function';

interface IVinylFile {
  path: string;
  relative: string;
}

export const logFiles = () =>
  gulp.src('./src/**/*.ts')
    .pipe(forEach<IVinylFile>(async (file) => {
      if (!file) return;
      console.log(`Processing ${file.relative}`);
    }))
    .pipe(gulp.dest('./dist'));
```

The function can return a promise or a plain value. If it throws or rejects, the transform reports the error to Gulp and the pipeline fails normally.

## API

### `forEach(func)`

Runs `func(file, enc)` for every Vinyl file in the stream. The file is pushed onward only after `func` has completed.

```ts
import { forEach } from '@push.rocks/gulp-function';

gulp.src('./content/**/*.md')
  .pipe(forEach(async (file) => {
    console.log(file?.relative);
  }))
  .pipe(gulp.dest('./public'));
```

### `forFirst(func)`

Runs `func(file, enc)` only for the first file. This is useful for one-time setup that should still be triggered by a stream.

```ts
import { forFirst } from '@push.rocks/gulp-function';

gulp.src('./assets/**/*')
  .pipe(forFirst(async (file) => {
    console.log(`Starting asset pipeline with ${file?.relative}`);
  }))
  .pipe(gulp.dest('./dist/assets'));
```

### `atEnd(func)`

Runs `func(null, null)` once after all files have passed through. This is ideal for final notifications, summary output, or flushing external state.

```ts
import { atEnd, forEach } from '@push.rocks/gulp-function';

let fileCount = 0;

gulp.src('./src/**/*')
  .pipe(forEach(() => {
    fileCount++;
  }))
  .pipe(atEnd(async () => {
    console.log(`Handled ${fileCount} files`);
  }))
  .pipe(gulp.dest('./dist'));
```

### Default Export

```ts
import gulpFunction from '@push.rocks/gulp-function';

gulp.src('./src/**/*')
  .pipe(gulpFunction([
    async (file) => console.log(file?.relative),
    async () => console.log('side effect complete')
  ], 'forEach'));
```

Supported TypeScript exports:

- `TExecutionMode`: `'forEach' | 'forFirst' | 'atEnd'`
- `TGulpFunctionEncoding`: `BufferEncoding | string | null`
- `TGulpFunctionResult`: `PromiseLike<unknown> | unknown`
- `IPromiseFunction<TFile = unknown>`: `(file?: TFile | null, enc?: TGulpFunctionEncoding) => TGulpFunctionResult`

## Behavior Notes

- Files are passed through unchanged.
- Async functions are awaited before the relevant transform or flush callback completes.
- `forEach` and `forFirst` receive the current file and stream encoding.
- `atEnd` receives `null` for both arguments because no single file is active during flush.
- Arrays passed to the default export are executed with `Promise.all`.
- Non-`Error` thrown values are normalized to `Error` instances before being passed to Gulp.

## Testing and Build

```bash
pnpm test
pnpm run build
```

## License and Legal Information

This repository contains open-source code licensed under the MIT License. A copy of the license can be found in the [LICENSE](./LICENSE) file.

**Please note:** The MIT License does not grant permission to use the trade names, trademarks, service marks, or product names of the project, except as required for reasonable and customary use in describing the origin of the work and reproducing the content of the NOTICE file.

### Trademarks

This project is owned and maintained by Task Venture Capital GmbH. The names and logos associated with Task Venture Capital GmbH and any related products or services are trademarks of Task Venture Capital GmbH or third parties, and are not included within the scope of the MIT license granted herein.

Use of these trademarks must comply with Task Venture Capital GmbH's Trademark Guidelines or the guidelines of the respective third-party owners, and any usage must be approved in writing. Third-party trademarks used herein are the property of their respective owners and used only in a descriptive manner, e.g. for an implementation of an API or similar.

### Company Information

Task Venture Capital GmbH  
Registered at District Court Bremen HRB 35230 HB, Germany

For any legal inquiries or further information, please contact us via email at hello@task.vc.

By using this repository, you acknowledge that you have read this section, agree to comply with its terms, and understand that the licensing of the code does not imply endorsement by Task Venture Capital GmbH of any derivative works.