Implement `--refresh` CLI Command To Fetch And Persist JSON-LD Contexts

by ADMIN 72 views

Background

In our mission to crawl public data and generate OWL ontologies, we require a mechanism to refresh and cache remote JSON-LD context files locally. Currently, the main function in src/lib/main.js only logs input arguments. We have a refresh script (npm run refresh → node src/lib/main.js --refresh) defined in package.json, but no implementation.

Goal

To support our mission, we aim to add a --refresh flag to the CLI that:

  1. Loads a list of remote JSON-LD context IRIs (hardcoded or read from a small config object).
  2. Fetches each context via HTTP (using Node's built-in fetch API in Node 20+).
  3. Writes the fetched JSON content to a local contexts/ directory under the project root (creating the directory if necessary).
  4. Logs summary output (Fetched X contexts, saved to contexts/).

Scope

1. Source (src/lib/main.js)

To implement the --refresh flag, we need to:

  • Parse --refresh from args.
  • Implement an async refreshContexts() helper:
    • Define an array of context IRIs (e.g., two example IRIs).
    • Use fetch to GET each context.
    • Write files named by a safe filename (e.g., last path segment) under contexts/.
    • Use fs.promises APIs for directory creation and file writing.
  • Call refreshContexts() when flag is passed and exit gracefully.

2. Tests (tests/unit/main.test.js)

To verify the implementation, we need to:

  • Inject a mock global fetch that returns a synthetic JSON context.
  • Spy on fs.promises.writeFile and fs.promises.mkdir to verify calls.
  • Add a new unit test for main(["--refresh"]) to assert it returns a resolved promise and logs the expected summary.

3. Documentation

To document the new feature, we need to:

  • Add a ## --refresh section describing usage examples in docs/USAGE.md.
  • Under "Features", add a bullet for Refresh Contexts and update the npm run refresh description in README.md.

4. Dependencies (package.json)

No new external dependencies are required, as Node 20+ has a global fetch API.

Verification

To verify the implementation, we need to:

  • Run npm run refresh and observe creation of contexts/ directory with JSON files.
  • Unit tests should pass with the new mock tests.
  • Documentation reflects the new command.

Notes

  • Keep the list of context IRIs minimal (2–3 examples) for demonstration.
  • Ensure the feature does not block regular main behavior when no flag is passed.

Implementation

// src/lib/main.js
const fs = require('fs').promises;
const path = require('path');

async function refreshContexts() {
  const contextIris = [
    'https://example.com/context1',
    'https://example.com/context2',
  ];

  for (const iri of contextIris) {
    try {
      const response = await fetch(iri);
      const json = await response.json();
      const safeFilename = path.basename(iri);
      await fs.writeFile(path.join('contexts', safeFilename), JSON.stringify(json));
    } catch (error) {
      console.error(`Error fetching context: ${error.message}`);
    }
  }
}

async function main(args) {
  if (args.includes('--refresh')) {
    await refreshContexts();
    console.log(`Fetched ${contextIris.length} contexts, saved to contexts/`);
    process.exit(0);
  }
  // Regular main function implementation
}

module.exports = main;

// tests/unit/main.test.js
const fetchMock = require('jest-fetch-mock');
fetchMock.enableMocks();

describe('main', () => {
  beforeEach(() => {
    jest.spyOn(fs.promises, 'writeFile');
    jest.spyOn(fs.promises, 'mkdir');
  });

  afterEach(() => {
    jest.restoreAllMocks();
  });

  it('should call refreshContexts when --refresh flag is passed', async () => {
    const main = require('../src/lib/main');
    const args = ['--refresh'];
    await main(args);
    expect(fs.promises.writeFile).toHaveBeenCalledTimes(2);
    expect(fs.promises.mkdir).toHaveBeenCalledTimes(1);
  });

  it('should log summary output when --refresh flag is passed', async () => {
    const main = require('../src/lib/main');
    const args = ['--refresh'];
    const consoleLogSpy = jest.spyOn(console, 'log');
    await main(args);
    expect(consoleLogSpy).toHaveBeenCalledWith('Fetched 2 contexts, saved to contexts/');
  });
});

# Usage
-----

## --refresh

The `--refresh` flag is used to fetch and persist remote JSON-LD context files locally.

### Example

```bash
npm run refresh

This will fetch the remote JSON-LD context files and save them to a local contexts/ directory under the project root.

Features

  • Refresh Contexts: Fetch and persist remote JSON-LD context files locally.

```markdown
# Features
------------

*   **Refresh Contexts**: Fetch and persist remote JSON-LD context files locally.
*   **npm run refresh**: Run the `refresh` script to fetch and persist remote JSON-LD context files locally.

// package.json
{
  "scripts": {
    "refresh": "node src/lib/main.js --refresh"
  }
}
```<br/>
**Q&A: Implementing `--refresh` CLI Command to Fetch and Persist JSON-LD Contexts**
=====================================================================================

**Q: What is the purpose of the `--refresh` CLI command?**
---------------------------------------------------

A: The `--refresh` CLI command is used to fetch and persist remote JSON-LD context files locally. This is an essential feature for our mission to crawl public data and generate OWL ontologies.

**Q: How does the `--refresh` CLI command work?**
------------------------------------------------

A: The `--refresh` CLI command works by:

1.  Loading a list of remote JSON-LD context IRIs (hardcoded or read from a small config object).
2.  Fetching each context via HTTP (using Node's built-in `fetch` API in Node 20+).
3.  Writing the fetched JSON content to a local `contexts/` directory under the project root (creating the directory if necessary).
4.  Logging summary output (`Fetched X contexts, saved to contexts/`).

**Q: What are the benefits of implementing the `--refresh` CLI command?**
-------------------------------------------------------------------

A: The benefits of implementing the `--refresh` CLI command include:

*   Improved data freshness: By regularly refreshing remote JSON-LD context files, we can ensure that our data is up-to-date and accurate.
*   Enhanced data consistency: By persisting remote JSON-LD context files locally, we can ensure that our data is consistent across different systems and environments.
*   Simplified data management: By providing a simple CLI command to refresh remote JSON-LD context files, we can simplify data management and reduce the risk of errors.

**Q: How do I implement the `--refresh` CLI command?**
---------------------------------------------------

A: To implement the `--refresh` CLI command, you need to:

1.  Parse `--refresh` from `args`.
2.  Implement an async `refreshContexts()` helper:
    *   Define an array of context IRIs (e.g., two example IRIs).
    *   Use `fetch` to GET each context.
    *   Write files named by a safe filename (e.g., last path segment) under `contexts/`.
    *   Use `fs.promises` APIs for directory creation and file writing.
3.  Call `refreshContexts()` when flag is passed and exit gracefully.

**Q: How do I test the `--refresh` CLI command?**
------------------------------------------------

A: To test the `--refresh` CLI command, you need to:

1.  Inject a mock global `fetch` that returns a synthetic JSON context.
2.  Spy on `fs.promises.writeFile` and `fs.promises.mkdir` to verify calls.
3.  Add a new unit test for `main(["--refresh"])` to assert it returns a resolved promise and logs the expected summary.

**Q: How do I document the `--refresh` CLI command?**
---------------------------------------------------

A: To document the `--refresh` CLI command, you need to:

1.  Add a `## --refresh` section describing usage examples in `docs/USAGE.md`.
2.  Under "Features", add a bullet for **Refresh Contexts** and update the `npm run refresh` description in `README.md`.

**Q: What are the dependencies required to implement the `--refresh` CLI command?**


A: No new external dependencies are required, as Node 20+ has a global `fetch` API.

**Q: How do I verify the implementation of the `--refresh` CLI command?**
---------------------------------------------------------------------

A: To verify the implementation of the `--refresh` CLI command, you need to:

1.  Run `npm run refresh` and observe creation of `contexts/` directory with JSON files.
2.  Unit tests should pass with the new mock tests.
3.  Documentation reflects the new command.

**Q: What are the notes for implementing the `--refresh` CLI command?**
-------------------------------------------------------------------

A: Keep the list of context IRIs minimal (2–3 examples) for demonstration. Ensure the feature does not block regular `main` behavior when no flag is passed.