Support Writing Generated Plot Output To File Via --file Option

Apr 26, 2025 by ADMIN 64 views

Introduction

The CLI and API of our plotting library can generate plot content using various renderers, but currently, the output is only logged or returned. Users expect to be able to save the generated plot image directly to disk using the --file flag. This issue aims to add high-impact value by enabling file output, completing the end-to-end CLI workflow.

Background

Our plotting library can generate plot content using QuickChart JS or other renderers, but the output is only logged or returned. This limitation prevents users from saving the generated plot image directly to disk. To address this issue, we need to modify the library to support writing the generated plot output to a file using the --file flag.

Changes

1. src/lib/main.js

To support writing the generated plot output to a file, we need to parse the --file <path> argument and write the output to the specified file path using the Node.js fs API.

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

// Parse the --file <path> argument
const fileOption = process.argv.find((arg) => arg.startsWith('--file'));
const filePath = fileOption ? fileOption.split('=')[1] : null;

// After plot generation, write the output to the specified file path
if (filePath) {
  const fileExtension = filePath.split('.').pop();
  const fileContent = getPlotContent(); // Obtain the plot content (e.g., SVG string or Buffer for PNG)

  if (fileExtension === 'svg') {
    fs.writeFileSync(filePath, fileContent, 'utf8');
  } else if (fileExtension === 'png') {
    fs.writeFileSync(filePath, fileContent);
  } else {
    console.error(`Unsupported file extension: ${fileExtension}`);
  }
} else {
  // If no --file is provided, default to logging the content (current behavior)
  console.log(getPlotContent());
}

2. tests/unit/main.test.js

To ensure that the --file flag works correctly, we need to add unit tests mocking the fs module using Vitest vi.mock('fs').

// tests/unit/main.test.js
import { vi } from 'vitest';
import { main } from '../main';

describe('main', () => {
  it('writes SVG content to file when --file is provided', async () => {
    const fs = vi.mock('fs', () => ({
      writeFileSync: vi.fn(),
    }));
    const filePath = 'output.svg';
    const fileContent = '<svg>...</svg>';

    await main(['--file', filePath]);
    expect(fs.writeFileSync).toHaveBeenCalledTimes(1);
    expect(fs.writeFileSync).toHaveBeenCalledWith(filePath, fileContent, 'utf8');
  });

  it('writes PNG content to file when --file is provided', async () => {
    const fs = vi.mock('fs', () => ({
      writeFileSync: vi.fn(),
    }));
    const filePath = 'plot.png';
    const fileContent = Buffer.from('<png>...</png>');

    await main(['--file', filePath]);
    expect(fs.writeFileSync).toHaveBeenCalledTimes(1);
    expect(fs.writeFileSync).toHaveBeenCalledWith(filePath, fileContent);
  });

  it('logs content whenfile is not provided', async () => {
    const console = vi.mockConsole();
    await main([]);
    expect(console.log).toHaveBeenCalledTimes(1);
    expect(console.log).toHaveBeenCalledWith('<svg>...</svg>');
  });
});

3. README.md and docs/USAGE.md

To demonstrate the --file flag behavior, we need to update the CLI usage examples in the README and docs.

# Usage

To generate a plot and save it to a file, use the following command:

```bash
npx repository0-plot-code-lib --expression "y=sin(x)" --range "x=0:2*pi" --file output.svg

This will generate an SVG plot and save it to a file named output.svg in the current working directory.

To generate a PNG plot and save it to a file, use the following command:

npx repository0-plot-code-lib --expression "y=cos(x)" --range "x=0:2*pi" --file output.png

This will generate a PNG plot and save it to a file named output.png in the current working directory.

Note that .svg files are written as text and .png files are written as binary.


### 4. package.json

If we are using any additional dependencies for rendering or buffer handling, we need to add them under `dependencies`.

```json
{
  "dependencies": {
    "quickchart-js": "^1.0.0",
    "buffer": "^6.0.3"
  }
}

Verification

To verify that the changes work correctly, we need to run npm test and ensure that the new tests pass without regressions.

npm test

We also need to manually test the --file flag using the following commands:

npx repository0-plot-code-lib --expression "y=sin(x)" --range "x=0:2*pi" --file output.svg

npx repository0-plot-code-lib --expression "y=cos(x)" --range "x=0:2*pi" --file output.png

We should verify that the output.svg file is created with valid SVG content and that the output.png file exists and opens as a PNG image.

Q: What is the purpose of this change?

A: The purpose of this change is to enable end-to-end file output from expression to image, allowing users to save the generated plot image directly to disk using the --file flag.

Q: Why is this change important?

A: This change is important because it completes a core piece of the plotting feature, making it more user-friendly and convenient. Users expect to be able to save the generated plot image directly to disk, and this change addresses that need.

Q: How does the --file flag work?

A: The --file flag allows users to specify a file path where the generated plot image will be saved. The file path can be in the format of --file output.svg or --file plot.png, depending on the file type.

Q: What file types are supported?

A: The --file flag supports two file types: SVG and PNG. SVG files are written as text, while PNG files are written as binary.

Q: How do I use the --file flag?

A: To use the --file flag, simply add the flag followed by the file path to the command. For example:

npx repository0-plot-code-lib --expression "y=sin(x)" --range "x=0:2*pi" --file output.svg

Q: What if I don't provide a file path?

A: If you don't provide a file path, the generated plot image will be logged to the console instead of being saved to a file.

Q: How do I verify that the --file flag works correctly?

A: To verify that the --file flag works correctly, you can run npm test to ensure that the new tests pass without regressions. You can also manually test the --file flag using the following commands:

npx repository0-plot-code-lib --expression "y=sin(x)" --range "x=0:2*pi" --file output.svg

npx repository0-plot-code-lib --expression "y=cos(x)" --range "x=0:2*pi" --file output.png

You should verify that the output.svg file is created with valid SVG content and that the output.png file exists and opens as a PNG image.

Q: What are the benefits of this change?

A: The benefits of this change include:

Improved user experience: Users can now save the generated plot image directly to disk, making it easier to work with the plot.
Increased flexibility: Users can choose to save the plot image in either SVG or PNG format, depending on their needs.
Enhanced functionality: The --file flag adds a new feature to the plotting library, making it more powerful and useful.

Q: Are there any limitations or edge cases to consider?

A: Yes, there are a few limitations and edge cases to consider:

The --file flag only supports SVG and PNG file types.
If the file path is not provided, the generated plot image will be logged to the console instead of being saved to a file.
If the file path is provided but the file does not exist, the plotting library will create a new file with the specified name.

By understanding these limitations and edge cases, users can use the --file flag effectively and get the most out of the plotting library.