feat: Add badge subcommand for shields.io endpoint JSON generation #1

Problem

When integrating codedash into CI pipelines (e.g., GitHub Actions), users need to generate badge data (shields.io endpoint JSON) for README badges. Currently this requires writing custom Python/shell scripts to parse codedash analyze -o json output and produce the correct JSON format.

Badge generation is a standard responsibility of metrics tools (e.g., cargo-tarpaulin --out badge), and codedash should support it natively.

Proposed Solution

Add a badge subcommand that outputs shields.io Endpoint Badge JSON files.

CLI Interface

codedash badge [OPTIONS] [path]

Arguments:
  [path]  Source directory (default: .)

Options:
  -o, --out-dir <dir>        Output directory (default: ./badges)
  -c, --config <config>      Config file path (.codedash.lua)
      --cov-file <cov-file>  Coverage JSON (cargo llvm-cov --json)
      --format <format>      Badge format: shields-endpoint (default), svg
      --only <metrics>       Comma-separated filter: coverage,fn-coverage,complexity,modules

Example Usage

codedash badge . --cov-file coverage.json -o _site/badges/

Output Files

badges/
  coverage.json       # line coverage %
  fn-coverage.json    # function coverage %
  complexity.json     # avg/max cyclomatic complexity
  modules.json        # total code units

Each file follows the shields.io endpoint format:

{
  "schemaVersion": 1,
  "label": "coverage",
  "message": "86.3%",
  "color": "brightgreen"
}

Color Logic

Configuration Override

Thresholds should be overridable via .codedash.lua:

return {
  extends = "recommended",
  badges = {
    coverage = { green = 80, yellow = 60 },
    complexity = { green = 5, yellow = 10 },
  },
}

CI Integration (Before/After)

# Before: custom Python script required
- run: |
    python3 <<'PY'
    import json
    cov = json.load(open("coverage.json"))
    # ... 20+ lines of badge generation logic
    PY

# After: single command
- run: codedash badge . --cov-file coverage.json -o _site/badges/

README Badge Embedding

![coverage](https://img.shields.io/endpoint?url=https://user.github.io/repo/badges/coverage.json)
![complexity](https://img.shields.io/endpoint?url=https://user.github.io/repo/badges/complexity.json)

Future Extensions

• --format svg: self-contained SVG badge generation (no shields.io dependency)
• Auto-embed badges into codedash view HTML output
• Custom badge definitions in .codedash.lua badges section