_detect-changed.yml

name: "Detect changed subjects"

on:
  workflow_call:
    inputs:
      paths:
        description: "Space-separated root paths whose immediate child directories are the subjects (e.g., 'features/src features/test' or 'images')"
        required: true
        type: string
    outputs:
      names:
        description: "JSON array of changed subject names"
        value: ${{ jobs.detect.outputs.names }}

jobs:
  detect:
    runs-on: ubuntu-latest
    outputs:
      names: ${{ steps.set-matrix.outputs.names }}
    steps:
      - name: Checkout
        uses: actions/checkout@v6
        with:
          fetch-depth: 0

      - name: Detect changed subjects
        id: set-matrix
        env:
          PATHS: ${{ inputs.paths }}
        run: |
          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
            # List all subjects under the first path
            first_path=$(echo "$PATHS" | cut -d' ' -f1)
            names=$(ls -d "$first_path"/*/ 2>/dev/null | xargs -n1 basename | sort -u | jq -R -s -c 'split("\n")[:-1]')
          else
            if [ "${{ github.event_name }}" = "pull_request" ]; then
              base="${{ github.event.pull_request.base.sha }}"
            else
              base="${{ github.event.before }}"
            fi
            # For each path, get changed files, strip the path prefix, take the first component
            names=$(
              for p in $PATHS; do
                git diff --name-only "$base" HEAD -- "$p" | sed "s|^${p}/||" | cut -d/ -f1
              done | sort -u | jq -R -s -c 'split("\n")[:-1]'
            )
          fi
          echo "names=$names" >> "$GITHUB_OUTPUT"