action.yml

name: Setup Matrix
description: Load a YAML matrix file and optionally filter to a single target.

inputs:
  file:
    description: Path to the YAML matrix file
    required: false
    default: .github/matrix.yml
  target:
    description: Only include the target with this name
    required: false

outputs:
  matrix:
    description: JSON matrix for use with fromJSON()
    value: ${{ steps.set-matrix.outputs.matrix }}

runs:
  using: composite
  steps:
    # GitHub Actions has fromJSON() but no fromYAML(), so we convert to JSON.
    # This also lets us use jq for validation and filtering.
    - name: Set matrix
      id: set-matrix
      shell: bash
      run: |
        file="${{ inputs.file }}"

        if [ ! -f "$file" ]; then
          echo "::error::$file not found"
          exit 1
        fi

        matrix=$(yq -o=json -c . "$file")

        count=$(echo "$matrix" | jq '.target | length')
        if [ -z "$count" ] || [ "$count" -eq 0 ]; then
          echo "::error::$file must have a non-empty 'target' array"
          exit 1
        fi

        bad=$(echo "$matrix" | jq '[.target[] | select(.name == null or .["runs-on"] == null)] | length')
        if [ "$bad" -gt 0 ]; then
          echo "::error::$bad target(s) in $file missing required fields (name, runs-on)"
          exit 1
        fi

        target="${{ inputs.target }}"
        if [ -n "$target" ]; then
          matrix=$(echo "$matrix" | jq -c --arg t "$target" '{target: [.target[] | select(.name == $t)]}')

          if [ "$(echo "$matrix" | jq '.target | length')" -eq 0 ]; then
            echo "::error::Target '$target' not found in $file"
            echo "Available targets:"
            yq -r '.target[].name' "$file"
            exit 1
          fi
        fi

        {
          echo "matrix<<EOF"
          echo "$matrix"
          echo "EOF"
        } >> $GITHUB_OUTPUT