name: "Detect backend-relevant changes"
description: >-
  Classify the pull request's changed files with .circleci/scripts/classify_changes.sh
  and expose decision=run|skip. decision=skip means only ui/**, **.md or **.mdx files
  changed, so callers can short-circuit expensive steps while the job still completes
  successfully and satisfies its required status check. The decision defaults to run for
  any non pull_request event or whenever the changed set cannot be resolved, so tests are
  never skipped when the classification is uncertain.

outputs:
  decision:
    description: "run when backend-relevant files changed, otherwise skip"
    value: ${{ steps.classify.outputs.decision }}

runs:
  using: composite
  steps:
    - id: classify
      shell: bash
      env:
        BASE_SHA: ${{ github.event.pull_request.base.sha }}
      run: |
        set -uo pipefail
        if [ -z "${BASE_SHA:-}" ]; then
          echo "detect-backend-changes: not a pull_request event; running job"
          echo "decision=run" >> "${GITHUB_OUTPUT}"
          exit 0
        fi
        if ! git fetch --no-tags --depth=1 origin "${BASE_SHA}" >/dev/null 2>&1; then
          echo "detect-backend-changes: could not fetch base ${BASE_SHA}; running job"
          echo "decision=run" >> "${GITHUB_OUTPUT}"
          exit 0
        fi
        changed="$(git diff --name-only "${BASE_SHA}" HEAD 2>/dev/null)" || {
          echo "detect-backend-changes: git diff failed; running job"
          echo "decision=run" >> "${GITHUB_OUTPUT}"
          exit 0
        }
        if [ -z "${changed}" ]; then
          echo "detect-backend-changes: no changed files vs ${BASE_SHA}; skipping job"
          echo "decision=skip" >> "${GITHUB_OUTPUT}"
          exit 0
        fi
        echo "detect-backend-changes: changed files vs ${BASE_SHA}:"
        printf '%s\n' "${changed}" | sed 's/^/  /'
        decision="$(printf '%s\n' "${changed}" | bash .circleci/scripts/classify_changes.sh backend)" || decision="run"
        echo "detect-backend-changes: decision=${decision}"
        echo "decision=${decision}" >> "${GITHUB_OUTPUT}"