name: Find mutants
on:
  schedule:
    - cron: "0 0 * * 0" # Weekly on Sunday at midnight UTC
  workflow_dispatch:

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

permissions:
  contents: read

env:
  SHARDS: 64
  RUST_BACKTRACE: 1
  MUTANTS_ARGS: --no-shuffle --in-place --profile mutants -- --all-targets -- -Zunstable-options --fail-fast

jobs:
  baseline:
    name: Baseline test
    runs-on: ubuntu-24.04
    outputs:
      timeout: ${{ steps.baseline.outputs.timeout }}
      shards: ${{ steps.baseline.outputs.shards }}
      max_shard: ${{ steps.baseline.outputs.max_shard }}
    steps:
      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
        with:
          persist-credentials: false

      - id: nss-version
        run: echo "minimum=$(cat min_version.txt)" >> "$GITHUB_OUTPUT"

      - uses: ./.github/actions/nss
        with:
          minimum-version: ${{ steps.nss-version.outputs.minimum }}

      - uses: ./.github/actions/rust
        with:
          version: nightly
          token: ${{ secrets.GITHUB_TOKEN }}

      - name: Run baseline test
        id: baseline
        run: |
          SECONDS=0
          cargo test --all-targets -- -Zunstable-options --fail-fast
          {
            # Minimum timeout is 30s, maximum is 90s, otherwise 3x the baseline test time.
            echo "timeout=$(( SECONDS * 3 < 30 ? 30 : SECONDS * 3 > 90 ? 90 : SECONDS * 3 ))"
            echo "shards=$(jq -nc '[$ARGS.positional[] | tonumber]' --args $(seq 0 $((SHARDS - 1))))"
            echo "max_shard=$((SHARDS - 1))"
          } >> "$GITHUB_OUTPUT"

  mutants:
    name: Find mutants (shard ${{ matrix.shard }}/${{ needs.baseline.outputs.max_shard }})
    needs: baseline
    runs-on: ubuntu-24.04
    strategy:
      fail-fast: false
      matrix:
        shard: ${{ fromJSON(needs.baseline.outputs.shards) }}
    steps:
      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
        with:
          persist-credentials: false

      - id: nss-version
        run: echo "minimum=$(cat min_version.txt)" >> "$GITHUB_OUTPUT"

      - uses: ./.github/actions/nss
        with:
          minimum-version: ${{ steps.nss-version.outputs.minimum }}

      - uses: ./.github/actions/rust
        with:
          version: nightly
          tools: cargo-mutants
          token: ${{ secrets.GITHUB_TOKEN }}

      - name: Find mutants
        env:
          SHARD: ${{ matrix.shard }}/${{ strategy.job-total }}
          TIMEOUT: ${{ needs.baseline.outputs.timeout }}
        run: |
          # shellcheck disable=SC2086
          # Exit codes: 0=success, 1=build/test failure (fail workflow),
          # 2=missed, 3=timeout, 4=unviable (suppress, report in summary).
          (cargo mutants --shard "$SHARD" --sharding round-robin --baseline=skip --timeout "$TIMEOUT" $MUTANTS_ARGS 2>&1 \
            || { ec=$?; [ $ec -ge 2 ] && [ $ec -le 4 ] && exit 0; exit $ec; }) | tee results.txt
          # Some sharded runs get killed by GitHub with error code 143.
          # This seems to be a GitHub-internal protection feature that we can't control:
          # https://github.com/actions/runner-images/issues/6680

      - uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
        if: always()
        with:
          name: mutants.out-${{ matrix.shard }}
          path: mutants.out
          retention-days: 1

  results:
    name: Results
    if: ${{ !cancelled() }}
    needs: mutants
    runs-on: ubuntu-24.04
    steps:
      - uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
        with:
          pattern: mutants.out-*
          path: shards

      - name: Merge shard results
        run: |
          mkdir -p mutants.out
          # Move each shard to a subfolder and concatenate result files.
          for dir in shards/mutants.out-*; do
            shard="${dir##*-}"
            mv "$dir" "mutants.out/shard-$shard"
          done
          for category in caught missed timeout unviable; do
            cat mutants.out/shard-*/"$category.txt" 2>/dev/null | sort -u > "mutants.out/$category.txt" || true
            rm -f mutants.out/shard-*/"$category.txt"
          done

      - uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
        id: upload
        with:
          name: mutants.out
          path: mutants.out
          compression-level: 9

      - name: Post step summary
        env:
          ARTIFACT_URL: ${{ steps.upload.outputs.artifact-url }}
        run: |
          {
            echo "## Mutation Testing Results"
            echo "| Category | Count |"
            echo "|----------|------:|"
            for category in caught missed timeout unviable; do
              count=$(wc -l < "mutants.out/$category.txt" 2>/dev/null | tr -d ' ' || echo 0)
              echo "| $category | $count |"
            done
            echo ""
            for category in missed timeout; do
              if [ -s "mutants.out/$category.txt" ]; then
                echo "### Files with most $category mutants"
                echo '```'
                # Group by file, count occurrences, show top 10.
                cut -d: -f1 "mutants.out/$category.txt" | sort | uniq -c | sort -rn | head -10
                echo '```'
              fi
            done
            echo ""
            echo "[Download full results]($ARTIFACT_URL)"
          } >> "$GITHUB_STEP_SUMMARY"