name: CI - Cache cleanup

# This implements automatic cache cleanup after merging pull requests. See
# https://docs.github.com/en/actions/how-tos/manage-workflow-runs/manage-caches
#
# When the cache quota is reached GitHub automatically deletes the least used
# caches. But they might belong to a still open PR, while the left-over caches
# for the recently closed PR might be still kept.
#
# To check the embedded script with shellcheck run:
#
#    yq ".jobs.cleanup.steps[0].run" ci-cache-cleanup.yml | shellcheck -s bash /dev/stdin

on:
  pull_request:
    types:
      - closed

jobs:
  cleanup:
    runs-on: ubuntu-latest
    permissions:
      actions: write
    steps:
      - name: "Cleanup (PR #${{ github.event.pull_request.number }}, branch \"${{ github.event.pull_request.head.ref }}\")"
        # explicitly require bash, we use bash arrays here
        shell: bash
        run: |
          echo "Fetching list of caches for $PR_BRANCH"
          readarray -t prCacheIds < <(gh cache list --ref "$PR_BRANCH" --json id --jq ".[].id")
          echo "Found ${#prCacheIds[@]} caches"

          echo "Fetching list of caches for $BRANCH"
          readarray -t branchCacheIds < <(gh cache list --ref "$BRANCH" --json id --jq ".[].id")
          echo "Found ${#branchCacheIds[@]} caches"

          ## merge the arrays
          cacheIds=("${prCacheIds[@]}" "${branchCacheIds[@]}")

          # do not fail the workflow while deleting caches
          # (possible race condition when multiple pulls are merged at the same time)
          set +e

          for cacheId in "${cacheIds[@]}"; do
            echo "Deleting cache ${cacheId}..."
            gh cache delete "${cacheId}"
          done

          echo "Done"
        env:
          GH_TOKEN: ${{ github.token }}
          GH_REPO: ${{ github.repository }}
          BRANCH: refs/heads/${{ github.event.pull_request.head.ref }}
          PR_BRANCH: refs/pull/${{ github.event.pull_request.number }}/merge