name: Auto-close harvested PRs

# When a commit on main contains a "Harvested from PR #N" line in its
# message, close PR #N with a templated thank-you that links back to
# the merged commit. Solves the long-standing problem where contributor
# PRs whose code lands via maintainer cherry-pick stay open and
# `CONFLICTING` forever, even though their fix is credited in the
# CHANGELOG.
#
# The expected commit-message convention is documented in
# CONTRIBUTING.md. Two patterns are recognised:
#
#   * `Harvested from PR #1234 by @username`  (preferred)
#   * `harvested from #1234`                  (case-insensitive fallback)
#
# The first match's PR number is closed; multiple PRs can be closed
# per commit by repeating the line. The match runs on the commit
# body only, not on the subject line, so the subject can describe
# the change naturally without baking a number into it.

on:
  push:
    branches: [main]

permissions:
  contents: read
  pull-requests: write
  issues: write

# Only one auto-close run at a time so two near-simultaneous main
# pushes can't both try to close the same PR (the second would just
# fail with "Pull request is already closed", harmless but noisy).
concurrency:
  group: auto-close-harvested
  cancel-in-progress: false

jobs:
  close:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          # We need at least the commits that this push introduced.
          # fetch-depth: 0 is the simplest correct option; the
          # alternative (fetching just `before..after`) is fragile
          # when force-pushes happen.
          fetch-depth: 0

      - name: Close PRs referenced by harvested-from lines
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          BEFORE_SHA: ${{ github.event.before }}
          AFTER_SHA: ${{ github.event.after }}
        shell: bash
        run: |
          set -euo pipefail

          # The first push to a fresh branch has BEFORE_SHA = 0000…0000.
          # In that case fall back to the latest commit only — we don't
          # want to scan the entire history.
          if [[ "${BEFORE_SHA}" == "0000000000000000000000000000000000000000" || -z "${BEFORE_SHA:-}" ]]; then
            RANGE="${AFTER_SHA}"
            RANGE_ARGS=("-1" "${AFTER_SHA}")
          else
            RANGE="${BEFORE_SHA}..${AFTER_SHA}"
            RANGE_ARGS=("${RANGE}")
          fi
          echo "Scanning commit range: ${RANGE}"

          # `git log --format=%H%n%B%n--END--` separates commits with a
          # sentinel so multi-line bodies don't get mangled.
          mapfile -t commits < <(git log "${RANGE_ARGS[@]}" --format="%H")

          if [[ ${#commits[@]} -eq 0 ]]; then
            echo "No commits in range; nothing to do."
            exit 0
          fi

          declare -A processed_prs=()

          for sha in "${commits[@]}"; do
            body="$(git log -1 --format=%B "${sha}")"
            # Two patterns, both case-insensitive on the keyword:
            #   "Harvested from PR #1234 by @username"  (preferred form)
            #   "harvested from #1234"                  (short form)
            mapfile -t pr_numbers < <(
              printf '%s\n' "${body}" \
                | grep -oiE 'harvested from (pr )?#[0-9]+' \
                | grep -oE '#[0-9]+' \
                | tr -d '#' \
                | sort -u || true
            )

            if [[ ${#pr_numbers[@]} -eq 0 ]]; then
              continue
            fi

            short_sha="${sha:0:12}"
            subject="$(git log -1 --format=%s "${sha}")"

            for pr in "${pr_numbers[@]}"; do
              key="${pr}-${sha}"
              if [[ -n "${processed_prs[${key}]:-}" ]]; then
                continue
              fi
              processed_prs[${key}]=1

              # Idempotency: skip if the PR is already closed.
              state="$(gh pr view "${pr}" --json state --jq .state 2>/dev/null || echo "MISSING")"
              if [[ "${state}" == "CLOSED" || "${state}" == "MERGED" ]]; then
                echo "PR #${pr} is already ${state}; skipping."
                continue
              fi
              if [[ "${state}" == "MISSING" ]]; then
                echo "::warning::PR #${pr} not found or inaccessible; skipping."
                continue
              fi

              author="$(gh pr view "${pr}" --json author --jq '.author.login' 2>/dev/null || echo "")"
              greeting="Hi"
              if [[ -n "${author}" ]]; then
                greeting="Thanks @${author}"
              fi

              # NOTE: this block intentionally avoids `<<EOF` heredocs.
              # YAML's `|` block scalar requires consistent indentation,
              # but heredoc bodies have to start at column 0 — those two
              # constraints can't coexist in the same file. We assemble
              # the body with `printf` + `\n` so every line of the
              # message lives at the same indent as the surrounding
              # shell code.
              commit_url="https://github.com/${GITHUB_REPOSITORY}/commit/${sha}"
              contributing_url="https://github.com/${GITHUB_REPOSITORY}/blob/main/CONTRIBUTING.md"
              body_text="$(printf '%s\n' \
                "${greeting} — your contribution landed in [\`${short_sha}\`](${commit_url}) on \`main\`:" \
                "" \
                "> ${subject}" \
                "" \
                "Closing this PR now that the code is on \`main\`. Credit lives in the commit message and (where applicable) the \`CHANGELOG.md\` entry for the next release. Apologies for not closing this at the time of the merge — the auto-close workflow is new in v0.8.31." \
                "" \
                "If you want to land more work and would prefer your future PRs merge cleanly without a harvest step, the [\`CONTRIBUTING.md\`](${contributing_url}) doc has a short note on what makes a contribution mergeable as-is." \
              )"

              echo "Closing PR #${pr} (harvested in ${short_sha})"
              if ! gh pr close "${pr}" \
                  --repo "${GITHUB_REPOSITORY}" \
                  --comment "${body_text}"; then
                echo "::warning::Failed to close PR #${pr}; continuing"
              fi
            done
          done

          echo "Auto-close pass complete."