name: Discord PR Notify

on:
  pull_request:
    types: [closed]   # merged only (filtered in the job `if:`)

jobs:
  notify:
    # Only when a PR is actually merged; closed-unmerged skips silently.
    if: github.event.pull_request.merged == true
    runs-on: ubuntu-latest
    steps:
      - name: Send merged PR to Discord
        env:
          DISCORD_WEBHOOK_URL: ${{ secrets.DISCORD_WEBHOOK_URL }}
        run: |
          set -euo pipefail

          # Repository secrets are NOT exposed to `pull_request` runs triggered
          # from a fork, so a merged fork PR would reach curl with an empty URL
          # and fail the job for no useful reason. Skip cleanly instead. The
          # fix is deliberately NOT `pull_request_target`: that would hand a
          # write-scoped token and this webhook to an outsider-triggered run,
          # which is a poor trade for a chat notification.
          if [ -z "${DISCORD_WEBHOOK_URL:-}" ]; then
            echo "DISCORD_WEBHOOK_URL unavailable (fork PR?) — skipping notification."
            exit 0
          fi

          # Read everything from the event payload via jq: PR text is
          # attacker-controlled input, so it must never be interpolated
          # into the script (backticks/$() would execute).
          TITLE=$(jq -r '.pull_request.title' "$GITHUB_EVENT_PATH")
          URL=$(jq -r '.pull_request.html_url' "$GITHUB_EVENT_PATH")
          AUTHOR=$(jq -r '.pull_request.user.login' "$GITHUB_EVENT_PATH")
          BASE=$(jq -r '.pull_request.base.ref' "$GITHUB_EVENT_PATH")
          BODY=$(jq -r '.pull_request.body // ""' "$GITHUB_EVENT_PATH")
          NUMBER=$(jq -r '.pull_request.number' "$GITHUB_EVENT_PATH")
          MERGED_AT=$(jq -r '.pull_request.merged_at' "$GITHUB_EVENT_PATH")

          echo "title_len=${#TITLE} body_len=${#BODY}"

          # NOTE: use [ \t], never [[:space:]] — the runner's awk is mawk,
          # which silently mis-parses POSIX character classes.
          # Extract bullets from the "### Highlights" section (top 5).
          # Stops at the next heading or the <details> block.
          HIGHLIGHTS=$(printf '%s\n' "$BODY" | awk '
            /^#+[ \t]*Highlights/ { f=1; next }
            f && (/^#/ || /^</)   { exit }
            f && /^- /            { print }
          ' | head -5)

          if [ -n "$HIGHLIGHTS" ]; then
            DESC="$HIGHLIGHTS"
          else
            # Lazy PR with no Highlights section: use the first prose
            # paragraph of the body, truncated to 300 chars.
            FIRST_PARA=$(printf '%s\n' "$BODY" | awk '
              /^[ \t]*$/            { if (started) exit; next }
              /^(#|<|```|\||- )/    { if (started) exit; next }
              { started=1; print }
            ' | tr '\n' ' ' | sed 's/  */ /g' | cut -c1-300)
            if [ -n "$FIRST_PARA" ]; then
              DESC="$FIRST_PARA"
            else
              DESC="_Merged without a description._"
            fi
          fi

          # Discord embed descriptions cap at 4096 chars; stay under.
          DESC=$(printf '%s' "$DESC" | cut -c1-3900)

          jq -n \
            --arg title "$TITLE" \
            --arg url "$URL" \
            --arg desc "$DESC" \
            --arg author "$AUTHOR" \
            --arg author_url "https://github.com/$AUTHOR" \
            --arg avatar "https://github.com/$AUTHOR.png" \
            --arg footer "PR #$NUMBER merged into $BASE" \
            --arg ts "$MERGED_AT" \
            '{
              username: "ServerKit",
              embeds: [{
                author: { name: $author, url: $author_url, icon_url: $avatar },
                title: $title,
                url: $url,
                description: $desc,
                color: 10181046,
                footer: { text: $footer },
                timestamp: $ts
              }]
            }' > payload.json

          curl -sS -f -X POST -H "Content-Type: application/json" \
            -d @payload.json "$DISCORD_WEBHOOK_URL"