name: Sync stable CHANGELOG to master

on:
  push:
    branches: [stable]
    paths:
      - 'CHANGELOG.md'

jobs:
  merge-changelog:
    runs-on: ubuntu-latest
    permissions:
      contents: write
      pull-requests: write

    steps:
      # defaults to `fetch-depth:1` which only checks out the current branch
      # since the action runs on master, it will only checkout master.
      - name: Setup Repository
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          repository: flutteractionsbot/flutter
          token: ${{ secrets.FLUTTERACTIONSBOT_CP_TOKEN }}
          ref: master
          persist-credentials: false

      - name: Configure git
        run: |
          gh auth setup-git
          git config --global user.name "flutteractionsbot"
          git config --global user.email "<flutter-actions-bot@google.com>"
          git remote add upstream https://github.com/flutter/flutter.git
        env:
          GH_TOKEN: ${{ secrets.FLUTTERACTIONSBOT_CP_TOKEN }}

      # avoid downloading hundreds of other branches/history
      # utilizing `fetch-depth:0` in actions/checkout would clone everything.
      - name: Fetch upstream branches
        run: |
          git fetch upstream stable:stable --depth=1
          git fetch upstream master --depth=1
        env:
          GH_TOKEN: ${{ secrets.FLUTTERACTIONSBOT_CP_TOKEN }}

      - name: Prepare PR branch and commit changes
        id: prepare_pr_branch
        run: |
          PR_BRANCH="sync-changelog-stable-to-master-$(date +%s)"
          echo "pr_branch_name=$PR_BRANCH" >> "$GITHUB_OUTPUT"

          # Base the branch on upstream's master to avoid issues if the fork's master is out of date
          git checkout -b "$PR_BRANCH" upstream/master

          # Retrieve the file from stable directly into the working directory
          git show stable:CHANGELOG.md > CHANGELOG.md

          # Stop if no changes are detected
          if git diff --quiet CHANGELOG.md; then
            echo "No changes detected. Skipping PR creation."
            echo "has_changes=false" >> "$GITHUB_OUTPUT"
            exit 0
          fi

          echo "has_changes=true" >> "$GITHUB_OUTPUT"
          git add CHANGELOG.md
          git commit -m "Sync CHANGELOG.md from stable"
          git push origin "$PR_BRANCH"
        env:
          GH_TOKEN: ${{ secrets.FLUTTERACTIONSBOT_CP_TOKEN }}

      - name: Create Pull Request
        if: steps.prepare_pr_branch.outputs.has_changes == 'true'
        run: |
          gh pr create \
            --base master \
            --head flutteractionsbot:$PR_BRANCH_NAME \
            --repo flutter/flutter \
            --title "Sync CHANGELOG.md from stable" \
            --body "This PR automates the synchronization of \`CHANGELOG.md\` from the \`stable\` branch to the \`master\` branch." \
            --label autosubmit
        env:
          GH_TOKEN: ${{ secrets.FLUTTERACTIONSBOT_CP_TOKEN }}
          PR_BRANCH_NAME: ${{ steps.prepare_pr_branch.outputs.pr_branch_name }}