name: Draft new release

on:
  milestone:
    types: [closed]

jobs:
  draft-new-release:
    name: Draft a new release
    runs-on: ubuntu-latest
    steps:
      - name: Extract version from milestone
        shell: bash
        run: |
          VERSION="${{ github.event.milestone.title }}"
          RELEASE_VERSION="${VERSION/v/}"
          # Transforms 1.13.2 to 1.13 so that we can re-use the same
          # branch for patch releases.
          BRANCH_VERSION="${RELEASE_VERSION:$i:-2}"
          if [[ "${RELEASE_VERSION: -1}" == "0" ]]; then
            CHECKOUT_REF="develop"
          else
            CHECKOUT_REF="release-${BRANCH_VERSION}"
          fi

          # Export variables separately so the scripting above is more legible,
          # and we can actually use them within this block. Changes to $GITHUB_ENV
          # only affect the next step, not the current one.
          echo "RELEASE_VERSION=${RELEASE_VERSION}" >> $GITHUB_ENV
          echo "CHECKOUT_REF=${CHECKOUT_REF}" >> $GITHUB_ENV
          echo "BRANCH_VERSION=${BRANCH_VERSION}" >> $GITHUB_ENV
          echo "PR_BASE=release-${BRANCH_VERSION}" >> $GITHUB_ENV
          echo "PR_HEAD=release-prep" >> $GITHUB_ENV

      - uses: actions/checkout@v3.0.2
        with:
          ref: ${{ env.CHECKOUT_REF }}

      - name: Set up JDK
        uses: actions/setup-java@v3.3.0
        with:
          distribution: temurin
          java-version: 17

      - name: Update changelog
        uses: thomaseizinger/keep-a-changelog-new-release@1.3.0
        with:
          version: ${{ github.event.milestone.title }}

      - name: Initialize git config and commit changes
        shell: bash
        run: |
          # Configure name and email for Actions user
          git config user.name "GitHub Actions"
          git config user.email noreply@github.com

          # It is necessary to create the $PR_BASE branch if it doesn't
          # already exist because we want to start a PR against it.
          if [[ "${CHECKOUT_REF}" == "develop" ]]; then
            git branch -c develop "${PR_BASE}"
            git push origin "${PR_BASE}"
          fi

          # Stage and commit changes to the changelog
          git add CHANGELOG.md
          git commit -m "CHANGELOG: bump for ${{ github.event.milestone.title }}"

          # Increment the version as necessary. If we checked out develop it means
          # that the version number is already correct, and we only need to drop the
          # -SNAPSHOT suffix.
          if [[ "${CHECKOUT_REF}" == "develop" ]]; then
            ./gradlew --no-configuration-cache --no-daemon clearPreRelease
          else
            ./gradlew --no-configuration-cache --no-daemon bumpPatch
          fi

          # Commit changes to the versioning
          git add **/version.properties
          git commit -m "build: bump version"

      - name: Create Pull Request
        uses: peter-evans/create-pull-request@v4.0.4
        with:
          author: GitHub Actions <noreply@github.com>
          body: This is an automated pull request to bump the changelog for the ${{ github.event.milestone.title }} release.
          base: ${{ env.PR_BASE }}
          branch: ${{ env.PR_HEAD }}
          title: Release v${{ env.RELEASE_VERSION }}
          token: ${{ secrets.GITHUB_TOKEN }}