# Use git rebase to append new upstream commits
# inverted logic from imba-tjd/rebase-on-upstream
name: Reverse Rebase from Upstream
on:
  workflow_call:
    inputs:
      upstream:
        type: string
        description: <user>/<repo> or the full HTTP URL
        required: false
      branch:
        type: string
        description: The upstream branch that is rebased from
        required: false
        default:  master
      push:
        type: boolean
        description: Do the force push in this action
        required: false
        default:  true
      token:
        type: string
        description: GitHub Access Token
        required: true
        default:  ${{ github.token }}

permissions:
  contents: write

jobs:
  rebaser:
    runs-on: ubuntu-latest
    steps:
    - name: Main
      shell: bash
      run: |
        set -ex
        # Starting with current git branch (TARGET), get the UPSTREAM branch
        # as a temporary branch; rebase TARGET onto it; if that differs from TARGET,
        # make it the TARGET and push the result, if the remote hasn't changed.
        # Effect: commits specific to the TARGET repo stay in place; new UPSTREAM
        # commits are appended
        TARGET_SHA=$(git rev-parse HEAD)
        TARGET=$(git name-rev --name-only "$TARGET_SHA")
        if [ -z "$TARGET" ]; then echo "Can't find current branch" >&2; exit 1; fi
        UPSTREAM=${{ inputs.upstream }}
        if [ -z "$UPSTREAM" ]; then
          echo "${{ inputs.token }}" | gh auth login --with-token
          UPSTREAM=$(gh api repos/:owner/:repo --jq .parent.full_name
          if [ -z "$UPSTREAM" ]; then echo "Can't find upstream" >&2 && exit 1; fi
        fi
        if ! echo "$UPSTREAM" | grep -E '^(http|git@)'; then
          UPSTREAM=https://github.com/$UPSTREAM.git
        fi
        git remote add -f -t "${{ inputs.branch }}" --tags upstream "$UPSTREAM"
        REBASE=${TARGET}-rebase
        trap '{ git checkout "$TARGET"; git branch -D "$REBASE"; }' EXIT
        git checkout -B  "$REBASE" --no-track "upstream/${{ inputs.branch }}" 
        git config --local user.email "rebaser+github-actions[bot]@users.noreply.github.com"
        git config --local user.name  "GitHub Actions"
        # rebase new UPSTREAM commits onto TARGET
        UPSTREAM_SHA=$(git rev-parse HEAD)
        git rebase "refs/heads/${TARGET}"
        if [ -n "$(git log --max-count 1 --oneline "HEAD...${TARGET}")"  ]; then
          git branch -M "$REBASE" "$TARGET"
          if [ "${{ inputs.push }}" = true ]; then
            # rebase changed TARGET: push if remote TARGET unchanged
            git push origin --force-with-lease="${TARGET}"
          fi
        fi