name: Create a PR if one doesn't exists
description: >
  Creates a commit with the current changes to the repo, and opens a PR for that commit. If
  any PR with the same title exists, then this action is marked as succeeded.
inputs:
  commit-message:
    description: >
      The message for the commit to be created.
    required: true

  title:
    description: >
      The title of the PR. If empty, the title and body will be determined from the commit message.
    default: ''
    required: false

  body:
    description: >
      The body (description) of the PR. The `title` input must be specified in order for this input to be used.
    default: ''
    required: false

  head-branch:
    description: >
      The name of the branch to hold the new commit. If an existing open PR with the same head
      branch exists, the new branch will be force-pushed to that PR instead of creating a new PR.
    required: true

  base-branch:
    description: >
      The base branch to target with the new PR.
    required: true

  token:
    description: |
      The GitHub token to use. It must have enough privileges to
      make API calls to create and close pull requests.
    required: true

runs:
  using: composite
  steps:
    - name: Update git config
      shell: bash
      run: |
        git config --global user.email "github-actions@github.com"
        git config --global user.name "github-actions[bot]"
    - name: Commit, Push and Open PR
      shell: bash
      env:
        COMMIT_MESSAGE: ${{ inputs.commit-message }}
        HEAD_BRANCH: ${{ inputs.head-branch }}
        BASE_BRANCH: ${{ inputs.base-branch }}
        GH_TOKEN: ${{ inputs.token }}
        TITLE: ${{ inputs.title }}
        BODY: ${{ inputs.body }}
      run: |
        set -exu
        if ! [[ $(git diff --stat) != '' ]]; then
          exit 0 # exit early
        fi
        # stage changes in the working tree
        git add .
        git commit -m "$COMMIT_MESSAGE"
        git checkout -b "$HEAD_BRANCH"
        # CAUTION: gits history changes with the following
        git push --force origin "$HEAD_BRANCH"
        PR_JSON=$(gh pr list --state open --json number --head "$HEAD_BRANCH")
        if [[ $? -ne 0 ]]; then
          echo "Failed to fetch existing PRs."
          exit 1
        fi
        PR_NUMBERS=$(echo $PR_JSON | jq '. | length')
        if [[ $PR_NUMBERS -ne 0 ]]; then 
          echo "Found existing open PR: $PR_NUMBERS"
          exit 0
        fi
        gh pr create --head "$HEAD_BRANCH" --base "$BASE_BRANCH" --title "$TITLE" --body "$BODY" --assignee ${{ github.actor }} --draft
        if [[ $? -ne 0 ]]; then
          echo "Failed to create new PR."
          exit 1
        fi