name: Sync branches into main

on:
  schedule:
    - cron: "0 14 * * 1" # Monday
    - cron: "0 14 * * 3" # Wednesday

  workflow_dispatch:
    inputs:
      source:
        description: Branch to sync into main
        required: true
        type: choice
        options:
          - laptop
          - desktop

permissions:
  contents: write
  pull-requests: write

jobs:
  sync:
    runs-on: ubuntu-latest

    steps:
      - name: Determine source branch
        id: branch
        run: |
          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
            echo "source=${{ inputs.source }}" >> "$GITHUB_OUTPUT"
            exit 0
          fi

          DOW=$(date -u +%u)

          if [ "$DOW" = "1" ]; then
            echo "source=laptop" >> "$GITHUB_OUTPUT"
          elif [ "$DOW" = "3" ]; then
            echo "source=desktop" >> "$GITHUB_OUTPUT"
          else
            echo "No sync scheduled today."
            exit 1
          fi

      - name: Check for existing PR
        id: existing
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          REPO: ${{ github.repository }}
        run: |
          PR_NUMBER=$(gh pr list \
            --base main \
            --repo "$REPO" \
            --head "${{ steps.branch.outputs.source }}" \
            --state open \
            --json number \
            --jq '.[0].number')

          echo "number=$PR_NUMBER" >> "$GITHUB_OUTPUT"

      - name: Create PR if needed
        id: pr
        if: steps.existing.outputs.number == ''
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          PR_URL=$(gh pr create \
            --base main \
            --repo "$REPO" \
            --head "${{ steps.branch.outputs.source }}" \
            --title "Weekly sync: ${{ steps.branch.outputs.source }} → main" \
            --body "$(cat <<EOF
          This pull request was created automatically by GitHub Actions.

          If the branch can be merged cleanly, auto-merge will merge it automatically.

          If there are merge conflicts, this PR will remain open until they are resolved.
          EOF
          )")

          PR_NUMBER=$(gh pr view "$PR_URL" --json number --jq '.number')

          echo "url=$PR_URL" >> "$GITHUB_OUTPUT"
          echo "number=$PR_NUMBER" >> "$GITHUB_OUTPUT"

      - name: Determine PR number
        id: final
        run: |
          if [ -n "${{ steps.existing.outputs.number }}" ]; then
            echo "number=${{ steps.existing.outputs.number }}" >> "$GITHUB_OUTPUT"
          else
            echo "number=${{ steps.pr.outputs.number }}" >> "$GITHUB_OUTPUT"
          fi

      - name: Enable auto-merge
        if: steps.final.outputs.number != ''
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          gh pr merge \
            "${{ steps.final.outputs.number }}" \
            --repo "$REPO" \
            --auto \
            --merge