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: Checkout repository
        uses: actions/checkout@v4

      - 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)

          case "$DOW" in
            1)
              echo "source=laptop" >> "$GITHUB_OUTPUT"
              ;;
            3)
              echo "source=desktop" >> "$GITHUB_OUTPUT"
              ;;
            *)
              echo "No sync scheduled today."
              exit 1
              ;;
          esac
      - name: Check for changes
        run: |
          git fetch origin main "${{ steps.branch.outputs.source }}"
          HAS_CHANGES=true
          if git diff --quiet \
            "origin/main...origin/${{ steps.branch.outputs.source }}"; then
            HAS_CHANGES=false
          fi

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

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

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

            PR_NUMBER=$(gh pr list \
              --base main \
              --head "${{ steps.branch.outputs.source }}" \
              --state open \
              --json number \
              --jq '.[0].number')

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

      - name: Enable auto-merge
        if: steps.pr.outputs.number != ''
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          if $HAS_CHANGES; then
            gh pr merge \
              "${{ steps.pr.outputs.number }}" \
              --auto \
              --merge
          fi