name: Mypy New Error Check

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]


jobs:
  mypy-diff:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        python-version: ['3.10', '3.11', '3.12', '3.13',]
    steps:
      - name: Checkout code
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Set up Python
        uses: actions/setup-python@v5
        with:
          python-version: ${{ matrix.python-version }}

      - name: Install uv
        uses: astral-sh/setup-uv@v5

      - name: Generate Baseline (Main)
        run: |
          # Switch to main branch to generate baseline
          git checkout origin/main

          git checkout ${{ github.sha }} -- pyproject.toml
          
          # Install dependencies for main
          uv venv .venv
          source .venv/bin/activate
          uv sync --all-extras
          
          # Run mypy, filter for errors only, remove line numbers (file:123: -> file::), and sort
          # We ignore exit code (|| true) because we expect errors on main
          uv run mypy . | grep "error:" | sed 's/:\([0-9]\+\):/::/g' | sort > main_errors.txt || true
          
          echo "Found $(wc -l < main_errors.txt) errors on main."

      - name: Check PR Branch
        run: |
          # Switch back to the PR commit
          git checkout ${{ github.sha }}
          
          # Re-sync dependencies in case the PR changed them
          source .venv/bin/activate
          uv sync --all-extras
          
          # Run mypy on PR code, apply same processing
          uv run mypy . | grep "error:" | sed 's/:\([0-9]\+\):/::/g' | sort > pr_errors.txt || true
          
          echo "Found $(wc -l < pr_errors.txt) errors on PR branch."

      - name: Compare and Fail on New Errors
        run: |
          # 'comm -13' suppresses unique lines in file1 (main) and common lines, 
          # leaving only lines unique to file2 (PR) -> The new errors.
          comm -13 main_errors.txt pr_errors.txt > new_errors.txt
          
          if [ -s new_errors.txt ]; then
            echo "::error::The following NEW mypy errors were introduced:"
            cat new_errors.txt
            exit 1
          else
            echo "Great job! No new mypy errors introduced."
          fi