# Implementation Plan: Tier 4 Auto-Patching (tier4_auto_patching_20260306)

> **Reference:** [Spec](./spec.md) | [Architecture Guide](../../../docs/guide_architecture.md)

## Phase 1: Patch Generation
Focus: Generate unified diff on test failure

- [x] Task 1.1: Initialize MMA Environment
- [x] Task 1.2: Extend Tier 4 prompt for patch generation
    - WHERE: `src/mma_prompts.py` or inline in `ai_client.py`
    - WHAT: Prompt to generate unified diff
    - HOW:
      ```python
      TIER4_PATCH_PROMPT = """
      Analyze the error and generate a unified diff patch to fix it.
      Output format:
      --- a/path/to/file.py
      +++ b/path/to/file.py
      @@ -line,count +line,count @@
       context
      -removed line
      +added line
       context
      """
      ```

- [x] Task 1.3: Add patch generation function
    - WHERE: `src/ai_client.py`
    - WHAT: Generate patch from error
    - HOW:
      ```python
      def run_tier4_patch_generation(error: str, file_context: str) -> str:
       prompt = TIER4_PATCH_PROMPT + f"\n\nError:\n{error}\n\nFiles:\n{file_context}"
       return send(prompt, model="gemini-2.5-flash-lite")
      ```

## Phase 2: Diff Viewer UI
Focus: Display side-by-side diff

- [x] Task 2.1: Parse unified diff
    - WHERE: `src/gui_2.py` or new `src/diff_viewer.py`
    - WHAT: Parse diff into hunks
    - HOW:
      ```python
      def parse_diff(diff_text: str) -> list[dict]:
       hunks = []
       current_hunk = None
       for line in diff_text.split("\n"):
        if line.startswith("@@"):
         if current_hunk: hunks.append(current_hunk)
         current_hunk = {"header": line, "lines": []}
        elif current_hunk:
         current_hunk["lines"].append(line)
       if current_hunk: hunks.append(current_hunk)
       return hunks
      ```

- [x] Task 2.2: Render diff viewer
    - WHERE: `src/gui_2.py`
    - WHAT: Color-coded diff display
    - HOW:
      ```python
      for hunk in hunks:
       for line in hunk["lines"]:
        if line.startswith("+"):
         imgui.text_colored(vec4(100, 255, 100, 255), line)
        elif line.startswith("-"):
         imgui.text_colored(vec4(255, 100, 100, 255), line)
        else:
         imgui.text(line)
      ```

## Phase 3: Patch Application
Focus: Apply patch with backup

- [x] Task 3.1: Create backup before apply
    - WHERE: `src/gui_2.py` or `src/mcp_client.py`
    - WHAT: Backup file to .backup
    - HOW:
      ```python
      import shutil
      backup_path = file_path.with_suffix(file_path.suffix + ".backup")
      shutil.copy(file_path, backup_path)
      ```

- [x] Task 3.2: Apply patch
    - WHERE: `src/gui_2.py`
    - WHAT: Use patch command or difflib
    - HOW:
      ```python
      import subprocess
      result = subprocess.run(["patch", "-p1"], input=diff_text, capture_output=True, text=True)
      ```

- [x] Task 3.3: Restore on failure
    - WHERE: `src/gui_2.py`
    - WHAT: Restore from backup if patch fails
    - HOW: `shutil.copy(backup_path, file_path)`

## Phase 4: Modal UI
Focus: Approval modal for patches

- [x] Task 4.1: Create patch approval modal
    - WHERE: `src/gui_2.py`
    - WHAT: Modal with diff preview and Apply/Reject buttons
    - HOW:
      ```python
      if self._show_patch_modal:
       imgui.open_popup("Apply Patch?")
      if imgui.begin_popup_modal("Apply Patch?"):
       # Render diff
       if imgui.button("Apply"):
        self._apply_current_patch()
        imgui.close_current_popup()
       imgui.same_line()
       if imgui.button("Reject"):
        imgui.close_current_popup()
       imgui.end_popup()
      ```

## Phase 5: Testing
- [x] Task 5.1: Write unit tests
- [x] Task 5.2: Conductor - Phase Verification
