@startuml patcher-pipeline
!theme plain
title AI Patch Generation and Application Pipeline

start

:Receive source file + target file + instruction;

:Build prompt with:
- Source file diff (staged changes)
- Source file full content
- Target file current content
- Generation instructions from rules;

:Call AI via shell command
(configured via git config or env);

if (AI returned output?) then (yes)
  if (Output contains\n"API Error: Overloaded"?) then (yes)
    :Raise PatchGenerationError\n"Claude API is overloaded";
    stop
  endif

  :Save raw output to\n.git/ai-rules-debug/*.raw.out;

  if (Output contains\n<<<AI_DIFF_START>>>?) then (yes)
    :Extract content between\nSTART and END markers;
  else (no)
    if (Output contains\n"diff --git"?) then (yes)
      :Extract from\n"diff --git" onward;
    else (no)
      :Raise "AI output did not contain a diff";
      stop
    endif
  endif
else (no)
  :Raise "AI command failed";
  stop
endif

:Save to *.clean.diff;

:Sanitize patch:
- Remove "index ..." lines
- Remove "similarity index" lines
- Keep only diff content;

:Save to *.sanitized.diff;

if (New file and missing\n"new file mode"?) then (yes)
  :Add "new file mode 100644" header;
endif

:Save to *.final.diff;

if (Patch is empty?) then (yes)
  :Raise "AI returned empty patch";
  stop
endif

:Try git apply -p1 --index --check;

if (Check succeeded?) then (yes)
  :git apply -p1 --index;
  :Success!;
  stop
endif

:Try git apply -p1 --index --3way\n--recount --whitespace=nowarn;

if (3-way succeeded?) then (yes)
  :Applied with 3-way merge;
  :Success!;
  stop
endif

if (Is new file?) then (yes)
  :Try git apply -p1 (without --index);
  if (Succeeded?) then (yes)
    :git add target file;
    :Success!;
    stop
  endif
endif

:Raise "Failed to apply patch\n(strict and 3-way both failed)";
stop

note right
  **Debug Artifacts Location:**
  .git/ai-rules-debug/

  Files saved:
  - *.raw.out (full AI response)
  - *.clean.diff (extracted patch)
  - *.sanitized.diff (cleaned patch)
  - *.final.diff (applied patch)

  Filename format:
  {output_path_with_underscores}-{pid}.{ext}
end note

@enduml