# Windows Dictation App Design Document

## Goals
- Create a "polished" Windows app for dictation.
- Small memory footprint.
- Real-time transcription.
- Global hotkey support.
- On-demand GPU usage.

## Architecture

The application is a native **Win32 C++** application. It avoids heavy UI frameworks (Electron, .NET, Qt) to strictly adhere to the "small memory footprint" requirement and integration with the C++ codebase.

### Components

1.  **Main Entry (`WinMain`)**:
    - Initializes the application.
    - Registers the global hotkey (`RegisterHotKey`).
    - Creates the main window (hidden by default).
    - Creates the System Tray icon (`Shell_NotifyIcon`).
    - Runs the standard Windows Message Loop.

2.  **UI Layer (Win32 API)**:
    - **Main Window**: A simple Dialog or Window containing:
        - `EDIT` control (Multiline, VScroll) for text output.
        - `BUTTON` controls for Record/Stop/Clear.
        - `STATUS` bar for model state.
    - **Tray Icon**: Context menu for Open/Exit.

3.  **Audio & Inference Layer (`Transcriber`)**:
    - Runs in a separate **Worker Thread** to prevent freezing the UI.
    - **Audio Capture**: Uses `SDL2` (reusing `common-sdl.cpp` logic) for cross-platform consistency with the repo, or potentially native WASAPI if dependencies become an issue. For now, SDL2 is assumed as it's standard in this repo.
    - **Inference**: Uses `whisper.cpp` library (`whisper_full`).
    - **VAD (Voice Activity Detection)**: Uses the simple energy-based VAD from `common.cpp` to detect when to transcribe.

### Threading Model

- **UI Thread**: Handles Windows messages, paints the UI, processes hotkeys.
- **Worker Thread**:
    - Loops continuously when "Recording" is active.
    - Captures PCM audio chunks.
    - Runs `whisper_full` on the buffer.
    - Uses `PostMessage(hWindow, WM_USER_TEXT_READY, ...)` to send transcribed text back to the UI thread safely.

### Resource Management (GPU/Memory)

- **Startup**: Does *not* load the model immediately to save RAM/VRAM.
- **On Record**: Checks if context exists. If not, loads the model (`whisper_init_from_file`).
- **Inactive Timeout**: A timer in the UI thread monitors inactivity. If inactive for X minutes, it signals the worker to destroy the whisper context (`whisper_free`), releasing VRAM.

### Key APIs
- `RegisterHotKey`: For global shortcuts.
- `Shell_NotifyIcon`: For system tray.
- `CreateWindowEx` / `DialogBox`: For UI.
- `whisper_full`: For inference.

## File Structure

- `main.cpp`: Entry point, Window Proc, Message Loop.
- `transcriber.h/cpp`: Wraps the Whisper context and SDL audio loop.
- `resource.rc`: Defines the UI layout (dialogs, menus, icons).
- `CMakeLists.txt`: Build definition.

## Future Improvements
- Settings dialog to select Model path.
- Select Audio Input device.