# Auto Theme + Wallpaper Switcher (Windows)

This is a lightweight Windows tray app that **automatically switches between light and dark mode** based on the time of day (6 AM to 6 PM), and optionally changes your desktop wallpaper. It also silently restarts `explorer.exe` after theme changes to force a full UI refresh (taskbar, Start menu, etc.).

![cover](/screenshot/cover.jpg)

Runs quietly in the background with a tray icon and auto-starts on login (via `shell:startup`).

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## Features

- Automatically switches between **light** and **dark** mode
- Optionally changes wallpaper to match the theme
- Gracefully skips if wallpaper is missing (no crashes)
- Runs silently with a **tray icon** and no console window
- Uses native Windows APIs (registry + wallpaper)
- Automatically **restarts `explorer.exe`** for full theme refresh

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## Setup Instructions

Place these files in the same directory:

```
themechanger.exe       ← compiled binary  
icon.ico               ← tray icon (required)  
light.jpg/png/bmp/...  ← optional day wallpaper  
dark.jpg/png/bmp/...   ← optional night wallpaper  
```

Supported image formats: `.jpg`, `.jpeg`, `.png`, `.bmp`, `.webp`

The app will look for `light.*` and `dark.*` in its own folder. If no image is found, it simply skips the wallpaper change.

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## Auto-Start on Login

To launch the app automatically when you log in:

1.  Press `Win + R`
2.  Type: `shell:startup` and press Enter
3.  **Create a shortcut to `themechanger.exe`:**
    *   Right-click on `themechanger.exe`.
    *   Select "Create shortcut".
4.  **Move the shortcut you just created into the Startup folder.** The Startup folder is the one that opened in step 2.

Done! It will now auto-start silently every time.

> No need to edit the registry or install anything!

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## Build It Yourself

If you'd like to compile from source:

### 1. Install Go

[https://go.dev/dl](https://go.dev/dl)

### 2. Initialize your Go module

```bash
go mod init themechanger
go mod tidy
```

### 3. Build the executable

```bash
go build -ldflags="-H windowsgui" -o themechanger.exe
```

This produces a GUI app (no console window).

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## Technical Details

- Uses Go and the [`systray`](https://github.com/getlantern/systray) library for tray UI
- Theme switching via registry keys:
  - `AppsUseLightTheme`
  - `SystemUsesLightTheme`
- Wallpaper changes with `SystemParametersInfoW` API
- Explorer restart via:
  ```bash
  taskkill /f /im explorer.exe && start explorer.exe
  ```

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## Tray Preview

You must provide your own `icon.ico` in the same folder — this will be used as the tray icon.

![tray](/screenshot/tray.jpg)

> Tip: You can create `.ico` files from PNGs using online converters like [icoconvert.com](https://icoconvert.com)

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## Notes

- You can manually quit the app from the tray menu
- Time check runs every 60 seconds
- Changing the clock or timezone will trigger a switch automatically
- No admin rights needed
- ⚠️ **Warning:** This program will kill and restart `explorer.exe` to ensure proper theme application after a mode switch. This is necessary because `explorer.exe` can sometimes become buggy and not fully apply the new theme, leaving behind visual artifacts. **Please ensure `explorer.exe` is not performing any sensitive tasks like copying files before a theme switch occurs, as this process will interrupt those operations.**
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## Optional Ideas

- Add GUI to configure start/stop time
- Manual override options in tray menu
- Geo-based sunrise/sunset switching

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## License

MIT — free for personal and commercial use.

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Made with Go, Windows quirks, and Indocafe Coffeemix ☕