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.github/workflows/build.yml

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+name: Build & Release ThemeChanger
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  release:
+    name: Build and Upload Release ZIP
+    runs-on: windows-latest
+
+    permissions:
+      contents: write  # Needed for creating/updating releases
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.21'
+
+      - name: Tidy dependencies
+        run: go mod tidy
+
+      - name: Build executable
+        run: go build -ldflags="-H windowsgui" -o themechanger.exe
+
+      - name: Create ZIP with icon and binary
+        run: Compress-Archive -Path themechanger.exe,icon.ico -DestinationPath themechanger.zip
+
+      - name: Create or update release
+        uses: softprops/action-gh-release@v2
+        with:
+          tag_name: latest
+          name: Latest Build
+          files: themechanger.zip
+          body: |
+            ✅ Automatic build from latest commit to `main`  
+            🛠️ Includes `themechanger.exe` and `icon.ico`  
+            🔄 Ready to drop into `shell:startup`
+
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.gitignore

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+# Go build artifacts
+*.exe
+*.exe~
+*.out
+*.test
+
+# Go module files
+go.sum
+
+# IDE/editor files
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# Windows files
+Thumbs.db
+Desktop.ini
+
+# Logs
+*.log
+
+# Archive files
+*.zip
+*.tar
+*.tar.gz
+
+# Systray tray icon (you may want to ignore it if it's generated)
+# icon.ico
+
+# GitHub Actions artifacts (if manually downloaded)
+*.7z
+*.rar
+
+# Build folders (if any)
+bin/
+dist/

README.md

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+# 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`).
+
+---
+
+## 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
+
+---
+
+## 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.
+
+---
+
+## 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!
+
+---
+
+## 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).
+
+---
+
+## 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
+  ```
+
+---
+
+## 🖼 Tray Preview
+
+You must provide your own `icon.ico` in the same folder — this will be used as the tray icon.
+
+> Tip: You can create `.ico` files from PNGs using online converters like [icoconvert.com](https://icoconvert.com)
+
+---
+
+## 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
+
+---
+
+## Optional Ideas
+
+- Add GUI to configure start/stop time
+- Manual override options in tray menu
+- Geo-based sunrise/sunset switching
+
+---
+
+## License
+
+MIT — free for personal and commercial use.
+
+---
+
+Made with Go, Windows quirks, and coffee ☕  

go.mod

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+module themechanger
+
+go 1.23.1
+
+require (
+	github.com/getlantern/systray v1.2.2
+	golang.org/x/sys v0.32.0
+)
+
+require (
+	github.com/getlantern/context v0.0.0-20190109183933-c447772a6520 // indirect
+	github.com/getlantern/errors v0.0.0-20190325191628-abdb3e3e36f7 // indirect
+	github.com/getlantern/golog v0.0.0-20190830074920-4ef2e798c2d7 // indirect
+	github.com/getlantern/hex v0.0.0-20190417191902-c6586a6fe0b7 // indirect
+	github.com/getlantern/hidden v0.0.0-20190325191715-f02dbb02be55 // indirect
+	github.com/getlantern/ops v0.0.0-20190325191751-d70cb0d6f85f // indirect
+	github.com/go-stack/stack v1.8.0 // indirect
+	github.com/oxtoacart/bpool v0.0.0-20190530202638-03653db5a59c // indirect
+)

main.go

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+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"time"
+	"unsafe"
+
+	"github.com/getlantern/systray"
+	"golang.org/x/sys/windows/registry"
+)
+
+// Set Windows dark/light mode via registry
+func setMode(light bool) {
+	key, _ := registry.OpenKey(registry.CURRENT_USER, `Software\Microsoft\Windows\CurrentVersion\Themes\Personalize`, registry.SET_VALUE)
+	defer key.Close()
+	val := uint32(0)
+	if light {
+		val = 1
+	}
+	key.SetDWordValue("AppsUseLightTheme", val)
+	key.SetDWordValue("SystemUsesLightTheme", val)
+}
+
+// Restart Explorer to fully apply theme
+func restartExplorer() {
+	exec.Command("taskkill", "/f", "/im", "explorer.exe").Run()
+	time.Sleep(1 * time.Second)
+	exec.Command("explorer.exe").Start()
+}
+
+// Get current theme mode from registry
+func getCurrentMode() string {
+	key, _ := registry.OpenKey(registry.CURRENT_USER, `Software\Microsoft\Windows\CurrentVersion\Themes\Personalize`, registry.QUERY_VALUE)
+	defer key.Close()
+	val, _, _ := key.GetIntegerValue("AppsUseLightTheme")
+	if val == 1 {
+		return "light"
+	}
+	return "dark"
+}
+
+// Find image in same dir with any supported extension
+func findImageFile(name string) string {
+	exePath, _ := os.Executable()
+	dir := filepath.Dir(exePath)
+	matches, _ := filepath.Glob(filepath.Join(dir, name+".*"))
+	for _, f := range matches {
+		ext := strings.ToLower(filepath.Ext(f))
+		if ext == ".jpg" || ext == ".jpeg" || ext == ".png" || ext == ".bmp" || ext == ".webp" {
+			return f
+		}
+	}
+	return ""
+}
+
+// Get current wallpaper path from registry
+func getCurrentWallpaper() string {
+	key, _ := registry.OpenKey(registry.CURRENT_USER, `Control Panel\Desktop`, registry.QUERY_VALUE)
+	defer key.Close()
+	val, _, _ := key.GetStringValue("Wallpaper")
+	return val
+}
+
+// Set desktop wallpaper via Windows API
+func setWallpaper(path string) {
+	user32 := syscall.NewLazyDLL("user32.dll")
+	sysParam := user32.NewProc("SystemParametersInfoW")
+	p, _ := syscall.UTF16PtrFromString(path)
+	sysParam.Call(0x0014, 0, uintptr(unsafe.Pointer(p)), uintptr(0x01|0x02))
+}
+
+// Main background loop
+func backgroundLoop() {
+	lightImg := findImageFile("light")
+	darkImg := findImageFile("dark")
+	lastMode := getCurrentMode()
+
+	for {
+		hour := time.Now().Hour()
+		newMode := "dark"
+		var targetImg string
+
+		if hour >= 6 && hour < 18 {
+			newMode = "light"
+			targetImg = lightImg
+		} else {
+			targetImg = darkImg
+		}
+
+		if newMode != lastMode {
+			setMode(newMode == "light")
+			restartExplorer()
+			lastMode = newMode
+		}
+
+		if targetImg != "" && getCurrentWallpaper() != targetImg {
+			setWallpaper(targetImg)
+		}
+
+		time.Sleep(60 * time.Second)
+	}
+}
+
+// Load icon from local directory (icon.ico)
+func getIconBytes() []byte {
+	exePath, _ := os.Executable()
+	iconPath := filepath.Join(filepath.Dir(exePath), "icon.ico")
+	data, err := ioutil.ReadFile(iconPath)
+	if err != nil {
+		fmt.Println("icon.ico not found or unreadable.")
+		return nil
+	}
+	return data
+}
+
+// Systray startup
+func onReady() {
+	icon := getIconBytes()
+	if icon != nil {
+		systray.SetIcon(icon)
+	}
+	systray.SetTitle("Auto Theme")
+	systray.SetTooltip("Auto Theme + Wallpaper Switcher")
+
+	mQuit := systray.AddMenuItem("Quit", "Exit the program")
+
+	go func() {
+		go backgroundLoop()
+		<-mQuit.ClickedCh
+		systray.Quit()
+	}()
+}
+
+func onExit() {}
+
+func main() {
+	systray.Run(onReady, onExit)
+}