From c24c2829b284536215f43f9db3c3cebe9af7de92 Mon Sep 17 00:00:00 2001
From: hsiegeln <37154749+hsiegeln@users.noreply.github.com>
Date: Wed, 18 Mar 2026 09:09:52 +0100
Subject: [PATCH] feat: ThemeProvider with light/dark toggle and localStorage
 persistence

---
 .../providers/ThemeProvider.test.tsx          | 72 +++++++++++++++++++
 src/design-system/providers/ThemeProvider.tsx | 57 +++++++++++++++
 src/main.tsx                                  |  5 +-
 3 files changed, 133 insertions(+), 1 deletion(-)
 create mode 100644 src/design-system/providers/ThemeProvider.test.tsx
 create mode 100644 src/design-system/providers/ThemeProvider.tsx

diff --git a/src/design-system/providers/ThemeProvider.test.tsx b/src/design-system/providers/ThemeProvider.test.tsx
new file mode 100644
index 0000000..4b6726c
--- /dev/null
+++ b/src/design-system/providers/ThemeProvider.test.tsx
@@ -0,0 +1,72 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { ThemeProvider, useTheme } from './ThemeProvider'
+
+function TestConsumer() {
+  const { theme, toggleTheme } = useTheme()
+  return (
+    <div>
+      <span data-testid="theme">{theme}</span>
+      <button onClick={toggleTheme}>Toggle</button>
+    </div>
+  )
+}
+
+describe('ThemeProvider', () => {
+  beforeEach(() => {
+    localStorage.clear()
+    document.documentElement.removeAttribute('data-theme')
+  })
+
+  it('defaults to light theme', () => {
+    render(
+      <ThemeProvider>
+        <TestConsumer />
+      </ThemeProvider>,
+    )
+    expect(screen.getByTestId('theme').textContent).toBe('light')
+  })
+
+  it('sets data-theme attribute on document', () => {
+    render(
+      <ThemeProvider>
+        <TestConsumer />
+      </ThemeProvider>,
+    )
+    expect(document.documentElement.dataset.theme).toBe('light')
+  })
+
+  it('toggles theme on button click', async () => {
+    const user = userEvent.setup()
+    render(
+      <ThemeProvider>
+        <TestConsumer />
+      </ThemeProvider>,
+    )
+    await user.click(screen.getByText('Toggle'))
+    expect(screen.getByTestId('theme').textContent).toBe('dark')
+    expect(document.documentElement.dataset.theme).toBe('dark')
+  })
+
+  it('persists theme to localStorage', async () => {
+    const user = userEvent.setup()
+    render(
+      <ThemeProvider>
+        <TestConsumer />
+      </ThemeProvider>,
+    )
+    await user.click(screen.getByText('Toggle'))
+    expect(localStorage.getItem('cameleer-theme')).toBe('dark')
+  })
+
+  it('reads initial theme from localStorage', () => {
+    localStorage.setItem('cameleer-theme', 'dark')
+    render(
+      <ThemeProvider>
+        <TestConsumer />
+      </ThemeProvider>,
+    )
+    expect(screen.getByTestId('theme').textContent).toBe('dark')
+  })
+})
diff --git a/src/design-system/providers/ThemeProvider.tsx b/src/design-system/providers/ThemeProvider.tsx
new file mode 100644
index 0000000..3abe824
--- /dev/null
+++ b/src/design-system/providers/ThemeProvider.tsx
@@ -0,0 +1,57 @@
+import { createContext, useContext, useState, useEffect, useCallback, type ReactNode } from 'react'
+
+type Theme = 'light' | 'dark'
+
+interface ThemeContextValue {
+  theme: Theme
+  toggleTheme: () => void
+  setTheme: (theme: Theme) => void
+}
+
+const ThemeContext = createContext<ThemeContextValue | null>(null)
+
+const STORAGE_KEY = 'cameleer-theme'
+
+function getInitialTheme(): Theme {
+  try {
+    const stored = localStorage.getItem(STORAGE_KEY)
+    if (stored === 'dark' || stored === 'light') return stored
+  } catch {
+    // localStorage unavailable
+  }
+  return 'light'
+}
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  const [theme, setThemeState] = useState<Theme>(getInitialTheme)
+
+  const setTheme = useCallback((t: Theme) => {
+    setThemeState(t)
+    document.documentElement.dataset.theme = t
+    try {
+      localStorage.setItem(STORAGE_KEY, t)
+    } catch {
+      // localStorage unavailable
+    }
+  }, [])
+
+  const toggleTheme = useCallback(() => {
+    setTheme(theme === 'light' ? 'dark' : 'light')
+  }, [theme, setTheme])
+
+  useEffect(() => {
+    document.documentElement.dataset.theme = theme
+  }, [theme])
+
+  return (
+    <ThemeContext.Provider value={{ theme, toggleTheme, setTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  )
+}
+
+export function useTheme(): ThemeContextValue {
+  const ctx = useContext(ThemeContext)
+  if (!ctx) throw new Error('useTheme must be used within ThemeProvider')
+  return ctx
+}
diff --git a/src/main.tsx b/src/main.tsx
index 8e0deb1..83eded7 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -1,13 +1,16 @@
 import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 import { BrowserRouter } from 'react-router-dom'
+import { ThemeProvider } from './design-system/providers/ThemeProvider'
 import App from './App'
 import './index.css'
 
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
     <BrowserRouter>
-      <App />
+      <ThemeProvider>
+        <App />
+      </ThemeProvider>
     </BrowserRouter>
   </StrictMode>,
 )