feat: complete stage 2 core refactor

src/components/theme-provider.tsx

@@ -0,0 +1,120 @@
+import React, {
+  createContext,
+  useContext,
+  useEffect,
+  useMemo,
+  useState,
+} from "react";
+
+type Theme = "light" | "dark" | "system";
+
+interface ThemeProviderProps {
+  children: React.ReactNode;
+  defaultTheme?: Theme;
+  storageKey?: string;
+}
+
+interface ThemeContextValue {
+  theme: Theme;
+  setTheme: (theme: Theme) => void;
+}
+
+const ThemeProviderContext = createContext<ThemeContextValue | undefined>(
+  undefined,
+);
+
+export function ThemeProvider({
+  children,
+  defaultTheme = "system",
+  storageKey = "cc-switch-theme",
+}: ThemeProviderProps) {
+  const getInitialTheme = () => {
+    if (typeof window === "undefined") {
+      return defaultTheme;
+    }
+
+    const stored = window.localStorage.getItem(storageKey) as Theme | null;
+    if (stored === "light" || stored === "dark" || stored === "system") {
+      return stored;
+    }
+
+    return defaultTheme;
+  };
+
+  const [theme, setThemeState] = useState<Theme>(getInitialTheme);
+
+  useEffect(() => {
+    if (typeof window === "undefined") {
+      return;
+    }
+
+    window.localStorage.setItem(storageKey, theme);
+  }, [theme, storageKey]);
+
+  useEffect(() => {
+    if (typeof window === "undefined") {
+      return;
+    }
+
+    const root = window.document.documentElement;
+    root.classList.remove("light", "dark");
+
+    if (theme === "system") {
+      const isDark =
+        window.matchMedia &&
+        window.matchMedia("(prefers-color-scheme: dark)").matches;
+      root.classList.add(isDark ? "dark" : "light");
+      return;
+    }
+
+    root.classList.add(theme);
+  }, [theme]);
+
+  useEffect(() => {
+    if (typeof window === "undefined") {
+      return;
+    }
+
+    const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
+    const handleChange = () => {
+      if (theme !== "system") {
+        return;
+      }
+
+      const root = window.document.documentElement;
+      root.classList.toggle("dark", mediaQuery.matches);
+      root.classList.toggle("light", !mediaQuery.matches);
+    };
+
+    if (theme === "system") {
+      handleChange();
+    }
+
+    mediaQuery.addEventListener("change", handleChange);
+    return () => mediaQuery.removeEventListener("change", handleChange);
+  }, [theme]);
+
+  const value = useMemo<ThemeContextValue>(
+    () => ({
+      theme,
+      setTheme: (nextTheme: Theme) => {
+        setThemeState(nextTheme);
+      },
+    }),
+    [theme],
+  );
+
+  return (
+    <ThemeProviderContext.Provider value={value}>
+      {children}
+    </ThemeProviderContext.Provider>
+  );
+}
+
+export function useTheme() {
+  const context = useContext(ThemeProviderContext);
+  if (context === undefined) {
+    throw new Error("useTheme must be used within a ThemeProvider");
+  }
+  return context;
+}