'use client';

import { createContext, useCallback, useContext, useEffect, useMemo, useState } from 'react';

export type ThemeMode = 'light' | 'dim';

const THEME_STORAGE_KEY = 'gooseek_theme';

function readStoredTheme(): ThemeMode | null {
  try {
    const v = localStorage.getItem(THEME_STORAGE_KEY);
    if (v === 'light' || v === 'dim') return v;
    return null;
  } catch {
    return null;
  }
}

function prefersDark(): boolean {
  if (typeof window === 'undefined') return false;
  return !!window.matchMedia?.('(prefers-color-scheme: dark)')?.matches;
}

function applyTheme(theme: ThemeMode): void {
  if (typeof document === 'undefined') return;
  const root = document.documentElement;
  if (theme === 'dim') root.classList.add('theme-dim');
  else root.classList.remove('theme-dim');
  try {
    localStorage.setItem(THEME_STORAGE_KEY, theme);
  } catch {
    // ignore storage failures (private mode, quota, etc.)
  }
}

function resolveInitialTheme(): ThemeMode {
  if (typeof document !== 'undefined' && document.documentElement.classList.contains('theme-dim')) {
    return 'dim';
  }
  const stored = typeof window !== 'undefined' ? readStoredTheme() : null;
  if (stored) return stored;
  return prefersDark() ? 'dim' : 'light';
}

type ThemeContextValue = {
  theme: ThemeMode;
  setTheme: (theme: ThemeMode) => void;
  toggleTheme: () => void;
};

const ThemeContext = createContext<ThemeContextValue | null>(null);

export function ThemeProvider({ children }: { children: React.ReactNode }) {
  const [theme, setThemeState] = useState<ThemeMode>('light');

  useEffect(() => {
    const initial = resolveInitialTheme();
    setThemeState(initial);
    applyTheme(initial);
  }, []);

  const setTheme = useCallback((next: ThemeMode) => {
    setThemeState(next);
    applyTheme(next);
  }, []);

  const toggleTheme = useCallback(() => {
    setTheme(theme === 'light' ? 'dim' : 'light');
  }, [theme, setTheme]);

  useEffect(() => {
    const onStorage = (e: StorageEvent) => {
      if (e.key !== THEME_STORAGE_KEY) return;
      const v = e.newValue;
      if (v !== 'light' && v !== 'dim') return;
      setThemeState(v);
      applyTheme(v);
    };
    window.addEventListener('storage', onStorage);
    return () => window.removeEventListener('storage', onStorage);
  }, []);

  const value = useMemo(() => ({ theme, setTheme, toggleTheme }), [theme, setTheme, toggleTheme]);
  return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
}

export function useTheme(): ThemeContextValue {
  const ctx = useContext(ThemeContext);
  if (!ctx) {
    throw new Error('useTheme must be used within ThemeProvider');
  }
  return ctx;
}