'use client';

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

type Theme = 'light' | 'dark';

interface ThemeContextType {
  theme: Theme;
  toggleTheme: () => void;
  setTheme: (theme: Theme) => void;
  isSystemTheme: boolean;
}

const ThemeContext = createContext<ThemeContextType | undefined>(undefined);

// 纯函数，放在组件外避免闭包问题
function getSystemTheme(): Theme {
  if (typeof window === 'undefined') return 'light';
  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
}

function isNightTime(): boolean {
  if (typeof window === 'undefined') return false;
  const hour = new Date().getHours();
  return hour >= 18 || hour < 6;
}

function getAutoTheme(): Theme {
  if (getSystemTheme() === 'dark') return 'dark';
  if (isNightTime()) return 'dark';
  return 'light';
}

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setThemeState] = useState<Theme>('light');
  const [isSystemTheme, setIsSystemTheme] = useState(true);
  const [mounted, setMounted] = useState(false);

  // 设置主题（仅当前会话，不持久化）
  const setTheme = useCallback((newTheme: Theme) => {
    setThemeState(newTheme);
    setIsSystemTheme(false);
  }, []);

  // 切换主题
  const toggleTheme = useCallback(() => {
    setThemeState(prev => prev === 'light' ? 'dark' : 'light');
    setIsSystemTheme(false);
  }, []);

  // 初始化：始终跟随系统主题 + 时间
  useEffect(() => {
    setThemeState(getAutoTheme());
    setIsSystemTheme(true);
    setMounted(true);
  }, []);

  // 监听系统主题变化
  useEffect(() => {
    if (!isSystemTheme) return;

    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');

    const handleChange = () => {
      setThemeState(getAutoTheme());
    };

    mediaQuery.addEventListener('change', handleChange);
    return () => mediaQuery.removeEventListener('change', handleChange);
  }, [isSystemTheme]);

  // 每分钟检查时间变化
  useEffect(() => {
    if (!isSystemTheme) return;

    const interval = setInterval(() => {
      setThemeState(getAutoTheme());
    }, 60000);

    return () => clearInterval(interval);
  }, [isSystemTheme]);

  // 在 DOM 上设置主题属性
  useEffect(() => {
    if (mounted) {
      document.documentElement.setAttribute('data-theme', theme);
    }
  }, [theme, mounted]);

  const value = useMemo(
    () => ({ theme, toggleTheme, setTheme, isSystemTheme }),
    [theme, toggleTheme, setTheme, isSystemTheme]
  );

  return (
    <ThemeContext.Provider value={value}>
      {children}
    </ThemeContext.Provider>
  );
}

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