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

interface ThemeContextType {
  isDark: boolean
  toggleTheme: () => void
}

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

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [isDark, setIsDark] = useState(() => {
    // 从 localStorage 读取
    const saved = localStorage.getItem('theme')
    if (saved) return saved === 'dark'
    // 默认跟随系统
    return window.matchMedia('(prefers-color-scheme: dark)').matches
  })

  useEffect(() => {
    // 更新 document class
    document.documentElement.classList.toggle('light', !isDark)
    document.documentElement.classList.toggle('dark', isDark)
    // 保存到 localStorage
    localStorage.setItem('theme', isDark ? 'dark' : 'light')
  }, [isDark])

  const toggleTheme = () => setIsDark(!isDark)

  return (
    <ThemeContext.Provider value={{ isDark, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  )
}

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