import React, { createContext, useContext, useEffect, useState } from "react"

type Theme = "dark" | "light" | "system"

type ThemeProviderProps = {
  children: React.ReactNode
  defaultTheme?: Theme
  storageKey?: string
}

type ThemeProviderState = {
  theme: Theme
  setTheme: (theme: Theme) => void
}

const ThemeProviderContext = createContext<ThemeProviderState>({
  theme: "system",
  setTheme: () => null,
})

export function ThemeProvider({
  children,
  defaultTheme = "system",
  storageKey = "theme",
  ...props
}: ThemeProviderProps) {
  const [theme, setTheme] = useState<Theme>(() => {
    const stored = localStorage.getItem(storageKey)
    if (stored === "dark" || stored === "light" || stored === "system") {
      return stored
    }
    return defaultTheme
  })

  useEffect(() => {
    const root = window.document.documentElement
    root.classList.remove("light", "dark")

    if (theme === "system") {
      const systemTheme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light"
      root.classList.add(systemTheme)
      return
    }

    root.classList.add(theme)
  }, [theme])

  const value = {
    theme,
    setTheme: (theme: Theme) => {
      localStorage.setItem(storageKey, theme)
      setTheme(theme)
    },
  }

  return (
    <ThemeProviderContext.Provider {...props} value={value}>
      {children}
    </ThemeProviderContext.Provider>
  )
}

export const useTheme = () => useContext(ThemeProviderContext)