patrickulrich.com/src/components/ThemeProvider.tsx

import { useEffect, useState } from "react"
import { type Theme, ThemeContext } from "@/lib/ThemeContext"

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

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

  useEffect(() => {
    const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)")
    
    const handleChange = () => {
      if (theme === "system") {
        const root = window.document.documentElement
        root.classList.remove("light", "dark")
        
        const systemTheme = mediaQuery.matches ? "dark" : "light"
        root.classList.add(systemTheme)
      }
    }

    mediaQuery.addEventListener("change", handleChange)
    return () => mediaQuery.removeEventListener("change", handleChange)
  }, [theme])

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

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