app/lib/theme.tsx

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

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

interface ThemeContextType {
  theme: Theme;
  setTheme: (theme: Theme) => void;
  resolvedTheme: "light" | "dark";
}

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

export function ThemeProvider({ children }: { children: React.ReactNode }) {
  const [theme, setTheme] = useState<Theme>(() => {
    // Initialize with a more accurate default on client-side
    if (typeof window !== "undefined") {
      const stored = localStorage.getItem("theme") as Theme;
      if (stored && ["light", "dark", "system"].includes(stored)) {
        return stored;
      }
    }
    return "system";
  });

  const [resolvedTheme, setResolvedTheme] = useState<"light" | "dark">(() => {
    // Initialize resolved theme to match what the blocking script would set
    if (typeof window !== "undefined") {
      const stored = localStorage.getItem("theme") as Theme;
      const systemDark = window.matchMedia(
        "(prefers-color-scheme: dark)"
      ).matches;
      return stored === "dark" || (stored !== "light" && systemDark)
        ? "dark"
        : "light";
    }
    return "light";
  });

  useEffect(() => {
    const updateResolvedTheme = () => {
      let resolved: "light" | "dark";

      if (theme === "system") {
        resolved = window.matchMedia("(prefers-color-scheme: dark)").matches
          ? "dark"
          : "light";
      } else {
        resolved = theme;
      }

      // Only update if different to avoid unnecessary re-renders
      if (resolved !== resolvedTheme) {
        setResolvedTheme(resolved);
      }

      // Apply the theme to the document (defensive check)
      const root = document.documentElement;
      if (resolved === "dark") {
        root.classList.add("dark");
      } else {
        root.classList.remove("dark");
      }
    };

    updateResolvedTheme();

    // Listen for system theme changes
    const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
    const handleChange = () => {
      if (theme === "system") {
        updateResolvedTheme();
      }
    };

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

  const handleSetTheme = (newTheme: Theme) => {
    setTheme(newTheme);
    localStorage.setItem("theme", newTheme);
  };

  return (
    <ThemeContext.Provider
      value={{ theme, setTheme: handleSetTheme, resolvedTheme }}
    >
      {children}
    </ThemeContext.Provider>
  );
}

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