"use client";

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

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

const ThemeCtx = createContext<{ theme: Theme; resolvedTheme: "light" | "dark"; setTheme: (t: Theme) => void }>({
  theme: "system",
  resolvedTheme: "light",
  setTheme: () => {},
});

function getSystemTheme(): "light" | "dark" {
  if (typeof window === "undefined") return "light";
  return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
}

function applyTheme(theme: Theme) {
  const resolved = theme === "system" ? getSystemTheme() : theme;
  document.documentElement.classList.toggle("dark", resolved === "dark");
  return resolved;
}

export function ThemeProvider({ children }: { children: React.ReactNode }) {
  const [theme, setThemeState] = useState<Theme>("system");
  const [resolvedTheme, setResolvedTheme] = useState<"light" | "dark">("light");

  useEffect(() => {
    try {
      const stored = localStorage.getItem("theme") as Theme | null;
      if (stored === "dark" || stored === "light" || stored === "system") {
        setThemeState(stored);
      }
    } catch {}
  }, []);

  useEffect(() => {
    const resolved = applyTheme(theme);
    setResolvedTheme(resolved);
  }, [theme]);

  useEffect(() => {
    if (theme !== "system") return;
    const mql = window.matchMedia("(prefers-color-scheme: dark)");
    const handler = () => {
      const resolved = applyTheme(theme);
      setResolvedTheme(resolved);
    };
    mql.addEventListener("change", handler);
    return () => mql.removeEventListener("change", handler);
  }, [theme]);

  const setTheme = useCallback((t: Theme) => {
    setThemeState(t);
    try {
      localStorage.setItem("theme", t);
    } catch {}
  }, []);

  return <ThemeCtx.Provider value={{ theme, resolvedTheme, setTheme }}>{children}</ThemeCtx.Provider>;
}

export function useTheme() {
  return useContext(ThemeCtx);
}