"use client";

import { Moon, Sun } from "lucide-react";
import { useEffect, useState } from "react";

type Theme = "light" | "dark";

const STORAGE_KEY = "chatgpt2api-theme";

function resolveInitialTheme(): Theme {
  if (typeof window === "undefined") {
    return "light";
  }
  const stored = window.localStorage.getItem(STORAGE_KEY);
  if (stored === "light" || stored === "dark") {
    return stored;
  }
  return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
}

function applyTheme(theme: Theme) {
  document.documentElement.classList.toggle("dark", theme === "dark");
  document.documentElement.style.colorScheme = theme;
}

export function ThemeToggle() {
  const [theme, setTheme] = useState<Theme>("light");
  const isDark = theme === "dark";

  useEffect(() => {
    const nextTheme = resolveInitialTheme();
    setTheme(nextTheme);
    applyTheme(nextTheme);
  }, []);

  const toggleTheme = () => {
    const nextTheme: Theme = isDark ? "light" : "dark";
    window.localStorage.setItem(STORAGE_KEY, nextTheme);
    setTheme(nextTheme);
    applyTheme(nextTheme);
  };

  return (
    <button
      type="button"
      aria-label={isDark ? "切换到浅色模式" : "切换到深色模式"}
      title={isDark ? "浅色模式" : "深色模式"}
      className="inline-flex size-8 shrink-0 items-center justify-center rounded-full border border-stone-200/80 bg-white/80 text-stone-500 shadow-sm transition hover:border-stone-300 hover:text-stone-900 dark:border-white/10 dark:bg-white/8 dark:text-stone-300 dark:hover:border-white/20 dark:hover:text-white"
      onClick={toggleTheme}
    >
      {isDark ? <Sun className="size-4" /> : <Moon className="size-4" />}
    </button>
  );
}