"use client";

import {
  createContext,
  useContext,
  useEffect,
  useMemo,
  useState,
  type ReactNode,
} from "react";

type Theme = "light" | "dark";

interface ThemeContextValue {
  theme: Theme;
  toggleTheme: () => void;
  setTheme: (theme: Theme) => void;
}

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

function getInitialTheme(): Theme {
  if (typeof window === "undefined") return "light";
  const stored = localStorage.getItem("theme") as Theme | null;
  if (stored) return stored;
  // Keep the CRM light by default. Dark mode is opt-in so the inbox list does
  // not unexpectedly change when the operating system uses a dark theme.
  return "light";
}

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setTheme] = useState<Theme>(() => getInitialTheme());
  const [mounted, setMounted] = useState(false);

  useEffect(() => {
    // Keep the initial server render stable and only reveal theme-aware UI
    // after the client has mounted and read localStorage / system preference.
    // eslint-disable-next-line react-hooks/set-state-in-effect
    setMounted(true);
  }, []);

  useEffect(() => {
    if (!mounted) return;
    const root = document.documentElement;
    // Toggle both marker classes so every surface follows the explicit choice.
    root.classList.toggle("dark", theme === "dark");
    root.classList.toggle("light", theme !== "dark");
    localStorage.setItem("theme", theme);
  }, [theme, mounted]);

  const toggleTheme = useMemo(
    () => () => setTheme((prev) => (prev === "light" ? "dark" : "light")),
    []
  );

  const value = useMemo<ThemeContextValue>(
    () => ({ theme, toggleTheme, setTheme }),
    [theme, toggleTheme]
  );

  if (!mounted) {
    return (
      <ThemeContext.Provider value={{ theme: "light", toggleTheme: () => {}, setTheme: () => {} }}>
        {children}
      </ThemeContext.Provider>
    );
  }

  return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
}

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