"use client";

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

type Theme = "light" | "dark";

type ThemeContextType = {
  theme: Theme;
  toggleTheme: () => void;
};

const getTenantTheme = (): Theme | null => {
  if (typeof document === "undefined") return null;

  const tenantTheme = document.documentElement.dataset.tenantThemeMode;
  return tenantTheme === "dark" || tenantTheme === "light" ? tenantTheme : null;
};

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

export const ThemeProvider: React.FC<{ children: React.ReactNode }> = ({
  children,
}) => {
  // Initialize theme by reading from DOM class (set by inline script in layout.tsx)
  // This prevents flash because the script runs before React hydration
  const getInitialTheme = (): Theme => {
    if (typeof window === "undefined") return "light";
    
    // Read from DOM class first (set by inline script)
    const hasDarkClass = document.documentElement.classList.contains("dark");
    if (hasDarkClass) return "dark";
    
    // Fallback to localStorage if DOM doesn't have class yet
    try {
      const savedTheme = localStorage.getItem("theme") as Theme | null;
      if (savedTheme === "dark" || savedTheme === "light") {
        return savedTheme;
      }
    } catch {
      // localStorage might not be available
    }

    const tenantTheme = getTenantTheme();
    if (tenantTheme) return tenantTheme;
    
    // Last fallback to system preference
    try {
      const prefersDark = window.matchMedia("(prefers-color-scheme: dark)").matches;
      return prefersDark ? "dark" : "light";
    } catch {
      return "light";
    }
  };

  const [theme, setTheme] = useState<Theme>(getInitialTheme);

  // This effect runs only once after hydration to ensure sync
  useEffect(() => {
    let savedTheme: Theme | null = null;
    try {
      savedTheme = localStorage.getItem("theme") as Theme | null;
    } catch {
      savedTheme = null;
    }

    let prefersDark = false;
    try {
      prefersDark = window.matchMedia("(prefers-color-scheme: dark)").matches;
    } catch {
      prefersDark = false;
    }

    const tenantTheme = getTenantTheme();
    const expectedTheme = savedTheme || tenantTheme || (prefersDark ? "dark" : "light");
    
    // Ensure DOM class matches expected theme
    if (expectedTheme === "dark") {
      document.documentElement.classList.add("dark");
    } else {
      document.documentElement.classList.remove("dark");
    }
  }, []);

  useEffect(() => {
    try {
      localStorage.setItem("theme", theme);
    } catch {
      // localStorage can be unavailable or quota-limited in some browsers/modes.
    }
    if (theme === "dark") {
      document.documentElement.classList.add("dark");
    } else {
      document.documentElement.classList.remove("dark");
    }
  }, [theme]);

  const toggleTheme = () => {
    setTheme((prevTheme) => (prevTheme === "light" ? "dark" : "light"));
  };

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  );
};

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