import { createContext, useCallback, useContext, useEffect, useMemo, useState, type ReactNode } from "react";
import { Moon, Sun } from "lucide-react";
import { useI18n } from "./i18n";

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

const storageKey = "telesrv.admin.theme";

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

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

export function applyTheme(theme: Theme) {
  document.documentElement.setAttribute("data-theme", theme);
  document.documentElement.style.colorScheme = theme;
}

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setThemeState] = useState<Theme>(() => initialTheme());

  useEffect(() => {
    applyTheme(theme);
    try {
      localStorage.setItem(storageKey, theme);
    } catch {
      // Theme persistence is best-effort.
    }
  }, [theme]);

  // Follow the OS preference until the user makes an explicit choice.
  useEffect(() => {
    if (!window.matchMedia) {
      return;
    }
    const media = window.matchMedia("(prefers-color-scheme: dark)");
    const onChange = (event: MediaQueryListEvent) => {
      let stored: string | null = null;
      try {
        stored = localStorage.getItem(storageKey);
      } catch {
        stored = null;
      }
      if (stored !== "light" && stored !== "dark") {
        setThemeState(event.matches ? "dark" : "light");
      }
    };
    media.addEventListener("change", onChange);
    return () => media.removeEventListener("change", onChange);
  }, []);

  const setTheme = useCallback((next: Theme) => setThemeState(next), []);
  const toggleTheme = useCallback(() => setThemeState((current) => (current === "dark" ? "light" : "dark")), []);

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

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

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

export function ThemeSwitch() {
  const { theme, toggleTheme } = useTheme();
  const { t } = useI18n();
  const nextIsDark = theme === "light";
  const label = t(nextIsDark ? "theme.switchToDark" : "theme.switchToLight");
  return (
    <button
      className="theme-toggle"
      type="button"
      onClick={toggleTheme}
      aria-label={label}
      title={label}
    >
      {theme === "dark" ? <Sun size={16} /> : <Moon size={16} />}
    </button>
  );
}

function initialTheme(): Theme {
  try {
    const stored = localStorage.getItem(storageKey);
    if (stored === "light" || stored === "dark") {
      return stored;
    }
  } catch {
    // Storage is optional.
  }
  try {
    if (window.matchMedia && window.matchMedia("(prefers-color-scheme: dark)").matches) {
      return "dark";
    }
  } catch {
    // matchMedia can be unavailable in unusual embedded contexts.
  }
  return "light";
}