import { useCallback, useEffect, useState } from "react";

export type ThemeChoice = "system" | "dark" | "light";
const KEY = "pg-theme";

function read(): ThemeChoice {
  try {
    const v = localStorage.getItem(KEY);
    return v === "dark" || v === "light" ? v : "system";
  } catch {
    return "system";
  }
}

function apply(choice: ThemeChoice) {
  const root = document.documentElement;
  if (choice === "system") delete root.dataset.theme;
  else root.dataset.theme = choice;
  const dark = choice === "dark" || (choice === "system" && matchMedia("(prefers-color-scheme: dark)").matches);
  document.querySelector('meta[name="theme-color"]')?.setAttribute("content", dark ? "#0e1016" : "#f4f1ec");
}

export function useTheme() {
  const [choice, setChoice] = useState<ThemeChoice>(read);
  useEffect(() => {
    apply(choice);
    try {
      if (choice === "system") localStorage.removeItem(KEY);
      else localStorage.setItem(KEY, choice);
    } catch {
      /* private mode */
    }
  }, [choice]);
  const cycle = useCallback(
    () => setChoice((c) => (c === "system" ? "dark" : c === "dark" ? "light" : "system")),
    [],
  );
  return { choice, setChoice, cycle };
}