import { describe, expect, it } from "vitest";
import {
  readThemePreference,
  resolveTheme,
  saveThemePreference,
  THEME_STORAGE_KEY,
  toggleTheme,
} from "@/lib/theme-preference.js";

function makeStorage(initial = {}) {
  const values = new Map(Object.entries(initial));
  return {
    getItem: (key) => values.get(key) ?? null,
    setItem: (key, value) => values.set(key, value),
  };
}

describe("theme preference", () => {
  it("restores a saved dark preference ahead of system preference", () => {
    const storage = makeStorage({ [THEME_STORAGE_KEY]: "dark" });
    expect(resolveTheme({ savedTheme: readThemePreference(storage), systemPrefersDark: false })).toBe("dark");
  });

  it("uses system dark preference when no explicit choice exists", () => {
    expect(resolveTheme({ savedTheme: null, systemPrefersDark: true })).toBe("dark");
  });

  it("switches themes and persists the explicit choice", () => {
    const storage = makeStorage();
    const nextTheme = toggleTheme("light");
    saveThemePreference(nextTheme, storage);

    expect(nextTheme).toBe("dark");
    expect(readThemePreference(storage)).toBe("dark");
  });
});