// Browser storage for the autosave, the manual slots and the settings.
// Every access is wrapped: if localStorage is missing or throws (private window, blocked
// site data, full quota) the game keeps working and uses memory for the rest of the session.

export const SLOT_COUNT = 3;
export const KEYS = {
  auto: "cg.autosave",
  slot: (n) => `cg.slot.${n}`,
  settings: "cg.settings",
};

function browserStorage() {
  try {
    const probe = "cg.probe";
    globalThis.localStorage.setItem(probe, "1");
    globalThis.localStorage.removeItem(probe);
    return globalThis.localStorage;
  } catch {
    return null;
  }
}

// backend: anything with getItem/setItem/removeItem, for tests. Default: localStorage.
export function createStorage(backend = browserStorage()) {
  const memory = new Map();
  const store = { persistent: backend !== null };

  store.get = (key) => {
    try {
      if (backend) return backend.getItem(key);
    } catch {
      store.persistent = false;
    }
    return memory.get(key) ?? null;
  };

  // Returns false when the write could not be made durable.
  store.set = (key, value) => {
    try {
      if (backend) {
        backend.setItem(key, value);
        return true;
      }
    } catch {
      store.persistent = false;
    }
    memory.set(key, value);
    return false;
  };

  store.remove = (key) => {
    memory.delete(key);
    try {
      backend?.removeItem(key);
    } catch {
      store.persistent = false;
    }
  };

  return store;
}

// ---- Saved games: { meta, state } under one key ----

export function writeSave(store, key, state) {
  const meta = {
    savedAt: Date.now(),
    day: state.day,
    countryName: state.countryName,
    pronouns: state.pronouns,
    scenarioId: state.scenarioId,
    over: state.over?.type ?? null,
  };
  return store.set(key, JSON.stringify({ meta, state }));
}

// Returns { meta, state } or null when the slot is empty or unreadable.
export function readSave(store, key) {
  const raw = store.get(key);
  if (!raw) return null;
  try {
    const parsed = JSON.parse(raw);
    return parsed?.state && parsed?.meta ? parsed : null;
  } catch {
    return null;
  }
}

// ---- Settings ----

const DEFAULT_SETTINGS = { lang: null, slow: false };

export function loadSettings(store) {
  try {
    const s = JSON.parse(store.get(KEYS.settings) ?? "{}");
    return {
      lang: s.lang === "en" || s.lang === "fr" ? s.lang : DEFAULT_SETTINGS.lang,
      slow: s.slow === true,
    };
  } catch {
    return { ...DEFAULT_SETTINGS };
  }
}

export function saveSettings(store, settings) {
  return store.set(KEYS.settings, JSON.stringify(settings));
}