import type { Inventory, RabbitData, ResourceDropData, ResourceNodeData, Vec2 } from './types';
import type { UpgradeId } from './upgrades';

const STORAGE_KEY = 'forest-save-v1';

export interface SaveData {
  version: 3;
  inventory: Inventory;
  upgradeLevels: Record<UpgradeId, number>;
  /** World state (character/nodes/drops) is optional so older saves without it still load fine —
   * progress is restored either way, just with a freshly spawned world. */
  character?: Vec2;
  nodes?: ResourceNodeData[];
  resourceDrops?: ResourceDropData[];
  /** Absent on saves from before rabbits existed, which get a freshly spawned batch instead. */
  rabbits?: RabbitData[];
  /** Absent on older saves, which are treated as day 1. */
  day?: number;
  /** In-game clock hour (0-24). Absent on older saves, which are treated as noon. */
  hour?: number;
  /** Absent on saves from before the character had hp, which default to a full characterMaxHp. */
  characterHp?: number;
}

function isValidSave(value: unknown): value is SaveData {
  if (!value || typeof value !== 'object')
    return false;
  const data = value as Partial<SaveData>;
  return (
    data.version === 3
    && typeof data.inventory === 'object' && data.inventory !== null
    && typeof data.inventory.logs === 'number'
    && typeof data.inventory.twigs === 'number'
    && typeof data.inventory.coins === 'number'
    && typeof data.upgradeLevels === 'object' && data.upgradeLevels !== null
  );
}

/** Reads the saved game from localStorage, or null if there's none / it's corrupted (including a
 * save from an older, incompatible schema version — that's treated the same as no save). */
export function loadSave(): SaveData | null {
  try {
    const raw = localStorage.getItem(STORAGE_KEY);
    if (!raw)
      return null;
    const parsed: unknown = JSON.parse(raw);
    return isValidSave(parsed) ? parsed : null;
  } catch {
    // localStorage unavailable (private mode, disabled) or corrupted JSON — treat as no save.
    return null;
  }
}

/** Writes the save to localStorage. Best-effort: silently no-ops if storage is unavailable/full. */
export function writeSave(data: SaveData): void {
  try {
    localStorage.setItem(STORAGE_KEY, JSON.stringify(data));
  } catch {
    // Ignore — e.g. private browsing mode or quota exceeded.
  }
}

/** Deletes the saved game, if any — used when starting a brand new game. */
export function clearSave(): void {
  try {
    localStorage.removeItem(STORAGE_KEY);
  } catch {
    // Ignore — e.g. private browsing mode.
  }
}

/** Whether a valid, resumable save currently exists (used to enable/disable "Continue" in the menu). */
export function hasSave(): boolean {
  return loadSave() !== null;
}