import type { Inventory, LogDrop, TreeState, Vec2 } from './types';
import type { UpgradeId } from './upgrades';

const STORAGE_KEY = 'forest-save-v1';

export interface SaveData {
  version: 1;
  inventory: Inventory;
  upgradeLevels: Record<UpgradeId, number>;
  /** World state (character/trees/logs) is optional so older saves without it still load fine —
   * progress is restored either way, just with a freshly spawned world. */
  character?: Vec2;
  trees?: TreeState[];
  logDrops?: LogDrop[];
}

function isValidSave(value: unknown): value is SaveData {
  if (!value || typeof value !== 'object')
    return false;
  const data = value as Partial<SaveData>;
  return (
    data.version === 1
    && typeof data.inventory === 'object' && data.inventory !== null
    && typeof data.inventory.logs === '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. */
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.
  }
}