import { Engine, type Effect } from "../core.ts";
import type { PetCommand, PetState } from "../types.ts";
import { save } from "./storage.ts";
import { emit, store, toast } from "./store.ts";
import { errorMessage } from "./utils.ts";

// The browser's copy of the pet lives in the shared Rust engine (core/), the
// same one the host runs. `store.state` is a read-only snapshot for rendering.
// In remote mode the engine only holds the server's latest checkpoint.
let engine: Engine | null = null;
export function petEngine(): Engine {
  if (!engine) throw new Error("The pet has not loaded yet.");
  return engine;
}
/** `seed` is the deployment's weather seed, shared with its host. */
export function startEngine(state: PetState, seed: string) {
  engine?.raw.free();
  engine = new Engine(state, Date.now(), seed);
  store.state = engine.state();
}
let onChange: ((effects: Effect[]) => void) | null = null;
/** Runs after every change with its new effects (lifecycle.ts plays them). */
export function afterChanges(hook: (effects: Effect[]) => void) {
  onChange = hook;
}
/** Refreshes the snapshot (only the body fields when `full` is false), hands on new effects and saves. */
export function changed(full = true) {
  const e = petEngine();
  store.state = full ? e.state() : { ...store.state, ...e.body() };
  const effects = e.takeEffects();
  onChange?.(effects);
  save();
  emit();
}
/** Replaces the save: an import, a transfer or a server snapshot. */
export function setState(state: PetState, keepTurns = false) {
  const e = petEngine();
  if (keepTurns) e.edit(state);
  else e.replace(state, Date.now());
  changed();
}
/** Debug and test edits of the save, keeping the turn queue. */
export function editState(edit: (state: PetState) => void) {
  const state = petEngine().state();
  edit(state);
  setState(state, true);
}
/** Runs an owner command locally. Refusals become a toast. */
export function localCommand(command: PetCommand) {
  try {
    petEngine().command(command, Date.now());
    return true;
  } catch (error) {
    toast(errorMessage(error));
    return false;
  } finally {
    changed();
  }
}