import type { GameState } from '@ai-tycoon/shared';
import { processTick } from './tick';

export interface GameEngineCallbacks {
  getState: () => GameState;
  setState: (partial: Partial<GameState>) => void;
  onTick?: (tickCount: number) => void;
  onEraChange?: (era: GameState['meta']['currentEra']) => void;
}

export class GameEngine {
  private callbacks: GameEngineCallbacks;
  private lastFrameTime = 0;
  private accumulator = 0;
  private animFrameId: number | null = null;
  private tickIntervalMs = 1000;

  constructor(callbacks: GameEngineCallbacks) {
    this.callbacks = callbacks;
  }

  start(): void {
    if (this.animFrameId !== null) return;
    this.lastFrameTime = performance.now();
    this.accumulator = 0;
    this.loop(this.lastFrameTime);
  }

  stop(): void {
    if (this.animFrameId !== null) {
      cancelAnimationFrame(this.animFrameId);
      this.animFrameId = null;
    }
  }

  setSpeed(speed: number): void {
    this.tickIntervalMs = 1000 / speed;
  }

  processOfflineTicks(missedTicks: number): { revenue: number; expenses: number; ticksProcessed: number } {
    let totalRevenue = 0;
    let totalExpenses = 0;

    for (let i = 0; i < missedTicks; i++) {
      const state = this.callbacks.getState();
      const result = processTick(state);
      this.callbacks.setState(result);
      totalRevenue += result.economy?.revenuePerTick ?? 0;
      totalExpenses += result.economy?.expensesPerTick ?? 0;
    }

    return { revenue: totalRevenue, expenses: totalExpenses, ticksProcessed: missedTicks };
  }

  private loop = (now: number): void => {
    const delta = now - this.lastFrameTime;
    this.lastFrameTime = now;

    const state = this.callbacks.getState();
    if (!state.meta.isPaused) {
      this.accumulator += delta;

      let ticksThisFrame = 0;
      const maxTicksPerFrame = 10;

      while (this.accumulator >= this.tickIntervalMs && ticksThisFrame < maxTicksPerFrame) {
        const currentState = this.callbacks.getState();
        const result = processTick(currentState);
        this.callbacks.setState(result);
        this.accumulator -= this.tickIntervalMs;
        ticksThisFrame++;
        this.callbacks.onTick?.(currentState.meta.tickCount + 1);
      }

      if (this.accumulator > this.tickIntervalMs * maxTicksPerFrame) {
        this.accumulator = 0;
      }
    }

    this.animFrameId = requestAnimationFrame(this.loop);
  };
}