import { appConfig } from '../config';

interface TelemetrySnapshot {
  frameCpuStartedAt: number;
  encodeCpuMs: number;
  activeAgentCount: number;
  agentBudgetMax: number;
  canvas: HTMLCanvasElement;
  devicePixelRatio: number;
  renderSpeed: number;
}

const COMMON_DISPLAY_REFRESH_RATES = [
  50, 60, 72, 75, 90, 100, 120, 144, 165, 180, 240,
] as const;
const DISPLAY_REFRESH_CONFIRMATION_FRAMES = 8;
const DISPLAY_REFRESH_SNAP_TOLERANCE = 0.15;

export class FramePerformance {
  public latestFps = 60;
  public smoothedFps = 60;
  public displayRefreshFps = 60;
  public readonly refreshTargetFps = 60;

  private lastTelemetryAt = 0;
  private hasConfirmedDisplayRefreshFps = false;
  private pendingDisplayRefreshFps = 0;
  private pendingDisplayRefreshFrameCount = 0;

  public markCpuStart(): number {
    return appConfig.telemetry.enabled ? performance.now() : 0;
  }

  public measureSince(startedAt: number): number {
    return appConfig.telemetry.enabled ? performance.now() - startedAt : 0;
  }

  public update(deltaTime: number): void {
    const fps = 1 / Math.max(deltaTime, appConfig.deltaTime.minDeltaTimeSeconds);
    this.latestFps = fps;
    this.updateDisplayRefreshEstimate(fps);
    this.smoothedFps =
      this.smoothedFps * appConfig.simulation.budget.fpsSmoothingRetain +
      fps * appConfig.simulation.budget.fpsSmoothingNew;
  }

  public renderTelemetry({
    frameCpuStartedAt,
    encodeCpuMs,
    activeAgentCount,
    agentBudgetMax,
    canvas,
    devicePixelRatio,
    renderSpeed,
  }: TelemetrySnapshot): void {
    if (!appConfig.telemetry.enabled) {
      return;
    }

    const now = performance.now();
    if (now - this.lastTelemetryAt < appConfig.telemetry.intervalMs) {
      return;
    }

    this.lastTelemetryAt = now;
    console.debug('Fleeting Garden telemetry', {
      fps: Math.round(this.latestFps),
      smoothedFps: Math.round(this.smoothedFps),
      refreshTargetFps: Math.round(this.refreshTargetFps),
      displayRefreshFps: Math.round(this.displayRefreshFps),
      activeAgentCount,
      agentBudgetMax,
      canvasWidth: canvas.width,
      canvasHeight: canvas.height,
      dpr: devicePixelRatio,
      renderSpeed,
      frameCpuMs: now - frameCpuStartedAt,
      encodeCpuMs,
    });
  }

  private updateDisplayRefreshEstimate(fps: number): void {
    const displayRefreshFps = this.snapDisplayRefreshRate(fps);
    if (displayRefreshFps === null) {
      this.resetPendingDisplayRefreshEstimate();
      return;
    }

    if (
      this.hasConfirmedDisplayRefreshFps &&
      displayRefreshFps < this.displayRefreshFps
    ) {
      this.resetPendingDisplayRefreshEstimate();
      return;
    }

    if (displayRefreshFps !== this.pendingDisplayRefreshFps) {
      this.pendingDisplayRefreshFps = displayRefreshFps;
      this.pendingDisplayRefreshFrameCount = 1;
    } else {
      this.pendingDisplayRefreshFrameCount += 1;
    }

    if (this.pendingDisplayRefreshFrameCount < DISPLAY_REFRESH_CONFIRMATION_FRAMES) {
      return;
    }

    this.displayRefreshFps = displayRefreshFps;
    this.hasConfirmedDisplayRefreshFps = true;
    this.resetPendingDisplayRefreshEstimate();
  }

  private snapDisplayRefreshRate(fps: number): number | null {
    if (!Number.isFinite(fps) || fps <= 0) {
      return null;
    }

    let nearestRefreshRate: number = COMMON_DISPLAY_REFRESH_RATES[0];
    let nearestDifference = Math.abs(fps - nearestRefreshRate);

    COMMON_DISPLAY_REFRESH_RATES.forEach((refreshRate) => {
      const difference = Math.abs(fps - refreshRate);
      if (difference < nearestDifference) {
        nearestRefreshRate = refreshRate;
        nearestDifference = difference;
      }
    });

    return nearestDifference / nearestRefreshRate <= DISPLAY_REFRESH_SNAP_TOLERANCE
      ? nearestRefreshRate
      : null;
  }

  private resetPendingDisplayRefreshEstimate(): void {
    this.pendingDisplayRefreshFps = 0;
    this.pendingDisplayRefreshFrameCount = 0;
  }
}