fleeting-garden/src/audio/garden-audio-energy.ts

import type { GardenAudioEngineConfig } from '../config';
import { clamp01 } from '../utils/clamp';

const STROKE_IMMEDIATE_ACTIVITY_SCALE = 0.85;

export class GardenAudioEnergy {
  private isGestureActive = false;
  private energy = 0;
  private targetEnergy = 0;
  private lastEnergyUpdateAt = 0;

  public constructor(private readonly engineConfig: GardenAudioEngineConfig) {}

  public beginGesture(now: number): void {
    this.isGestureActive = true;
    this.lastEnergyUpdateAt = now;
  }

  public endGesture(): void {
    this.isGestureActive = false;
    this.targetEnergy = 0;
  }

  public recordStroke(strokeEnergy: number, now: number): void {
    const energy = clamp01(strokeEnergy);
    this.targetEnergy = Math.max(this.targetEnergy, energy);
    if (this.isGestureActive) {
      this.energy = Math.max(this.energy, energy * STROKE_IMMEDIATE_ACTIVITY_SCALE);
    }
    this.lastEnergyUpdateAt ||= now;
  }

  public recordEraserStroke(): void {
    this.targetEnergy = 0;
  }

  public silence(): void {
    this.targetEnergy = 0;
    this.energy = 0;
  }

  public update(now: number): void {
    if (this.lastEnergyUpdateAt <= 0) {
      this.lastEnergyUpdateAt = now;
      return;
    }

    const elapsedSeconds = Math.max(0, now - this.lastEnergyUpdateAt);
    this.lastEnergyUpdateAt = now;
    this.targetEnergy *= Math.exp(
      -elapsedSeconds / this.engineConfig.energy.strokeDecaySeconds
    );

    const target = this.isGestureActive ? this.targetEnergy : 0;
    let timeConstant = this.engineConfig.energy.decaySeconds;
    if (!this.isGestureActive) {
      timeConstant = this.engineConfig.energy.releaseSeconds;
    } else if (target > this.energy) {
      timeConstant = this.engineConfig.energy.attackSeconds;
    }
    const amount = 1 - Math.exp(-elapsedSeconds / timeConstant);
    this.energy += (target - this.energy) * amount;
  }

  public getActivity(): number {
    if (!this.isGestureActive) {
      return 0;
    }

    return this.getLevel();
  }

  public getLevel(): number {
    return clamp01(this.energy);
  }

  public reset(): void {
    this.isGestureActive = false;
    this.energy = 0;
    this.targetEnergy = 0;
    this.lastEnergyUpdateAt = 0;
  }
}