export interface TravelDistance {
  advance(deltaSeconds: number, speed: number, roadEnergy: number): number;
  snapshot(): number;
}

const MAX_FRAME_SECONDS = 0.1;
const CRUISE_UNITS_PER_SECOND = 18;
const SPEED_UNITS_PER_SECOND = 54;
const ENERGY_UNITS_PER_SECOND = 48;

export function createTravelDistance(): TravelDistance {
  let distance = 0;

  return {
    advance(deltaSeconds, speed, roadEnergy) {
      if (!Number.isFinite(deltaSeconds) || deltaSeconds <= 0) return distance;
      const dt = Math.min(MAX_FRAME_SECONDS, deltaSeconds);
      distance += dt * (
        CRUISE_UNITS_PER_SECOND
        + clamp01(speed) * SPEED_UNITS_PER_SECOND
        + clamp01(roadEnergy) * ENERGY_UNITS_PER_SECOND
      );
      return distance;
    },
    snapshot: () => distance,
  };
}

function clamp01(value: number): number {
  return Number.isFinite(value) ? Math.min(1, Math.max(0, value)) : 0;
}