import { describe, expect, it } from 'vitest';
import {
  HERO_CAR_HALF_WIDTH,
  TRAFFIC_BODY,
  TRAFFIC_FADE_LENGTH,
  TRAFFIC_LANE_JITTER,
  TRAFFIC_LANES,
  TRAFFIC_NEAR_Z,
  trafficLamps,
  trafficNearFade,
  wrapTrafficZ,
} from '@/scene/world/traffic';

describe('expressway traffic stays clear of the hero car', () => {
  it('keeps every body outside the hero car, with lane jitter', () => {
    for (const lane of TRAFFIC_LANES) {
      const inner = Math.abs(lane.x) - TRAFFIC_BODY[lane.kind].halfWidth - TRAFFIC_LANE_JITTER;
      expect(inner).toBeGreaterThan(HERO_CAR_HALF_WIDTH);
    }
  });

  it('never lets bodies in adjacent lanes overlap, and keeps them on the road', () => {
    const spans = TRAFFIC_LANES.map((lane) => {
      const half = TRAFFIC_BODY[lane.kind].halfWidth + TRAFFIC_LANE_JITTER;
      return [lane.x - half, lane.x + half] as const;
    }).sort((a, b) => a[0] - b[0]);
    for (let i = 1; i < spans.length; i++) expect(spans[i]![0]).toBeGreaterThan(spans[i - 1]![1]);
    for (const [left, right] of spans) {
      expect(left).toBeGreaterThan(-8);
      expect(right).toBeLessThan(8);
    }
  });

  it('runs each lane at one speed, so no vehicle drives through another', () => {
    const xs = TRAFFIC_LANES.map((lane) => lane.x);
    expect(new Set(xs).size).toBe(xs.length);
  });

  it('puts every lamp on the vehicle body', () => {
    for (const kind of ['car', 'truck'] as const) {
      const lamps = trafficLamps(kind, 0.5);
      expect(lamps.length).toBeGreaterThanOrEqual(3);
      for (const lamp of lamps) expect(Math.abs(lamp.x) + lamp.w / 2).toBeLessThanOrEqual(TRAFFIC_BODY[kind].halfWidth + 0.01);
    }
    // A readable pair: two tail lamps mirrored at one height.
    const [left, right] = trafficLamps('car', 0);
    expect(left!.x).toBe(-right!.x);
    expect(left!.y).toBe(right!.y);
  });

  it('is fully dark before the car near field and lit beyond the fade', () => {
    expect(trafficNearFade(TRAFFIC_NEAR_Z)).toBe(0);
    expect(trafficNearFade(0)).toBe(0);
    expect(trafficNearFade(40)).toBe(0);
    expect(trafficNearFade(TRAFFIC_NEAR_Z - TRAFFIC_FADE_LENGTH)).toBe(1);
    expect(trafficNearFade(-300)).toBe(1);
    // The car's nose is at about z = -5.5: the near field starts well ahead.
    expect(TRAFFIC_NEAR_Z).toBeLessThan(-18);
  });

  it('wraps vehicles inside the hidden band at any scroll speed', () => {
    // 110 units/s at a 0.1 s frame clamp is 11 units per step; test far more.
    for (const step of [0.5, 11, 64, 900, -11, -900]) {
      let z = -200;
      for (let i = 0; i < 400; i++) {
        z = wrapTrafficZ(z + step);
        expect(z).toBeLessThanOrEqual(TRAFFIC_NEAR_Z);
        expect(z).toBeGreaterThanOrEqual(-660);
      }
    }
  });
});