const { RateLimiter } = require('./solution');

function clock(start = 0) {
  let t = start;
  return { now: () => t, advance: (ms) => { t += ms; } };
}

describe('RateLimiter', () => {
  test('validates constructor arguments', () => {
    expect(() => new RateLimiter({ capacity: 0, refillPerSec: 1 })).toThrow(RangeError);
    expect(() => new RateLimiter({ capacity: 1, refillPerSec: -1 })).toThrow(RangeError);
  });

  test('uses the system clock by default', () => {
    const rl = new RateLimiter({ capacity: 1, refillPerSec: 1 });
    expect(rl.tryRemove()).toBe(true);
  });

  test('starts full and spends tokens', () => {
    const c = clock();
    const rl = new RateLimiter({ capacity: 2, refillPerSec: 1, now: c.now });
    expect(rl.tryRemove()).toBe(true);
    expect(rl.tryRemove()).toBe(true);
    expect(rl.tryRemove()).toBe(false);
  });

  test('can spend exactly all remaining tokens', () => {
    const c = clock();
    const rl = new RateLimiter({ capacity: 3, refillPerSec: 1, now: c.now });
    expect(rl.tryRemove(3)).toBe(true);
    expect(rl.tokens).toBe(0);
  });

  test('failed request spends nothing', () => {
    const c = clock();
    const rl = new RateLimiter({ capacity: 2, refillPerSec: 1, now: c.now });
    expect(rl.tryRemove(5)).toBe(false);
    expect(rl.tokens).toBe(2);
  });

  test('refills over time but never above capacity', () => {
    const c = clock();
    const rl = new RateLimiter({ capacity: 2, refillPerSec: 1, now: c.now });
    rl.tryRemove(2);
    c.advance(1000);
    expect(rl.tryRemove()).toBe(true);
    expect(rl.tryRemove()).toBe(false);
    c.advance(10000);
    rl.waitTime();
    expect(rl.tokens).toBe(2);
  });

  test('rejects non-positive cost', () => {
    const rl = new RateLimiter({ capacity: 1, refillPerSec: 1, now: clock().now });
    expect(() => rl.tryRemove(0)).toThrow(RangeError);
  });

  test('waitTime rounds up and handles zero refill', () => {
    const c = clock();
    const rl = new RateLimiter({ capacity: 1, refillPerSec: 3, now: c.now });
    expect(rl.waitTime()).toBe(0);
    rl.tryRemove();
    expect(rl.waitTime()).toBe(334);
    const frozen = new RateLimiter({ capacity: 1, refillPerSec: 0, now: c.now });
    frozen.tryRemove();
    expect(frozen.waitTime()).toBe(Infinity);
  });
});