import { validate20ftWeightPairing } from './container-pairing.util';

describe('validate20ftWeightPairing', () => {
  const MAX_DIFF = 10;

  it('passes when a balanced pairing exists (adjacent diffs within cap)', () => {
    // sorted: 8, 15, 18, 24 → pairs (8,15) diff 7, (18,24) diff 6 — both ≤ 10.
    const units = [
      { label: 'A', grossWeightTons: 24 },
      { label: 'B', grossWeightTons: 8 },
      { label: 'C', grossWeightTons: 18 },
      { label: 'D', grossWeightTons: 15 },
    ];
    expect(validate20ftWeightPairing(units, MAX_DIFF)).toEqual([]);
  });

  it('flags a pair whose weight difference exceeds the cap', () => {
    // sorted: 5, 25 → single pair diff 20 > 10.
    const units = [
      { label: 'HEAVY', grossWeightTons: 25 },
      { label: 'LIGHT', grossWeightTons: 5 },
    ];
    const result = validate20ftWeightPairing(units, MAX_DIFF);
    expect(result).toHaveLength(1);
    expect(result[0].labels).toEqual(['LIGHT', 'HEAVY']);
    expect(result[0].diffTons).toBe(20);
  });

  it('allows an odd leftover unit (goes to consolidation, not a violation)', () => {
    // sorted: 10, 12, 30 → pair (10,12) diff 2 ok; 30 is the odd leftover.
    const units = [
      { label: 'A', grossWeightTons: 10 },
      { label: 'B', grossWeightTons: 12 },
      { label: 'C', grossWeightTons: 30 },
    ];
    expect(validate20ftWeightPairing(units, MAX_DIFF)).toEqual([]);
  });

  it('adjacent-by-weight pairing succeeds where a naive input order would fail', () => {
    // Input order (20, 12, 22, 10) naively pairs (20,12)=8 and (22,10)=12 (fail),
    // but sorted (10,12,20,22) pairs (10,12)=2 and (20,22)=2 — valid, so no violation.
    const units = [
      { label: 'A', grossWeightTons: 20 },
      { label: 'B', grossWeightTons: 12 },
      { label: 'C', grossWeightTons: 22 },
      { label: 'D', grossWeightTons: 10 },
    ];
    expect(validate20ftWeightPairing(units, MAX_DIFF)).toEqual([]);
  });

  it('returns nothing for fewer than two units', () => {
    expect(validate20ftWeightPairing([{ label: 'A', grossWeightTons: 30 }], MAX_DIFF)).toEqual([]);
    expect(validate20ftWeightPairing([], MAX_DIFF)).toEqual([]);
  });
});