scrabble-game/ui/src/lib/placement.test.ts

import { describe, expect, it } from 'vitest';
import {
  BLANK,
  cellOccupied,
  isBlankSlot,
  newPlacement,
  place,
  placementFromHint,
  rackView,
  recallAt,
  recallIndex,
  recallToSlot,
  reorderIndices,
  reset,
  toSubmit,
} from './placement';

const rack = ['A', 'Q', BLANK, 'N', 'I', 'W', 'E'];

describe('placement state machine', () => {
  it('places a tile and marks the rack slot used', () => {
    const p = place(newPlacement(rack), 0, 7, 7);
    expect(p.pending).toHaveLength(1);
    expect(rackView(p)[0].used).toBe(true);
    expect(rackView(p)[1].used).toBe(false);
  });

  it('rejects reusing a slot or an occupied cell', () => {
    let p = place(newPlacement(rack), 0, 7, 7);
    p = place(p, 0, 7, 8); // same slot -> no-op
    expect(p.pending).toHaveLength(1);
    p = place(p, 1, 7, 7); // occupied cell -> no-op
    expect(p.pending).toHaveLength(1);
  });

  it('requires a letter for a blank slot', () => {
    const noLetter = place(newPlacement(rack), 2, 7, 7);
    expect(noLetter.pending).toHaveLength(0);
    const withLetter = place(newPlacement(rack), 2, 7, 7, 'x');
    expect(withLetter.pending[0]).toMatchObject({ letter: 'X', blank: true });
  });

  it('recalls a tile by cell', () => {
    let p = place(newPlacement(rack), 0, 7, 7);
    p = recallAt(p, 7, 7);
    expect(p.pending).toHaveLength(0);
    expect(reset(place(p, 0, 7, 7)).pending).toHaveLength(0);
  });

  it('builds a sorted submit payload and returns null when empty', () => {
    let p = place(newPlacement(rack), 1, 7, 9);
    p = place(p, 0, 7, 7);
    const sub = toSubmit(p);
    expect(sub?.tiles.map((t) => t.col)).toEqual([7, 9]);
    expect(toSubmit(newPlacement(rack))).toBeNull();
  });

  it('recalls a tile by rack index and reports occupied cells / blank slots', () => {
    let p = place(newPlacement(rack), 0, 7, 7);
    p = place(p, 1, 7, 8);
    expect(cellOccupied(p, 7, 7)).toBe(true);
    expect(cellOccupied(p, 6, 6)).toBe(false);
    p = recallIndex(p, 0);
    expect(p.pending.map((t) => t.rackIndex)).toEqual([1]);
    expect(isBlankSlot(newPlacement(rack), 2)).toBe(true); // '?' slot
    expect(isBlankSlot(newPlacement(rack), 0)).toBe(false);
  });

  it('submits a single tile as a one-tile payload', () => {
    const sub = toSubmit(place(newPlacement(rack), 0, 7, 7));
    expect(sub?.tiles).toHaveLength(1);
  });
});

describe('placementFromHint', () => {
  it('maps hint letters and blanks onto rack slots', () => {
    const p = placementFromHint(
      [
        { row: 7, col: 7, letter: 'C', blank: false },
        { row: 7, col: 8, letter: 'A', blank: false },
        { row: 7, col: 9, letter: 'B', blank: true },
      ],
      ['C', 'A', BLANK, 'T'],
    );
    expect(p.pending).toHaveLength(3);
    expect(p.pending[0]).toMatchObject({ rackIndex: 0, letter: 'C', blank: false });
    expect(p.pending[2]).toMatchObject({ rackIndex: 2, letter: 'B', blank: true });
  });

  it('falls back to a blank slot when the hint letter is not in the rack', () => {
    const p = placementFromHint([{ row: 7, col: 7, letter: 'Z', blank: false }], ['A', BLANK]);
    expect(p.pending).toHaveLength(1);
    expect(p.pending[0]).toMatchObject({ rackIndex: 1, letter: 'Z', blank: true });
  });

  it('skips hint tiles once the rack is exhausted', () => {
    const p = placementFromHint(
      [
        { row: 7, col: 7, letter: 'A', blank: false },
        { row: 7, col: 8, letter: 'B', blank: false },
      ],
      ['A'],
    );
    expect(p.pending.map((t) => t.letter)).toEqual(['A']);
  });
});

describe('reorderIndices', () => {
  it('lifts an element and drops it at the given slot among the others', () => {
    expect(reorderIndices(4, 0, 2)).toEqual([1, 2, 0, 3]);
    expect(reorderIndices(4, 3, 0)).toEqual([3, 0, 1, 2]);
    expect(reorderIndices(4, 1, 1)).toEqual([0, 1, 2, 3]); // back to identity
    expect(reorderIndices(3, 0, 99)).toEqual([1, 2, 0]); // slot clamped to the end
  });
});

describe('recallToSlot', () => {
  it('reinserts the recalled tile at the chosen visible slot, reordering the rack', () => {
    // Lift Q (slot 1) onto the board, then recall it to visible slot 4.
    const p = place(newPlacement(rack), 1, 7, 7);
    const { placement, order } = recallToSlot(p, 7, 7, 4);
    expect(placement.pending).toHaveLength(0);
    expect(placement.rack).toEqual(['A', BLANK, 'N', 'I', 'Q', 'W', 'E']);
    expect(order).toEqual([0, 2, 3, 4, 1, 5, 6]);
  });

  it('counts only still-visible slots and remaps the remaining pending tiles', () => {
    // A (slot 0) and N (slot 3) are on the board; recall A to visible slot 2 — the placed N is
    // skipped, and N's rackIndex follows the rack permutation.
    let p = place(newPlacement(rack), 0, 7, 7);
    p = place(p, 3, 7, 8);
    const { placement, order } = recallToSlot(p, 7, 7, 2);
    expect(placement.rack).toEqual(['Q', BLANK, 'N', 'A', 'I', 'W', 'E']);
    expect(order).toEqual([1, 2, 3, 0, 4, 5, 6]);
    expect(placement.pending).toHaveLength(1);
    expect(placement.pending[0].rackIndex).toBe(2);
    expect(placement.rack[placement.pending[0].rackIndex]).toBe('N');
  });

  it('clamps the slot to the end and is an identity no-op when no tile sits at the cell', () => {
    const p = place(newPlacement(rack), 1, 7, 7);
    expect(recallToSlot(p, 7, 7, 99).placement.rack).toEqual(['A', BLANK, 'N', 'I', 'W', 'E', 'Q']);
    const none = recallToSlot(p, 0, 0, 0);
    expect(none.placement).toBe(p);
    expect(none.order).toEqual([0, 1, 2, 3, 4, 5, 6]);
  });
});