brackt/app/lib/__tests__/fifa-2026-bracket.test.ts

import { describe, it, expect } from "vitest";
import {
  FIFA_2026_R32_TEMPLATE,
  THIRD_PLACE_SLOTS,
  assignThirdPlaceSlots,
  type R32Slot,
} from "../fifa-2026-bracket";

const GROUPS = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L"];

describe("FIFA_2026_R32_TEMPLATE", () => {
  it("has 16 matches with unique DB match numbers 1–16", () => {
    expect(FIFA_2026_R32_TEMPLATE).toHaveLength(16);
    const dbNums = FIFA_2026_R32_TEMPLATE.map((m) => m.dbMatchNumber).toSorted((a, b) => a - b);
    expect(dbNums).toEqual(Array.from({ length: 16 }, (_, i) => i + 1));
  });

  it("maps onto the official FIFA match numbers 73–88", () => {
    const fifaNums = FIFA_2026_R32_TEMPLATE.map((m) => m.fifaMatchNumber).toSorted((a, b) => a - b);
    expect(fifaNums).toEqual(Array.from({ length: 16 }, (_, i) => i + 73));
  });

  it("uses each group winner and runner-up exactly once across the 32 slots", () => {
    const winners: string[] = [];
    const runnersUp: string[] = [];
    for (const m of FIFA_2026_R32_TEMPLATE) {
      for (const slot of [m.slot1, m.slot2] as R32Slot[]) {
        if (slot.kind === "winner") winners.push(slot.group);
        if (slot.kind === "runnerUp") runnersUp.push(slot.group);
      }
    }
    expect(winners.toSorted()).toEqual(GROUPS);
    expect(runnersUp.toSorted()).toEqual(GROUPS);
  });

  it("has exactly 8 third-place slots", () => {
    expect(THIRD_PLACE_SLOTS).toHaveLength(8);
  });
});

describe("assignThirdPlaceSlots", () => {
  it("assigns all 8 qualifying thirds to distinct, eligible slots", () => {
    // Best-8 thirds come from groups A–H (a plausible qualifying set).
    const qualifying = ["A", "B", "C", "D", "E", "F", "G", "H"];
    const assignment = assignThirdPlaceSlots(qualifying);

    expect(assignment.size).toBe(8);

    // Every slot filled, each by an eligible & qualifying group, no group reused.
    const usedGroups = new Set<string>();
    for (const slot of THIRD_PLACE_SLOTS) {
      const group = assignment.get(slot.thirdSlotId) ?? "";
      expect(group).not.toBe("");
      expect(slot.eligibleGroups).toContain(group);
      expect(qualifying).toContain(group);
      expect(usedGroups.has(group)).toBe(false);
      usedGroups.add(group);
    }
    expect(usedGroups.size).toBe(8);
  });

  it("produces a valid matching for every 8-of-12 qualifying combination", () => {
    // Exhaustively check all C(12,8) = 495 combinations resolve to a complete,
    // eligibility-respecting, conflict-free assignment.
    let combinations = 0;
    const combos = (start: number, chosen: string[]) => {
      if (chosen.length === 8) {
        combinations++;
        const assignment = assignThirdPlaceSlots(chosen);
        expect(assignment.size).toBe(8);
        const used = new Set(assignment.values());
        expect(used.size).toBe(8);
        for (const slot of THIRD_PLACE_SLOTS) {
          const group = assignment.get(slot.thirdSlotId);
          expect(slot.eligibleGroups).toContain(group);
          expect(chosen).toContain(group);
        }
        return;
      }
      for (let i = start; i < GROUPS.length; i++) {
        combos(i + 1, [...chosen, GROUPS[i]]);
      }
    };
    combos(0, []);
    expect(combinations).toBe(495);
  });

  it("is deterministic for a given combination", () => {
    const qualifying = ["B", "D", "E", "F", "H", "I", "J", "L"];
    const a = assignThirdPlaceSlots(qualifying);
    const b = assignThirdPlaceSlots(qualifying.toReversed());
    expect([...a.entries()].toSorted()).toEqual([...b.entries()].toSorted());
  });

  it("matches FIFA's exact Annex C allocation for option 1 (groups E–L qualify)", () => {
    // Published row 1: 1A vs 3E, 1B vs 3J, 1D vs 3I, 1E vs 3F,
    //                  1G vs 3H, 1I vs 3G, 1K vs 3L, 1L vs 3K.
    // Mapped to DB third-slot ids (the match each winner plays in):
    const assignment = assignThirdPlaceSlots(["E", "F", "G", "H", "I", "J", "K", "L"]);
    expect(assignment.get(11)).toBe("E"); // winner A's match
    expect(assignment.get(15)).toBe("J"); // winner B's match
    expect(assignment.get(7)).toBe("I");  // winner D's match
    expect(assignment.get(1)).toBe("F");  // winner E's match
    expect(assignment.get(8)).toBe("H");  // winner G's match
    expect(assignment.get(2)).toBe("G");  // winner I's match
    expect(assignment.get(16)).toBe("L"); // winner K's match
    expect(assignment.get(12)).toBe("K"); // winner L's match
  });

  it("template eligible-group lists exactly match the Annex C table", () => {
    // For every slot, collect the set of groups the published table ever assigns
    // to it across all 495 combinations, and assert it equals the hand-written
    // eligibleGroups list in the template.
    const observed = new Map<number, Set<string>>(
      THIRD_PLACE_SLOTS.map((s) => [s.thirdSlotId, new Set<string>()])
    );
    const combos = (start: number, chosen: string[]) => {
      if (chosen.length === 8) {
        const assignment = assignThirdPlaceSlots(chosen);
        for (const [slotId, group] of assignment) observed.get(slotId)?.add(group);
        return;
      }
      for (let i = start; i < GROUPS.length; i++) combos(i + 1, [...chosen, GROUPS[i]]);
    };
    combos(0, []);

    for (const slot of THIRD_PLACE_SLOTS) {
      expect([...(observed.get(slot.thirdSlotId) ?? [])].toSorted()).toEqual(
        [...slot.eligibleGroups].toSorted()
      );
    }
  });
});