/**
 * Unit Tests: Round-Robin Schedule Generator
 *
 * Tests the correctness of the round-robin scheduling algorithm
 */

import { describe, test, expect } from 'bun:test';
import {
  generateRoundRobin,
  validateScheduleInput,
  expectedRounds,
  expectedMatchups,
} from '@/lib/schedule-generator';

// Helper to create team pairings from simple IDs
function createTeams(count: number): { player1Id: number; player2Id: number }[] {
  const teams = [];
  for (let i = 0; i < count; i++) {
    // Create teams with unique player IDs
    // Team 1: players 1, 2
    // Team 2: players 3, 4
    // etc.
    teams.push({
      player1Id: i * 2 + 1,
      player2Id: i * 2 + 2,
    });
  }
  return teams;
}

describe('Round-Robin Schedule Generator', () => {
  describe('generateRoundRobin', () => {
    test('should return empty array for fewer than 2 teams', () => {
      expect(generateRoundRobin([])).toEqual([]);
      expect(generateRoundRobin([{ player1Id: 1, player2Id: 2 }])).toEqual([]);
    });

    test('should generate correct schedule for 2 teams', () => {
      const rounds = generateRoundRobin([
        { player1Id: 1, player2Id: 2 },
        { player1Id: 3, player2Id: 4 },
      ]);
      expect(rounds).toHaveLength(1);
      expect(rounds[0].roundNumber).toBe(1);
      expect(rounds[0].matchups).toHaveLength(1);
      expect(rounds[0].matchups[0]).toEqual({
        player1P1Id: 1,
        player1P2Id: 2,
        player2P1Id: 3,
        player2P2Id: 4,
      });
    });

    test('should generate N-1 rounds for N even teams', () => {
      const teams = createTeams(4);
      const rounds = generateRoundRobin(teams);
      expect(rounds).toHaveLength(3);
    });

    test('should generate N rounds for N odd teams (with bye)', () => {
      const teams = createTeams(3);
      const rounds = generateRoundRobin(teams);
      expect(rounds).toHaveLength(3);
    });

    test('each team plays every other team exactly once (even)', () => {
      const teams = createTeams(4);
      const rounds = generateRoundRobin(teams);

      // Collect all pairings as sorted tuples
      const pairings = new Set<string>();
      for (const round of rounds) {
        for (const matchup of round.matchups) {
          const key = [
            matchup.player1P1Id,
            matchup.player1P2Id,
            matchup.player2P1Id,
            matchup.player2P2Id,
          ].sort().join('-');
          pairings.add(key);
        }
      }

      // 4 teams = 6 unique pairings
      expect(pairings.size).toBe(6);
    });

    test('each team plays every other team exactly once (odd)', () => {
      const teams = createTeams(5);
      const rounds = generateRoundRobin(teams);

      const pairings = new Set<string>();
      for (const round of rounds) {
        for (const matchup of round.matchups) {
          const key = [
            matchup.player1P1Id,
            matchup.player1P2Id,
            matchup.player2P1Id,
            matchup.player2P2Id,
          ].sort().join('-');
          pairings.add(key);
        }
      }

      // 5 teams = 10 unique pairings
      expect(pairings.size).toBe(10);
    });

    test('each team plays exactly once per round (even teams)', () => {
      const teams = createTeams(6);
      const rounds = generateRoundRobin(teams);

      for (const round of rounds) {
        const teamsInRound = new Set<string>();
        for (const matchup of round.matchups) {
          teamsInRound.add([matchup.player1P1Id, matchup.player1P2Id].sort().join('-'));
          teamsInRound.add([matchup.player2P1Id, matchup.player2P2Id].sort().join('-'));
        }
        // Each team appears exactly once
        expect(teamsInRound.size).toBe(6);
      }
    });

    test('each team plays at most once per round (odd teams)', () => {
      const teams = createTeams(5);
      const rounds = generateRoundRobin(teams);

      for (const round of rounds) {
        const teamsInRound = new Set<string>();
        for (const matchup of round.matchups) {
          teamsInRound.add([matchup.player1P1Id, matchup.player1P2Id].sort().join('-'));
          teamsInRound.add([matchup.player2P1Id, matchup.player2P2Id].sort().join('-'));
        }
        // 5 teams, one has bye each round, so 4 play
        expect(teamsInRound.size).toBe(4);
      }
    });

    test('should handle 8 teams (typical euchre tournament)', () => {
      const teams = createTeams(8);
      const rounds = generateRoundRobin(teams);

      expect(rounds).toHaveLength(7);

      const totalMatchups = rounds.reduce((sum, r) => sum + r.matchups.length, 0);
      expect(totalMatchups).toBe(28);
    });

    test('round numbers should be sequential starting from 1', () => {
      const teams = createTeams(6);
      const rounds = generateRoundRobin(teams);

      rounds.forEach((round, idx) => {
        expect(round.roundNumber).toBe(idx + 1);
      });
    });
  });

  describe('validateScheduleInput', () => {
    test('should reject empty team list', () => {
      const result = validateScheduleInput([]);
      expect(result.valid).toBe(false);
      expect(result.error).toContain('At least 2');
    });

    test('should reject single team', () => {
      const result = validateScheduleInput([{ player1Id: 1, player2Id: 2 }]);
      expect(result.valid).toBe(false);
    });

    test('should reject duplicate team pairings', () => {
      const result = validateScheduleInput([
        { player1Id: 1, player2Id: 2 },
        { player1Id: 3, player2Id: 4 },
        { player1Id: 1, player2Id: 2 }, // Duplicate
      ]);
      expect(result.valid).toBe(false);
      expect(result.error).toContain('Duplicate');
    });

    test('should accept valid team list', () => {
      const result = validateScheduleInput(createTeams(4));
      expect(result.valid).toBe(true);
      expect(result.error).toBeUndefined();
    });
  });

  describe('expectedRounds', () => {
    test('should return 0 for fewer than 2 teams', () => {
      expect(expectedRounds(0)).toBe(0);
      expect(expectedRounds(1)).toBe(0);
    });

    test('should return N-1 for even N', () => {
      expect(expectedRounds(4)).toBe(3);
      expect(expectedRounds(6)).toBe(5);
      expect(expectedRounds(8)).toBe(7);
    });

    test('should return N for odd N', () => {
      expect(expectedRounds(3)).toBe(3);
      expect(expectedRounds(5)).toBe(5);
      expect(expectedRounds(7)).toBe(7);
    });
  });

  describe('expectedMatchups', () => {
    test('should return 0 for fewer than 2 teams', () => {
      expect(expectedMatchups(0)).toBe(0);
      expect(expectedMatchups(1)).toBe(0);
    });

    test('should return N*(N-1)/2 for N teams', () => {
      expect(expectedMatchups(4)).toBe(6);
      expect(expectedMatchups(6)).toBe(15);
      expect(expectedMatchups(8)).toBe(28);
    });
  });
});