using FluentAssertions;
using Game.TicTacToe;
using OECS;
using R3;
using Xunit;

namespace Game.TicTacToe.Tests;

public class PlayTests
{
    [Fact]
    public void Play_GreedyVsRandom()
    {
        var log = new PlayLog();

        var (world, group) = SetupGame();
        var agentX = new GreedyAgent(GreedyAgent.Strategy.WinOrBlock);
        var agentO = new RandomAgent();

        // Subscribe reactivity.
        world.ObserveComponentChanges<Mark>().Subscribe(change =>
        {
            var mark = world.ReadComponent<Mark>(change.Entity);
            log.Reactivity.Add($"{change.Kind} Mark = {mark} on {change.Entity}");
        });

        log.Header = "TicTacToe: Greedy X vs Random O";

        RunGame(world, group, agentX, agentO, log);

        log.FinalSnapshot = SnapshotWorld(world);

        var path = SavePlayLog("tic_tac_toe_greedy_vs_random.playlog", log);
        ReadAndVerify(path);
    }

    [Fact]
    public void Play_RandomVsRandom()
    {
        var log = new PlayLog();

        var (world, group) = SetupGame();
        var agentX = new RandomAgent();
        var agentO = new RandomAgent();

        world.ObserveComponentChanges<Mark>().Subscribe(change =>
        {
            var mark = world.ReadComponent<Mark>(change.Entity);
            log.Reactivity.Add($"{change.Kind} Mark = {mark} on {change.Entity}");
        });

        log.Header = "TicTacToe: Random X vs Random O";

        RunGame(world, group, agentX, agentO, log);

        log.FinalSnapshot = SnapshotWorld(world);

        var path = SavePlayLog("tic_tac_toe_random_vs_random.playlog", log);
        ReadAndVerify(path);
    }

    [Fact]
    public void Play_GreedyVsGreedy()
    {
        var log = new PlayLog();

        var (world, group) = SetupGame();
        var agentX = new GreedyAgent(GreedyAgent.Strategy.WinOrBlock);
        var agentO = new GreedyAgent(GreedyAgent.Strategy.WinOrBlock);

        world.ObserveComponentChanges<Mark>().Subscribe(change =>
        {
            var mark = world.ReadComponent<Mark>(change.Entity);
            log.Reactivity.Add($"{change.Kind} Mark = {mark} on {change.Entity}");
        });

        log.Header = "TicTacToe: Greedy X vs Greedy O";

        RunGame(world, group, agentX, agentO, log);

        log.FinalSnapshot = SnapshotWorld(world);

        var path = SavePlayLog("tic_tac_toe_greedy_vs_greedy.playlog", log);
        ReadAndVerify(path);
    }

    // ── Play Log ──────────────────────────────────────────────────────

    private sealed class PlayLog
    {
        public string Header { get; set; } = "";
        public readonly List<string> Moves = new();
        public readonly List<string> Reactivity = new();
        public string FinalSnapshot { get; set; } = "";

        public string Build()
        {
            var sb = new System.Text.StringBuilder();
            sb.AppendLine(Header);
            sb.AppendLine(new string('=', Header.Length));
            sb.AppendLine();
            sb.AppendLine("--- Moves ---");
            for (int i = 0; i < Moves.Count; i++)
                sb.AppendLine($"  {i + 1}. {Moves[i]}");
            sb.AppendLine();
            sb.AppendLine("--- Reactivity ---");
            foreach (var entry in Reactivity)
                sb.AppendLine($"  {entry}");
            sb.AppendLine();
            sb.AppendLine("--- Final Board ---");
            sb.AppendLine(FinalSnapshot);
            return sb.ToString();
        }
    }

    // ── Game Runner ───────────────────────────────────────────────────

    private static (World, SystemGroup) SetupGame()
    {
        var world = new World();
        var group = new SystemGroup(world);
        group.Add(new WinCheckSystem());

        for (int r = 0; r < 3; r++)
            for (int c = 0; c < 3; c++)
                world.AddComponent(world.CreateEntity(), new Cell { Row = r, Col = c });

        world.SetSingleton(new GameState
        {
            CurrentPlayer = Player.X,
            Status = GameStatus.Playing,
            MoveCount = 0
        });
        world.PostChanges();

        return (world, group);
    }

    private static void RunGame(World world, SystemGroup group, IAgent agentX, IAgent agentO, PlayLog log)
    {
        while (world.ReadSingleton<GameState>().Status == GameStatus.Playing)
        {
            var state = world.ReadSingleton<GameState>();
            var agent = state.CurrentPlayer == Player.X ? agentX : agentO;
            var cmd = agent.Decide(world);

            world.Commands.Enqueue(cmd);
            group.RunLogical();

            log.Moves.Add($"{state.CurrentPlayer} → ({cmd.Row},{cmd.Col})");
        }

        var final = world.ReadSingleton<GameState>();
        log.Header += $" — Result: {final.Status}";
    }

    // ── Snapshot ──────────────────────────────────────────────────────

    private static string SnapshotWorld(World world)
    {
        var sb = new System.Text.StringBuilder();
        var grid = new char?[3, 3];
        using (var iter = world.Select<Cell, Mark>())
        {
            while (iter.MoveNext())
                grid[iter.Item1.Row, iter.Item1.Col] =
                    iter.Item2.Player == Player.X ? 'X' : 'O';
        }

        for (int r = 0; r < 3; r++)
        {
            sb.Append("  ");
            for (int c = 0; c < 3; c++)
                sb.Append(grid[r, c]?.ToString() ?? ".");
            sb.AppendLine();
        }
        return sb.ToString().TrimEnd();
    }

    // ── File I/O ──────────────────────────────────────────────────────

    private static string SavePlayLog(string filename, PlayLog log)
    {
        var dir = Path.Combine(AppContext.BaseDirectory, "playlogs");
        Directory.CreateDirectory(dir);
        var path = Path.Combine(dir, filename);
        File.WriteAllText(path, log.Build());
        return path;
    }

    private static void ReadAndVerify(string path)
    {
        var content = File.ReadAllText(path);

        // Verify the play log is well-formed.
        content.Should().Contain("--- Moves ---");
        content.Should().Contain("--- Reactivity ---");
        content.Should().Contain("--- Final Board ---");

        // The game must have finished.
        content.Should().Contain("Result:");
        content.Should().NotContain("Result: Playing");
    }

    // ── Agents ────────────────────────────────────────────────────────

    private interface IAgent
    {
        PlaceMarkCommand Decide(World world);
    }

    private sealed class RandomAgent : IAgent
    {
        private static readonly Random _rng = new();
        public PlaceMarkCommand Decide(World world)
        {
            var empty = GetEmptyCells(world);
            var (row, col) = empty[_rng.Next(empty.Count)];
            return new PlaceMarkCommand { Row = row, Col = col };
        }
    }

    private sealed class GreedyAgent : IAgent
    {
        public enum Strategy { WinOrBlock }
        private readonly Strategy _strategy;
        private static readonly Random _rng = new();
        public GreedyAgent(Strategy strategy) => _strategy = strategy;

        public PlaceMarkCommand Decide(World world)
        {
            var state = world.ReadSingleton<GameState>();
            var me = state.CurrentPlayer;
            var empty = GetEmptyCells(world);

            foreach (var (r, c) in empty)
                if (WouldWin(world, r, c, me))
                    return new PlaceMarkCommand { Row = r, Col = c };

            var opponent = me == Player.X ? Player.O : Player.X;
            foreach (var (r, c) in empty)
                if (WouldWin(world, r, c, opponent))
                    return new PlaceMarkCommand { Row = r, Col = c };

            if (empty.Any(c => c.Row == 1 && c.Col == 1))
                return new PlaceMarkCommand { Row = 1, Col = 1 };

            var (rr, cc) = empty[_rng.Next(empty.Count)];
            return new PlaceMarkCommand { Row = rr, Col = cc };
        }
    }

    private static List<(int Row, int Col)> GetEmptyCells(World world)
    {
        var empty = new List<(int, int)>();
        var query = new Query<Cell>().Without<Mark>();
        using var iter = world.Select(query);
        while (iter.MoveNext())
            empty.Add((iter.Item1.Row, iter.Item1.Col));
        return empty;
    }

    private static bool WouldWin(World world, int row, int col, Player player)
    {
        var grid = new Player[3, 3];
        using (var iter = world.Select<Cell, Mark>())
            while (iter.MoveNext())
                grid[iter.Item1.Row, iter.Item1.Col] = iter.Item2.Player;
        grid[row, col] = player;

        for (int r = 0; r < 3; r++)
            if (grid[r, 0] == player && grid[r, 1] == player && grid[r, 2] == player)
                return true;
        for (int c = 0; c < 3; c++)
            if (grid[0, c] == player && grid[1, c] == player && grid[2, c] == player)
                return true;
        if (grid[0, 0] == player && grid[1, 1] == player && grid[2, 2] == player)
            return true;
        if (grid[0, 2] == player && grid[1, 1] == player && grid[2, 0] == player)
            return true;

        return false;
    }
}