using System.Collections.Concurrent;
using Microsoft.Extensions.Options;
using NeonSprawl.Server.Game.PositionState;

namespace NeonSprawl.Server.Game.Contracts;

/// <summary>Thread-safe in-memory contract instances; seeds the configured dev player (NEO-146).</summary>
public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions> options) : IContractInstanceStore
{
    private sealed class InstanceRow(
        string contractInstanceId,
        string templateId,
        string playerId,
        ContractInstanceStatus status,
        string seedBucket,
        DateTimeOffset issuedAt,
        DateTimeOffset? completedAt)
    {
        public string ContractInstanceId { get; } = contractInstanceId;

        public string TemplateId { get; } = templateId;

        public string PlayerId { get; } = playerId;

        public ContractInstanceStatus Status { get; private set; } = status;

        public string SeedBucket { get; } = seedBucket;

        public DateTimeOffset IssuedAt { get; } = issuedAt;

        public DateTimeOffset? CompletedAt { get; private set; } = completedAt;

        public ContractInstanceState ToSnapshot() =>
            new(ContractInstanceId, TemplateId, PlayerId, Status, SeedBucket, IssuedAt, CompletedAt);

        public void MarkCompleted(DateTimeOffset completedAt)
        {
            Status = ContractInstanceStatus.Completed;
            CompletedAt = completedAt;
        }
    }

    private readonly HashSet<string> knownPlayers = CreateKnownPlayers(options.Value);

    private readonly ConcurrentDictionary<string, InstanceRow> byInstanceId = new(StringComparer.Ordinal);

    private readonly ConcurrentDictionary<string, string> activeInstanceByPlayer = new(StringComparer.Ordinal);

    private readonly ConcurrentDictionary<string, object> instanceLocks = new(StringComparer.Ordinal);

    private static string PlayerLockKey(string player) => $"{player}\0active";

    private static HashSet<string> CreateKnownPlayers(GamePositionOptions o)
    {
        var id = ContractInstanceIds.NormalizePlayerId(o.DevPlayerId);
        if (id.Length == 0)
        {
            throw new InvalidOperationException("Game:DevPlayerId must be non-empty.");
        }

        return new HashSet<string>(StringComparer.OrdinalIgnoreCase) { id };
    }

    /// <inheritdoc />
    public bool CanWritePlayer(string playerId)
    {
        var player = ContractInstanceIds.NormalizePlayerId(playerId);
        return player.Length > 0 && knownPlayers.Contains(player);
    }

    /// <inheritdoc />
    public bool TryGet(string playerId, string contractInstanceId, out ContractInstanceState snapshot)
    {
        snapshot = null!;
        var player = ContractInstanceIds.NormalizePlayerId(playerId);
        var instanceId = ContractInstanceIds.NormalizeContractInstanceId(contractInstanceId);
        if (player.Length == 0 || instanceId.Length == 0 || !knownPlayers.Contains(player))
        {
            return false;
        }

        var lockKey = ContractInstanceIds.MakeInstanceKey(player, instanceId);
        if (lockKey.Length == 0)
        {
            return false;
        }

        lock (instanceLocks.GetOrAdd(lockKey, _ => new object()))
        {
            if (!byInstanceId.TryGetValue(instanceId, out var row) ||
                !string.Equals(row.PlayerId, player, StringComparison.Ordinal))
            {
                return false;
            }

            snapshot = row.ToSnapshot();
            return true;
        }
    }

    /// <inheritdoc />
    public bool TryGetActiveForPlayer(string playerId, out ContractInstanceState snapshot)
    {
        snapshot = null!;
        var player = ContractInstanceIds.NormalizePlayerId(playerId);
        if (player.Length == 0 || !knownPlayers.Contains(player))
        {
            return false;
        }

        lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
        {
            if (!activeInstanceByPlayer.TryGetValue(player, out var instanceId))
            {
                return false;
            }

            if (!byInstanceId.TryGetValue(instanceId, out var row) ||
                row.Status != ContractInstanceStatus.Active ||
                !string.Equals(row.PlayerId, player, StringComparison.Ordinal))
            {
                activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, instanceId));
                return false;
            }

            snapshot = row.ToSnapshot();
            return true;
        }
    }

    /// <inheritdoc />
    public bool TryCreateActive(
        string playerId,
        string contractInstanceId,
        string templateId,
        string seedBucket,
        DateTimeOffset issuedAt,
        out ContractInstanceState snapshot)
    {
        snapshot = null!;
        var player = ContractInstanceIds.NormalizePlayerId(playerId);
        var instanceId = ContractInstanceIds.NormalizeContractInstanceId(contractInstanceId);
        var normalizedTemplateId = ContractInstanceIds.NormalizeTemplateId(templateId);
        var normalizedSeedBucket = ContractInstanceIds.NormalizeSeedBucket(seedBucket);
        if (player.Length == 0 ||
            instanceId.Length == 0 ||
            normalizedTemplateId.Length == 0 ||
            normalizedSeedBucket.Length == 0 ||
            !knownPlayers.Contains(player))
        {
            return false;
        }

        lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
        {
            lock (instanceLocks.GetOrAdd(ContractInstanceIds.MakeInstanceKey(player, instanceId), _ => new object()))
            {
                if (activeInstanceByPlayer.TryGetValue(player, out var existingActiveId))
                {
                    if (byInstanceId.TryGetValue(existingActiveId, out var existingActive) &&
                        existingActive.Status == ContractInstanceStatus.Active)
                    {
                        snapshot = existingActive.ToSnapshot();
                        return false;
                    }

                    activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, existingActiveId));
                }

                if (byInstanceId.TryGetValue(instanceId, out var existing))
                {
                    snapshot = existing.ToSnapshot();
                    return false;
                }

                var row = new InstanceRow(
                    instanceId,
                    normalizedTemplateId,
                    player,
                    ContractInstanceStatus.Active,
                    normalizedSeedBucket,
                    issuedAt,
                    null);
                byInstanceId[instanceId] = row;
                activeInstanceByPlayer[player] = instanceId;
                snapshot = row.ToSnapshot();
                return true;
            }
        }
    }

    /// <inheritdoc />
    public bool TryMarkComplete(
        string playerId,
        string contractInstanceId,
        DateTimeOffset completedAt,
        out ContractInstanceState snapshot)
    {
        snapshot = null!;
        var player = ContractInstanceIds.NormalizePlayerId(playerId);
        var instanceId = ContractInstanceIds.NormalizeContractInstanceId(contractInstanceId);
        if (player.Length == 0 || instanceId.Length == 0 || !knownPlayers.Contains(player))
        {
            return false;
        }

        var lockKey = ContractInstanceIds.MakeInstanceKey(player, instanceId);
        if (lockKey.Length == 0)
        {
            return false;
        }

        lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
        {
            lock (instanceLocks.GetOrAdd(lockKey, _ => new object()))
            {
                if (!byInstanceId.TryGetValue(instanceId, out var row) ||
                    !string.Equals(row.PlayerId, player, StringComparison.Ordinal))
                {
                    return false;
                }

                if (row.Status == ContractInstanceStatus.Completed)
                {
                    snapshot = row.ToSnapshot();
                    return false;
                }

                if (row.Status != ContractInstanceStatus.Active)
                {
                    snapshot = row.ToSnapshot();
                    return false;
                }

                row.MarkCompleted(completedAt);
                activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, instanceId));
                snapshot = row.ToSnapshot();
                return true;
            }
        }
    }

    /// <inheritdoc />
    public IReadOnlyList<ContractInstanceState> ListForPlayer(string playerId, int maxCompletedRows)
    {
        var player = ContractInstanceIds.NormalizePlayerId(playerId);
        if (player.Length == 0 || !knownPlayers.Contains(player) || maxCompletedRows < 0)
        {
            return [];
        }

        lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
        {
            ContractInstanceState? active = null;
            if (activeInstanceByPlayer.TryGetValue(player, out var activeId) &&
                byInstanceId.TryGetValue(activeId, out var activeRow) &&
                activeRow.Status == ContractInstanceStatus.Active &&
                string.Equals(activeRow.PlayerId, player, StringComparison.Ordinal))
            {
                active = activeRow.ToSnapshot();
            }

            var completed = new List<ContractInstanceState>();
            foreach (var row in byInstanceId.Values)
            {
                if (!string.Equals(row.PlayerId, player, StringComparison.Ordinal) ||
                    row.Status != ContractInstanceStatus.Completed)
                {
                    continue;
                }

                completed.Add(row.ToSnapshot());
            }

            completed.Sort(static (a, b) =>
            {
                var cmp = b.IssuedAt.CompareTo(a.IssuedAt);
                return cmp != 0
                    ? cmp
                    : string.CompareOrdinal(a.ContractInstanceId, b.ContractInstanceId);
            });

            if (completed.Count > maxCompletedRows)
            {
                completed.RemoveRange(maxCompletedRows, completed.Count - maxCompletedRows);
            }

            if (active is null)
            {
                return completed;
            }

            var result = new List<ContractInstanceState>(1 + completed.Count) { active };
            result.AddRange(completed);
            return result;
        }
    }

    /// <inheritdoc />
    public bool TryClearInstance(string playerId, string contractInstanceId)
    {
        var player = ContractInstanceIds.NormalizePlayerId(playerId);
        var instanceId = ContractInstanceIds.NormalizeContractInstanceId(contractInstanceId);
        if (player.Length == 0 || instanceId.Length == 0 || !knownPlayers.Contains(player))
        {
            return false;
        }

        var lockKey = ContractInstanceIds.MakeInstanceKey(player, instanceId);
        if (lockKey.Length == 0)
        {
            return false;
        }

        lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
        {
            lock (instanceLocks.GetOrAdd(lockKey, _ => new object()))
            {
                if (!byInstanceId.TryGetValue(instanceId, out var row) ||
                    !string.Equals(row.PlayerId, player, StringComparison.Ordinal))
                {
                    return true;
                }

                _ = byInstanceId.TryRemove(instanceId, out _);
                if (row.Status == ContractInstanceStatus.Active)
                {
                    activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, instanceId));
                }

                return true;
            }
        }
    }
}