using System.Security.Cryptography;
using System.Text.Json;
using Microsoft.Extensions.Logging;
using StellaOps.Messaging.Abstractions;
using StackExchange.Redis;

namespace StellaOps.Messaging.Transport.Valkey;

/// <summary>
/// Valkey/Redis implementation of <see cref="IAtomicTokenStore{TPayload}"/>.
/// Uses Lua scripts for atomic compare-and-delete operations.
/// </summary>
public sealed class ValkeyAtomicTokenStore<TPayload> : IAtomicTokenStore<TPayload>
{
    private readonly ValkeyConnectionFactory _connectionFactory;
    private readonly string _name;
    private readonly ILogger<ValkeyAtomicTokenStore<TPayload>>? _logger;
    private readonly JsonSerializerOptions _jsonOptions;
    private readonly TimeProvider _timeProvider;

    // Lua script for atomic consume: GET, compare, DELETE if matches
    private const string ConsumeScript = @"
        local value = redis.call('GET', KEYS[1])
        if not value then
            return {0, nil}
        end
        local data = cjson.decode(value)
        if data.token ~= ARGV[1] then
            return {2, value}
        end
        redis.call('DEL', KEYS[1])
        return {1, value}
    ";

    public ValkeyAtomicTokenStore(
        ValkeyConnectionFactory connectionFactory,
        string name,
        ILogger<ValkeyAtomicTokenStore<TPayload>>? logger = null,
        JsonSerializerOptions? jsonOptions = null,
        TimeProvider? timeProvider = null)
    {
        _connectionFactory = connectionFactory ?? throw new ArgumentNullException(nameof(connectionFactory));
        _name = name ?? throw new ArgumentNullException(nameof(name));
        _logger = logger;
        _jsonOptions = jsonOptions ?? new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            WriteIndented = false
        };
        _timeProvider = timeProvider ?? TimeProvider.System;
    }

    /// <inheritdoc />
    public string ProviderName => "valkey";

    /// <inheritdoc />
    public async ValueTask<TokenIssueResult> IssueAsync(
        string key,
        TPayload payload,
        TimeSpan ttl,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(key);

        var redisKey = BuildKey(key);
        var now = _timeProvider.GetUtcNow();
        var expiresAt = now.Add(ttl);

        // Generate secure random token
        var tokenBytes = new byte[32];
        RandomNumberGenerator.Fill(tokenBytes);
        var token = Convert.ToBase64String(tokenBytes);

        var entry = new TokenData<TPayload>
        {
            Token = token,
            Payload = payload,
            IssuedAt = now,
            ExpiresAt = expiresAt
        };

        var serialized = JsonSerializer.Serialize(entry, _jsonOptions);
        var db = await _connectionFactory.GetDatabaseAsync(cancellationToken).ConfigureAwait(false);

        await db.StringSetAsync(redisKey, serialized, ttl).ConfigureAwait(false);

        return TokenIssueResult.Succeeded(token, expiresAt);
    }

    /// <inheritdoc />
    public async ValueTask<TokenIssueResult> StoreAsync(
        string key,
        string token,
        TPayload payload,
        TimeSpan ttl,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(key);
        ArgumentNullException.ThrowIfNull(token);

        var redisKey = BuildKey(key);
        var now = _timeProvider.GetUtcNow();
        var expiresAt = now.Add(ttl);

        var entry = new TokenData<TPayload>
        {
            Token = token,
            Payload = payload,
            IssuedAt = now,
            ExpiresAt = expiresAt
        };

        var serialized = JsonSerializer.Serialize(entry, _jsonOptions);
        var db = await _connectionFactory.GetDatabaseAsync(cancellationToken).ConfigureAwait(false);

        await db.StringSetAsync(redisKey, serialized, ttl).ConfigureAwait(false);

        return TokenIssueResult.Succeeded(token, expiresAt);
    }

    /// <inheritdoc />
    public async ValueTask<TokenConsumeResult<TPayload>> TryConsumeAsync(
        string key,
        string expectedToken,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(key);
        ArgumentNullException.ThrowIfNull(expectedToken);

        var redisKey = BuildKey(key);
        var db = await _connectionFactory.GetDatabaseAsync(cancellationToken).ConfigureAwait(false);
        var now = _timeProvider.GetUtcNow();

        try
        {
            var result = await db.ScriptEvaluateAsync(
                ConsumeScript,
                new RedisKey[] { redisKey },
                new RedisValue[] { expectedToken }).ConfigureAwait(false);

            var results = (RedisResult[])result!;
            var status = (int)results[0];

            switch (status)
            {
                case 0: // Not found
                    return TokenConsumeResult<TPayload>.NotFound();

                case 1: // Success
                    var data = JsonSerializer.Deserialize<TokenData<TPayload>>((string)results[1]!, _jsonOptions);
                    if (data is null)
                    {
                        return TokenConsumeResult<TPayload>.NotFound();
                    }

                    if (data.ExpiresAt < now)
                    {
                        return TokenConsumeResult<TPayload>.Expired(data.IssuedAt, data.ExpiresAt);
                    }

                    return TokenConsumeResult<TPayload>.Success(data.Payload!, data.IssuedAt, data.ExpiresAt);

                case 2: // Mismatch
                    return TokenConsumeResult<TPayload>.Mismatch();

                default:
                    return TokenConsumeResult<TPayload>.NotFound();
            }
        }
        catch (RedisServerException ex) when (ex.Message.Contains("NOSCRIPT"))
        {
            // Fallback: non-atomic approach (less safe but works without Lua)
            return await TryConsumeNonAtomicAsync(db, redisKey, expectedToken, now).ConfigureAwait(false);
        }
    }

    private async ValueTask<TokenConsumeResult<TPayload>> TryConsumeNonAtomicAsync(
        IDatabase db,
        string redisKey,
        string expectedToken,
        DateTimeOffset now)
    {
        var value = await db.StringGetAsync(redisKey).ConfigureAwait(false);
        if (value.IsNullOrEmpty)
        {
            return TokenConsumeResult<TPayload>.NotFound();
        }

        var data = JsonSerializer.Deserialize<TokenData<TPayload>>((string)value!, _jsonOptions);
        if (data is null)
        {
            return TokenConsumeResult<TPayload>.NotFound();
        }

        if (data.ExpiresAt < now)
        {
            await db.KeyDeleteAsync(redisKey).ConfigureAwait(false);
            return TokenConsumeResult<TPayload>.Expired(data.IssuedAt, data.ExpiresAt);
        }

        if (!string.Equals(data.Token, expectedToken, StringComparison.Ordinal))
        {
            return TokenConsumeResult<TPayload>.Mismatch();
        }

        // Try to delete - if someone else deleted it first, we lost the race
        if (await db.KeyDeleteAsync(redisKey).ConfigureAwait(false))
        {
            return TokenConsumeResult<TPayload>.Success(data.Payload!, data.IssuedAt, data.ExpiresAt);
        }

        return TokenConsumeResult<TPayload>.NotFound();
    }

    /// <inheritdoc />
    public async ValueTask<bool> ExistsAsync(string key, CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(key);

        var redisKey = BuildKey(key);
        var db = await _connectionFactory.GetDatabaseAsync(cancellationToken).ConfigureAwait(false);
        return await db.KeyExistsAsync(redisKey).ConfigureAwait(false);
    }

    /// <inheritdoc />
    public async ValueTask<bool> RevokeAsync(string key, CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(key);

        var redisKey = BuildKey(key);
        var db = await _connectionFactory.GetDatabaseAsync(cancellationToken).ConfigureAwait(false);
        return await db.KeyDeleteAsync(redisKey).ConfigureAwait(false);
    }

    private string BuildKey(string key) => $"token:{_name}:{key}";

    private sealed class TokenData<T>
    {
        public required string Token { get; init; }
        public T? Payload { get; init; }
        public DateTimeOffset IssuedAt { get; init; }
        public DateTimeOffset ExpiresAt { get; init; }
    }
}

/// <summary>
/// Factory for creating Valkey atomic token store instances.
/// </summary>
public sealed class ValkeyAtomicTokenStoreFactory : IAtomicTokenStoreFactory
{
    private readonly ValkeyConnectionFactory _connectionFactory;
    private readonly ILoggerFactory? _loggerFactory;
    private readonly JsonSerializerOptions? _jsonOptions;
    private readonly TimeProvider _timeProvider;

    public ValkeyAtomicTokenStoreFactory(
        ValkeyConnectionFactory connectionFactory,
        ILoggerFactory? loggerFactory = null,
        JsonSerializerOptions? jsonOptions = null,
        TimeProvider? timeProvider = null)
    {
        _connectionFactory = connectionFactory ?? throw new ArgumentNullException(nameof(connectionFactory));
        _loggerFactory = loggerFactory;
        _jsonOptions = jsonOptions;
        _timeProvider = timeProvider ?? TimeProvider.System;
    }

    /// <inheritdoc />
    public string ProviderName => "valkey";

    /// <inheritdoc />
    public IAtomicTokenStore<TPayload> Create<TPayload>(string name)
    {
        ArgumentNullException.ThrowIfNull(name);
        return new ValkeyAtomicTokenStore<TPayload>(
            _connectionFactory,
            name,
            _loggerFactory?.CreateLogger<ValkeyAtomicTokenStore<TPayload>>(),
            _jsonOptions,
            _timeProvider);
    }
}