using System;
using System.Threading;
using System.Threading.Tasks;
using RudderSdk.Core.Abstractions;
using RudderSdk.Core.Models.Auth;

namespace RudderSdk.Core;

/// <summary>
/// Entry point of the Rudder SDK. Composes all feature services around one
/// configuration (<see cref="RudderClientOptions"/>) and owns the session
/// lifecycle: every API call goes through here, a 401 triggers a single-flight
/// token refresh and one transparent retry.
/// </summary>
public sealed class RudderClient
{
    private readonly object _refreshGate = new();
    private Task<bool>? _pendingRefresh;

    /// <summary>Authentication: device login, token refresh, logout.</summary>
    public AuthService Auth { get; }

    /// <summary>Player profile and wallets.</summary>
    public PlayerService Player { get; }

    /// <summary>Remote configuration values.</summary>
    public RemoteConfigService RemoteConfig { get; }

    /// <summary>Player key-value storage.</summary>
    public StorageService Storage { get; }

    /// <summary>In-game stores and offer purchases.</summary>
    public StoresService Stores { get; }

    /// <summary>Leaderboards.</summary>
    public LeaderboardsService Leaderboards { get; }

    /// <summary>Player inventory.</summary>
    public InventoryService Inventory { get; }

    /// <summary>Battle pass progress and rewards.</summary>
    public BattlePassService BattlePass { get; }

    /// <summary>Global quests.</summary>
    public QuestsService Quests { get; }

    /// <summary>User-generated content.</summary>
    public UgcService Ugc { get; }

    /// <summary>Scenario runtime: triggers, node sessions, persistence.</summary>
    public ScenarioService Scenario { get; }

    /// <summary>Realtime websocket channel.</summary>
    public RealtimeService Realtime { get; }

    internal RudderClientOptions Options { get; }
    internal IRudderTransport Transport => Options.Transport!;
    internal ITokenStore TokenStore => Options.TokenStore!;
    internal IDeviceIdProvider DeviceIdProvider => Options.DeviceIdProvider!;

    /// <summary>Project key from <see cref="RudderClientOptions.ProjectKey"/>.</summary>
    public string ProjectKey => Options.ProjectKey!;

    /// <summary>Realtime URL from <see cref="RudderClientOptions.RealtimeUrl"/>.</summary>
    public string? RealtimeUrl => Options.RealtimeUrl;

    /// <summary>Time source used by the scenario runtime.</summary>
    public IClock Clock => Options.Clock ?? SystemClock.Instance;

    /// <summary>
    /// Creates the client. <see cref="RudderClientOptions.BaseUrl"/> and
    /// <see cref="RudderClientOptions.ProjectKey"/> are required; transport,
    /// token store and device id provider fall back to defaults.
    /// </summary>
    public RudderClient(RudderClientOptions options)
    {
        Options = options ?? throw new ArgumentNullException(nameof(options));
        if (string.IsNullOrEmpty(Options.BaseUrl)) throw new ArgumentException("BaseUrl is required.", nameof(options));
        if (string.IsNullOrEmpty(Options.ProjectKey)) throw new ArgumentException("ProjectKey is required.", nameof(options));

        Options.Transport ??= new HttpClientTransport(Options.BaseUrl);
        Options.TokenStore ??= new InMemoryTokenStore();
        Options.DeviceIdProvider ??= new GuidDeviceIdProvider();

        Auth = new AuthService(this);
        Player = new PlayerService(this);
        RemoteConfig = new RemoteConfigService(this);
        Storage = new StorageService(this);
        Stores = new StoresService(this);
        Leaderboards = new LeaderboardsService(this);
        Inventory = new InventoryService(this);
        Ugc = new UgcService(this);
        Scenario = new ScenarioService(this);
        BattlePass = new BattlePassService(this);
        Quests = new QuestsService(this);
        Realtime = new RealtimeService(this);
    }

    /// <summary>Pumps time-dependent services; call every frame.</summary>
    public void Update(float deltaTime)
    {
        Scenario.Update(deltaTime);
        Realtime.Update(deltaTime);
    }

    internal Task<TResponse> SendAsync<TRequest, TResponse>(
        string method,
        string path,
        TRequest? request,
        CancellationToken cancellationToken = default)
    {
        return SendWithRetryAsync<TRequest, TResponse>(method, path, request, cancellationToken);
    }

    internal Task<TResponse> SendAsync<TResponse>(
        string method,
        string path,
        CancellationToken cancellationToken = default)
    {
        return SendWithRetryAsync<object, TResponse>(method, path, null, cancellationToken);
    }

    internal Task SendAsync<TRequest>(
        string method,
        string path,
        TRequest? request,
        CancellationToken cancellationToken = default)
    {
        return SendWithRetryAsync<TRequest, EmptyResponse>(method, path, request, cancellationToken);
    }

    internal Task SendAsync(
        string method,
        string path,
        CancellationToken cancellationToken = default)
    {
        return SendWithRetryAsync<object, EmptyResponse>(method, path, null, cancellationToken);
    }

    private async Task<TResponse> SendWithRetryAsync<TRequest, TResponse>(
        string method,
        string path,
        TRequest? request,
        CancellationToken cancellationToken)
    {
        try
        {
            return await Transport
                .SendAsync<TRequest, TResponse>(method, path, request, TokenStore.GetAccessToken(), cancellationToken)
                .ConfigureAwait(false);
        }
        catch (RudderAuthException)
        {
            // Session rejected — refresh once (single-flight) and retry the call once.
            if (!await RefreshTokensAsync().ConfigureAwait(false))
                throw;

            return await Transport
                .SendAsync<TRequest, TResponse>(method, path, request, TokenStore.GetAccessToken(), cancellationToken)
                .ConfigureAwait(false);
        }
    }

    /// <summary>
    /// Single-flight refresh: concurrent 401s share one refresh request.
    /// Resolves to true when a new token pair was stored. On failure the tokens
    /// are cleared and subscribers are notified via
    /// <see cref="AuthService.AuthStateChanged"/>.
    /// </summary>
    internal Task<bool> RefreshTokensAsync()
    {
        lock (_refreshGate)
        {
            if (_pendingRefresh != null)
                return _pendingRefresh;

            var task = DoRefreshTokensAsync();
            _pendingRefresh = task;
            task.ContinueWith(
                _ =>
                {
                    lock (_refreshGate)
                    {
                        if (ReferenceEquals(_pendingRefresh, task))
                            _pendingRefresh = null;
                    }
                },
                CancellationToken.None,
                TaskContinuationOptions.ExecuteSynchronously,
                TaskScheduler.Default);
            return task;
        }
    }

    private async Task<bool> DoRefreshTokensAsync()
    {
        var refreshToken = TokenStore.GetRefreshToken();
        if (!string.IsNullOrEmpty(refreshToken))
        {
            try
            {
                var response = await Transport
                    .SendAsync<RefreshAccessTokenRequest, RefreshAccessTokenResponse>(
                        "POST",
                        "/sdk/v1/authorization/refresh",
                        new RefreshAccessTokenRequest { RefreshToken = refreshToken },
                        null,
                        CancellationToken.None)
                    .ConfigureAwait(false);

                if (response != null
                    && !string.IsNullOrEmpty(response.AccessToken)
                    && !string.IsNullOrEmpty(response.RefreshToken))
                {
                    TokenStore.SaveTokens(response.AccessToken, response.RefreshToken);
                    return true;
                }
            }
            catch
            {
                // Transport-level failure during refresh — session is over.
            }
        }

        TokenStore.Clear();
        Auth.NotifySignedOut();
        return false;
    }

    private sealed class SystemClock : IClock
    {
        public static readonly SystemClock Instance = new();
        public DateTimeOffset UtcNow => DateTimeOffset.UtcNow;
    }
}

internal sealed class EmptyResponse
{
}