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

namespace RudderSdk.Core;

/// <summary>
/// Authentication: device login, explicit token refresh and logout.
/// Token refresh also happens automatically — see <see cref="RudderClient"/>.
/// </summary>
public sealed class AuthService
{
    private readonly RudderClient _client;

    internal AuthService(RudderClient client) => _client = client;

    /// <summary>
    /// Raised when the session state flips: after a successful login
    /// (<see cref="RudderAuthState.SignedIn"/>) and after logout or a failed
    /// token refresh (<see cref="RudderAuthState.SignedOut"/>).
    /// </summary>
    public event Action<RudderAuthState>? AuthStateChanged;

    /// <summary>
    /// Signs the player in with the device identifier. The returned token pair
    /// is stored in the configured token store.
    /// </summary>
    public async Task<LoginViaDeviceResponse> LoginWithDeviceAsync(
        string region,
        string language,
        string? nickname = null,
        CancellationToken cancellationToken = default)
    {
        var response = await _client.SendAsync<LoginViaDeviceRequest, LoginViaDeviceResponse>(
            "POST",
            "/sdk/v1/authorization/device",
            new LoginViaDeviceRequest
            {
                Key = _client.ProjectKey,
                DeviceId = _client.DeviceIdProvider.DeviceId,
                Region = region,
                Language = language,
                Nickname = nickname!
            },
            cancellationToken).ConfigureAwait(false);

        if (response == null || string.IsNullOrEmpty(response.AccessToken) || string.IsNullOrEmpty(response.RefreshToken))
            throw new InvalidOperationException("The server returned an incomplete session.");

        _client.TokenStore.SaveTokens(response.AccessToken, response.RefreshToken);
        NotifySignedIn();
        return response;
    }

    /// <summary>
    /// Exchanges the stored refresh token for a new token pair. Concurrent
    /// callers share one refresh request. Returns false when the session could
    /// not be renewed; the stored tokens are cleared in that case.
    /// </summary>
    public Task<bool> RefreshAsync() => _client.RefreshTokensAsync();

    /// <summary>Drops the stored session.</summary>
    public void Logout()
    {
        _client.TokenStore.Clear();
        NotifySignedOut();
    }

    internal void NotifySignedIn() => AuthStateChanged?.Invoke(RudderAuthState.SignedIn);

    internal void NotifySignedOut() => AuthStateChanged?.Invoke(RudderAuthState.SignedOut);
}