hrynco-notification-service/HrynCo.NotificationService.Worker.Services/Push/FirebasePushClient.cs

namespace HrynCo.NotificationService.Worker.Services.Push;

using FirebaseAdmin.Messaging;
using FirebaseAdmin;
using Google.Apis.Auth.OAuth2;
using System.Text;
using System.Text.Json;
using HrynCo.NotificationService.DAL.Abstract.Push;
using HrynCo.NotificationService.DAL.Abstract.PushChannels;

public sealed class FirebasePushClient : IFirebasePushClient
{
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
    {
        DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.WhenWritingNull
    };
    public async Task<PushDeliveryOutcome> SendAsync(Guid messageId, RenderedPushMessageData data,
        FirebaseServiceAccountCredentials credentials, CancellationToken cancellationToken)
    {
        if (!PushMessageValidator.IsSupportedVersion(data.Delivery.Version))
            return new PushDeliveryOutcome("Unsupported push payload version. Supported versions are 1 and 2.");
        var remaining = data.Delivery.ExpiresAt - DateTimeOffset.UtcNow;
        if (remaining <= TimeSpan.Zero) return new PushDeliveryOutcome("Push expired.");
        var payload = BuildPayload(messageId, data);
        if (data.Delivery.Version == 2 && Encoding.UTF8.GetByteCount(JsonSerializer.Serialize(payload)) > 3500)
            return new PushDeliveryOutcome("Rendered push payload is too large.");
        return await SendMessageAsync(new Message
        {
            Token = data.Delivery.Token,
            Android = new AndroidConfig { Priority = Priority.High, TimeToLive = remaining },
            Data = payload
        }, credentials, cancellationToken);
    }

    internal static Dictionary<string, string> BuildPayload(Guid messageId, RenderedPushMessageData data)
    {
        var payload = BasePayload(messageId, data.Delivery.BindingId, data.Delivery.ExpiresAt, data.Title, data.Body);
        switch (data.Delivery.Version)
        {
            case 1:
                payload["version"] = "1";
                payload["route"] = data.Delivery.Route;
                break;
            case 2:
                AddActions(payload, data.DefaultAction, data.Buttons);
                break;
            default: throw new ArgumentOutOfRangeException(nameof(data), "Unsupported push payload version.");
        }
        return payload;
    }

    private static Dictionary<string, string> BasePayload(Guid messageId, Guid bindingId, DateTimeOffset expiresAt, string title, string body) => new()
    {
        ["messageId"] = messageId.ToString("D"), ["bindingId"] = bindingId.ToString("D"),
        ["title"] = title, ["body"] = body,
        ["expiresAt"] = expiresAt.ToUnixTimeSeconds().ToString(System.Globalization.CultureInfo.InvariantCulture)
    };

    private static void AddActions(Dictionary<string, string> payload, RenderedPushAction? defaultAction, IReadOnlyList<RenderedPushAction> buttons)
    {
        payload["version"] = "2";
        payload["actions"] = JsonSerializer.Serialize(new { defaultAction, buttons }, JsonOptions);
    }

    public Task<PushDeliveryOutcome> SendTestAsync(PushChannelTestMessage message, FirebaseServiceAccountCredentials credentials,
        CancellationToken cancellationToken)
    {
        if (message.Validate() is { } error) return Task.FromResult(new PushDeliveryOutcome(error));
        return SendMessageAsync(BuildTestMessage(message), credentials, cancellationToken);
    }

    internal static Message BuildTestMessage(PushChannelTestMessage test)
    {
        if (test.Validate() is { } error) throw new ArgumentException(error, nameof(test));
        const string title = "Notification Service test";
        const string body = "This is a test notification from the channel administration page.";
        var message = new Message
        {
            Token = test.Token,
            Android = new AndroidConfig { Priority = Priority.High, TimeToLive = TimeSpan.FromMinutes(5) }
        };
        if (test.Version == 1) message.Notification = new Notification { Title = title, Body = body };
        else
        {
            var payload = BasePayload(Guid.NewGuid(), test.BindingId!.Value, DateTimeOffset.UtcNow.AddMinutes(5), title, body);
            AddActions(payload, new RenderedPushAction(test.ActionKey!), [new RenderedPushAction(test.ActionKey!, Label: test.ButtonLabel)]);
            message.Data = payload;
        }
        return message;
    }

    public async Task<PushDeliveryOutcome> CheckAuthorizationAsync(FirebaseServiceAccountCredentials credentials,
        CancellationToken cancellationToken)
    {
        using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeout.CancelAfter(TimeSpan.FromSeconds(30));
        try
        {
            var credential = CreateCredential(credentials).CreateScoped("https://www.googleapis.com/auth/firebase.messaging");
            await credential.UnderlyingCredential.GetAccessTokenForRequestAsync(cancellationToken: timeout.Token);
            return new PushDeliveryOutcome(null);
        }
        catch (Google.Apis.Auth.OAuth2.Responses.TokenResponseException)
        {
            return new PushDeliveryOutcome("Firebase OAuth authorization failed.");
        }
        catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
        {
            return new PushDeliveryOutcome("Firebase authorization check timed out.");
        }
        catch (HttpRequestException)
        {
            return new PushDeliveryOutcome("Could not reach Firebase authorization service.");
        }
    }

    private static GoogleCredential CreateCredential(FirebaseServiceAccountCredentials credentials) =>
        GoogleCredential.FromServiceAccountCredential(new ServiceAccountCredential(
            new ServiceAccountCredential.Initializer(credentials.ClientEmail)
            { ProjectId = credentials.ProjectId }.FromPrivateKey(credentials.PrivateKey)));

    private static async Task<PushDeliveryOutcome> SendMessageAsync(Message message,
        FirebaseServiceAccountCredentials credentials, CancellationToken cancellationToken)
    {
        using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeout.CancelAfter(TimeSpan.FromSeconds(30));
        FirebaseApp? app = null;
        try
        {
            app = FirebaseApp.Create(new AppOptions
            {
                ProjectId = credentials.ProjectId,
                Credential = CreateCredential(credentials)
            }, "push-" + Guid.NewGuid().ToString("N"));
            await FirebaseMessaging.GetMessaging(app).SendAsync(message, timeout.Token);
            return new PushDeliveryOutcome(null);
        }
        catch (FirebaseMessagingException exception)
        {
            var header = exception.HttpResponse?.Headers.RetryAfter;
            var retryAfter = header?.Delta ?? (header?.Date - DateTimeOffset.UtcNow) ?? TimeSpan.Zero;
            return Classify(exception.MessagingErrorCode, retryAfter);
        }
        catch (Google.Apis.Auth.OAuth2.Responses.TokenResponseException)
        {
            return new PushDeliveryOutcome("FCM authorization failed.");
        }
        catch (FirebaseException)
        {
            return new PushDeliveryOutcome("FCM configuration failed.");
        }
        catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
        {
            throw new PushRetryException(TimeSpan.FromMinutes(1));
        }
        catch (HttpRequestException)
        {
            throw new PushRetryException(TimeSpan.FromMinutes(1));
        }
        finally
        {
            app?.Delete();
        }
    }

    internal static PushDeliveryOutcome Classify(MessagingErrorCode? code, TimeSpan retryAfter = default) => code switch
    {
        MessagingErrorCode.Unregistered => new PushDeliveryOutcome("FCM registration is no longer valid.", true),
        MessagingErrorCode.Unavailable or MessagingErrorCode.Internal or MessagingErrorCode.QuotaExceeded =>
            throw new PushRetryException(retryAfter),
        MessagingErrorCode.SenderIdMismatch => new PushDeliveryOutcome("FCM sender configuration does not match."),
        MessagingErrorCode.InvalidArgument => new PushDeliveryOutcome("FCM rejected the push payload."),
        _ => new PushDeliveryOutcome("FCM authorization or configuration failure.")
    };
}