✅ Npgsql.PostgresException

public class CreatePostHandler(
    IHttpContextAccessor contextAccessor,
    DatabaseContext db,
    ISender mediator,
    IValidator<CreatePostCommand> validator)
    : RequestHandler(contextAccessor), IRequestHandler<CreatePostCommand, Result<Post>>
{
    private const string StorageContainer = "images";

    public async Task<Result<Post>> Handle(CreatePostCommand request, CancellationToken cancellationToken)
    {
        try
        {
            var validationResult = await ValidateInputAsync(request, cancellationToken);
            if (!validationResult.IsValid)
                return Result<Post>.Failure("Invalid input received.",
                    validationResult.ErrorMessages(), 400);

            var newBlobName = $"{Guid.NewGuid()}{request.File.GetExtensionType()}";
            var uploadResult = await UploadFileAsync(newBlobName, request.File, cancellationToken);

            if (!uploadResult.IsSuccessful)
                return uploadResult.ToResult(_ => new Post());

            var uri = uploadResult.Data;
            var nsfwResult = await ClassifyFileAsync(uri, cancellationToken);
            if (!nsfwResult.IsSuccessful)
            {
                await DeleteNewlyUploadedFileAsync(newBlobName, cancellationToken);
                return nsfwResult.ToResult<Post>(default!);
            }

            var post = new Post
            {
                Caption = request.Caption,
                Url = uri.ToString(),
                AuthorId = UserId
            };

            return await CreatePostAsync(post, cancellationToken);
        }
        catch (Exception e)
        {
            return Result<Post>.Failure("Something unexpected occurred.", [e.ToString()], 500);
        }
    }

    private async Task<ValidationResult> ValidateInputAsync(CreatePostCommand request,
        CancellationToken cancellationToken)
    {
        return await validator.ValidateAsync(request, cancellationToken);
    }

    private async Task DeleteNewlyUploadedFileAsync(string blobName, CancellationToken cancellationToken)
    {
        await mediator.Send(
            new DeleteFileFromStorageCommand(blobName, StorageContainer),
            cancellationToken);
    }

    private async Task<Result<Uri>> UploadFileAsync(string blobName, IFormFile file,
        CancellationToken cancellationToken)
    {
        return await mediator.Send(new UploadFileToStorageCommand
        {
            ContainerName = StorageContainer,
            BlobName = blobName,
            ContentType = file.ContentType,
            Stream = file.OpenReadStream()
        }, cancellationToken);
    }

    private async Task<Result> ClassifyFileAsync(Uri uri, CancellationToken cancellationToken)
    {
        return await mediator.Send(new ClassifyImageCommand(uri), cancellationToken);
    }

    private async Task<Result<Post>> CreatePostAsync(Post post, CancellationToken cancellationToken)
    {
        var hashtags = await mediator.Send(new ExtractHashtagsCommand(post.Caption), cancellationToken);
        foreach (var hashtag in hashtags)
            post.Hashtags.Add(hashtag);

        db.Posts.Add(post);
        await db.SaveChangesAsync(cancellationToken);
        return Result<Post>.Success(post);
    }
}

public class CreatePostHandler(
    IHttpContextAccessor contextAccessor,
    DatabaseContext db,
    ISender mediator,
    IValidator<CreatePostCommand> validator)
    : RequestHandler(contextAccessor), IRequestHandler<CreatePostCommand, Result<Post>>
{
    private const string StorageContainer = "images";

    public async Task<Result<Post>> Handle(CreatePostCommand request, CancellationToken cancellationToken)
    {
        try
        {
            var validationResult = await ValidateInputAsync(request, cancellationToken);
            if (!validationResult.IsValid)
                return Result<Post>.Failure("Invalid input received.",
                    validationResult.ErrorMessages(), 400);

            var newBlobName = $"{Guid.NewGuid()}{request.File.GetExtensionType()}";
            var uploadResult = await UploadFileAsync(newBlobName, request.File, cancellationToken);

            if (!uploadResult.IsSuccessful)
                return uploadResult.ToResult(_ => new Post());

            var uri = uploadResult.Data;
            var nsfwResult = await ClassifyFileAsync(uri, cancellationToken);
            if (!nsfwResult.IsSuccessful)
            {
                await DeleteNewlyUploadedFileAsync(newBlobName, cancellationToken);
                return nsfwResult.ToResult<Post>(default!);
            }

            var post = new Post
            {
                Caption = request.Caption,
                Url = uri.ToString(),
                AuthorId = UserId
            };

            return await CreatePostAsync(post, cancellationToken);
        }
        catch (Exception e)
        {
            return Result<Post>.Failure("Something unexpected occurred.", [e.ToString()], 500);
        }
    }

    private async Task<ValidationResult> ValidateInputAsync(CreatePostCommand request,
        CancellationToken cancellationToken)
    {
        return await validator.ValidateAsync(request, cancellationToken);
    }

    private async Task DeleteNewlyUploadedFileAsync(string blobName, CancellationToken cancellationToken)
    {
        await mediator.Send(
            new DeleteFileFromStorageCommand(blobName, StorageContainer),
            cancellationToken);
    }

    private async Task<Result<Uri>> UploadFileAsync(string blobName, IFormFile file,
        CancellationToken cancellationToken)
    {
        return await mediator.Send(new UploadFileToStorageCommand
        {
            ContainerName = StorageContainer,
            BlobName = blobName,
            ContentType = file.ContentType,
            Stream = file.OpenReadStream()
        }, cancellationToken);
    }

    private async Task<Result> ClassifyFileAsync(Uri uri, CancellationToken cancellationToken)
    {
        return await mediator.Send(new ClassifyImageCommand(uri), cancellationToken);
    }

    private async Task<Result<Post>> CreatePostAsync(Post post, CancellationToken cancellationToken)
    {
        var hashtags = await mediator.Send(new ExtractHashtagsCommand(post.Caption), cancellationToken);
        foreach (var hashtag in hashtags)
            post.Hashtags.Add(hashtag);

        db.Posts.Add(post);
        await db.SaveChangesAsync(cancellationToken);
        return Result<Post>.Success(post);
    }
}