using System.Text;
using FozFc.Api.Configuration;
using MongoDB.Bson;

namespace FozFc.Api.Infrastructure.Storage;

/// <summary>
/// Stores uploads on the local disk (the container's <c>uploads/</c> volume) and
/// serves them from <c>/uploads/&lt;name&gt;</c>.
/// </summary>
public sealed class LocalFileStorage : IFileStorage
{
    public const string UploadsDirectory = "uploads";
    public const string PublicPathPrefix = "/uploads/";

    private readonly AppOptions _options;

    public LocalFileStorage(AppOptions options)
    {
        _options = options;
        Directory.CreateDirectory(UploadsDirectory);
    }

    public async Task<StoredFile> SaveAsync(Stream content, string originalFileName, CancellationToken ct = default)
    {
        var storedName = $"{ObjectId.GenerateNewId()}_{Sanitize(originalFileName)}";
        var fullPath = Path.Combine(UploadsDirectory, storedName);

        await using (var file = File.Create(fullPath))
        {
            await content.CopyToAsync(file, ct);
        }

        var url = $"{_options.PublicBaseUrl}{PublicPathPrefix}{storedName}";
        return new StoredFile(url, $"{PublicPathPrefix}{storedName}", storedName);
    }

    private static string Sanitize(string fileName)
    {
        var name = Path.GetFileName(fileName);
        var builder = new StringBuilder(name.Length);
        foreach (var ch in name)
        {
            builder.Append(char.IsLetterOrDigit(ch) || ch is '.' or '-' or '_' ? ch : '_');
        }
        var result = builder.ToString();
        return result.Length == 0 ? "file" : result;
    }
}