FileShare/FileShare-Services/Services/FileLibrary/ThumbnailStreamService.cs

using FileShare_EFCore.Database;
using FileShare_Services.Core;
using Microsoft.EntityFrameworkCore;

namespace FileShare_Services.Services.FileLibrary
{
    /// <summary>
    /// 缩略图流服务接口，根据缩略图 ID 返回文件流响应。
    /// </summary>
    public interface IThumbnailStreamService
    {
        /// <summary>
        /// 根据缩略图记录 ID 获取缩略图文件流响应。
        /// </summary>
        /// <param name="id">缩略图记录 ID。</param>
        /// <param name="cancellationToken">取消令牌。</param>
        /// <returns>文件流响应，不存在或文件丢失时返回 null。</returns>
        Task<FileStreamResponse?> GetThumbnailAsync(int id, CancellationToken cancellationToken = default);
    }

    /// <summary>
    /// 缩略图流服务实现，从数据库查找缩略图映射并返回对应的物理文件流。
    /// </summary>
    public sealed class ThumbnailStreamService(AppDataContext db, IVideoThumbnailService thumbnails) : IThumbnailStreamService
    {
        /// <inheritdoc />
        public async Task<FileStreamResponse?> GetThumbnailAsync(int id, CancellationToken cancellationToken = default)
        {
            var thumbnail = await db.ManagedThumbnailMaps
                .AsNoTracking()
                .FirstOrDefaultAsync(item => item.Id == id, cancellationToken);

            if (thumbnail is null)
            {
                return null;
            }

            var absolutePath = thumbnails.GetAbsolutePath(thumbnail.RelativePath);
            if (!File.Exists(absolutePath))
            {
                return null;
            }

            return new FileStreamResponse(
                absolutePath,
                Path.GetFileName(absolutePath),
                thumbnail.ContentType,
                File.GetLastWriteTimeUtc(absolutePath));
        }
    }
}