using System.Text;
using File.Application.Common;
using File.Application.Features.Files.Handlers;
using File.Application.Features.Files.Queries;
using File.Infrastructure.Storage;
using FluentAssertions;
using Moq;
using Xunit;

namespace BuildFlow.File.Tests;

/// <summary>
/// 下载文件查询处理器单元测试。覆盖正常下载、空内容两个场景。
/// Mock IS3StorageService 隔离 S3 外部依赖。
/// </summary>
public class DownloadFileQueryHandlerTests
{
    /// <summary>测试用 bucket 解析器，固定返回 "test-bucket"。</summary>
    private static IBucketResolver BucketResolver()
    {
        var mock = new Mock<IBucketResolver>();
        mock.Setup(r => r.GetDefaultBucketAsync(It.IsAny<CancellationToken>())).ReturnsAsync("test-bucket");
        return mock.Object;
    }

    /// <summary>创建 Mock S3 + Handler。</summary>
    private static (Mock<IS3StorageService> s3Mock, DownloadFileQueryHandler handler) Setup(string content = "hello world")
    {
        var s3Mock = new Mock<IS3StorageService>();
        var stream = new MemoryStream(Encoding.UTF8.GetBytes(content));
        s3Mock
            .Setup(x => x.DownloadFileAsync("test-bucket", "test-key", It.IsAny<CancellationToken>()))
            .ReturnsAsync((stream, "text/plain"));

        var handler = new DownloadFileQueryHandler(s3Mock.Object, BucketResolver());
        return (s3Mock, handler);
    }

    [Fact]
    public async Task DownloadFile_WithValidPath_ReturnsContent()
    {
        // Arrange
        var (s3Mock, handler) = Setup("hello world");

        // Act
        var result = await handler.Handle(
            new DownloadFileQuery("test-key"),
            CancellationToken.None);

        // Assert — 返回的是 S3 原始流，透传给调用方；ContentType 取 S3 返回的真实类型
        result.Should().NotBeNull();
        result.Stream.Should().NotBeNull();
        result.ContentType.Should().Be("text/plain");
        result.FileName.Should().Be("test-key");
        s3Mock.Verify(x => x.DownloadFileAsync("test-bucket", "test-key", It.IsAny<CancellationToken>()), Times.Once);
    }

    [Fact]
    public async Task DownloadFile_S3ReturnsEmpty_ReturnsReadableEmptyStream()
    {
        // Arrange — DownloadFileQueryHandler 透传 S3 流，空内容对应空 MemoryStream
        var s3Mock = new Mock<IS3StorageService>();
        var emptyStream = new MemoryStream();
        s3Mock
            .Setup(x => x.DownloadFileAsync(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<CancellationToken>()))
            .ReturnsAsync((emptyStream, "application/octet-stream"));

        var handler = new DownloadFileQueryHandler(s3Mock.Object, BucketResolver());

        // Act
        var result = await handler.Handle(
            new DownloadFileQuery("test-key"),
            CancellationToken.None);

        // Assert — Handler 透传空流，长度为 0
        result.Stream.Should().NotBeNull();
        result.Stream.Length.Should().Be(0);
    }
}