using System.Buffers;
using System.IO.Pipelines;

namespace Dpz.Core.WebApi.Middleware;

/// <summary>
/// 记录 HTTP 请求参数
/// </summary>
/// <param name="next"></param>
/// <param name="diagnosticContext"></param>
public class HttpRequestRecord(RequestDelegate next, IDiagnosticContext diagnosticContext)
{
    /// <summary>
    ///
    /// </summary>
    /// <param name="httpContext"></param>
    public async Task InvokeAsync(HttpContext httpContext)
    {
        await EnrichFromRequestAsync(httpContext.Request);

        await next.Invoke(httpContext);
    }

    private async Task EnrichFromRequestAsync(HttpRequest request)
    {
        if (request.Query is { Count: > 0 })
        {
            diagnosticContext.Set("QueryString", request.Query);
        }

        var bodyContent = await GetBodyContentAsync(request.BodyReader);
        if (bodyContent != string.Empty)
        {
            diagnosticContext.Set("RequestBody", bodyContent);
        }
    }

    /// <summary>
    /// 读取 http body
    /// 如果 body 超过 1 &lt;&lt; 10 字节，则不记录 body
    /// </summary>
    /// <param name="reader"></param>
    /// <returns></returns>
    private static async Task<string> GetBodyContentAsync(PipeReader reader)
    {
        var result = new StringBuilder();
        const long maxLength = 1 << 10;
        long totalLength = 0;

        while (true)
        {
            var readResult = await reader.ReadAsync();
            var buffer = readResult.Buffer;
            // 如果 buffer 长度已经大于等于 maxLength，直接截取并返回
            if (buffer.Length >= maxLength)
            {
                var span = buffer.Slice(0, maxLength);
                AppendString(result, span);
                result.Append("...");
                reader.AdvanceTo(buffer.Start, buffer.GetPosition(maxLength));
                //await reader.CompleteAsync();
                break;
            }

            totalLength += buffer.Length;

            if (readResult.IsCompleted && buffer.Length > 0)
            {
                AppendString(result, in buffer);
            }

            reader.AdvanceTo(buffer.Start, buffer.End);
            if (totalLength >= maxLength)
            {
                result.Append("...");
                break;
            }

            if (readResult.IsCompleted)
            {
                break;
            }
        }

        return result.ToString();
    }

    private static void AppendString(
        StringBuilder result,
        in ReadOnlySequence<byte> readOnlySequence
    )
    {
        var span = readOnlySequence.IsSingleSegment
            ? readOnlySequence.First.Span
            : readOnlySequence.ToArray().AsSpan();
        result.Append(Encoding.UTF8.GetString(span));
    }
}