using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using FastEndpoints;
using Npgsql;
using ExcelDataReader;
using Microsoft.Extensions.Configuration;

namespace QuantEngine.Web.Endpoints;

/// <summary>
/// BFF FastEndpoints for streaming Excel file upload and importing to PostgreSQL using COPY binary protocol.
/// SOLID: Single Responsibility for streaming large files to prevent OOM.
/// </summary>
public class BulkInsertMarketExcelEndpoint : EndpointWithoutRequest
{
    private readonly string _connectionString;

    public BulkInsertMarketExcelEndpoint(IConfiguration config)
    {
        _connectionString = config.GetConnectionString("DefaultConnection") 
            ?? throw new ArgumentNullException("ConnectionStrings__DefaultConnection");
        System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);
    }

    public override void Configure()
    {
        Post("/api/admin/market/upload-excel-stream");
        AllowFileUploads();
        AllowAnonymous();
    }

    public override async Task HandleAsync(CancellationToken ct)
    {
        if (Files.Count == 0)
        {
            await SendAsync(new { success = false, message = "업로드된 파일이 없습니다." }, 400, ct);
            return;
        }

        var file = Files[0];
        using var fileStream = file.OpenReadStream();
        using var reader = ExcelReaderFactory.CreateReader(fileStream);

        using var conn = new NpgsqlConnection(_connectionString);
        await conn.OpenAsync(ct);

        using var writer = await conn.BeginBinaryImportAsync(
            "COPY quantengine.market_raw_history (ticker, as_of_date, close_price, nav_price, disparate_ratio, raw_payload, provenance) FROM STDIN (FORMAT BINARY)",
            ct
        );

        bool isHeader = true;
        int processedRows = 0;

        while (reader.Read())
        {
            if (isHeader)
            {
                isHeader = false;
                continue;
            }

            string ticker = reader.GetValue(0)?.ToString() ?? string.Empty;
            string asOfDate = reader.GetValue(1)?.ToString() ?? string.Empty;
            decimal closePrice = Convert.ToDecimal(reader.GetValue(2) ?? 0);
            decimal navPrice = Convert.ToDecimal(reader.GetValue(3) ?? 0);
            decimal disparateRatio = navPrice > 0 ? (closePrice - navPrice) / navPrice : 0;

            if (string.IsNullOrWhiteSpace(ticker) || ticker.Length < 6) continue;

            await writer.StartRowAsync(ct);
            await writer.WriteAsync(ticker, ct);
            await writer.WriteAsync(asOfDate, ct);
            await writer.WriteAsync(closePrice, ct);
            await writer.WriteAsync(navPrice, ct);
            await writer.WriteAsync(disparateRatio, ct);
            await writer.WriteAsync("{}", ct);
            await writer.WriteAsync("{\"source\": \"excel_stream_uploader\"}", ct);

            processedRows++;
        }

        await writer.CompleteAsync(ct);
        await SendAsync(new { success = true, count = processedRows, message = "성공적으로 스트리밍 적재 완료되었습니다." }, cancellation: ct);
    }
}