using Laservall.Solidworks.Model;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Laservall.Solidworks.Server.Handlers
{
    internal sealed class ExportHandler
    {
        private readonly Func<BomLoadResult> _getLastResult;
        private readonly IBomDataProvider _dataProvider;

        public ExportHandler(Func<BomLoadResult> getLastResult, IBomDataProvider dataProvider)
        {
            _getLastResult = getLastResult;
            _dataProvider = dataProvider;
        }

        public async Task HandleExport(HttpListenerContext context, CancellationToken ct)
        {
            var result = _getLastResult();
            if (result == null || result.Items == null || result.Items.Count == 0)
            {
                context.Response.StatusCode = 404;
                byte[] err = Encoding.UTF8.GetBytes("{\"error\":\"No BOM data loaded\"}");
                context.Response.ContentType = "application/json; charset=utf-8";
                context.Response.ContentLength64 = err.Length;
                await context.Response.OutputStream.WriteAsync(err, 0, err.Length, ct);
                context.Response.Close();
                return;
            }

            bool isFlatView = context.Request.QueryString["flat"] == "true";
            var items = isFlatView ? _dataProvider.GetFlatBomItems(result.Items) : result.Items;
            var settings = result.Settings;

            var csv = BuildCsv(items, result.DynamicKeys, settings, isFlatView);

            // UTF-8 BOM for Excel compatibility
            byte[] bom = new byte[] { 0xEF, 0xBB, 0xBF };
            byte[] csvBytes = Encoding.UTF8.GetBytes(csv);
            byte[] body = new byte[bom.Length + csvBytes.Length];
            Buffer.BlockCopy(bom, 0, body, 0, bom.Length);
            Buffer.BlockCopy(csvBytes, 0, body, bom.Length, csvBytes.Length);

            context.Response.StatusCode = 200;
            context.Response.ContentType = "text/csv; charset=utf-8";
            context.Response.Headers.Set("Content-Disposition", "attachment; filename=\"BOM_Export.csv\"");
            context.Response.ContentLength64 = body.Length;
            await context.Response.OutputStream.WriteAsync(body, 0, body.Length, ct);
            context.Response.Close();
        }

        private static string BuildCsv(
            List<BomItemModel> items,
            List<string> dynamicKeys,
            BomSettings settings,
            bool isFlatView)
        {
            var builtInDefs = new List<(string Name, Func<BomItemModel, string> Getter)>
            {
                ("层级", item => item.LevelDisplay ?? ""),
                ("图号", item => item.DrawingNo ?? ""),
                ("零件名称", item => item.ConfigName ?? ""),
                ("属性", item => item.Classification ?? ""),
                ("材料", item => item.MaterialProp ?? ""),
                ("材质", item => item.Material ?? ""),
                ("数量", item => item.Quantity.ToString()),
                ("装配体", item => item.IsAssembly ? "是" : "否"),
                ("外购件", item => item.IsOutSourcing ? "是" : "否")
            };

            var exportBuiltIns = builtInDefs
                .Where(d => settings.IsColumnExport(d.Name))
                .Where(d => !isFlatView || (d.Name != "层级" && d.Name != "装配体"))
                .ToList();

            var exportDynamicKeys = (dynamicKeys ?? new List<string>())
                .Where(k => settings.IsColumnExport(k))
                .ToList();

            var sb = new StringBuilder();

            var headers = exportBuiltIns.Select(d => d.Name).Concat(exportDynamicKeys).ToList();
            sb.AppendLine(string.Join(",", headers.Select(EscapeCsvField)));

            foreach (var item in items)
            {
                var fields = new List<string>();
                foreach (var def in exportBuiltIns)
                {
                    fields.Add(def.Getter(item));
                }
                foreach (var key in exportDynamicKeys)
                {
                    fields.Add(item.GetProp(key));
                }
                sb.AppendLine(string.Join(",", fields.Select(EscapeCsvField)));
            }

            return sb.ToString();
        }

        private static string EscapeCsvField(string field)
        {
            if (string.IsNullOrEmpty(field)) return "";
            if (field.Contains(",") || field.Contains("\"") || field.Contains("\n"))
            {
                return "\"" + field.Replace("\"", "\"\"") + "\"";
            }
            return field;
        }
    }
}