using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Spreadsheet;

namespace AxCopilot.Services.Agent;

/// <summary>XLSX 파일을 HTML 테이블로 변환하여 WebView2에서 미리보기합니다.</summary>
internal static class XlsxToHtmlConverter
{
    private const int MaxRows = 500;
    private const int MaxCols = 50;

    public static string Convert(string xlsxPath)
    {
        try
        {
            using var doc = SpreadsheetDocument.Open(xlsxPath, false);
            var workbookPart = doc.WorkbookPart;
            if (workbookPart == null)
                return WrapHtml("<p style='color:#888'>스프레드시트 내용이 없습니다.</p>");

            var sheets = workbookPart.Workbook?.Sheets?.Elements<Sheet>().ToList();
            if (sheets == null || sheets.Count == 0)
                return WrapHtml("<p style='color:#888'>시트가 없습니다.</p>");

            var sharedStrings = workbookPart.SharedStringTablePart?.SharedStringTable;
            var sb = new StringBuilder();

            // 시트 탭 UI
            if (sheets.Count > 1)
            {
                sb.AppendLine("<div class='sheet-tabs'>");
                for (int i = 0; i < sheets.Count; i++)
                {
                    var name = sheets[i].Name?.Value ?? $"Sheet{i + 1}";
                    var activeClass = i == 0 ? " active" : "";
                    sb.AppendLine($"<button class='sheet-tab{activeClass}' onclick='showSheet({i})'>{Escape(name)}</button>");
                }
                sb.AppendLine("</div>");
            }

            // 시트별 테이블
            for (int si = 0; si < sheets.Count; si++)
            {
                var sheet = sheets[si];
                var partId = sheet.Id?.Value;
                if (string.IsNullOrEmpty(partId)) continue;

                WorksheetPart sheetPart;
                try { sheetPart = (WorksheetPart)workbookPart.GetPartById(partId); }
                catch { continue; }

                var display = si == 0 ? "block" : "none";
                sb.AppendLine($"<div class='sheet-content' id='sheet-{si}' style='display:{display}'>");
                sb.AppendLine(RenderSheet(sheetPart, sharedStrings));
                sb.AppendLine("</div>");
            }

            return WrapHtml(sb.ToString());
        }
        catch (Exception ex)
        {
            return WrapHtml($"<p style='color:#e53e3e'>XLSX 파싱 오류: {Escape(ex.Message)}</p>");
        }
    }

    private static string RenderSheet(WorksheetPart sheetPart, SharedStringTable? sharedStrings)
    {
        var sheetData = sheetPart.Worksheet?.GetFirstChild<SheetData>();
        if (sheetData == null)
            return "<p style='color:#888'>시트 데이터가 없습니다.</p>";

        var rows = sheetData.Elements<Row>().Take(MaxRows + 1).ToList();
        if (rows.Count == 0)
            return "<p style='color:#888'>데이터가 없습니다.</p>";

        // 병합 셀 정보
        var mergeCells = sheetPart.Worksheet?.GetFirstChild<MergeCells>()
            ?.Elements<MergeCell>().ToList() ?? new List<MergeCell>();
        var mergeMap = BuildMergeMap(mergeCells);

        var sb = new StringBuilder();
        sb.AppendLine("<div style='overflow-x:auto'><table>");

        var rowIndex = 0;
        foreach (var row in rows.Take(MaxRows))
        {
            rowIndex++;
            sb.Append(rowIndex == 1 ? "<tr class='header'>" : "<tr>");

            var cells = row.Elements<Cell>().Take(MaxCols).ToList();
            foreach (var cell in cells)
            {
                var cellRef = cell.CellReference?.Value ?? "";
                if (mergeMap.TryGetValue(cellRef, out var merge))
                {
                    if (merge.IsHidden) continue; // 병합된 셀 건너뛰기
                    var spanAttrs = "";
                    if (merge.ColSpan > 1) spanAttrs += $" colspan='{merge.ColSpan}'";
                    if (merge.RowSpan > 1) spanAttrs += $" rowspan='{merge.RowSpan}'";
                    var tag = rowIndex == 1 ? "th" : "td";
                    sb.Append($"<{tag}{spanAttrs}>{Escape(GetCellValue(cell, sharedStrings))}</{tag}>");
                }
                else
                {
                    var tag = rowIndex == 1 ? "th" : "td";
                    sb.Append($"<{tag}>{Escape(GetCellValue(cell, sharedStrings))}</{tag}>");
                }
            }
            sb.AppendLine("</tr>");
        }

        sb.AppendLine("</table></div>");

        if (rows.Count > MaxRows)
            sb.AppendLine($"<p class='truncated'>... {MaxRows}행까지 표시 (전체 데이터는 Excel에서 확인)</p>");

        return sb.ToString();
    }

    private static string GetCellValue(Cell cell, SharedStringTable? sharedStrings)
    {
        var value = cell.CellValue?.Text ?? cell.InnerText ?? "";
        if (string.IsNullOrEmpty(value)) return "";

        if (cell.DataType?.Value == CellValues.SharedString && sharedStrings != null)
        {
            if (int.TryParse(value, out var idx) && idx >= 0 && idx < sharedStrings.Count())
                return sharedStrings.ElementAt(idx).InnerText;
        }

        return value;
    }

    private sealed record MergeCellInfo(int ColSpan, int RowSpan, bool IsHidden);

    private static Dictionary<string, MergeCellInfo> BuildMergeMap(List<MergeCell> mergeCells)
    {
        var map = new Dictionary<string, MergeCellInfo>(StringComparer.OrdinalIgnoreCase);
        foreach (var mc in mergeCells)
        {
            var range = mc.Reference?.Value;
            if (string.IsNullOrEmpty(range)) continue;
            var parts = range.Split(':');
            if (parts.Length != 2) continue;

            var (startCol, startRow) = ParseCellRef(parts[0]);
            var (endCol, endRow) = ParseCellRef(parts[1]);
            var colSpan = endCol - startCol + 1;
            var rowSpan = endRow - startRow + 1;

            // 시작 셀: span 정보 포함
            map[parts[0]] = new MergeCellInfo(colSpan, rowSpan, false);

            // 나머지 셀: 숨김
            for (int r = startRow; r <= endRow; r++)
            for (int c = startCol; c <= endCol; c++)
            {
                var cellRef = ColumnIndexToLetter(c) + r;
                if (!string.Equals(cellRef, parts[0], StringComparison.OrdinalIgnoreCase))
                    map[cellRef] = new MergeCellInfo(1, 1, true);
            }
        }
        return map;
    }

    private static (int Col, int Row) ParseCellRef(string cellRef)
    {
        int col = 0, i = 0;
        while (i < cellRef.Length && char.IsLetter(cellRef[i]))
        {
            col = col * 26 + (char.ToUpper(cellRef[i]) - 'A' + 1);
            i++;
        }
        int.TryParse(cellRef[i..], out var row);
        return (col, row);
    }

    private static string ColumnIndexToLetter(int col)
    {
        var sb = new StringBuilder();
        while (col > 0)
        {
            col--;
            sb.Insert(0, (char)('A' + col % 26));
            col /= 26;
        }
        return sb.ToString();
    }

    private static string Escape(string text)
        => System.Net.WebUtility.HtmlEncode(text);

    private static string WrapHtml(string body)
    {
        return $@"<!DOCTYPE html>
<html lang='ko'>
<head>
<meta charset='UTF-8'>
<style>
  * {{ margin: 0; padding: 0; box-sizing: border-box; }}
  body {{ font-family: 'Noto Sans KR', 'Segoe UI', sans-serif; background: #fff; color: #1a1a1a;
         line-height: 1.5; padding: 16px; font-size: 12.5px; }}
  .sheet-tabs {{ display: flex; gap: 2px; margin-bottom: 12px; border-bottom: 2px solid #e5e7eb; padding-bottom: 0; }}
  .sheet-tab {{ padding: 6px 14px; border: none; background: #f3f4f6; cursor: pointer;
                font-size: 11.5px; border-radius: 6px 6px 0 0; color: #6b7280; }}
  .sheet-tab.active {{ background: #fff; color: #2563eb; font-weight: 600;
                       border-bottom: 2px solid #2563eb; margin-bottom: -2px; }}
  .sheet-tab:hover {{ background: #e5e7eb; }}
  table {{ width: 100%; border-collapse: collapse; font-size: 12px; }}
  th, td {{ border: 1px solid #d1d5db; padding: 5px 8px; text-align: left; white-space: nowrap; }}
  th, .header td {{ background: #f3f4f6; font-weight: 600; position: sticky; top: 0; }}
  tr:nth-child(even) {{ background: #f9fafb; }}
  .truncated {{ color: #9ca3af; font-size: 11px; margin-top: 8px; font-style: italic; }}
</style>
<script>
function showSheet(idx) {{
  document.querySelectorAll('.sheet-content').forEach(el => el.style.display = 'none');
  document.querySelectorAll('.sheet-tab').forEach(el => el.classList.remove('active'));
  document.getElementById('sheet-' + idx).style.display = 'block';
  document.querySelectorAll('.sheet-tab')[idx].classList.add('active');
}}
</script>
</head>
<body>
{body}
</body>
</html>";
    }
}