// Copyright (c) 2022- schick Informatik
// Description: Compares excel files and highlights changes
//

using System;
using System.IO;
using ClosedXML.Excel;

namespace ENI2.Excel
{

    /// <summary>
    /// Diese Klasse beinhaltet den von Anmeldungen unabhängigen Vergleich von Excel Sheets. Damit 
    /// können dann Updates von "außen" einfacher abgearbeitet werden. Zellen und sheets werden bei
    /// Aktualisierung bunt eingefärbt
    /// </summary>
    public static class ExcelComparer
    {
        private static readonly XLColor diffColor = XLColor.FromArgb(150, 150, 255); // blue

        private static bool GetSheetRange(IXLWorksheet sheet, out int lastUsedRow, out int lastUsedColumn)
        {
            try
            {
                var usedRange = sheet.RangeUsed();
                if (usedRange != null)
                {
                    lastUsedRow = usedRange.RowCount();
                    lastUsedColumn = usedRange.ColumnCount();
                    return true;
                }
                else
                {
                    lastUsedColumn = 0;
                    lastUsedRow = 0;
                    return false;
                }
            }
            catch (Exception)
            {
                lastUsedColumn = 0;
                lastUsedRow = 0;
                return false;
            }
        }        

        public static string Compare(string sourcePath, string targetPath, string comparisonFileName, out string errorMessage)
        {
            errorMessage = "";
            int counter = 0;

            try
            {
                File.Copy(targetPath, comparisonFileName, true);

                using (var sourceWorkbook = new XLWorkbook(sourcePath))
                using (var comparisonWorkbook = new XLWorkbook(comparisonFileName))
                {
                    // Es werden Zellen der "used range" miteinander verglichen
                    foreach (var sourceSheet in sourceWorkbook.Worksheets)
                    {
                        IXLWorksheet targetSheet = null;
                        foreach (var sheet in comparisonWorkbook.Worksheets)
                        {
                            if (sourceSheet.Name.Equals(sheet.Name))
                            {
                                targetSheet = sheet;
                                break;
                            }
                        }

                        if (targetSheet == null) continue;
                        System.Diagnostics.Trace.WriteLine(string.Format("Processing sheet {0}", targetSheet.Name));

                        if (GetSheetRange(sourceSheet, out int sourceRows, out int sourceCols) && GetSheetRange(targetSheet, out int targetRows, out int targetCols))
                        {
                            int maxRows = Math.Max(sourceRows, targetRows);
                            int maxCols = Math.Max(sourceCols, targetCols);

                            for (int rowidx = 1; rowidx <= maxRows; rowidx++)
                            {
                                for (int colidx = 1; colidx <= maxCols; colidx++)
                                {
                                    string sourceText = null;
                                    string targetText = null;

                                    // Get source cell value
                                    if (rowidx <= sourceRows && colidx <= sourceCols)
                                    {
                                        var sourceCell = sourceSheet.Cell(rowidx, colidx);
                                        if (!sourceCell.IsEmpty())
                                        {
                                            sourceText = sourceCell.GetString();
                                        }
                                    }

                                    // Get target cell value
                                    if (rowidx <= targetRows && colidx <= targetCols)
                                    {
                                        var targetCell = targetSheet.Cell(rowidx, colidx);
                                        if (!targetCell.IsEmpty())
                                        {
                                            targetText = targetCell.GetString();
                                        }
                                    }

                                    if (sourceText == null)
                                    {
                                        if (targetText != null)
                                        {
                                            var cellToHighlight = targetSheet.Cell(rowidx, colidx);
                                            cellToHighlight.Style.Fill.BackgroundColor = diffColor;
                                            counter++;
                                        }
                                    }
                                    else if (targetText == null)
                                    {
                                        if (sourceText != null)
                                        {
                                            var cellToHighlight = targetSheet.Cell(rowidx, colidx);
                                            cellToHighlight.Style.Fill.BackgroundColor = diffColor;
                                            counter++;
                                        }
                                    }
                                    else if ((sourceText != null) && (targetText != null))
                                    {
                                        if (!sourceText.Equals(targetText))
                                        {
                                            var cellToHighlight = targetSheet.Cell(rowidx, colidx);
                                            cellToHighlight.Style.Fill.BackgroundColor = diffColor;
                                            counter++;
                                        }
                                    }
                                }
                            }
                        }
                        else
                        {
                            errorMessage = "failed to get sheet ranges";
                        }
                    }

                    comparisonWorkbook.SaveAs(comparisonFileName);
                }
                errorMessage = string.Format("{0} differences found", counter);
            }
            catch (Exception ex)
            {
                errorMessage = ex.Message;
            }

            return comparisonFileName;
        }
    }
}