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

using System;
using System.IO;
using System.Drawing;
using Microsoft.Office.Interop.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 int diffColor = ColorTranslator.ToOle(Color.FromArgb(150, 150, 255)); // blue

        private static bool GetSheetRange(Worksheet sheet, out int lastUsedRow, out int lastUsedColumn)
        {
            try
            {
                // sheet.Columns.ClearFormats();
                // sheet.Rows.ClearFormats();
                Range usedRange = sheet.UsedRange;
                lastUsedRow = usedRange.Rows.Count;
                lastUsedColumn = usedRange.Columns.Count;

                /*
                Range last = sheet.Cells.SpecialCells(XlCellType.xlCellTypeLastCell, Type.Missing);
                Range range = sheet.get_Range("A1", last);

                lastUsedRow = last.Row;
                lastUsedColumn = last.Column;
                */

                return true;
            }
            catch(Exception)
            {
                lastUsedColumn = 0;
                lastUsedRow = 0;
                return false;
            }
        }

        private static string GetExcelColumnName(int columnNumber)
        {
            string columnName = "";

            while (columnNumber > 0)
            {
                int modulo = (columnNumber - 1) % 26;
                columnName = Convert.ToChar('A' + modulo) + columnName;
                columnNumber = (columnNumber - modulo) / 26;
            }

            return columnName;
        }

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

            try
            {
                File.Copy(targetPath, comparisonFileName);
                ExcelReader source = new ExcelReader(sourcePath, true, false);
                ExcelReader comparison = new ExcelReader(comparisonFileName, false, false);

                /* erste Variante Vergleich über Namen der Zellen
                 
                // loop through named cells
                foreach (string name in comparison.NameDict.Keys)
                {
                    if (!source.NameDict.ContainsKey(name)) continue;
                    string sourceText = source.ReadText(name);
                    string targetText = comparison.ReadText(name);

                    if (sourceText == null)
                    {
                        if (targetText != null)
                        {
                            comparison.Colorize(name, diffColor);
                            counter++;
                        }
                    }
                    else if (targetText == null)
                    {
                        if (sourceText != null)
                        {
                            comparison.Colorize(name, diffColor);
                            counter++;
                        }
                    }
                    else if ((sourceText != null) && (targetText != null))
                    {
                        if (!sourceText.Equals(targetText))
                        {
                            // turn cell blue
                            comparison.Colorize(name, diffColor);
                            counter++;
                        }
                    }
                }
                */

                // Zweite Version durch alle Sheets werden Zellen der "used range" miteinander verglichen

                foreach(Worksheet sourceSheet in source.Worksheets)
                {
                    Worksheet targetSheet = null;
                    foreach(Worksheet sheet in comparison.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))
                    {
                        // read source into 2 dim array
                        string rangeString = string.Format("A1:{0}{1}", GetExcelColumnName(Math.Max(sourceCols, targetCols)), Math.Max(sourceRows, targetRows));
                        object[,] sourceArray = sourceSheet.get_Range(rangeString).Value;
                        // read target into 2 dim array
                        object[,] targetArray = targetSheet.get_Range(rangeString).Value;

                        for (int rowidx = 1; rowidx <= Math.Max(sourceRows, targetRows); rowidx++)
                        {
                            for( int colidx = 1; colidx <= Math.Max(sourceCols, targetCols); colidx++)
                            {
                                string sourceText = null;
                                if(sourceArray[rowidx,colidx] != null) sourceText = sourceArray[rowidx,colidx].ToString();
                                string targetText = null;
                                if(targetArray[rowidx,colidx] != null) targetText = targetArray[rowidx, colidx].ToString();
                                
                                if (sourceText == null)
                                {
                                    if (targetText != null)
                                    {
                                        string targetRangeName = string.Format("{0}{1}", GetExcelColumnName(colidx), rowidx);
                                        comparison.Colorize(targetSheet.Range[targetRangeName], diffColor);
                                        counter++;
                                    }
                                }
                                else if (targetText == null)
                                {
                                    if (sourceText != null)
                                    {
                                        string targetRangeName = string.Format("{0}{1}", GetExcelColumnName(colidx), rowidx);
                                        comparison.Colorize(targetSheet.Range[targetRangeName], diffColor);
                                        counter++;
                                    }
                                }
                                else if ((sourceText != null) && (targetText != null))
                                {
                                    if (!sourceText.Equals(targetText))
                                    {
                                        string targetRangeName = string.Format("{0}{1}", GetExcelColumnName(colidx), rowidx);
                                        // turn cell blue
                                        comparison.Colorize(targetSheet.Range[targetRangeName], diffColor);
                                        counter++;
                                    }
                                }

                            }
                        }
                    }
                    else
                    {
                        errorMessage = "failed to get sheet ranges";
                    }
                }

                comparison.Save(comparisonFileName);
                source.Dispose();
                comparison.Dispose();
                errorMessage = string.Format("{0} differences found", counter);
            }
            catch (Exception ex)
            {
                errorMessage = ex.Message;
            }

            return comparisonFileName;
        }

    }
}