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

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Drawing;

namespace ENI2.Excel
{
    public static class ExcelComparer
    {
        private static int diffColor = ColorTranslator.ToOle(Color.FromArgb(150, 150, 255)); // blue

        public static string Compare(string sourcePath, string targetPath, out string errorMessage)
        {
            string fileName = Path.GetTempPath() + Guid.NewGuid().ToString() + ".xlsx";
            errorMessage = "";
            int counter = 0;

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

                // 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++;
                        }
                    }
                    if (targetText == null)
                    {
                        if (sourceText != null)
                        {
                            comparison.Colorize(name, diffColor);
                            counter++;
                        }
                    }
                    if ((sourceText != null) && (targetText != null))
                    {
                        if (!sourceText.Equals(targetText))
                        {
                            // turn cell blue
                            comparison.Colorize(name, diffColor);
                            counter++;
                        }
                    }
                }
                comparison.Save(fileName);
                errorMessage = string.Format("{0} differences found", counter);
            }
            catch (Exception ex)
            {
                errorMessage = ex.Message;
            }

            return fileName;
        }

    }
}