Comprehensive Revamp of the Workbook Class

- Overhauled the structure and functionality of the `Workbook` class for improved clarity and encapsulation:
    * Separated internal and public-facing members to provide a cleaner interface.
    * Initialized resources like `SpreadsheetDocument`, `WorkbookPart`, and `WorksheetPart` in constructors for consistent setup.

- Enhanced workbook creation and reading functionalities:
    * Introduced default constructor to create a new workbook with essential parts, and another constructor for reading from a file.
    * Added validation for file existence and non-empty paths.

- Incorporated worksheet management methods:
    * Added `AddSheet`, `RemoveSheet`, and `SyncWorksheets` to facilitate adding, removing, and syncing worksheets in the workbook.

- Optimized style management:
    * Integrated a `StyleUtility` member to handle style-related tasks.
    * Added `UpdateDefaultStyle` and `CreateStyle` methods for better style handling.
    * Validated hex colors and other style parameters.

- Improved document properties access:
    * Provided getters and setters for built-in document properties, allowing direct interaction with essential metadata.

- Enhanced saving capabilities:
    * Implemented multiple save methods to support saving to a specified file path, a stream, or the original file path.
    * Ensured memory streams are written back to the files appropriately.

- Implemented IDisposable pattern:
    * Properly released resources with the `Dispose` method to ensure efficient memory management.

Overall, this revamp focuses on making the `Workbook` class more efficient, modular, and user-friendly.

Author: Fahad Adeel

FileFormat.Cells/BuiltInDocumentProperties.cs

@@ -0,0 +1,17 @@
+using System;
+namespace FileFormat.Cells
+{
+    public class BuiltInDocumentProperties
+    {
+        public string Author { get; set; }
+        public string Title { get; set; }
+        public DateTime CreatedDate { get; set; }
+        public string ModifiedBy { get; set; }
+        public DateTime ModifiedDate { get; set; }
+        public string Subject { get; set; }
+
+        // ... other properties as needed ...
+    }
+
+}
+

FileFormat.Cells/CellStyle.cs

@@ -0,0 +1,80 @@
+using DocumentFormat.OpenXml;
+using DocumentFormat.OpenXml.Packaging;
+using DocumentFormat.OpenXml.Spreadsheet;
+using System;
+
+public class StyleUtility
+{
+    private readonly WorkbookStylesPart stylesPart;
+    private readonly Stylesheet stylesheet;
+
+    public uint CreateDefaultStyle()
+    {
+        return CreateStyle("Arial", 12, "000000"); 
+    }
+
+    public StyleUtility(WorkbookStylesPart stylesPart)
+    {
+        this.stylesPart = stylesPart ?? throw new ArgumentNullException(nameof(stylesPart));
+        this.stylesheet = this.stylesPart.Stylesheet ?? new Stylesheet();
+
+        // Initialize Fonts, Fills, Borders, and CellFormats if they are null
+        this.stylesheet.Fonts = this.stylesheet.Fonts ?? new Fonts();
+        this.stylesheet.Fills = this.stylesheet.Fills ?? new Fills();
+        this.stylesheet.Borders = this.stylesheet.Borders ?? new Borders();
+        this.stylesheet.CellFormats = this.stylesheet.CellFormats ?? new CellFormats();
+    }
+
+    public uint CreateStyle(string fontName, double fontSize, string hexColor)
+    {
+        // Validate inputs
+        if (string.IsNullOrEmpty(fontName))
+            throw new ArgumentNullException(nameof(fontName));
+        if (fontSize <= 0)
+            throw new ArgumentOutOfRangeException(nameof(fontSize), "Font size must be greater than zero");
+        if (string.IsNullOrEmpty(hexColor) || !IsHexColor(hexColor))
+            throw new ArgumentException("Invalid hex color", nameof(hexColor));
+
+        // Create and append Font
+        var font = new Font(
+            new FontSize() { Val = fontSize },
+            new Color() { Rgb = new HexBinaryValue() { Value = hexColor } },
+            new FontName() { Val = fontName }
+        );
+        this.stylesheet.Fonts.Append(font);
+
+        // Create and append Fill
+        var fill = new Fill(new PatternFill() { PatternType = PatternValues.None });
+        this.stylesheet.Fills.Append(fill);
+
+        // Create and append Border
+        var border = new Border(new LeftBorder(), new RightBorder(), new TopBorder(), new BottomBorder(), new DiagonalBorder());
+        this.stylesheet.Borders.Append(border);
+
+        // Create and append CellFormat
+        var cellFormat = new CellFormat
+        {
+            FontId = new UInt32Value((uint)this.stylesheet.Fonts.ChildElements.Count - 1),
+            FillId = new UInt32Value((uint)this.stylesheet.Fills.ChildElements.Count - 1),
+            BorderId = new UInt32Value((uint)this.stylesheet.Borders.ChildElements.Count - 1)
+        };
+        this.stylesheet.CellFormats.Append(cellFormat);
+
+        return (uint)this.stylesheet.CellFormats.ChildElements.Count - 1;
+    }
+
+    private static bool IsHexColor(string color)
+    {
+        return System.Text.RegularExpressions.Regex.IsMatch(color, "^(#)?([0-9a-fA-F]{3})([0-9a-fA-F]{3})?$");
+    }
+
+
+    public void SaveStylesheet()
+    {
+        if (this.stylesPart.Stylesheet == null)
+        {
+            this.stylesPart.Stylesheet = this.stylesheet;
+        }
+        this.stylesheet.Save();
+    }
+}