fix reading comment from excel file

Sources/CoreXLSX/Comments.swift

@@ -36,12 +36,25 @@ public struct Comment: Codable, Equatable {
     case reference = "ref"
     case text
   }
+
+  public var plain: String? {
+      return self.text.r?.t
+  }
 }
 
 public struct Text: Codable, Equatable {
-  public let plain: String?
+  public let r: R?
 
   enum CodingKeys: String, CodingKey {
-    case plain = "t"
+    case r = "r"
   }
 }
+
+public struct R: Codable, Equatable {
+  public let t: String?
+
+  enum CodingKeys: String, CodingKey {
+    case t = "t"
+  }
+}
+

Sources/CoreXLSX/Relationships.swift

@@ -130,6 +130,14 @@ public struct Relationship: Codable, Equatable {
       """
       http://purl.oclc.org/ooxml/officeDocument/relationships/extendedProperties
       """
+    case sheetComment =
+      """
+      http://schemas.openxmlformats.org/officeDocument/2006/relationships/comments
+      """
+    case sheetVmlDrawing =
+      """
+      http://schemas.openxmlformats.org/officeDocument/2006/relationships/vmlDrawing
+      """
   }
 
   /// The identifier for this entity.

Sources/CoreXLSX/XLSXFile.swift

@@ -157,15 +157,23 @@ public class XLSXFile {
        let worksheetIdRange = Range(match.range(at: 1), in: path)
     {
       let worksheetId = path[worksheetIdRange]
-      return "xl/comments\(worksheetId).xml"
+        decoder.keyDecodingStrategy = .convertFromCapitalized
+        if let relationships = try? parseEntry("xl/worksheets/_rels/sheet\(worksheetId).xml.rels", Relationships.self) {
+            if let commentRelationship = relationships.items.filter({  $0.type == .sheetComment }).first {
+                return "xl/\(commentRelationship.target.replacingOccurrences(of: "../", with: ""))"
+            }
+        }
+      return ""//"xl/comments\(worksheetId).xml"
     }
 
     throw CoreXLSXError.unsupportedWorksheetPath
   }
 
   public func parseComments(forWorksheet path: String) throws -> Comments {
     let commentsPath = try buildCommentsPath(forWorksheet: path)
-
+    if commentsPath.isEmpty {
+      return Comments(commentList: CommentList(items: []))
+    }
     decoder.keyDecodingStrategy = .useDefaultKeys
 
     return try parseEntry(commentsPath, Comments.self)

Tests/CoreXLSXTests/Comments.swift

@@ -25,7 +25,7 @@ final class CommentsTests: XCTestCase {
     }
     let paths = try file.parseWorksheetPaths()
     let comments = try file.parseComments(forWorksheet: paths[0])
-    XCTAssertEqual(comments.commentList.itemsByReference["A1"]?.text.plain,
+    XCTAssertEqual(comments.commentList.itemsByReference["A1"]?.plain,
                    "my note")
   }
 }