Add TextLines.ReadOnly() method to get read-only collection

Author: Kapil Borle

Engine/Strings.resx

@@ -294,6 +294,9 @@
   <data name="TextLinesNoNullItem" xml:space="preserve">
     <value>Line element cannot be null.</value>
   </data>
+  <data name="TextLinesReadOnlyCollection" xml:space="preserve">
+    <value>Collection is read-only.</value>
+  </data>
   <data name="TextEditNoNullItem" xml:space="preserve">
     <value>Line element cannot be null.</value>
   </data>

Engine/TextLines.cs

@@ -30,6 +30,7 @@ public TextLines()
         {
             lines = new LinkedList<string>();
             Count = 0;
+            IsReadOnly = false;
             InvalidateLastAccessed();
         }
 
@@ -60,7 +61,7 @@ public TextLines(IEnumerable<string> inputLines) : this()
         /// <summary>
         /// If the object is ReadOnly or not.
         /// </summary>
-        public bool IsReadOnly => false;
+        public bool IsReadOnly { get; private set; }
 
         /// <summary>
         /// Sets or gets the element at the given index.
@@ -80,6 +81,19 @@ public string this[int index]
             }
         }
 
+        /// <summary>
+        /// Creates a readonly shallow copy.
+        /// </summary>
+        /// <returns>A readonly shallow copy of the current object.</returns>
+        public IList<string> ReadOnly()
+        {
+            var ret = new TextLines();
+            ret.IsReadOnly = true;
+            ret.Count = this.Count;
+            ret.lines = this.lines;
+            return ret;
+        }
+
         /// <summary>
         /// Adds the given string to the end of the list.
         /// </summary>
@@ -94,6 +108,7 @@ public void Add(string item)
         /// </summary>
         public void Clear()
         {
+            ValidateReadOnly();
             lines.Clear();
         }
 
@@ -154,6 +169,7 @@ public int IndexOf(string item)
         /// </summary>
         public void Insert(int index, string item)
         {
+            ValidateReadOnly();
             ThrowIfNull(item, nameof(item));
             LinkedListNode<string> itemInserted;
             if (Count == 0 && index == 0)
@@ -180,6 +196,7 @@ public void Insert(int index, string item)
         /// <returns>true if removal is successful, otherwise false.</returns>
         public bool Remove(string item)
         {
+            ValidateReadOnly();
             var itemIndex = IndexOf(item);
             if (itemIndex == -1)
             {
@@ -195,6 +212,7 @@ public bool Remove(string item)
         /// </summary>
         public void RemoveAt(int index)
         {
+            ValidateReadOnly();
             ValidateIndex(index);
             var node = GetNodeAt(index);
             if (node.Next != null)
@@ -340,5 +358,13 @@ private static void ThrowIfNull<T>(T param, string paramName)
                 throw new ArgumentNullException(paramName);
             }
         }
+
+        private void ValidateReadOnly()
+        {
+            if (IsReadOnly)
+            {
+                throw new NotSupportedException(Strings.TextLinesReadOnlyCollection);
+            }
+        }
     }
 }