Add DeprecationPolicy class

Author: Matthias Gessinger

src/Abstractions/src/Asp.Versioning.Abstractions/DeprecationPolicy.cs

@@ -0,0 +1,77 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+
+namespace Asp.Versioning;
+
+/// <summary>
+/// Represents an API version deprecation policy.
+/// </summary>
+public class DeprecationPolicy
+{
+    private readonly LinkList links;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DeprecationPolicy"/> class.
+    /// </summary>
+    public DeprecationPolicy()
+    {
+        links = new DeprecationLinkList();
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DeprecationPolicy"/> class.
+    /// </summary>
+    /// <param name="date">The date and time when the API version will be deprecated.</param>
+    /// <param name="link">The optional link which provides information about the deprecation policy.</param>
+    public DeprecationPolicy( DateTimeOffset date, LinkHeaderValue? link = default )
+        : this()
+    {
+        Date = date;
+
+        if ( link is not null )
+        {
+            links.Add( link );
+        }
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DeprecationPolicy"/> class.
+    /// </summary>
+    /// <param name="link">The link which provides information about the deprecation policy.</param>
+    public DeprecationPolicy( LinkHeaderValue link )
+        : this()
+    {
+        links.Add( link );
+    }
+
+    /// <summary>
+    /// Gets the date and time when the API version will be deprecated.
+    /// </summary>
+    /// <value>The date and time when the API version will be deprecated, if any.</value>
+    public DateTimeOffset? Date { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the deprecation policy has any associated links.
+    /// </summary>
+    /// <value>True if the deprecation policy has associated links; otherwise, false.</value>
+    public bool HasLinks => links.Count > 0;
+
+    /// <summary>
+    /// Gets a read-only list of links that provide information about the deprecation policy.
+    /// </summary>
+    /// <value>A read-only list of HTTP links.</value>
+    /// <remarks>If a link is provided, generally only one link is necessary; however, additional
+    /// links might be provided for different languages or different formats such as a HTML page
+    /// or a JSON file.</remarks>
+    public IList<LinkHeaderValue> Links => links;
+
+    internal sealed class DeprecationLinkList : LinkList
+    {
+        protected override void EnsureRelationType( LinkHeaderValue item )
+        {
+            if ( !item.RelationType.Equals( "deprecation", StringComparison.OrdinalIgnoreCase ) )
+            {
+                throw new ArgumentException( SR.InvalidDeprecationRelationType, nameof( item ) );
+            }
+        }
+    }
+}

src/Abstractions/src/Asp.Versioning.Abstractions/SR.Designer.cs

@@ -144,4 +144,7 @@
   <data name="InvalidSunsetRelationType" xml:space="preserve">
     <value>The relation type for a sunset policy link must be "sunset".</value>
   </data>
+  <data name="InvalidDeprecationRelationType" xml:space="preserve">
+    <value>The relation type for a deprecation policy link must be "deprecation".</value>
+  </data>
 </root>