Add interactive prompts for selecting values

* Adds SelectionPrompt
* Adds MultiSelectionPrompt

Closes #210

src/Spectre.Console/Widgets/Prompt/MultiSelectionPromptExtensions.cs

@@ -0,0 +1,164 @@
+using System;
+using System.Collections.Generic;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="MultiSelectionPrompt{T}"/>.
+    /// </summary>
+    public static class MultiSelectionPromptExtensions
+    {
+        /// <summary>
+        /// Adds a choice.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <param name="choice">The choice to add.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> AddChoice<T>(this MultiSelectionPrompt<T> obj, T choice)
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            obj.Choices.Add(choice);
+            return obj;
+        }
+
+        /// <summary>
+        /// Adds multiple choices.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <param name="choices">The choices to add.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> AddChoices<T>(this MultiSelectionPrompt<T> obj, params T[] choices)
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            obj.Choices.AddRange(choices);
+            return obj;
+        }
+
+        /// <summary>
+        /// Adds multiple choices.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <param name="choices">The choices to add.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> AddChoices<T>(this MultiSelectionPrompt<T> obj, IEnumerable<T> choices)
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            obj.Choices.AddRange(choices);
+            return obj;
+        }
+
+        /// <summary>
+        /// Sets the title.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <param name="title">The title markup text.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> Title<T>(this MultiSelectionPrompt<T> obj, string? title)
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            obj.Title = title;
+            return obj;
+        }
+
+        /// <summary>
+        /// Sets how many choices that are displayed to the user.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <param name="pageSize">The number of choices that are displayed to the user.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> PageSize<T>(this MultiSelectionPrompt<T> obj, int pageSize)
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            if (pageSize <= 2)
+            {
+                throw new ArgumentException("Page size must be greater or equal to 3.", nameof(pageSize));
+            }
+
+            obj.PageSize = pageSize;
+            return obj;
+        }
+
+        /// <summary>
+        /// Requires no choice to be selected.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> NotRequired<T>(this MultiSelectionPrompt<T> obj)
+        {
+            return Required(obj, false);
+        }
+
+        /// <summary>
+        /// Requires a choice to be selected.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> Required<T>(this MultiSelectionPrompt<T> obj)
+        {
+            return Required(obj, true);
+        }
+
+        /// <summary>
+        /// Sets a value indicating whether or not at least one choice must be selected.
+        /// </summary>
+        /// <typeparam name="T">The prompt result type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <param name="required">Whether or not at least one choice must be selected.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> Required<T>(this MultiSelectionPrompt<T> obj, bool required)
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            obj.Required = required;
+            return obj;
+        }
+
+        /// <summary>
+        /// Sets the function to create a display string for a given choice.
+        /// </summary>
+        /// <typeparam name="T">The prompt type.</typeparam>
+        /// <param name="obj">The prompt.</param>
+        /// <param name="displaySelector">The function to get a display string for a given choice.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static MultiSelectionPrompt<T> UseConverter<T>(this MultiSelectionPrompt<T> obj, Func<T, string>? displaySelector)
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            obj.Converter = displaySelector;
+            return obj;
+        }
+    }
+}