Add calendar control

Closes #101

src/Spectre.Console/Extensions/CalendarExtensions.cs

@@ -0,0 +1,83 @@
+using System;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="Calendar"/>.
+    /// </summary>
+    public static class CalendarExtensions
+    {
+        /// <summary>
+        /// Adds a calendar event.
+        /// </summary>
+        /// <param name="calendar">The calendar to add the calendar event to.</param>
+        /// <param name="date">The calendar event date.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static Calendar AddCalendarEvent(this Calendar calendar, DateTime date)
+        {
+            return AddCalendarEvent(calendar, string.Empty, date.Year, date.Month, date.Day);
+        }
+
+        /// <summary>
+        /// Adds a calendar event.
+        /// </summary>
+        /// <param name="calendar">The calendar to add the calendar event to.</param>
+        /// <param name="description">The calendar event description.</param>
+        /// <param name="date">The calendar event date.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static Calendar AddCalendarEvent(this Calendar calendar, string description, DateTime date)
+        {
+            return AddCalendarEvent(calendar, description, date.Year, date.Month, date.Day);
+        }
+
+        /// <summary>
+        /// Adds a calendar event.
+        /// </summary>
+        /// <param name="calendar">The calendar to add the calendar event to.</param>
+        /// <param name="year">The year of the calendar event.</param>
+        /// <param name="month">The month of the calendar event.</param>
+        /// <param name="day">The day of the calendar event.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static Calendar AddCalendarEvent(this Calendar calendar, int year, int month, int day)
+        {
+            return AddCalendarEvent(calendar, string.Empty, year, month, day);
+        }
+
+        /// <summary>
+        /// Adds a calendar event.
+        /// </summary>
+        /// <param name="calendar">The calendar.</param>
+        /// <param name="description">The calendar event description.</param>
+        /// <param name="year">The year of the calendar event.</param>
+        /// <param name="month">The month of the calendar event.</param>
+        /// <param name="day">The day of the calendar event.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static Calendar AddCalendarEvent(this Calendar calendar, string description, int year, int month, int day)
+        {
+            if (calendar is null)
+            {
+                throw new ArgumentNullException(nameof(calendar));
+            }
+
+            calendar.CalendarEvents.Add(new CalendarEvent(description, year, month, day));
+            return calendar;
+        }
+
+        /// <summary>
+        /// Sets the calendar's highlight <see cref="Style"/>.
+        /// </summary>
+        /// <param name="calendar">The calendar.</param>
+        /// <param name="style">The highlight style.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static Calendar SetHighlightStyle(this Calendar calendar, Style? style)
+        {
+            if (calendar is null)
+            {
+                throw new ArgumentNullException(nameof(calendar));
+            }
+
+            calendar.HightlightStyle = style ?? Style.Plain;
+            return calendar;
+        }
+    }
+}