Add autocomplete for text prompt

Closes #166

src/Spectre.Console/Widgets/Figlet/FigletFont.cs

@@ -0,0 +1,137 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using Spectre.Console.Internal;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Represents a FIGlet font.
+    /// </summary>
+    public sealed class FigletFont
+    {
+        private const string StandardFont = "Spectre.Console/Widgets/Figlet/Fonts/Standard.flf";
+
+        private readonly Dictionary<int, FigletCharacter> _characters;
+        private static readonly Lazy<FigletFont> _standard;
+
+        /// <summary>
+        /// Gets the number of characters in the font.
+        /// </summary>
+        public int Count => _characters.Count;
+
+        /// <summary>
+        /// Gets the height of the font.
+        /// </summary>
+        public int Height { get; }
+
+        /// <summary>
+        /// Gets the font's baseline.
+        /// </summary>
+        public int Baseline { get; }
+
+        /// <summary>
+        /// Gets the font's maximum width.
+        /// </summary>
+        public int MaxWidth { get; }
+
+        /// <summary>
+        /// Gets the default FIGlet font.
+        /// </summary>
+        public static FigletFont Default => _standard.Value;
+
+        static FigletFont()
+        {
+            _standard = new Lazy<FigletFont>(() => Parse(
+                ResourceReader.ReadManifestData(StandardFont)));
+        }
+
+        internal FigletFont(IEnumerable<FigletCharacter> characters, FigletHeader header)
+        {
+            _characters = new Dictionary<int, FigletCharacter>();
+
+            foreach (var character in characters)
+            {
+                if (_characters.ContainsKey(character.Code))
+                {
+                    throw new InvalidOperationException("Character already exist");
+                }
+
+                _characters[character.Code] = character;
+            }
+
+            Height = header.Height;
+            Baseline = header.Baseline;
+            MaxWidth = header.MaxLength;
+        }
+
+        /// <summary>
+        /// Loads a FIGlet font from the specified stream.
+        /// </summary>
+        /// <param name="stream">The stream to load the FIGlet font from.</param>
+        /// <returns>The loaded FIGlet font.</returns>
+        public static FigletFont Load(Stream stream)
+        {
+            using (var reader = new StreamReader(stream))
+            {
+                return Parse(reader.ReadToEnd());
+            }
+        }
+
+        /// <summary>
+        /// Loads a FIGlet font from disk.
+        /// </summary>
+        /// <param name="path">The path of the FIGlet font to load.</param>
+        /// <returns>The loaded FIGlet font.</returns>
+        public static FigletFont Load(string path)
+        {
+            return Parse(File.ReadAllText(path));
+        }
+
+        /// <summary>
+        /// Parses a FIGlet font from the specified <see cref="string"/>.
+        /// </summary>
+        /// <param name="source">The FIGlet font source.</param>
+        /// <returns>The parsed FIGlet font.</returns>
+        public static FigletFont Parse(string source)
+        {
+            return FigletFontParser.Parse(source);
+        }
+
+        internal int GetWidth(string text)
+        {
+            var width = 0;
+            foreach (var character in text)
+            {
+                width += GetCharacter(character)?.Width ?? 0;
+            }
+
+            return width;
+        }
+
+        internal FigletCharacter? GetCharacter(char character)
+        {
+            _characters.TryGetValue(character, out var result);
+            return result;
+        }
+
+        internal IEnumerable<FigletCharacter> GetCharacters(string text)
+        {
+            if (text is null)
+            {
+                throw new ArgumentNullException(nameof(text));
+            }
+
+            var result = new List<FigletCharacter>();
+            foreach (var character in text)
+            {
+                if (_characters.TryGetValue(character, out var figletCharacter))
+                {
+                    result.Add(figletCharacter);
+                }
+            }
+
+            return result;
+        }
+    }
+}