Finish Day 08

src/core/SymbolGrid.cs

@@ -0,0 +1,126 @@
+using System.Diagnostics.CodeAnalysis;
+using System.IO.MemoryMappedFiles;
+using System.Numerics;
+
+namespace core;
+
+public class SymbolGrid
+{
+	private char[]? _map;
+
+	[DisallowNull]
+	public char? this[int x, int y]
+	{
+		get
+		{
+			EnsureMap();
+			return IsValid(x, y) ? _map[y * Height + x] : null;
+		}
+		set
+		{
+			EnsureMap();
+			if (IsValid(x, y))
+			{
+				_map[y * Height + x] = value.Value;
+			}
+		}
+	}
+
+	[DisallowNull]
+	public char? this[Vector2I i]
+	{
+		get => this[i.X, i.Y];
+		set => this[i.X, i.Y] = value;
+	}
+
+	public int Width { get; private set; }
+
+	public int Height { get; private set; }
+
+	public void Load(string file)
+	{
+		using var fileView = MemoryMappedFile.CreateFromFile(file, FileMode.Open);
+		using var accessor = fileView.CreateViewAccessor();
+		(Width, var stride, Height) = Parse(accessor);
+		_map = new char[Width * Height];
+		for (int x = 0; x < Width; x++)
+		{
+			for (int y = 0; y < Height; y++)
+			{
+				_map[y * Height + x] = (char)accessor.ReadByte(y * stride + x);
+			}
+		}
+
+		static (int Width, int Stride, int Height) Parse(MemoryMappedViewAccessor map)
+		{
+			bool hasNewLine = false;
+			int? width = null, stride = null;
+			for (int i = 0; i < map.Capacity; i++)
+			{
+				if ((char)map.ReadByte(i) is '\r' or '\n')
+				{
+					if (!hasNewLine)
+					{
+						width = i;
+					}
+
+					hasNewLine = true;
+				}
+				else if (hasNewLine)
+				{
+					stride = i;
+					break;
+				}
+			}
+
+			return (width!.Value, stride!.Value, (int)((map.Capacity + width.Value) / stride.Value));
+		}
+	}
+
+	public SymbolEnumerator GetEnumerator() => new(this);
+
+	public bool IsValid(Vector2I p) => IsValid(p.X, p.Y);
+
+	public bool IsValid(int x, int y)
+	{
+		EnsureMap();
+		return x >= 0 && x < Width && y >= 0 && y < Height;
+	}
+
+	public ref struct SymbolEnumerator
+	{
+		private readonly SymbolGrid _grid;
+		private readonly int _length;
+		private int? _current;
+
+		internal SymbolEnumerator(SymbolGrid grid)
+		{
+			_grid = grid;
+			_length = grid.Width * grid.Height;
+		}
+
+		public (Vector2I Position, char Symbol) Current { get; private set; }
+
+		public bool MoveNext()
+		{
+			_current = _current.HasValue ? _current + 1 : 0;
+			if (_current == _length)
+			{
+				return false;
+			}
+
+			Current = (_grid.ToVector(_current.Value), _grid._map![_current.Value]);
+
+			return true;
+		}
+	}
+
+	private Vector2I ToVector(int index) => new()
+	{
+		Y = index / Height,
+		X = index % Height
+	};
+
+	[MemberNotNull(nameof(_map))]
+	private void EnsureMap() => ArgumentNullException.ThrowIfNull(_map);
+}