Update EntityPath

- Add this[Range] indexer
- Add TryParse method
- Add GetParts method
- Fix not being able to handle entity IDs

src/gaemstone/ECS/EntityPath.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Buffers;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Text;
 using gaemstone.Utility;
@@ -23,19 +24,23 @@ public class EntityPath
 		=> (index >= 0 && index < Count) ? new(_parts[index].AsSpan()[..^1])
 			: throw new ArgumentOutOfRangeException(nameof(index));
 
+	public EntityPath this[Range range]
+		=> new(IsAbsolute && (range.GetOffsetAndLength(Count).Offset == 0), _parts[range]);
+
 	internal EntityPath(bool absolute, params byte[][] parts)
 	{
 		if (parts.Length == 0) throw new ArgumentException(
 			"Must have at least one part", nameof(parts));
 		IsAbsolute = absolute;
-		_parts     = parts;
+		_parts = parts;
 	}
 
 	public EntityPath(params string[] parts)
 		: this(false, parts) {  }
 	public EntityPath(bool absolute, params string[] parts)
 		: this(absolute, parts.Select(part => {
-			ValidateName(part);
+			if (GetNameValidationError(part) is string error)
+				throw new ArgumentException(error);
 			var byteCount = Encoding.UTF8.GetByteCount(part);
 			// Includes NUL character at the end of bytes.
 			var bytes = new byte[byteCount + 1];
@@ -43,6 +48,33 @@ public class EntityPath
 			return bytes;
 		}).ToArray()) {  }
 
+	public static bool TryParse(string str, [NotNullWhen(true)] out EntityPath? result)
+	{
+		result = null;
+		if (str.Length == 0) return false;
+
+		var strSpan = str.AsSpan();
+		var isAbsolute = (str[0] == '/');
+		if (isAbsolute) strSpan = strSpan[1..];
+
+		var numSeparators = 0;
+		foreach (var chr in strSpan) if (chr == '/') numSeparators++;
+
+		var index = 0;
+		var parts = new byte[numSeparators + 1][];
+		foreach (var part in strSpan.Split('/')) {
+			if (GetNameValidationError(part) != null) return false;
+			var byteCount = Encoding.UTF8.GetByteCount(part);
+			// Includes NUL character at the end of bytes.
+			var bytes = new byte[byteCount + 1];
+			Encoding.UTF8.GetBytes(part, bytes);
+			parts[index++] = bytes;
+		}
+
+		result = new(isAbsolute, parts);
+		return true;
+	}
+
 	public static EntityPath Parse(string str)
 	{
 		if (str.Length == 0) throw new ArgumentException(
@@ -52,18 +84,15 @@ public class EntityPath
 		return (parts[0].Length == 0) ? new(true, parts[1..]) : new(parts);
 	}
 
-	public static void ValidateName(string name)
+	public static string? GetNameValidationError(ReadOnlySpan<char> name)
 	{
-		if (name.Length == 0) throw new ArgumentException(
-			"Must not be empty");
-
+		if (name.Length == 0) return "Must not be empty";
 		// NOTE: This is a hopefully straightforward way to also prevent "."
 		//       and ".." to be part of paths which may access the file system.
-		if (name[0] == '.') throw new ArgumentException(
-			"Must not begin with a dot");
-
+		if (name[0] == '.') return "Must not begin with a dot";
 		foreach (var chr in name) if (char.IsControl(chr))
-			throw new ArgumentException("Must not contain contol characters");
+			return "Must not contain contol characters";
+		return null;
 	}
 
 	// private static readonly Rune[] _validRunes = { (Rune)'-', (Rune)'.', (Rune)'_' };
@@ -77,6 +106,13 @@ public class EntityPath
 	// 		throw new ArgumentException($"Must not contain {Rune.GetUnicodeCategory(rune)} character");
 	// }
 
+	public string[] GetParts()
+	{
+		var result = new string[Count];
+		for (var i = 0; i < Count; i++) result[i] = this[i];
+		return result;
+	}
+
 	public override string ToString()
 	{
 		var builder = new StringBuilder();
@@ -106,9 +142,12 @@ public class EntityPath
 		else if (parent.IsNone) parent = new(ecs_get_scope(universe));
 
 		foreach (var part in path)
-			fixed (byte* ptr = part.AsSpan())
-				if ((parent = new(ecs_lookup_child(universe, parent, ptr))).IsNone)
+			fixed (byte* ptr = part.AsSpan()) {
+				// FIXME: This breaks when using large entity IDs.
+				parent = new(ecs_lookup_child(universe, parent, ptr));
+				if (parent.IsNone || !ecs_is_alive(universe, parent))
 					return Entity.None;
+			}
 
 		return parent;
 	}
@@ -141,8 +180,17 @@ public static class EntityPathExtensions
 		var current = (Entity)entity;
 		var parts   = new List<byte[]>(32);
 
-		do { parts.Add(ecs_get_name(entity.Universe, current).FlecsToBytes()!); }
-		while ((current = new(ecs_get_target(entity.Universe, current, EcsChildOf, 0))).IsSome);
+		do {
+			var name = ecs_get_name(entity.Universe, current).FlecsToBytes();
+			if (name != null) parts.Add(name);
+			else {
+				// If name is not set, use the numeric ID, instead.
+				var id = current.ID.ToString();
+				var bytes = new byte[Encoding.UTF8.GetByteCount(id) + 1];
+				Encoding.UTF8.GetBytes(id, bytes);
+				parts.Add(bytes);
+			}
+		} while ((current = new(ecs_get_target(entity.Universe, current, EcsChildOf, 0))).IsSome);
 
 		parts.Reverse();
 		return new(true, parts.ToArray());