Mapping merge driver: continued (#2803)

Co-authored-by: DrSmugleaf <DrSmugleaf@users.noreply.github.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Tools/Map.cs

@@ -0,0 +1,83 @@
+using System.IO;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using YamlDotNet.Core;
+using Robust.Shared.Utility;
+using YamlDotNet.RepresentationModel;
+
+namespace Content.Tools
+{
+    public class Map
+    {
+        public Map(string path)
+        {
+            Path = path;
+
+            using var reader = new StreamReader(path);
+            var stream = new YamlStream();
+
+            stream.Load(reader);
+
+            Root = stream.Documents[0].RootNode;
+            TilemapNode = (YamlMappingNode) Root["tilemap"];
+            GridsNode = (YamlSequenceNode) Root["grids"];
+            _entitiesNode = (YamlSequenceNode) Root["entities"];
+
+            foreach (var entity in _entitiesNode)
+            {
+                var uid = uint.Parse(entity["uid"].AsString());
+                if (uid >= NextAvailableEntityId)
+                    NextAvailableEntityId = uid + 1;
+                Entities[uid] = (YamlMappingNode) entity;
+            }
+        }
+
+        // Core
+
+        public string Path { get; }
+
+        public YamlNode Root { get; }
+
+        // Useful
+
+        public YamlMappingNode TilemapNode { get; }
+
+        public YamlSequenceNode GridsNode { get; }
+
+        // Entities lookup
+
+        private YamlSequenceNode _entitiesNode { get; }
+
+        public Dictionary<uint, YamlMappingNode> Entities { get; } = new Dictionary<uint, YamlMappingNode>();
+
+        public uint MaxId => Entities.Max(entry => entry.Key);
+
+        public uint NextAvailableEntityId { get; set; }
+
+        // ----
+
+        public void Save(string fileName)
+        {
+            // Update entities node
+            _entitiesNode.Children.Clear();
+            foreach (var kvp in Entities)
+                _entitiesNode.Add(kvp.Value);
+
+            using var writer = new StreamWriter(fileName);
+            var document = new YamlDocument(Root);
+            var stream = new YamlStream(document);
+            var emitter = new Emitter(writer);
+            var fixer = new TypeTagPreserver(emitter);
+
+            stream.Save(fixer, false);
+
+            writer.Flush();
+        }
+
+        public void Save()
+        {
+            Save(Path);
+        }
+    }
+}