finish implementing path parameters

SimpleHttpServer/Types/PathTree.cs

@@ -0,0 +1,107 @@
+using System.Data;
+using System.Diagnostics.CodeAnalysis;
+
+namespace SimpleHttpServer.Types;
+
+internal class PathTree<T> where T : class {
+    private readonly Node? rootNode = null;
+
+    public PathTree() : this(new()) { }
+    public PathTree(Dictionary<string, T> dict) {
+        if (dict == null || dict.Count == 0)
+            return;
+
+        rootNode = new();
+        var currNode = rootNode;
+        var unpackedPaths = dict.Keys.Select(p => p.Split('/').ToArray()).ToArray();
+        var unpackedLeafData = dict.Values.ToArray();
+        for (int i = 0; i < unpackedPaths.Length; i++) {
+            var path = unpackedPaths[i];
+            var catchallidx = Array.IndexOf(path, "$*");
+            if (catchallidx != -1 && catchallidx != path.Length - 1) {
+                throw new Exception($"Found illegal catchall-wildcard in path: '{string.Join('/', path)}'");
+            }
+
+            var leafdata = unpackedLeafData[i];
+            rootNode.AddSuccessor(path, leafdata);
+        }
+    }
+
+    internal bool TryGetPath(string reqPath, [MaybeNullWhen(false)] out T? endpoint) {
+        if (rootNode == null) {
+            endpoint = null;
+            return false;
+        }
+
+        // try to find path-match
+        Node currNode = rootNode;
+        Assert(reqPath[0] == '/');
+        var splittedPath = reqPath[1..].Split("/");
+        Node? lastCatchallNode = null;
+        for (int i = 0; i < splittedPath.Length; i++) {
+
+            // keep track of the current best catchallNode
+            if (currNode.catchAllNext != null) {
+                lastCatchallNode = currNode.catchAllNext;
+            }
+
+            var seg = splittedPath[i];
+            if (currNode.next?.TryGetValue(seg, out var next) == true) { // look for an explicit path to follow greedily
+                currNode = next;
+            } else if (currNode.pathWildcardNext != null) { // otherwise look for a single-wildcard to follow
+                currNode = currNode.pathWildcardNext;
+            } else { // otherwise we are done, there is no valid path --> fall back to the most specific catchall
+                endpoint = lastCatchallNode?.leafData;
+                return lastCatchallNode != null;
+            }
+        }
+
+        // return found path
+        endpoint = currNode.leafData;
+        return true;
+    }
+
+    private class Node {
+        public T? leafData = null;
+        public Dictionary<string, Node>? next = null;
+        public Node? pathWildcardNext = null; // path wildcard
+        public Node? catchAllNext = null; // trailing-catchall wildcard
+
+        public void AddSuccessor(string[] segments, T? newLeafData) {
+            if (segments.Length == 0) { // actually add the data to this node
+                Assert(leafData == null);
+                leafData = newLeafData;
+                return;
+            }
+
+            var seg = segments[0];
+            bool newIsWildcard = seg.Length > 1 && seg[0] == '$';
+            if (newIsWildcard) {
+                bool newIsCatchallWildcard = newIsWildcard && seg.Length == 2 && seg[1] == '*';
+                if (newIsCatchallWildcard) { // this is a catchall wildcard
+                    Assert(catchAllNext == null);
+                    catchAllNext = new();
+                    catchAllNext.AddSuccessor(segments[1..], newLeafData);
+                    return;
+                } else { // must be single wildcard otherwise
+                    Assert(pathWildcardNext == null);
+                    pathWildcardNext = new();
+                    pathWildcardNext.AddSuccessor(segments[1..], newLeafData);
+                    return;
+                }
+            }
+
+            // otherwise we want to add a new constant path successor
+            if (next == null) {
+                next = new();
+            }
+
+            if (next.TryGetValue(seg, out var existingNode)) {
+                existingNode.AddSuccessor(segments[1..], newLeafData);
+            } else {
+                var newNode = next[seg] = new();
+                newNode.AddSuccessor(segments[1..], newLeafData);
+            }
+        }
+    }
+}