Lua: Implement most API functions

src/Client.cpp

@@ -1,7 +1,9 @@
 #include "Client.h"
 
 #include "CustomAssert.h"
+#include "TServer.h"
 #include <memory>
+#include <optional>
 
 // FIXME: add debug prints
 
@@ -100,3 +102,19 @@ int TClient::SecondsSinceLastPing() {
                        .count();
     return int(seconds);
 }
+
+std::optional<std::weak_ptr<TClient>> GetClient(TServer& Server, int ID) {
+    std::optional<std::weak_ptr<TClient>> MaybeClient { std::nullopt };
+    Server.ForEachClient([&](std::weak_ptr<TClient> CPtr) -> bool {
+        ReadLock Lock(Server.GetClientMutex());
+        if (!CPtr.expired()) {
+            auto C = CPtr.lock();
+            if (C->GetID() == ID) {
+                MaybeClient = CPtr;
+                return false;
+            }
+        }
+        return true;
+    });
+    return MaybeClient;
+}