[WIP] Convert most of Chunking to Entity-based system

Player and all NPCs now have a common superclass, with virtual functions
so smooth over shared behavior. EntityRef is a simple class that points
to an arbitrary Entity.

This commit is not yet functional.

src/Entities.cpp

@@ -0,0 +1,120 @@
+#include "core/Core.hpp"
+#include "Entities.hpp"
+#include "Chunking.hpp"
+#include "PlayerManager.hpp"
+#include "NPCManager.hpp"
+#include "Eggs.hpp"
+
+#include <type_traits>
+
+static_assert(std::is_standard_layout<EntityRef>::value);
+static_assert(std::is_trivially_copyable<EntityRef>::value);
+
+EntityRef::EntityRef(CNSocket *s) {
+    type = EntityType::PLAYER;
+    sock = s;
+}
+
+EntityRef::EntityRef(int32_t i) {
+    id = i;
+
+    assert(NPCManager::NPCs.find(id) != NPCManager::NPCs.end());
+    type = NPCManager::NPCs[id]->type;
+}
+
+bool EntityRef::isValid() const {
+    if (type == EntityType::PLAYER)
+        return PlayerManager::players.find(sock) != PlayerManager::players.end();
+
+    return NPCManager::NPCs.find(id) != NPCManager::NPCs.end();
+}
+
+Entity *EntityRef::getEntity() const {
+    assert(isValid());
+
+    if (type == EntityType::PLAYER)
+        return PlayerManager::getPlayer(sock);
+
+    return NPCManager::NPCs[id];
+}
+
+/*
+ * Entity coming into view.
+ */
+void BaseNPC::enterIntoViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_NPC_ENTER, pkt);
+    pkt.NPCAppearanceData = appearanceData;
+    sock->sendPacket(pkt, P_FE2CL_NPC_ENTER);
+
+    playersInView++;
+}
+
+void Bus::enterIntoViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_TRANSPORTATION_ENTER, pkt);
+
+    // TODO: Potentially decouple this from BaseNPC?
+    pkt.AppearanceData = {
+        3, appearanceData.iNPC_ID, appearanceData.iNPCType,
+        appearanceData.iX, appearanceData.iY, appearanceData.iZ
+    };
+
+    sock->sendPacket(pkt, P_FE2CL_TRANSPORTATION_ENTER);
+}
+
+void Egg::enterIntoViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_SHINY_ENTER, pkt);
+
+    Eggs::npcDataToEggData(&appearanceData, &pkt.ShinyAppearanceData);
+
+    sock->sendPacket(pkt, P_FE2CL_SHINY_ENTER);
+}
+    
+// TODO: this is less effiecient than it was, because of memset()
+void Player::enterIntoViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_PC_NEW, pkt);
+
+    pkt.PCAppearanceData.iID = iID;
+    pkt.PCAppearanceData.iHP = HP;
+    pkt.PCAppearanceData.iLv = level;
+    pkt.PCAppearanceData.iX = x;
+    pkt.PCAppearanceData.iY = y;
+    pkt.PCAppearanceData.iZ = z;
+    pkt.PCAppearanceData.iAngle = angle;
+    pkt.PCAppearanceData.PCStyle = PCStyle;
+    pkt.PCAppearanceData.Nano = Nanos[activeNano];
+    pkt.PCAppearanceData.iPCState = iPCState;
+    pkt.PCAppearanceData.iSpecialState = iSpecialState;
+    memcpy(pkt.PCAppearanceData.ItemEquip, Equip, sizeof(sItemBase) * AEQUIP_COUNT);
+
+    sock->sendPacket(pkt, P_FE2CL_PC_NEW);
+}
+
+/*
+ * Entity leaving view.
+ */
+void BaseNPC::disappearFromViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_NPC_EXIT, pkt);
+    pkt.iNPC_ID = appearanceData.iNPC_ID;
+    sock->sendPacket(pkt, P_FE2CL_NPC_EXIT);
+
+    playersInView--;
+}
+
+void Bus::disappearFromViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_TRANSPORTATION_EXIT, pkt);
+    pkt.eTT = 3;
+    pkt.iT_ID = appearanceData.iNPC_ID;
+    sock->sendPacket(pkt, P_FE2CL_TRANSPORTATION_EXIT);
+}
+
+void Egg::disappearFromViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_SHINY_EXIT, pkt);
+    pkt.iShinyID = appearanceData.iNPC_ID;
+    sock->sendPacket(pkt, P_FE2CL_SHINY_EXIT);
+}
+
+void Player::disappearFromViewOf(CNSocket *sock) {
+    INITSTRUCT(sP_FE2CL_PC_EXIT, pkt);
+    pkt.iID = iID;
+    sock->sendPacket(pkt, P_FE2CL_PC_EXIT);
+}