Implement check_spawn function

Buildings can recruit now, it is faction sensitive, so the units are appropriatly colored

src/game/Building.cpp

 #include "Building.hpp"
 #include "Spritesheet.hpp"
+#include <iostream>
 
 namespace advanced_wars
 {
@@ -28,4 +29,79 @@ void Building::render(Engine& engine, int scale)
         &dst, 0, NULL, SDL_FLIP_NONE);
 }
 
+void Building::switch_faction(BuildingFaction faction)
+{
+
+    this->m_faction = faction;
+
+    if (this->m_id == BuildingId::HEADQUARTER)
+    {
+        std::cout << "The game is over!" << std::endl;
+    }
+}
+
+// implement call to UI to show available units
+void Building::on_click()
+{
+    std::cout << "A building is selected!" << std::endl;
+};
+
+bool Building::check_spawn(std::unordered_map<int, advanced_wars::Unit>& units)
+{
+
+    for (auto& [id, unit] : units)
+    {
+        if (unit.m_x == this->m_x && unit.m_y == this->m_y)
+        {
+            return false;
+        }
+    }
+
+    return true;
+}
+// can be added as soon as the playerobject is available
+bool Building::check_money(int price)
+{
+    // replace 400 with player.money and replace price with chosenUnit.price
+    if (400 > price)
+    {
+        return false;
+    }
+    return true;
+}
+
+std::vector<UnitId> Building::recruitableUnits()
+{
+
+    if (this->m_id == BuildingId::FACTORY)
+    {
+        return {
+            UnitId::INFANTERY,
+            UnitId::MECHANIZED_INFANTERY,
+            UnitId::RECON,
+            UnitId::APC,
+            UnitId::ARTILLERY,
+            UnitId::ANTI_AIR_TANK,
+            UnitId::ANTI_AIR_MISSILE_LAUNCHER,
+            UnitId::ROCKET_ARTILLERY,
+            UnitId::MEDIUM_TANK,
+            UnitId::NEO_TANK,
+            UnitId::HEAVY_TANK};
+    }
+
+    if (this->m_id == BuildingId::PORT)
+    {
+        return {UnitId::LANDER, UnitId::CRUISER, UnitId::SUBMARINE, UnitId::BATTLESHIP};
+    }
+
+    if (this->m_id == BuildingId::AIRPORT)
+    {
+        return {
+            UnitId::TRANSPORT_HELICOPTER, UnitId::BATTLE_HELICOPTER, UnitId::FIGHTER,
+            UnitId::BOMBER};
+    }
+
+    return {};
+}
+
 } // namespace advanced_wars
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