Implement unit action queueing and busy state validation

unit.h

@@ -4,6 +4,7 @@
 #include <QString>
 #include <QVector3D>
 #include <vector>
+#include <deque>
 #include <utility>
 #include "unitconfig.h"
 #include "terrain.h"
@@ -16,6 +17,31 @@ enum class UnitState {
     Building
 };
 
+enum class UnitActionType {
+    None,
+    Move,
+    BuildImprovement,
+    BuildCity,
+    Attack
+};
+
+struct UnitAction {
+    UnitActionType type = UnitActionType::None;
+    int targetX = -1;
+    int targetY = -1;
+    int targetUnitId = -1;
+    QString extraData = ""; // e.g. improvementId ("farm")
+
+    UnitAction() = default;
+    UnitAction(UnitActionType t) : type(t) {}
+    UnitAction(UnitActionType t, int x, int y, const QString &data = "")
+        : type(t), targetX(x), targetY(y), extraData(data) {}
+    UnitAction(UnitActionType t, int targetId)
+        : type(t), targetUnitId(targetId) {}
+
+    bool isValid() const { return type != UnitActionType::None; }
+};
+
 class Unit {
 public:
     Unit(int uId, int pId, const UnitConfig &cfg, int startX, int startY, float groundZ);
@@ -38,6 +64,19 @@ public:
     int targetTileX;
     int targetTileY;
 
+    // Action Queue
+    std::deque<UnitAction> actionQueue;
+    int maxQueueSize = 5;
+
+    bool queueAction(const UnitAction &action);
+    void clearActionQueue();
+    bool hasQueuedAction() const { return !actionQueue.empty(); }
+    bool hasQueuedActionType(UnitActionType type) const;
+    void removeQueuedActionsOfType(UnitActionType type);
+    UnitAction popNextQueuedAction();
+    const UnitAction* peekNextQueuedAction() const;
+    QString getQueuedActionSummary() const;
+
     // Attack cooldown / flash
     float attackFlashTimer;
 
@@ -54,6 +93,7 @@ public:
     void startBuilding(const QString &impId, float duration);
     void cancelBuilding();
     bool isBuilding() const { return state == UnitState::Building; }
+    bool isBusy() const { return state == UnitState::Building; }
 
     bool canAttack(const Unit &other) const;
     void performAttack(Unit &target);