inertia and refactor

source/scripts/tankSprite.lua

@@ -16,9 +16,14 @@ function Tank:init(x, y, player, ground)
     Graphics.popContext()
 
     -- Collision properties
-    self:setZIndex(99)
+    self:setZIndex(ZIndex.enemy)
     self:setTag(2)
     self:setCollideRect(4, 56, 147, 65)
+    self:setGroups(CollideGroups.enemy)
+    self:setCollidesWithGroups(
+        {
+            CollideGroups.player
+        })
 
     -- Main properties
     Tank.moveSpeed = 2