feat: implement gravity on current piece

entity/Piece.py

@@ -9,7 +9,9 @@ from util.ConfigurationManager import ConfigurationManager
     https://tetris.fandom.com/wiki/Tetromino
 '''
 class Piece(Entity):
-        
+    
+    GRAVITY = 800 # A move down every 800 ms
+
     def __init__(self, shape: Tuple, position: Tuple, color: str, border_color: str):
         super().__init__(self.__get_points(shape, position), color, border_color)
         self.center = self.__get_center(shape, position)
@@ -17,7 +19,24 @@ class Piece(Entity):
         self.previous_points = None
         self.previous_center = None
 
+    def update(self, elapsed_time: int, well: Entity, stack: Entity):
+        super().update(elapsed_time)
+
+        tile_size =  ConfigurationManager.configuration["engine"]["tile-size"]
+        if self.elapsed_time >= Piece.GRAVITY:
+            self.elapsed_time -= Piece.GRAVITY
+
+            self.move((0, tile_size))
+            if well and self.collide(well):     
+                self.revert()
+            if stack and self.collide(stack):     
+                self.revert()
+
     def move(self, vector: Tuple) -> None:
+        # reset elapsed time if user moves down to stall gravity
+        if vector[1] > 0:
+            self.elapsed_time = 0
+
         self.previous_points = copy.deepcopy(self.points)
         self.previous_center = copy.deepcopy(self.center)