Started retro tetris game

Started developing a retro version of Tetris, following
the planning on the board of the classroom
(see planning.jpg).

Moved cursor work into cursor.

cursor/tetris.py

@@ -0,0 +1,123 @@
+import random
+
+
+class Tetris:
+    W = 10
+    H = 20
+
+    PIECES = {
+        'I': [[(0,1),(1,1),(2,1),(3,1)], [(2,0),(2,1),(2,2),(2,3)]],
+        'O': [[(1,0),(2,0),(1,1),(2,1)]],
+        'T': [[(1,0),(0,1),(1,1),(2,1)], [(1,0),(1,1),(2,1),(1,2)], [(0,1),(1,1),(2,1),(1,2)], [(1,0),(0,1),(1,1),(1,2)]],
+        'L': [[(2,0),(0,1),(1,1),(2,1)], [(1,0),(1,1),(1,2),(2,2)], [(0,1),(1,1),(2,1),(0,2)], [(0,0),(1,0),(1,1),(1,2)]],
+        'J': [[(0,0),(0,1),(1,1),(2,1)], [(1,0),(2,0),(1,1),(1,2)], [(0,1),(1,1),(2,1),(2,2)], [(1,0),(1,1),(1,2),(0,2)]],
+        'S': [[(1,0),(2,0),(0,1),(1,1)], [(1,0),(1,1),(2,1),(2,2)]],
+        'Z': [[(0,0),(1,0),(1,1),(2,1)], [(2,0),(1,1),(2,1),(1,2)]],
+    }
+
+    def __init__(self, agents=None, state=None):
+        self.score = 0
+        self.over = False
+        self.grid = [[0] * self.W for _ in range(self.H)]
+        self.rng = random.Random(0)
+        self.next_piece = self._rand_piece()
+        self._spawn()
+        self.last_render = ''
+
+    def _rand_piece(self):
+        return self.rng.choice(list(self.PIECES.keys()))
+
+    def _spawn(self):
+        self.piece = self.next_piece
+        self.next_piece = self._rand_piece()
+        self.rot = 0
+        self.px = (self.W // 2) - 2
+        self.py = 0
+        if not self._fits(self.px, self.py, self.rot):
+            self.over = True
+
+    def _cells(self, px, py, rot):
+        rstates = self.PIECES[self.piece]
+        r = rot % len(rstates)
+        return [(px + x, py + y) for (x, y) in rstates[r]]
+
+    def _fits(self, px, py, rot):
+        for x, y in self._cells(px, py, rot):
+            if x < 0 or x >= self.W or y < 0 or y >= self.H:
+                return False
+            if self.grid[y][x]:
+                return False
+        return True
+
+    def _lock(self):
+        for x, y in self._cells(self.px, self.py, self.rot):
+            if 0 <= y < self.H and 0 <= x < self.W:
+                self.grid[y][x] = 1
+        # clear lines
+        newg = [row for row in self.grid if not all(row)]
+        cleared = self.H - len(newg)
+        if cleared:
+            for _ in range(cleared):
+                newg.insert(0, [0] * self.W)
+            self.grid = newg
+            self.score += 100 * cleared
+        self._spawn()
+
+    # API methods used by tests / agent
+    def step(self, action=0):
+        # actions: 0 noop, 1 left, 2 right, 3 rotate, 4 soft drop
+        if self.over:
+            return
+        if action == 1:
+            if self._fits(self.px - 1, self.py, self.rot):
+                self.px -= 1
+        elif action == 2:
+            if self._fits(self.px + 1, self.py, self.rot):
+                self.px += 1
+        elif action == 3:
+            if self._fits(self.px, self.py, self.rot + 1):
+                self.rot += 1
+        elif action == 4:
+            if self._fits(self.px, self.py + 1, self.rot):
+                self.py += 1
+            else:
+                self._lock()
+            return
+        # gravity
+        if self._fits(self.px, self.py + 1, self.rot):
+            self.py += 1
+        else:
+            self._lock()
+
+    def is_over(self):
+        return bool(self.over)
+
+    def get_score(self):
+        return int(self.score)
+
+    # rendering stubs (retro compatibility)
+    def clear(self):
+        pass
+
+    def draw_board(self):
+        lines = []
+        occupied = set(self._cells(self.px, self.py, self.rot)) if not self.over else set()
+        for y in range(self.H):
+            row = ''
+            for x in range(self.W):
+                if (x, y) in occupied:
+                    row += '[]'
+                else:
+                    row += '##' if self.grid[y][x] else '..'
+            lines.append(row)
+        self.last_render = '\n'.join(lines)
+        return self.last_render
+
+    def draw_piece(self):
+        return
+
+    def refresh(self):
+        return
+
+    def reset(self):
+        self.__init__()