feat(scala): m11 pong capstone (model, rules, view, app) with tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scala/solutions/pong/Model.scala

@@ -0,0 +1,73 @@
+package snake
+package pong
+
+// m11 pong model: the same ideas as the snake model, for a different game.
+
+/** The ball's direction of travel, one cell per frame on each axis. */
+final case class Velocity(dx: Int, dy: Int)
+
+/** Which of the player's two keys are being held down right now. */
+final case class Held(up: Boolean, down: Boolean)
+
+final case class Score(player: Int, cpu: Int)
+
+enum PongStatus:
+  case Playing, Over
+
+/** The two keys that move the player's paddle. */
+enum Paddle:
+  case Up, Down
+
+/**
+ * A whole match. Positions are in cells: `ball` is a cell of the 80x50 court; `player` and `cpu` are the y of the
+ * top cell of each paddle. `seed` is the unsigned 32-bit random seed used to pick the direction of each serve.
+ */
+final case class PongState(
+    ball: Point,
+    vel: Velocity,
+    player: Int,
+    cpu: Int,
+    held: Held,
+    score: Score,
+    status: PongStatus,
+    seed: Long,
+    frame: Int
+)
+
+/** Everything that can happen in a match, as data. */
+enum PongAction:
+  case Press(key: Paddle)
+  case Release(key: Paddle)
+  case Frame
+  case Restart
+
+object PongModel:
+
+  // The court, in cells.
+  val W: Int = 80
+  val H: Int = 50
+
+  /** Pixels per cell. */
+  val PCELL: Int = 8
+
+  /** Paddle height in cells. */
+  val PADDLE: Int = 8
+
+  /** Column of the player's paddle (left) and of the cpu's paddle (right). */
+  val PLAYER_X: Int = 2
+  val CPU_X: Int = 77
+
+  /** Points needed to win the match. */
+  val WIN: Int = 5
+
+  def initialPong(seed: Long): PongState = PongState(
+    ball = Point(40, 25),
+    vel = Velocity(1, 1),
+    player = 21,
+    cpu = 21,
+    held = Held(up = false, down = false),
+    score = Score(player = 0, cpu = 0),
+    status = PongStatus.Playing,
+    seed = seed,
+    frame = 0
+  )