DEV 1303: Add empty and royale maps and update game map interface (#72)

* move random generator into Settings

* add empty and royale maps

* place snakes on either cardinal or corner positions first

maps/empty.go

@@ -0,0 +1,49 @@
+package maps
+
+import (
+	"github.com/BattlesnakeOfficial/rules"
+)
+
+type EmptyMap struct{}
+
+func init() {
+	globalRegistry.RegisterMap("empty", EmptyMap{})
+}
+
+func (m EmptyMap) ID() string {
+	return "empty"
+}
+
+func (m EmptyMap) Meta() Metadata {
+	return Metadata{
+		Name:        "Empty",
+		Description: "Default snake placement with no food",
+		Author:      "Battlesnake",
+	}
+}
+
+func (m EmptyMap) SetupBoard(initialBoardState *rules.BoardState, settings rules.Settings, editor Editor) error {
+	rand := settings.GetRand(0)
+
+	snakeIDs := make([]string, 0, len(initialBoardState.Snakes))
+	for _, snake := range initialBoardState.Snakes {
+		snakeIDs = append(snakeIDs, snake.ID)
+	}
+
+	tempBoardState := rules.NewBoardState(initialBoardState.Width, initialBoardState.Height)
+	err := rules.PlaceSnakesAutomatically(rand, tempBoardState, snakeIDs)
+	if err != nil {
+		return err
+	}
+
+	// Copy snakes from temp board state
+	for _, snake := range tempBoardState.Snakes {
+		editor.PlaceSnake(snake.ID, snake.Body, snake.Health)
+	}
+
+	return nil
+}
+
+func (m EmptyMap) UpdateBoard(lastBoardState *rules.BoardState, settings rules.Settings, editor Editor) error {
+	return nil
+}