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/royale.go

@@ -0,0 +1,74 @@
+package maps
+
+import (
+	"errors"
+
+	"github.com/BattlesnakeOfficial/rules"
+)
+
+type RoyaleHazardsMap struct{}
+
+func init() {
+	globalRegistry.RegisterMap("royale", RoyaleHazardsMap{})
+}
+
+func (m RoyaleHazardsMap) ID() string {
+	return "royale"
+}
+
+func (m RoyaleHazardsMap) Meta() Metadata {
+	return Metadata{
+		Name:        "Royale",
+		Description: "A map where hazards are generated every N turns",
+		Author:      "Battlesnake",
+	}
+}
+
+func (m RoyaleHazardsMap) SetupBoard(lastBoardState *rules.BoardState, settings rules.Settings, editor Editor) error {
+	return StandardMap{}.SetupBoard(lastBoardState, settings, editor)
+}
+
+func (m RoyaleHazardsMap) UpdateBoard(lastBoardState *rules.BoardState, settings rules.Settings, editor Editor) error {
+	// Royale uses the current turn to generate hazards, not the previous turn that's in the board state
+	turn := lastBoardState.Turn + 1
+
+	if settings.RoyaleSettings.ShrinkEveryNTurns < 1 {
+		return errors.New("royale game can't shrink more frequently than every turn")
+	}
+
+	if turn < settings.RoyaleSettings.ShrinkEveryNTurns {
+		return nil
+	}
+
+	// Reset hazards every turn and re-generate them
+	editor.ClearHazards()
+
+	// Get random generator for turn zero, because we're regenerating all hazards every time.
+	randGenerator := settings.GetRand(0)
+
+	numShrinks := turn / settings.RoyaleSettings.ShrinkEveryNTurns
+	minX, maxX := int32(0), lastBoardState.Width-1
+	minY, maxY := int32(0), lastBoardState.Height-1
+	for i := int32(0); i < numShrinks; i++ {
+		switch randGenerator.Intn(4) {
+		case 0:
+			minX += 1
+		case 1:
+			maxX -= 1
+		case 2:
+			minY += 1
+		case 3:
+			maxY -= 1
+		}
+	}
+
+	for x := int32(0); x < lastBoardState.Width; x++ {
+		for y := int32(0); y < lastBoardState.Height; y++ {
+			if x < minX || x > maxX || y < minY || y > maxY {
+				editor.AddHazard(rules.Point{X: x, Y: y})
+			}
+		}
+	}
+
+	return nil
+}