Restrict fixed food spawns to only locations further from center.

board.go

@@ -1,6 +1,8 @@
 package rules
 
-import "math/rand"
+import (
+	"math/rand"
+)
 
 type BoardState struct {
 	Turn    int32
@@ -156,7 +158,9 @@ func PlaceFoodAutomatically(b *BoardState) error {
 }
 
 func PlaceFoodFixed(b *BoardState) error {
-	// Place 1 food within exactly 2 moves of each snake
+	centerCoord := Point{(b.Width - 1) / 2, (b.Height - 1) / 2}
+
+	// Place 1 food within exactly 2 moves of each snake, but never towards the center
 	for i := 0; i < len(b.Snakes); i++ {
 		snakeHead := b.Snakes[i].Body[0]
 		possibleFoodLocations := []Point{
@@ -165,8 +169,9 @@ func PlaceFoodFixed(b *BoardState) error {
 			{snakeHead.X + 1, snakeHead.Y - 1},
 			{snakeHead.X + 1, snakeHead.Y + 1},
 		}
-		availableFoodLocations := []Point{}
 
+		// Remove any positions already occupied by food or closer to center
+		availableFoodLocations := []Point{}
 		for _, p := range possibleFoodLocations {
 			isOccupiedAlready := false
 			for _, food := range b.Food {
@@ -175,8 +180,14 @@ func PlaceFoodFixed(b *BoardState) error {
 					break
 				}
 			}
+			if isOccupiedAlready {
+				continue
+			}
+			// availableFoodLocations = append(availableFoodLocations, p)
 
-			if !isOccupiedAlready {
+			snakeHeadToCenter := getDistanceBetweenPoints(snakeHead, centerCoord)
+			foodToCenter := getDistanceBetweenPoints(p, centerCoord)
+			if snakeHeadToCenter <= foodToCenter {
 				availableFoodLocations = append(availableFoodLocations, p)
 			}
 		}
@@ -192,7 +203,6 @@ func PlaceFoodFixed(b *BoardState) error {
 
 	// Finally, always place 1 food in center of board for dramatic purposes
 	isCenterOccupied := true
-	centerCoord := Point{(b.Width - 1) / 2, (b.Height - 1) / 2}
 	unoccupiedPoints := getUnoccupiedPoints(b, true)
 	for _, point := range unoccupiedPoints {
 		if point == centerCoord {
@@ -220,17 +230,26 @@ func PlaceFoodRandomly(b *BoardState, n int32) error {
 	return nil
 }
 
-func isKnownBoardSize(b *BoardState) bool {
+func absInt32(n int32) int32 {
-	if b.Height == BoardSizeSmall && b.Width == BoardSizeSmall {
+	if n < 0 {
-		return true
+		return -n
 	}
-	if b.Height == BoardSizeMedium && b.Width == BoardSizeMedium {
+	return n
-		return true
+}
+
+func getEvenUnoccupiedPoints(b *BoardState) []Point {
+	// Start by getting unoccupied points
+	unoccupiedPoints := getUnoccupiedPoints(b, true)
+
+	// Create a new array to hold points that are  even
+	evenUnoccupiedPoints := []Point{}
+
+	for _, point := range unoccupiedPoints {
+		if ((point.X + point.Y) % 2) == 0 {
+			evenUnoccupiedPoints = append(evenUnoccupiedPoints, point)
 		}
-	if b.Height == BoardSizeLarge && b.Width == BoardSizeLarge {
-		return true
 	}
-	return false
+	return evenUnoccupiedPoints
 }
 
 func getUnoccupiedPoints(b *BoardState, includePossibleMoves bool) []Point {
@@ -284,17 +303,19 @@ func getUnoccupiedPoints(b *BoardState, includePossibleMoves bool) []Point {
 	return unoccupiedPoints
 }
 
-func getEvenUnoccupiedPoints(b *BoardState) []Point {
+func getDistanceBetweenPoints(a, b Point) int32 {
-	// Start by getting unoccupied points
+	return absInt32(a.X-b.X) + absInt32(a.Y-b.Y)
-	unoccupiedPoints := getUnoccupiedPoints(b, true)
+}
-
+
-	// Create a new array to hold points that are  even
+func isKnownBoardSize(b *BoardState) bool {
-	evenUnoccupiedPoints := []Point{}
+	if b.Height == BoardSizeSmall && b.Width == BoardSizeSmall {
-
+		return true
-	for _, point := range unoccupiedPoints {
+	}
-		if ((point.X + point.Y) % 2) == 0 {
+	if b.Height == BoardSizeMedium && b.Width == BoardSizeMedium {
-			evenUnoccupiedPoints = append(evenUnoccupiedPoints, point)
+		return true
-		}
+	}
-	}
+	if b.Height == BoardSizeLarge && b.Width == BoardSizeLarge {
-	return evenUnoccupiedPoints
+		return true
+	}
+	return false
 }

board_test.go

@@ -2,6 +2,7 @@ package rules
 
 import (
 	"fmt"
+	"sort"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -390,6 +391,8 @@ func TestPlaceFoodFixed(t *testing.T) {
 		require.NoError(t, err)
 		require.Equal(t, len(test.BoardState.Snakes)+1, len(test.BoardState.Food))
 
+		midPoint := Point{(test.BoardState.Width - 1) / 2, (test.BoardState.Height - 1) / 2}
+
 		// Make sure every snake has food within 2 moves of it
 		for _, snake := range test.BoardState.Snakes {
 			head := snake.Body[0]
@@ -403,6 +406,8 @@ func TestPlaceFoodFixed(t *testing.T) {
 			for _, food := range test.BoardState.Food {
 				if food == bottomLeft || food == topLeft || food == bottomRight || food == topRight {
 					foundFoodInTwoMoves = true
+					// Ensure it's not closer to the center than snake
+					require.True(t, getDistanceBetweenPoints(head, midPoint) <= getDistanceBetweenPoints(food, midPoint))
 					break
 				}
 			}
@@ -411,7 +416,6 @@ func TestPlaceFoodFixed(t *testing.T) {
 
 		// Make sure one food exists in center of board
 		foundFoodInCenter := false
-		midPoint := Point{(test.BoardState.Width - 1) / 2, (test.BoardState.Height - 1) / 2}
 		for _, food := range test.BoardState.Food {
 			if food == midPoint {
 				foundFoodInCenter = true
@@ -442,6 +446,9 @@ func TestPlaceFoodFixedNoRoom(t *testing.T) {
 		},
 		Food: []Point{},
 	}
+
+	// There are 3 possible spawn locations: {0, 0}, {0, 2}, {2, 0}
+	// So repeat calls to place food should fail after 3 successes
 	err = PlaceFoodFixed(boardState)
 	require.NoError(t, err)
 	boardState.Food = boardState.Food[:len(boardState.Food)-1] // Center food
@@ -457,14 +464,41 @@ func TestPlaceFoodFixedNoRoom(t *testing.T) {
 	boardState.Food = boardState.Food[:len(boardState.Food)-1] // Center food
 	require.Equal(t, 3, len(boardState.Food))
 
-	err = PlaceFoodFixed(boardState)
-	require.NoError(t, err)
-	boardState.Food = boardState.Food[:len(boardState.Food)-1] // Center food
-	require.Equal(t, 4, len(boardState.Food))
-
 	// And now there should be no more room.
 	err = PlaceFoodFixed(boardState)
 	require.Error(t, err)
+
+	expectedFood := []Point{{0, 0}, {0, 2}, {2, 0}}
+	sort.Slice(boardState.Food, func(i, j int) bool {
+		if boardState.Food[i].X != boardState.Food[j].X {
+			return boardState.Food[i].X < boardState.Food[j].X
+		}
+		return boardState.Food[i].Y < boardState.Food[j].Y
+	})
+	require.Equal(t, expectedFood, boardState.Food)
+}
+
+func TestGetDistanceBetweenPoints(t *testing.T) {
+	tests := []struct {
+		A        Point
+		B        Point
+		Expected int32
+	}{
+		{Point{0, 0}, Point{0, 0}, 0},
+		{Point{0, 0}, Point{1, 0}, 1},
+		{Point{0, 0}, Point{0, 1}, 1},
+		{Point{0, 0}, Point{1, 1}, 2},
+		{Point{0, 0}, Point{4, 4}, 8},
+		{Point{0, 0}, Point{4, 6}, 10},
+		{Point{8, 0}, Point{8, 0}, 0},
+		{Point{8, 0}, Point{8, 8}, 8},
+		{Point{8, 0}, Point{0, 8}, 16},
+	}
+
+	for _, test := range tests {
+		require.Equal(t, getDistanceBetweenPoints(test.A, test.B), test.Expected)
+		require.Equal(t, getDistanceBetweenPoints(test.B, test.A), test.Expected)
+	}
 }
 
 func TestIsKnownBoardSize(t *testing.T) {