Add new constants for standard ruleset errors, resolves #5 (#24)

* Convert errors to constant error interfaces.

ruleset.go

@@ -37,3 +37,7 @@ type Ruleset interface {
 	CreateNextBoardState(prevState *BoardState, moves []SnakeMove) (*BoardState, error)
 	IsGameOver(state *BoardState) (bool, error)
 }
+
+type RulesetError string
+
+func (err RulesetError) Error() string { return string(err) }

standard.go

@@ -1,7 +1,7 @@
 package rules
 
 import (
-	"errors"
+	//"errors"
 	"math/rand"
 	"sort"
 )
@@ -28,6 +28,14 @@ const (
 	EliminatedByOutOfBounds         = "wall-collision"
 
 	// TODO - Error consts
+	ErrorTooManySnakes  = RulesetError("too many snakes for fixed start positions")
+	ErrorNoRoomForSnake = RulesetError("not enough space to place snake")
+	ErrorNoRoomForFood  = RulesetError("not enough space to place food")
+	ErrorNoMoveFound    = RulesetError("move not provided for snake")
+
+	// TODO: These two error codes seem equivalent, Do we only need one ?
+	ErrorSizeZeroBody    = RulesetError("found snake with zero size body")
+	ErrorZeroLengthSnake = RulesetError("snake is length zero")
 )
 
 func (r *StandardRuleset) CreateInitialBoardState(width int32, height int32, snakeIDs []string) (*BoardState, error) {
@@ -80,7 +88,7 @@ func (r *StandardRuleset) placeSnakesFixed(b *BoardState) error {
 
 	// Sanity check
 	if len(b.Snakes) > len(startPoints) {
-		return errors.New("too many snakes for fixed start positions")
+		return ErrorTooManySnakes
 	}
 
 	// Randomly order them
@@ -103,7 +111,7 @@ func (r *StandardRuleset) placeSnakesRandomly(b *BoardState) error {
 	for i := 0; i < len(b.Snakes); i++ {
 		unoccupiedPoints := r.getEvenUnoccupiedPoints(b)
 		if len(unoccupiedPoints) <= 0 {
-			return errors.New("not enough space to place snake")
+			return ErrorNoRoomForSnake
 		}
 		p := unoccupiedPoints[rand.Intn(len(unoccupiedPoints))]
 		for j := 0; j < SnakeStartSize; j++ {
@@ -147,7 +155,7 @@ func (r *StandardRuleset) placeFoodFixed(b *BoardState) error {
 		}
 
 		if len(availableFoodLocations) <= 0 {
-			return errors.New("not enough space to place food")
+			return ErrorNoRoomForFood
 		}
 
 		// Select randomly from available locations
@@ -166,7 +174,7 @@ func (r *StandardRuleset) placeFoodFixed(b *BoardState) error {
 		}
 	}
 	if isCenterOccupied {
-		return errors.New("not enough space to place food")
+		return ErrorNoRoomForFood
 	}
 	b.Food = append(b.Food, centerCoord)
 
@@ -255,7 +263,7 @@ func (r *StandardRuleset) moveSnakes(b *BoardState, moves []SnakeMove) error {
 		}
 
 		if len(snake.Body) == 0 {
-			return errors.New("found snake with zero size body")
+			return ErrorSizeZeroBody
 		}
 		moveFound := false
 		for _, move := range moves {
@@ -265,7 +273,7 @@ func (r *StandardRuleset) moveSnakes(b *BoardState, moves []SnakeMove) error {
 			}
 		}
 		if !moveFound {
-			return errors.New("move not provided for snake")
+			return ErrorNoMoveFound
 		}
 	}
 
@@ -346,7 +354,7 @@ func (r *StandardRuleset) maybeEliminateSnakes(b *BoardState) error {
 			continue
 		}
 		if len(snake.Body) <= 0 {
-			return errors.New("snake is length zero")
+			return ErrorZeroLengthSnake
 		}
 
 		if r.snakeIsOutOfHealth(snake) {
@@ -374,7 +382,7 @@ func (r *StandardRuleset) maybeEliminateSnakes(b *BoardState) error {
 			continue
 		}
 		if len(snake.Body) <= 0 {
-			return errors.New("snake is length zero")
+			return ErrorZeroLengthSnake
 		}
 
 		// Check for self-collisions first

standard_test.go

@@ -1,7 +1,7 @@
 package rules
 
 import (
-	"errors"
+	//"errors"
 	"math"
 	"math/rand"
 	"testing"
@@ -49,8 +49,8 @@ func TestCreateInitialBoardState(t *testing.T) {
 		{2, 2, []string{"one"}, 1, nil},
 		{9, 8, []string{"one"}, 1, nil},
 		{2, 2, []string{"one", "two"}, 0, nil},
-		{1, 1, []string{"one", "two"}, 2, errors.New("not enough space to place snake")},
+		{1, 1, []string{"one", "two"}, 2, ErrorNoRoomForSnake},
-		{1, 2, []string{"one", "two"}, 2, errors.New("not enough space to place snake")},
+		{1, 2, []string{"one", "two"}, 2, ErrorNoRoomForSnake},
 		{BoardSizeSmall, BoardSizeSmall, []string{"one", "two"}, 3, nil},
 	}
 
@@ -95,7 +95,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: 1,
 				Snakes: make([]Snake, 2),
 			},
-			errors.New("not enough space to place snake"),
+			ErrorNoRoomForSnake,
 		},
 		{
 			&BoardState{
@@ -103,7 +103,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: 1,
 				Snakes: make([]Snake, 2),
 			},
-			errors.New("not enough space to place snake"),
+			ErrorNoRoomForSnake,
 		},
 		{
 			&BoardState{
@@ -111,7 +111,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: 2,
 				Snakes: make([]Snake, 2),
 			},
-			errors.New("not enough space to place snake"),
+			ErrorNoRoomForSnake,
 		},
 		{
 			&BoardState{
@@ -135,7 +135,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: 5,
 				Snakes: make([]Snake, 49),
 			},
-			errors.New("not enough space to place snake"),
+			ErrorNoRoomForSnake,
 		},
 		{
 			&BoardState{
@@ -143,7 +143,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: 10,
 				Snakes: make([]Snake, 50),
 			},
-			errors.New("not enough space to place snake"),
+			ErrorNoRoomForSnake,
 		},
 		{
 			&BoardState{
@@ -151,7 +151,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: 2,
 				Snakes: make([]Snake, 51),
 			},
-			errors.New("not enough space to place snake"),
+			ErrorNoRoomForSnake,
 		},
 		{
 			&BoardState{
@@ -175,7 +175,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: BoardSizeSmall,
 				Snakes: make([]Snake, 9),
 			},
-			errors.New("too many snakes for fixed start positions"),
+			ErrorTooManySnakes,
 		},
 		{
 			&BoardState{
@@ -191,7 +191,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: BoardSizeMedium,
 				Snakes: make([]Snake, 9),
 			},
-			errors.New("too many snakes for fixed start positions"),
+			ErrorTooManySnakes,
 		},
 		{
 			&BoardState{
@@ -207,7 +207,7 @@ func TestPlaceSnakes(t *testing.T) {
 				Height: BoardSizeLarge,
 				Snakes: make([]Snake, 9),
 			},
-			errors.New("too many snakes for fixed start positions"),
+			ErrorTooManySnakes,
 		},
 	}
 
@@ -488,7 +488,7 @@ func TestCreateNextBoardState(t *testing.T) {
 				Food: []Point{{0, 0}, {1, 0}},
 			},
 			[]SnakeMove{},
-			errors.New("move not provided for snake"),
+			ErrorNoMoveFound,
 			nil,
 		},
 		{
@@ -513,7 +513,7 @@ func TestCreateNextBoardState(t *testing.T) {
 				{ID: "one", Move: MoveUp},
 				{ID: "two", Move: MoveDown},
 			},
-			errors.New("found snake with zero size body"),
+			ErrorSizeZeroBody,
 			nil,
 		},
 		{
@@ -940,7 +940,7 @@ func TestMoveSnakesWrongID(t *testing.T) {
 
 	r := StandardRuleset{}
 	err := r.moveSnakes(b, moves)
-	require.Equal(t, errors.New("move not provided for snake"), err)
+	require.Equal(t, ErrorNoMoveFound, err) // TODO: @bvanvugt is this a place where an "==" comparision should be used ?
 }
 
 func TestMoveSnakesNotEnoughMoves(t *testing.T) {
@@ -965,7 +965,7 @@ func TestMoveSnakesNotEnoughMoves(t *testing.T) {
 
 	r := StandardRuleset{}
 	err := r.moveSnakes(b, moves)
-	require.Equal(t, errors.New("move not provided for snake"), err)
+	require.Equal(t, ErrorNoMoveFound, err)
 }
 
 func TestMoveSnakesExtraMovesIgnored(t *testing.T) {
@@ -1366,7 +1366,7 @@ func TestMaybeEliminateSnakes(t *testing.T) {
 			},
 			[]string{NotEliminated},
 			[]string{""},
-			errors.New("snake is length zero"),
+			ErrorZeroLengthSnake,
 		},
 		{
 			"Single Starvation",