Add TeamRuleset (#13)

This builds on work done by @dlsteuer in #10

team.go

@@ -0,0 +1,110 @@
+package rules
+
+import (
+	"errors"
+)
+
+type TeamRuleset struct {
+	StandardRuleset
+
+	TeamMap map[string]string
+
+	// These are intentionally designed so that they default to a standard game.
+	AllowBodyCollisions bool
+	SharedElimination   bool
+	SharedHealth        bool
+	SharedLength        bool
+}
+
+const EliminatedByTeam = "team-eliminated"
+
+func (r *TeamRuleset) CreateNextBoardState(prevState *BoardState, moves []SnakeMove) (*BoardState, error) {
+	nextBoardState, err := r.StandardRuleset.CreateNextBoardState(prevState, moves)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO: LOG?
+	err = r.resurrectTeamBodyCollisions(nextBoardState)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO: LOG?
+	err = r.shareTeamAttributes(nextBoardState)
+	if err != nil {
+		return nil, err
+	}
+
+	return nextBoardState, nil
+}
+
+func (r *TeamRuleset) areSnakesOnSameTeam(snake *Snake, other *Snake) bool {
+	return r.areSnakeIDsOnSameTeam(snake.ID, other.ID)
+}
+
+func (r *TeamRuleset) areSnakeIDsOnSameTeam(snakeID string, otherID string) bool {
+	return snakeID != otherID && r.TeamMap[snakeID] == r.TeamMap[otherID]
+}
+
+func (r *TeamRuleset) resurrectTeamBodyCollisions(b *BoardState) error {
+	if !r.AllowBodyCollisions {
+		return nil
+	}
+
+	for i := 0; i < len(b.Snakes); i++ {
+		snake := &b.Snakes[i]
+		if snake.EliminatedCause == EliminatedByCollision {
+			if snake.EliminatedBy == "" {
+				return errors.New("snake eliminated by collision and eliminatedby is not set")
+			}
+			if r.areSnakeIDsOnSameTeam(snake.ID, snake.EliminatedBy) {
+				snake.EliminatedCause = NotEliminated
+				snake.EliminatedBy = ""
+			}
+		}
+	}
+
+	return nil
+}
+
+func (r *TeamRuleset) shareTeamAttributes(b *BoardState) error {
+	if !(r.SharedElimination || r.SharedLength || r.SharedHealth) {
+		return nil
+	}
+
+	for i := 0; i < len(b.Snakes); i++ {
+		snake := &b.Snakes[i]
+		if snake.EliminatedCause != NotEliminated {
+			continue
+		}
+
+		for j := 0; j < len(b.Snakes); j++ {
+			other := &b.Snakes[j]
+			if r.areSnakesOnSameTeam(snake, other) {
+				if r.SharedHealth {
+					if snake.Health < other.Health {
+						snake.Health = other.Health
+					}
+				}
+				if r.SharedLength {
+					if len(snake.Body) == 0 || len(other.Body) == 0 {
+						return errors.New("found snake of zero length")
+					}
+					for len(snake.Body) < len(other.Body) {
+						r.growSnake(snake)
+					}
+				}
+				if r.SharedElimination {
+					if snake.EliminatedCause == NotEliminated && other.EliminatedCause != NotEliminated {
+						snake.EliminatedCause = EliminatedByTeam
+						// We intentionally do not set snake.EliminatedBy because there might be multiple culprits.
+						snake.EliminatedBy = ""
+					}
+				}
+			}
+		}
+	}
+
+	return nil
+}