package snakesimulator

func (p Point) Copy() (pCopy *Point) {
	pCopy = &Point{
		X: p.X,
		Y: p.Y,
	}
	return
}

func NewSnake(direction Direction, field Field) (s *Snake) {
	fieldCenterX := field.Width / 2
	fieldCenterY := field.Height / 2
	switch direction {
	case Direction_Left:
		s = &Snake{
			Points: []*Point{
				&Point{X: fieldCenterX - 1, Y: fieldCenterY},
				&Point{X: fieldCenterX, Y: fieldCenterY},
				&Point{X: fieldCenterX + 1, Y: fieldCenterY},
			},
		}
	case Direction_Right:
		s = &Snake{
			Points: []*Point{
				&Point{X: fieldCenterX + 1, Y: fieldCenterY},
				&Point{X: fieldCenterX, Y: fieldCenterY},
				&Point{X: fieldCenterX - 1, Y: fieldCenterY},
			},
		}
	case Direction_Down:
		s = &Snake{
			Points: []*Point{
				&Point{X: fieldCenterX, Y: fieldCenterY - 1},
				&Point{X: fieldCenterX, Y: fieldCenterY},
				&Point{X: fieldCenterX, Y: fieldCenterY + 1},
			},
		}
	default:
		s = &Snake{
			Points: []*Point{
				&Point{X: fieldCenterX, Y: fieldCenterY + 1},
				&Point{X: fieldCenterX, Y: fieldCenterY},
				&Point{X: fieldCenterX, Y: fieldCenterY - 1},
			},
		}
	}
	return
}

func (s *Snake) NewHead(direction Direction) (newHead *Point) {
	newHead = s.Points[0].Copy()
	switch direction {
	case Direction_Up:
		newHead.Y -= 1
	case Direction_Down:
		newHead.Y += 1
	case Direction_Right:
		newHead.X += 1
	case Direction_Left:
		newHead.X -= 1
	}
	return
}

func (s *Snake) Move(newHead *Point) {
	s.Points = s.Points[:len(s.Points)-1]
	s.Points = append([]*Point{newHead}, s.Points...)
}

func (s *Snake) Feed(food *Point) {
	s.Points = append([]*Point{food}, s.Points...)
}

func (s *Snake) selfCollision(head *Point, direction Direction) bool {
	selfCollisionIndex := -1
	for index, point := range s.Points[:len(s.Points)-1] {
		if point.X == head.X && point.Y == head.Y {
			selfCollisionIndex = index
			break
		}
	}

	if selfCollisionIndex == 1 {
		switch direction {
		case Direction_Up:
			head.Y += 2
		case Direction_Down:
			head.Y -= 2
		case Direction_Left:
			head.X += 2
		default:
			head.X -= 2
		}
		return false
	}
	return selfCollisionIndex >= 0
}

func wallCollision(head *Point, field Field) bool {
	return head.X >= field.Width || head.Y >= field.Height || head.X < 0 || head.Y < 0
}

func foodCollision(head *Point, food *Point) bool {
	return head.X == food.X && head.Y == food.Y
}