package xy

import (
	"fmt"
)

type Point struct {
	X int `json:"x"`
	Y int `json:"y"`
}

func (p Point) Go(dir Direction) (Point, error) {
	switch dir {
	case Up:
		return Point{X: p.X, Y: p.Y - 1}, nil
	case Down:
		return Point{X: p.X, Y: p.Y + 1}, nil
	case Left:
		return Point{X: p.X - 1, Y: p.Y}, nil
	case Right:
		return Point{X: p.X + 1, Y: p.Y}, nil
	}
	return p, fmt.Errorf("invalid direction: %s", dir)
}

type Direction string

const (
	Up    Direction = "up"
	Down  Direction = "down"
	Left  Direction = "left"
	Right Direction = "right"
)

func (d Direction) Validate() error {
	if d == Up || d == Down || d == Left || d == Right {
		return nil
	}
	return fmt.Errorf("invalid direction: %s (out of %v)", d, []Direction{Up, Down, Left, Right})
}