package common

import (
	"bufio"
	"strconv"
)


type Direction int

const (
  Right Direction = iota
  Left
  Down
  Up
)


type Movement struct {
  direction Direction
  distance int
}


type Position struct {
  x int
  y int
}

func NewPosition(x int, y int) *Position {
  return &Position{x, y}
}


type Grid struct {
  rope []Position
  head *Position
  tail *Position
}

func NewGrid(size int) *Grid {
  rope := make([]Position, size)
  return &Grid{rope, &rope[0], &rope[size-1]}
}

func (grid *Grid) Move(movement Movement) (map[Position]struct{}) {
  visitedTail := make(map[Position]struct{})

  visitedTail[*grid.tail] = struct{}{}

  for i := 0; i < movement.distance; i++ {
    switch movement.direction {
      case Right:
        grid.head.x++
      case Left:
        grid.head.x--
      case Up:
        grid.head.y--
      case Down:
        grid.head.y++
    }
    grid.Update()
    visitedTail[*grid.tail] = struct{}{}
  }

  return visitedTail
}

func (grid *Grid) Update() {
  for i := 1; i < len(grid.rope); i++ {
    head := &(grid.rope[i-1])
    tail := &(grid.rope[i])
    if tail.x < head.x - 1 || tail.x > head.x + 1 ||
       tail.y < head.y - 1 || tail.y > head.y + 1 {
      if tail.x == head.x {
        tail.y = (tail.y + head.y) / 2
      } else if tail.y == head.y {
        tail.x = (tail.x + head.x) / 2
      } else if tail.x == head.x - 1 || tail.x == head.x + 1 {
        tail.x = head.x
        tail.y = (tail.y + head.y) / 2
      } else if tail.y == head.y - 1 || tail.y == head.y + 1 {
        tail.x = (tail.x + head.x) / 2
        tail.y = head.y
      } else {
        tail.x = (tail.x + head.x) / 2
        tail.y = (tail.y + head.y) / 2
      }
    }
  }
}


func Parse(scanner bufio.Scanner) []Movement {
  movements := []Movement{}

  for scanner.Scan() {
    line := scanner.Text()

    var movement Movement
    distance, _ := strconv.Atoi(line[2:])
    switch line[0] {
      case 'L':
        movement = Movement{Left, distance}
      case 'R':
        movement = Movement{Right, distance}
      case 'U':
        movement = Movement{Up, distance}
      case 'D':
        movement = Movement{Down, distance}
    }
    movements = append(movements, movement)
  }

  return movements
}