playground

import gleam/list
import gleam/string

pub type Direction {
  North
  East
  South
  West
}

pub type Position {
  Position(x: Int, y: Int)
}

pub type Robot {
  Robot(direction: Direction, position: Position)
}

pub fn create(direction: Direction, position: Position) -> Robot {
  Robot(direction, position)
}

pub fn move(
  direction: Direction,
  position: Position,
  instructions: String,
) -> Robot {
  let robot = create(direction, position)

  let move_folder = fn(robot, instruction) {
    case instruction {
      "R" -> turn_right(robot)
      "L" -> turn_left(robot)
      "A" -> advance(robot)
      _ -> panic as "unreachable"
    }
  }

  instructions
  |> string.to_graphemes()
  |> list.fold(robot, move_folder)
}

fn turn_right(robot: Robot) {
  case robot.direction {
    North -> Robot(..robot, direction: East)
    East -> Robot(..robot, direction: South)
    South -> Robot(..robot, direction: West)
    West -> Robot(..robot, direction: North)
  }
}

fn turn_left(robot: Robot) {
  case robot.direction {
    North -> Robot(..robot, direction: West)
    East -> Robot(..robot, direction: North)
    South -> Robot(..robot, direction: East)
    West -> Robot(..robot, direction: South)
  }
}

fn advance(robot: Robot) {
  let Position(x: x, y: y) = robot.position

  case robot.direction {
    North -> Robot(..robot, position: Position(x: x, y: y + 1))
    East -> Robot(..robot, position: Position(x: x + 1, y: y))
    South -> Robot(..robot, position: Position(x: x, y: y - 1))
    West -> Robot(..robot, position: Position(x: x - 1, y: y))
  }
}