Advent of Typescript - Day 24 - Santa Maze

maze.ts

type Alley = "  ";
type MazeItem = "🎄" | "🎅" | Alley;
type Maze = MazeItem[][]
type DELICIOUS_COOKIES = "🍪";
type MazeMatrix = MazeItem[][];
type Directions = "up" | "down" | "left" | "right";
type CoordState = 'win' | 'valid' | 'invalid'

type Inc<N extends number> = [
  1,2,3,4,5,6,7,8,9,10,11,
  ...number[]
][N]

type Dec<N extends number> = [
  -1,0,1,2,3,4,5,6,7,8,9,
  ...number[]
][N]

// Moves santa to new position and replaces last one with Alley (no validation)
type MoveSanta<TMaze extends Maze, RI extends number, CI extends number> = {
  [K in keyof TMaze]: TMaze[K] extends infer Row extends MazeItem[] ? {
    [J in keyof Row]: Row[J] extends "🎅"
      ? Alley
      : [K, J] extends [`${RI}`, `${CI}`] ? `🎅` : Row[J]
  } : never
}

// Replaces all cells with a specific item (used for winning cookies)
type FillMaze<TMaze extends Maze, Value extends any> = {
  [K in keyof TMaze]: TMaze[K] extends infer Row extends MazeItem[] ? {
    [J in keyof Row]: Value
  } : never
}

// Finds Cell coordinate of Santa
type FindSantaRow<Row extends MazeItem[], Counter extends number[] = []> =
  Row extends [infer Cell, ...infer Rest extends MazeItem[]]
    ? Cell extends '🎅'
      ? Counter['length']
      : FindSantaRow<Rest, [...Counter, 0]>
    : 'nope'

// Finds [Row, Cell] coordinates of Santa
type FindSanta<TMaze extends Maze, Counter extends number[] = []> =
  TMaze extends [infer Row extends MazeItem[], ...infer Rest extends Maze]
    ? FindSantaRow<Row> extends infer CI extends number
      ? [Counter['length'], CI]
      : FindSanta<Rest, [...Counter, 0]>
    : never

// Takes current Santa's coords and modifies them based on Move
type GetNewCoords<RI extends number, CI extends number, Move extends Directions> =
  Move extends 'up'
  ? [Dec<RI>, CI]
  : Move extends 'down'
  ? [Inc<RI>, CI]
  : Move extends 'left'
  ? [RI, Dec<CI>]
  : [RI, Inc<CI>]

// Examines new coordinates and determines if they are valid/invalid or if we got out of maze
type ValidateCoords<TMaze extends Maze, RI extends number, CI extends number> =
  RI extends -1 | TMaze['length']
  ? 'win'
  : CI extends -1 | TMaze[0]['length']
  ? 'win'
  : TMaze[RI][CI] extends '🎄'
  ? 'invalid'
  : 'valid'

// Main logic: Find Santa Coords -> New coords -> Validate coords -> Move Santa / Win / Hit tree
type Move<TMaze extends Maze, Move extends Directions> =
  FindSanta<TMaze> extends [infer RI extends number, infer CI extends number]
    ? GetNewCoords<RI, CI, Move> extends [infer NewRI extends number, infer NewCI extends number]
      ? ValidateCoords<TMaze, NewRI, NewCI> extends infer State extends CoordState
        ? State extends 'valid'
          ? MoveSanta<TMaze, NewRI, NewCI>
          : State extends 'win'
          ? FillMaze<TMaze, DELICIOUS_COOKIES>
          : TMaze
        : never
      : never
    : TMaze

type Test = [
  ["🎄", "🎄", "🎄", "🎄", "🎄", "🎄"],
  ["🎄", "  ", "  ", "  ", "🎄", "🎄"],
  ["🎄", "  ", "  ", "  ", "🎅", "  "],
  ["🎄", "🎄", "🎄", "🎄", "  ", "🎄"],
]
type Res = Move<Test, 'right'>