import { map, filter, pipe, curry, sum } from 'rambda';

const stringTo2DArray = (str: string): number[][] =>
  str.split('\n').map(x => x.split('').map(Number));

type Coordinate = [y: number, x: number];
type Direction = [dy: number, dx: number];

const directions: Direction[] = [
  [-1, 0],
  [1, 0],
  [0, -1],
  [0, 1],
];

const findStarts = (grid: number[][]): Coordinate[] => {
  const starts: Coordinate[] = [];

  for (let y = 0; y < grid.length; y++) {
    for (let x = 0; x < grid[y].length; x++) {
      if (grid[y][x] === 0) starts.push([y, x]);
    }
  }

  return starts;
};

const isInBounds = (grid: number[][], [y, x]: Coordinate): boolean =>
  y >= 0 && y < grid.length && x >= 0 && x < grid[y].length;

const getValidMoves = (grid: number[][], [y, x]: Coordinate): Coordinate[] => {
  const value = grid[y][x];

  return pipe<[Direction[]], Coordinate[], Coordinate[], Coordinate[]>(
    map(([dy, dx]) => [y + dy, x + dx]),
    filter(([y, x]) => isInBounds(grid, [y, x])),
    filter(([y, x]) => grid[y][x] === value + 1),
  )(directions);
};

const countCompletePaths = (
  grid: number[][],
  [y, x]: Coordinate,
  reachableNines = new Set<string>(),
): number => {
  const value = grid[y][x];

  if (value === 9) {
    reachableNines.add(`${y},${x}`);
    return 0;
  }

  getValidMoves(grid, [y, x]).forEach(coord =>
    countCompletePaths(grid, coord, reachableNines),
  );

  return reachableNines.size;
};

export default (input: string): number => {
  const grid = stringTo2DArray(input);
  const countCompletePathsOnGrid = curry(countCompletePaths)(grid);

  return pipe(findStarts, map(countCompletePathsOnGrid), sum)(grid);
};