#! /usr/bin/env ruby

if ARGV.length != 1 and ARGV.length != 2
    abort("Incorrect arguments - needs input file and optional second arg")
elsif not File.exist? (ARGV[0])
abort("File #{ARGV[0]} did not exist")
end

file = ARGV[0]

lines = File.open(file, "r").each_line(chomp: true).to_a
start_pos = [lines[0].index("."), 0]
end_pos = [lines[-1].index("."), lines.length - 1]
maze = lines.map {|line| line.each_char.to_a}

$maze_width = 0...maze[0].length
$maze_height = 0...maze.length
$can_climb_hills = ARGV.length == 2

open_routes = [[start_pos]]

distances = Array.new(maze.length) {Array.new(maze[0].length) {Hash.new}}

$moves = [[0,1], [0,-1], [1,0], [-1,0]]

def valid_move(move, space, maze)
    if $maze_width.cover?(space[0]) && $maze_height.cover?(space[1])
        case maze[space[1]][space[0]]
        when "#" then false
        when "." then true
        when "^" then $can_climb_hills || move == [0,-1]
        when "v" then $can_climb_hills || move == [0, 1]
        when ">" then $can_climb_hills || move == [1, 0]
        when "<" then $can_climb_hills || move == [-1,0]
        end
    else
        false
    end
end

def next_steps(route, maze)
    last_space = route[-1]
    $moves.map do |move|
        new_space = [move[0] + last_space[0], move[1] + last_space[1]]
        [move, new_space]
    end.filter do |move, new_space|
        valid_move(move, new_space, maze) && !route.include?(new_space)
    end
end

while open_routes != []
    num_routes = open_routes.length
    open_routes = open_routes.flat_map do |route|
        next_steps(route, maze).map do |move, next_step|
            new_route = route + [next_step]
            # Simple "distance to this point" doesn't work when if can approach from different
            # directions, because the other route may be shorter to here but longer to the end
            # so we use the movement direction to track different directionality
            current_distances = distances[next_step[1]][next_step[0]]
            if !current_distances.key?(move) || new_route.length > current_distances[move]
                distances[next_step[1]][next_step[0]][move] = new_route.length
                new_route
            else
                # We have a longer route to this space in this direction, so prune
                nil
            end
        end.filter {|route| !route.nil?}
    end
    # if open_routes.length != num_routes
    #     puts "Now have:"
    #     open_routes.each {|route| puts "  * #{route.length} to #{route[-1]}"}
    # end
end

# Subtract 1 because we don't count the first step
puts "#{distances[end_pos[1]][end_pos[0]].values.max - 1}"