#! /usr/bin/env ruby

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

file = ARGV[0]

Coord = Struct.new(:x, :y)

city_map = File.open(file, "r").each_line(chomp: true).map{ |line| line.each_char.map(&:to_i)}

distances = Array.new(city_map.length) {Array.new(city_map[0].length) {Float::INFINITY}}
distances[0][0] = 0

visited = Array.new(city_map.length) {Array.new(city_map[0].length)}

unvisited = []
(0...city_map.length).each {|y| (0...city_map[0].length).each {|x| unvisited << Coord.new(x,y)}}

def get_neighbours(city_map, x, y)
	[Coord.new(-1,0), Coord.new(1,0), Coord.new(0,-1), Coord.new(0,1)].map {|coord| Coord.new(coord.x + x, coord.y + y)}.filter {|coord| coord.x >= 0 and coord.y >= 0 and coord.x < city_map[0].length and coord.y < city_map.length}
end

until unvisited.empty?
	min_node = nil
	unvisited.each do |node|
		if min_node.nil? || distances[node.y][node.x] < distances[min_node.y][min_node.x]
			min_node = node unless visited[node.y][node.x]
		end
	end

	break if distances[min_node.y][min_node.x] == Float::INFINITY

	cur_distance = distances[min_node.y][min_node.x]

	get_neighbours(city_map, min_node.x, min_node.y).each do |neighbour|
		value = city_map[neighbour.y][neighbour.x]
		alt = cur_distance + value
		distances[neighbour.y][neighbour.x] = alt if alt < distances[neighbour.y][neighbour.x]
	end

	visited[min_node.y][min_node.x] = true
	unvisited.delete(min_node)
	distances
end

puts distances[-1][-1]