#!/usr/bin/ruby -w

SCALES = [1, 2, 3]

def usage
  name = File.basename(__FILE__)
  puts "Usage: #{name} <size> <input-image> <output-directory>"
end

def generate_all_scales(size, in_file, out_dir)
  SCALES.each do |scale|
    scale_retina(size, scale, in_file, out_dir)
  end
end

def scale_retina(points, scale, in_file, out_dir)
  file_scale = scale > 1 ? "@#{scale}x" : ''
  ext = "_#{points}#{file_scale}.png"
  filename = File.basename(in_file).sub(/\.\w+$/, ext)
  size = points * scale
  out_file = File.join(out_dir, filename)
  puts "> convert '#{in_file}' -scale #{size}x#{size} '#{out_file}'"
  output = `convert '#{in_file}' -scale #{size}x#{size} '#{out_file}'`.strip
  puts output if output.length > 0
end

raw_size, in_file, out_dir = ARGV
size = raw_size.to_f
unless size > 0
  puts "Invalid size: #{raw_size.inspect}"
  usage
  exit 1
end
unless File.exist?(in_file)
  puts "Input image not found: #{in_file}"
  usage
  exit 2
end
unless File.directory?(out_dir)
  puts "Output directory not found: #{out_dir}"
  usage
  exit 1
end
generate_all_scales(size, in_file, out_dir)