require 'net/http'
require 'pp'
require 'rubygems'
require 'xmlsimple'

# <settings>
desktop_width  = 1280
desktop_height = 1024
num_desktops   = 6
# </settings>

target_ratio = desktop_width.to_f / desktop_height
target_range = (target_ratio.floor)..(target_ratio.ceil)

Photo = Struct.new(:farm, :sid, :id, :oid, :secret, :ext, :title, 
                   :width, :height, :ratio, :host, :path, :x_diff)

params = [
  [:api_key,  '6efcde4b429a5569196d2a99a2669097'],
  [:method,   'flickr.interestingness.getList'],
  [:extras,   'o_dims,original_format,original_secret'],
  [:per_page, '250']
]
path = "/services/rest/?#{params.collect { |p| p.join("=") }.join("&")}"
body = Net::HTTP.get("api.flickr.com", path)

result = XmlSimple.xml_in(body)['photos'].first
photos = result['photo'].collect do |photo|
  farm, sid, id, oid, secret, ext, title, w, h = photo.values_at(*[
    'farm', 'server', 'id', 'owner', 'originalsecret',
    'originalformat', 'title', 'o_width', 'o_height'
  ])
  p = Photo.new(farm, sid, id, oid, secret, ext, title, w, h)
  if p.width && p.height
    p.width  = p.width.to_i
    p.height = p.height.to_i
    p.ratio  = p.width.to_f / p.height
    p.x_diff = p.ratio != target_ratio ? (p.width - (target_ratio * p.height)).round : 0
  end
  p
end.select do |photo|
  if photo.width && photo.height && target_range.include?(photo.ratio) && (photo.width - photo.x_diff) > desktop_width
    photo.host = "farm#{photo.farm}.static.flickr.com"
    photo.path = "/#{photo.sid}/#{photo.id}_#{photo.secret}_o.#{photo.ext}"
    true
  else
    false
  end
end

index = 0
Dir.mkdir("images")  unless File.exist?("images")
num_desktops.times do |i|
  index = 0 if photos.length == index
  photo = photos[index]
  index += 1

  # save image
  fn = File.expand_path("images/#{photo.id}.#{photo.ext}")
  puts "Downloading #{photo.title}..."
  File.open(fn, "w") { |f| f.write(Net::HTTP.get(photo.host, photo.path)) }

  if target_ratio != photo.ratio
    # crop image; x - 1.25y = w - 1.25h
    h = photo.height
    w = photo.width - photo.x_diff
    x_offset = photo.x_diff / 2
    y_offset = 0

    puts "  Cropping..." 
    cmd = "mogrify -crop #{w}x#{h}+#{x_offset}+#{y_offset} #{fn}"
    system(cmd)
  end

  # scale
  puts "  Scaling..." 
  `mogrify -scale #{desktop_width}x#{desktop_height} #{fn}`
  
  # set desktop 
  puts "  Setting to desktop #{i+1}..."
  `dcop kdesktop KBackgroundIface setWallpaper #{i+1} #{fn} 1`
end