class Avatar < ActiveRecord::Base  
  # Image sizes
  IMG_SIZE = '"240x300>"'
  THUMB_SIZE = '"50x64>"'
  
  # Image directories
  URL_STUB = "/images/avatars"
  DIRECTORY = File.join("public", "images", "avatars")
  
  def initialize(user, image = nil)
    @user = user
    @image = image
    Dir.mkdir(DIRECTORY) unless File.directory?(DIRECTORY)
  end
  
  def exists?
    File.exists?(File.join(DIRECTORY, filename))
  end

  def exist?
    exists?
  end
  
  def url
    "#{URL_STUB}/#{filename}"
  end
  
  def thumbnail_url
    "#{URL_STUB}/#{thumbnail_name}"
  end
  
  # Save the avatar images.
  def save
    valid_file? and successful_conversion?
  end

  private
  
  # Return the filename of the main avatar.
  def filename
    "#{@user.screen_name}.png"
  end  
  
  # Return the filename of the avatar thumbnail.
  def thumbnail_name
    "#{@user.screen_name}_thumbnail.png"
  end
  
  # Return the (system-dependent) ImageMagick convert executable.
  def convert
    if ENV["OS"] =~ /Windows/
      # Set this to point to the right Windows directory for ImageMagick.
      "C:\\Program Files\\ImageMagick-6.3.1-Q16\\convert"
    else
      "/usr/bin/convert"
    end
  end
  
  # Try to resize image file and convert to PNG.
  # We use ImageMagick's convert command to ensure sensible image sizes.
  def successful_conversion? 
    # Prepare the filenames for the conversion.
    source = File.join("tmp", "#{@user.screen_name}_full_size")
    full_size = File.join(DIRECTORY, filename)
    thumbnail = File.join(DIRECTORY, thumbnail_name)
    # Ensure that small and large images both work by writing to a normal file. 
    # (Small files show up as StringIO, larger ones as Tempfiles.)
    File.open(source, "wb") { |f| f.write(@image.read) }
    # Convert the files.
    img   = system("#{convert} #{source} -resize #{IMG_SIZE} #{full_size}")
    thumb = system("#{convert} #{source} -resize #{THUMB_SIZE} #{thumbnail}")
    File.delete(source) if File.exists?(source)
    # Both conversions must succeed, else it's an error.
    unless img and thumb
      errors.add_to_base("File upload failed.  Try a different image?")
      return false
    end
    return true
  end
  
  # Return true for a valid, nonempty image file.
  def valid_file?
    # The upload should be nonempty.
    if @image.size.zero?
      errors.add_to_base("Please enter an image filename")
      return false
    end   
    unless @image.content_type =~ /^image/
      errors.add(:image, "is not a recognized format")
      return false
    end
    if @image.size > 1.megabyte
      errors.add(:image, "can't be bigger than 1 megabyte")
      return false    
    end
    return true
  end
end