module Compass::SassExtensions::Functions::Sprites
  ZERO = Sass::Script::Number::new(0)
  VALID_SELECTORS = %w(hover active target)
  # Provides a consistent interface for getting a variable in ruby
  # from a keyword argument hash that accounts for underscores/dash equivalence
  # and allows the caller to pass a symbol instead of a string.
  module VariableReader
    def get_var(variable_name)
      self[variable_name.to_s.gsub(/-/,"_")]
    end
  end

  # Creates a Compass::SassExtensions::Sprites::SpriteMap object. A sprite map, when used in a property is the same
  # as calling sprite-url. So the following background properties are equivalent:
  #
  #     $icons: sprite-map("icons/*.png");
  #     background: sprite-url($icons) no-repeat;
  #     background: $icons no-repeat;
  #
  # The sprite map object will generate the sprite map image, if necessary,
  # the first time it is converted to a url. Simply constructing it has no side-effects.
  def sprite_map(glob, kwargs = {})
    kwargs.extend VariableReader
    Compass::SassExtensions::Sprites::SpriteMap.from_uri(glob, self, kwargs)
  end 
  Sass::Script::Functions.declare :sprite_map, [:glob], :var_kwargs => true

  # Returns the image and background position for use in a single shorthand property:
  #
  #     $icons: sprite-map("icons/*.png"); // contains icons/new.png among others.
  #     background: sprite($icons, new) no-repeat;
  #
  # Becomes:
  #
  #     background: url('/images/icons.png?12345678') 0 -24px no-repeat;
  def sprite(map, sprite, offset_x = ZERO, offset_y = ZERO)
    sprite = convert_sprite_name(sprite)
    verify_map(map)
    unless sprite.is_a?(Sass::Script::String)
      raise Sass::SyntaxError, %Q(The second argument to sprite() must be a sprite name. See http://beta.compass-style.org/help/tutorials/spriting/ for more information.)
    end
    url = sprite_url(map)
    position = sprite_position(map, sprite, offset_x, offset_y)
    Sass::Script::List.new([url] + position.value, :space)
  end
  Sass::Script::Functions.declare :sprite, [:map, :sprite]
  Sass::Script::Functions.declare :sprite, [:map, :sprite, :offset_x]
  Sass::Script::Functions.declare :sprite, [:map, :sprite, :offset_x, :offset_y]

  # Returns the name of a sprite map
  # The name is derived from the folder than contains the sprites.
  def sprite_map_name(map)
    verify_map(map, "sprite-map-name")
    Sass::Script::String.new(map.name)
  end
  Sass::Script::Functions.declare :sprite_name, [:sprite]

  # Returns the path to the original image file for the sprite with the given name
  def sprite_file(map, sprite)
    sprite = convert_sprite_name(sprite)
    verify_map(map, "sprite")
    verify_sprite(sprite)
    if image = map.image_for(sprite.value)
      Sass::Script::String.new(image.relative_file)
    else
      missing_image!(map, sprite)
    end
  end
  Sass::Script::Functions.declare :sprite_file, [:map, :sprite]

  # Returns voolean if sprite has a parent
  def sprite_does_not_have_parent(map, sprite)
    sprite = convert_sprite_name(sprite)
    verify_map map
    verify_sprite sprite
    Sass::Script::Bool.new map.image_for(sprite.value).parent.nil?
  end
  
  Sass::Script::Functions.declare :sprite_does_not_have_parent, [:map, :sprite]

  # Returns boolean if sprite has the selector
  def sprite_has_selector(map, sprite, selector)
    sprite = convert_sprite_name(sprite)
    verify_map map
    verify_sprite sprite
    unless VALID_SELECTORS.include?(selector.value)
      raise Sass::SyntaxError, "Invalid Selctor did you mean one of: #{VALID_SELECTORS.join(', ')}"
    end
    Sass::Script::Bool.new map.send(:"has_#{selector.value}?", sprite)
  end
  
  Sass::Script::Functions.declare :sprite_has_selector, [:map, :sprite, :selector]


  # Returns a url to the sprite image.
  def sprite_url(map)
    verify_map(map, "sprite-url")
    map.generate
    image_url(Sass::Script::String.new("#{map.path}-s#{map.uniqueness_hash}.png"),
              Sass::Script::Bool.new(false),
              Sass::Script::Bool.new(false))
  end
  Sass::Script::Functions.declare :sprite_url, [:map]

  # Returns the position for the original image in the sprite.
  # This is suitable for use as a value to background-position:
  #
  #     $icons: sprite-map("icons/*.png");
  #     background-position: sprite-position($icons, new);
  #
  # Might generate something like:
  #
  #     background-position: 0 -34px;
  #
  # You can adjust the background relative to this position by passing values for
  # `$offset-x` and `$offset-y`:
  #
  #     $icons: sprite-map("icons/*.png");
  #     background-position: sprite-position($icons, new, 3px, -2px);
  #
  # Would change the above output to:
  #
  #     background-position: 3px -36px;
  def sprite_position(map, sprite = nil, offset_x = ZERO, offset_y = ZERO)
    sprite = convert_sprite_name(sprite)
    verify_map(map, "sprite-position")
    unless sprite && sprite.is_a?(Sass::Script::String)
      raise Sass::SyntaxError, %Q(The second argument to sprite-position must be a sprite name. See http://beta.compass-style.org/help/tutorials/spriting/ for more information.)
    end
    image = map.image_for(sprite.value)
    unless image
      missing_image!(map, sprite)
    end
    if offset_x.unit_str == "%"
      x = offset_x # CE: Shouldn't this be a percentage of the total width?
    else
      x = offset_x.value - image.left
      x = Sass::Script::Number.new(x, x == 0 ? [] : ["px"])
    end
    y = offset_y.value - image.top
    y = Sass::Script::Number.new(y, y == 0 ? [] : ["px"])
    Sass::Script::List.new([x, y],:space)
  end
  Sass::Script::Functions.declare :sprite_position, [:map]
  Sass::Script::Functions.declare :sprite_position, [:map, :sprite]
  Sass::Script::Functions.declare :sprite_position, [:map, :sprite, :offset_x]
  Sass::Script::Functions.declare :sprite_position, [:map, :sprite, :offset_x, :offset_y]

  def sprite_image(*args)
    raise Sass::SyntaxError, %Q(The sprite-image() function has been replaced by sprite(). See http://beta.compass-style.org/help/tutorials/spriting/ for more information.)
  end

protected

  def convert_sprite_name(sprite)
    if sprite.is_a?(Sass::Script::Color)
      return Sass::Script::String.new(Sass::Script::Color::HTML4_COLORS_REVERSE[sprite.rgb])
    end
    sprite
  end

  def verify_map(map, error = "sprite")
    unless map.is_a?(Compass::SassExtensions::Sprites::SpriteMap)
      missing_sprite!(error)
    end
  end

  def verify_sprite(sprite)
    unless sprite.is_a?(Sass::Script::String)
      raise Sass::SyntaxError, %Q(The second argument to sprite() must be a sprite name. See http://beta.compass-style.org/help/tutorials/spriting/ for more information.)
    end
  end

  def missing_image!(map, sprite)
    raise Sass::SyntaxError, "No sprite called #{sprite} found in sprite map #{map.path}/#{map.name}. Did you mean one of: #{map.sprite_names.join(", ")}"
  end

  def missing_sprite!(function_name)
    raise Sass::SyntaxError, %Q(The first argument to #{function_name}() must be a sprite map. See http://beta.compass-style.org/help/tutorials/spriting/ for more information.)
  end

end