class Sass::Tree::Visitors::CheckNesting

def initialize
  @parents = []
  @parent = nil
  @current_mixin_def = nil
end

def invalid_charset_parent?(parent, child)
  "@charset may only be used at the root of a document." unless parent.is_a?(Sass::Tree::RootNode)
end

def invalid_content_parent?(parent, child)
  if @current_mixin_def
    @current_mixin_def.has_content = true
    nil
  else
    "@content may only be used within a mixin."
  end
end

def invalid_extend_parent?(parent, child)
  return if is_any_of?(parent, VALID_EXTEND_PARENTS)
  "Extend directives may only be used within rules."
end

def invalid_function_child?(parent, child)
  return if is_any_of?(child, VALID_FUNCTION_CHILDREN)
  "Functions can only contain variable declarations and control directives."
end

def invalid_function_parent?(parent, child)
  return if (@parents.map {|p| p.class} & INVALID_IMPORT_PARENTS).empty?
  "Functions may not be defined within control directives or other mixins."
end

def invalid_import_parent?(parent, child)
  unless (@parents.map {|p| p.class} & INVALID_IMPORT_PARENTS).empty?
    return "Import directives may not be used within control directives or mixins."
  end
  return if parent.is_a?(Sass::Tree::RootNode)
  return "CSS import directives may only be used at the root of a document." if child.css_import?
rescue Sass::SyntaxError => e
  e.modify_backtrace(:filename => child.imported_file.options[:filename])
  e.add_backtrace(:filename => child.filename, :line => child.line)
  raise e
end

def invalid_mixindef_parent?(parent, child)
  return if (@parents.map {|p| p.class} & INVALID_IMPORT_PARENTS).empty?
  "Mixins may not be defined within control directives or other mixins."
end

def invalid_prop_child?(parent, child)
  return if is_any_of?(child, VALID_PROP_CHILDREN)
  "Illegal nesting: Only properties may be nested beneath properties."
end

def invalid_prop_parent?(parent, child)
  return if is_any_of?(parent, VALID_PROP_PARENTS)
  "Properties are only allowed within rules, directives, mixin includes, or other properties." +
    child.pseudo_class_selector_message
end

def invalid_return_parent?(parent, child)
  "@return may only be used within a function." unless parent.is_a?(Sass::Tree::FunctionNode)
end

def is_any_of?(val, classes)
  classes.each do |c|
    return true if val.is_a?(c)
  end
  false
end

def transparent_parent?(parent, grandparent)
  is_any_of?(parent, SCRIPT_NODES) ||
    (parent.bubbles? &&
     !grandparent.is_a?(Sass::Tree::RootNode) &&
     !grandparent.is_a?(Sass::Tree::AtRootNode))
end

def try_send(method, *args)
  return unless respond_to?(method, true)
  send(method, *args)
end

def visit(node)
  if (error = @parent && (
      try_send(@parent.class.invalid_child_method_name, @parent, node) ||
      try_send(node.class.invalid_parent_method_name, @parent, node)))
    raise Sass::SyntaxError.new(error)
  end
  super
rescue Sass::SyntaxError => e
  e.modify_backtrace(:filename => node.filename, :line => node.line)
  raise e
end

def visit_children(parent)
  old_parent = @parent
  # When checking a static tree, resolve at-roots to be sure they won't send
  # nodes where they don't belong.
  if parent.is_a?(Sass::Tree::AtRootNode) && parent.resolved_value
    old_parents = @parents
    @parents = @parents.reject {|p| parent.exclude_node?(p)}
    @parent = @parents.reverse.each_with_index.
      find {|p, i| !transparent_parent?(p, @parents[-i - 2])}.first
    begin
      return super
    ensure
      @parents = old_parents
      @parent = old_parent
    end
  end
  unless transparent_parent?(parent, old_parent)
    @parent = parent
  end
  @parents.push parent
  begin
    super
  ensure
    @parent = old_parent
    @parents.pop
  end
end

def visit_import(node)
  yield
rescue Sass::SyntaxError => e
  e.modify_backtrace(:filename => node.children.first.filename)
  e.add_backtrace(:filename => node.filename, :line => node.line)
  raise e
end

def visit_mixindef(node)
  @current_mixin_def, old_mixin_def = node, @current_mixin_def
  yield
ensure
  @current_mixin_def = old_mixin_def
end

def visit_root(node)
  yield
rescue Sass::SyntaxError => e
  e.sass_template ||= node.template
  raise e
end