class Sass::Tree::Visitors::CheckNesting

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_extend_parent?(parent, child)
  unless is_any_of?(parent, INVALID_EXTEND_PARENTS)
    "Extend directives may only be used within rules."
  end
end

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

def invalid_function_parent?(parent, child)
  "Functions may only be defined at the root of a document." unless parent.is_a?(Sass::Tree::RootNode)
end

def invalid_import_parent?(parent, child)
  if is_any_of?(@real_parent, INVALID_IMPORT_PARENTS)
    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?
  # If this is a nested @import, we need to make sure it doesn't have anything
  # that's legal at top-level but not in the current context (e.g. mixin defs).
  child.imported_file.to_tree.children.each {|c| visit(c)}
  nil
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_import_real_parent?(parent, child)
  
end

def invalid_mixindef_parent?(parent, child)
  "Mixins may only be defined at the root of a document." unless parent.is_a?(Sass::Tree::RootNode)
end

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

def invalid_prop_parent?(parent, child)
  unless is_any_of?(parent, INVALID_PROP_PARENTS)
    "Properties are only allowed within rules, directives, or other properties." + child.pseudo_class_selector_message
  end
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)
  for c in classes
    return true if val.is_a?(c)
  end
  return false
end

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

def visit(node)
  if error = (@parent && (
        try_send("invalid_#{node_name @parent}_child?", @parent, node) ||
        try_send("invalid_#{node_name node}_parent?", @parent, node))) ||
      (@real_parent && (
        try_send("invalid_#{node_name @real_parent}_real_child?", @real_parent, node) ||
        try_send("invalid_#{node_name node}_real_parent?", @real_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
  @parent = parent unless is_any_of?(parent, PARENT_CLASSES)
  old_real_parent, @real_parent = @real_parent, parent
  super
ensure
  @parent = old_parent
  @real_parent = old_real_parent
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_root(node)
  yield
rescue Sass::SyntaxError => e
  e.sass_template ||= node.template
  raise e
end