class Parser::Source::Comment::Associator

def advance_comment
  @comment_num += 1
end

def advance_through_directives
  # Skip shebang.
  if current_comment && current_comment.text =~ /^#!/
    advance_comment
  end
  # Skip encoding line.
  if current_comment && current_comment.text =~ Buffer::ENCODING_RE
    advance_comment
  end
end

def associate
  @mapping     = Hash.new { |h, k| h[k] = [] }
  @comment_num = 0
  advance_through_directives if @skip_directives
  process(nil, @ast)
  @mapping
end

def associate_and_advance_comment(node)
  @mapping[node] << current_comment
  advance_comment
end

def current_comment
  @comments[@comment_num]
end

def current_comment_between?(prev_node, next_node)
  return false if current_comment.nil?
  comment_loc = current_comment.location.expression
  next_loc    = next_node.location.expression
  if prev_node.nil?
    comment_loc.end_pos <= next_loc.begin_pos
  else
    prev_loc  = prev_node.location.expression
    comment_loc.begin_pos >= prev_loc.end_pos &&
          comment_loc.end_pos <= next_loc.begin_pos
  end
end

def initialize(comments, ast)
  @comments    = comments
  @ast         = ast
  @skip_directives = true
end

def process(upper_node, node)
  if node.type == :begin
    prev_node, next_node = nil, upper_node
  else
    while current_comment_between?(prev_node, node)
      associate_and_advance_comment(node)
    end
    prev_node, next_node = nil, upper_node
  end
  node.children.each do |child|
    if child.is_a?(AST::Node) && child.location.expression
      prev_node, next_node = next_node, child
      process(prev_node, child)
    end
  end
end