class Prism::Translation::Parser::Lexer

def calculate_heredoc_whitespace(heredoc_token_index)
  next_token_index = heredoc_token_index
  nesting_level = 0
  previous_line = -1
  result = Float::MAX
  while (lexed[next_token_index] && next_token = lexed[next_token_index][0])
    next_token_index += 1
    next_next_token = lexed[next_token_index] && lexed[next_token_index][0]
    first_token_on_line = next_token.location.start_column == 0
    # String content inside nested heredocs and interpolation is ignored
    if next_token.type == :HEREDOC_START || next_token.type == :EMBEXPR_BEGIN
      # When interpolation is the first token of a line there is no string
      # content to check against. There will be no common whitespace.
      if nesting_level == 0 && first_token_on_line
        result = 0
      end
      nesting_level += 1
    elsif next_token.type == :HEREDOC_END || next_token.type == :EMBEXPR_END
      nesting_level -= 1
      # When we encountered the matching heredoc end, we can exit
      break if nesting_level == -1
    elsif next_token.type == :STRING_CONTENT && nesting_level == 0 && first_token_on_line
      common_whitespace = 0
      next_token.value[/^\s*/].each_char do |char|
        if char == "\t"
          common_whitespace = (common_whitespace / 8 + 1) * 8;
        else
          common_whitespace += 1
        end
      end
      is_first_token_on_line = next_token.location.start_line != previous_line
      # Whitespace is significant if followed by interpolation
      whitespace_only = common_whitespace == next_token.value.length && next_next_token&.location&.start_line != next_token.location.start_line
      if is_first_token_on_line && !whitespace_only && common_whitespace < result
        result = common_whitespace
        previous_line = next_token.location.start_line
      end
    end
  end
  result
end