module Erubis::InterpolationEnhancer

def self.desc   # :nodoc:
  "convert '<p><%=text%></p>' into '_buf << %Q`<p>\#{text}</p>`'"
end

def _add_text_to_str(str, text)
  return if !text || text.empty?
  str << text.gsub(/[`\#\\]/, '\\\\\&')
end

def add_expr_escaped(str, code)
  str << "\#{#{escaped_expr(code)}}"
end

def add_expr_literal(str, code)
  str << "\#{#{code}}"
end

def add_text(src, text)
  return if !text || text.empty?
  #src << " _buf << %Q`" << text << "`;"
  if text[-1] == ?\n
    text[-1] = "\\n"
    src << " #{@bufvar} << %Q`#{text}`\n"
  else
    src << " #{@bufvar} << %Q`#{text}`;"
  end
end

def convert_input(src, input)
  pat = @pattern
  regexp = pat.nil? || pat == '<% %>' ? Basic::Converter::DEFAULT_REGEXP : pattern_regexp(pat)
  pos = 0
  is_bol = true     # is beginning of line
  str = ''
  input.scan(regexp) do |indicator, code, tailch, rspace|
    match = Regexp.last_match()
    len  = match.begin(0) - pos
    text = input[pos, len]
    pos  = match.end(0)
    ch   = indicator ? indicator[0] : nil
    lspace = ch == ?= ? nil : detect_spaces_at_bol(text, is_bol)
    is_bol = rspace ? true : false
    _add_text_to_str(str, text)
    ## * when '<%= %>', do nothing
    ## * when '<% %>' or '<%# %>', delete spaces iff only spaces are around '<% %>'
    if ch == ?=              # <%= %>
      rspace = nil if tailch && !tailch.empty?
      str << lspace if lspace
      add_expr(str, code, indicator)
      str << rspace if rspace
    elsif ch == ?\#          # <%# %>
      n = code.count("\n") + (rspace ? 1 : 0)
      if @trim && lspace && rspace
        add_text(src, str)
        str = ''
        add_stmt(src, "\n" * n)
      else
        str << lspace if lspace
        add_text(src, str)
        str = ''
        add_stmt(src, "\n" * n)
        str << rspace if rspace
      end
    else                     # <% %>
      if @trim && lspace && rspace
        add_text(src, str)
        str = ''
        add_stmt(src, "#{lspace}#{code}#{rspace}")
      else
        str << lspace if lspace
        add_text(src, str)
        str = ''
        add_stmt(src, code)
        str << rspace if rspace
      end
    end
  end
  #rest = $' || input                       # ruby1.8
  rest = pos == 0 ? input : input[pos..-1]  # ruby1.9
  _add_text_to_str(str, rest)
  add_text(src, str)
end