class ActionView::Template::Error

def annotated_source_code
  source_extract(4)
end

def file_name
  @template.identifier
end

def formatted_code_for(source_code, line_counter, indent)
  indent_template = "%#{indent}s: %s"
  source_code.map do |line|
    line_counter += 1
    indent_template % [line_counter, line]
  end
end

def initialize(template)
  super($!.message)
  set_backtrace($!.backtrace)
  @cause = $!
  @template, @sub_templates = template, nil
end

def line_number
  @line_number ||=
    if file_name
      regexp = /#{Regexp.escape File.basename(file_name)}:(\d+)/
      $1 if message =~ regexp || backtrace.find { |line| line =~ regexp }
    end
end

def source_extract(indentation = 0)
  return [] unless num = line_number
  num = num.to_i
  source_code = @template.encode!.split("\n")
  start_on_line = [ num - SOURCE_CODE_RADIUS - 1, 0 ].max
  end_on_line   = [ num + SOURCE_CODE_RADIUS - 1, source_code.length].min
  indent = end_on_line.to_s.size + indentation
  return [] unless source_code = source_code[start_on_line..end_on_line]
  formatted_code_for(source_code, start_on_line, indent)
end

def source_location
  if line_number
    "on line ##{line_number} of "
  else
    "in "
  end + file_name
end

def sub_template_message
  if @sub_templates
    "Trace of template inclusion: " +
    @sub_templates.collect(&:inspect).join(", ")
  else
    ""
  end
end

def sub_template_of(template_path)
  @sub_templates ||= []
  @sub_templates << template_path
end