module TraceFiles

# File lib/trace_files.rb, line 12
def self.set spec_opts
  targets   = []
  files     = {}
  last_file = ''
  last_line = -1

  files_to_trace = spec_opts.fetch(:trace, []);
  io    = spec_opts.fetch(:io, $stdout)
  color = spec_opts.fetch(:color, "\e[32m") # ANSI.green default
  # target only existing readable files
  files_to_trace.each do |f|
    if File.exists?(f) && File.readable?(f)
      targets.push File.expand_path f
      targets.push File.basename f # sometimes the file is relative
    end
  end
  return if targets.empty?

  trace_point = TracePoint.new do |trace|
    file_path = trace.path
    if targets.include?(file_path)
      line_number = trace.lineno
      # never repeat a line
      unless file_path == last_file && line_number == last_line
        file_sym        = file_path.intern
        files[file_sym] = IO.readlines(file_path) if files[file_sym].nil?
        lines           = files[file_sym]

        # arrays are 0 indexed and line numbers start at one.
        io.print color if color # ANSI code
        io.puts lines[line_number - 1]
        io.print "\e[0m" if color # ANSI.clear

        last_file = file_path
        last_line = line_number
      end
    end
  end

  trace_point.enable
  trace_point
end