#!/usr/bin/env ruby
# mend [-v] [-d] [-i[.BAK]] [FILES...] - parallel in-place line editor
#
#   {default}    print changed file contents
#   -v           verbose, print changed file contents with file and line numbers
#   -d           show unified diff against original file
#   -i[.bak]     change files inplace (keep a backup with extension if given)
#
# The input consists of lines (e.g. output of grep -nH):
#   FILE:NUMBER:CONTENT
# mend will then replace the line NUMBER of the FILE by CONTENT.
# Use
#   FILE:NUMBERd
# to delete the line instead.

require 'tempfile'

mode = :print
ext = nil

while ARGV.first =~ /\A-/
  arg = ARGV.shift
  if arg == "-d"
    mode = :diff
  elsif arg == "-v"
    mode = :verbose
  elsif arg =~ /\A-i(.*)/
    mode = :inplace
    ext = $1.empty? ? nil : $1
  else
    abort "Usage: mend [-d] [-i[.BAK]] [FILES...]"
  end
end

changes = {}

ARGF.each { |line|
  if line =~ /\A([^:]*):(\d+)(:(.*)|d$)/
    file, line, content = $1, $2.to_i, ($3 == "d" ? :delete : $4)
    changes[file] ||= {}
    changes[file][line] = content
  end
}

status = 0

changes.sort.each { |file, replacements|
  begin
    f = File.open(file)
  rescue SystemCallError => e
    warn "mend: can't read #{file}: #{e.message.sub(/ @ .*/, '')}"
    status = 2
    next
  end

  begin
    case mode
    when :print
      out = STDOUT
    when :diff
      pipe_in, out = IO.pipe
      diff = Process.spawn("diff", "-u",
                           "--label", file, "--label", file,
                           file, "-",
                           0 => pipe_in)
      pipe_in.close
    when :inplace
      begin
        perm = File.stat(file).mode
        out = Tempfile.new(File.basename(file), File.dirname(file))
      rescue SystemCallError => e
        warn "mend: can't create tempfile for #{file}: #{e.message}"
        status = 2
        next
      end
    end

    while line = f.gets
      next  if replacements[f.lineno] == :delete
      if mode == :verbose
        puts "#{file}:#{f.lineno}:#{replacements[f.lineno] || line}"
      else
        out.puts replacements[f.lineno] || line
      end
    end

    case mode
    when :diff
      out.close
      Process.wait(diff)
    when :inplace
      out.chmod(perm)
      out.close
      File.rename(file, file + ext)  if ext
      File.rename(out.path, file)
    end
  rescue SystemCallError => e
    warn "mend: fatal error: #{e}"
    exit 4
  ensure
    f.close
  end
}

exit status