fastdiff.nim

import os, sets, hashes, strutils, sequtils


type
  HString = object
    str: string
    hash: Hash

proc hash*(str: HString): Hash =
  str.hash

proc toHString*(str: string): HString =
  result.hash = hash(str)
  shallowCopy(result.str, str)

converter toString*(str: HString): string =
  str.str

if paramCount() != 2:
  echo "mydiff file1 file2" 
  quit()

proc main(): void =
  let old_lines = readFile(paramStr(1)).splitLines().mapIt(it.toHString)
  let new_lines = readFile(paramStr(2)).splitLines().mapIt(it.toHString)

  let old_lines_set = toSet(old_lines) 
  let new_lines_set = toSet(new_lines)

  let old_added = old_lines_set - new_lines_set 
  let old_removed = new_lines_set - old_lines_set

  for line in old_lines:
    if line in old_added:
      echo "-", line.strip()
    elif line in old_removed:
      echo "+", line.strip()

  for line in new_lines:
    if line in old_added:
      echo "-", line.strip()
    elif line in old_removed:
      echo "+", line.strip()

main()