Day 13 part 1

var
  answer: Natural

iterator pairs(inpLines: seq[seq[string]]): (string, string) =
  for i in 0..<inpLines.len:
    yield (inpLines[i][0], inpLines[i][1])

proc isNumber(s: string): bool {.inline.} =
  result = true
  for c in s:
    result = result and c.isDigit

proc isEmptyList(s: string): bool = s.strip == "[]"

proc isFullEnclosed(s: string): bool =  # might be buggy for '[]'
  if s[0] != '[' or s[s.len-1] != ']': return false
  var brCounter: int
  for i in 0..<s.len:
    if s[i] == '[': brCounter.inc
    elif s[i] == ']': brCounter.dec
    if brCounter == 0 and i != s.len-1: return false
  return true

proc isNumSerie(s: string): bool = 
  return ',' in s and s[0..<s.find(',')-1].isNumber

proc isListSerie(s: string): bool =
  if s[0] != '[': return false
  var brCounter: int
  for i in 0..<s.len:
    if s[i] == '[': brCounter.inc
    if brCounter == 0:
      return s[i] == ','
    elif s[i] == ']': brCounter.dec

proc stripList(s: string): string = result = s[1..<s.len-1]

proc ensureList(s: string): string {.inline.} =
  result = s
  if s.strip == "": return  # ignore empty stirngs
  if not s.isFullEnclosed: return '[' & s & ']'

proc getFirstNumber(s: string): string = 
  if ',' notin s: return s
  s[0..<s.find(',')]

proc getFirstList(s: string): string =
  if s[0] != '[': raise newException(OSError, "Unable to get List element")
  var brCounter: int
  for i in 0..<s.len:
    if s[i] == '[': brCounter.inc
    elif s[i] == ']': brCounter.dec
    if brCounter == 0: return s[1..<i]

proc getFirstElement(s: string): string =
  if s[0] == '[': return s.getFirstList
  s.getFirstNumber

proc discardFirstElement(s: string): string =
  if ',' notin s: return
  result = s[s.find(',')+1..<s.len]

proc correctOrder(left, right: string): bool =
  if left.strip == "": return true
  if right.strip == "": return false
  if left.isEmptyList:
    return true
  if right.isEmptyList: 
    return false    
  if left.isNumber and right.isNumber:
    return left.parseInt < right.parseInt
  if left.isNumSerie and right.isNumSerie:
    if left.getFirstNumber == right.getFirstNumber: 
      return correctOrder(left.discardFirstElement, right.discardFirstElement)
    return left.getFirstNumber.parseInt < right.getFirstNumber.parseInt
  if left.isNumSerie and right.isNumber or left.isNumber and right.isNumSerie:
    if left.getFirstNumber == right.getFirstNumber:
      result = correctOrder(left.discardFirstElement, right.discardFirstElement)
      return result
    return correctOrder(left.getFirstNumber, right.getFirstNumber)
  if left.isListSerie and right.isListSerie:
    if left.getFirstElement == right.getFirstElement:
      return correctOrder(left.discardFirstElement, right.discardFirstElement)
    return correctOrder(left.getFirstElement, right.getFirstElement)
  if left.isListSerie xor right.isListSerie:
    return correctOrder(left.getFirstElement.ensureList, right.getFirstElement.ensureList)
  if left.isFullEnclosed and right.isFullEnclosed:
    return correctOrder(left.stripList, right.stripList)
  if left.isFullEnclosed xor right.isFullEnclosed:
    return correctOrder(left.ensureList, right.ensureList)

let input = "input.txt".readFile.strip.split("\n\n").mapIt(it.split("\n"))

var idx: Natural
for left, right in input.pairs:
  idx.inc
  if correctOrder(left, right): 
    answer.inc idx

Answer is: 5675