import strutils


type
  Color* = enum
    cRed, cGreen, cBlue, cYellow, cPurple

  ColorStack* = object
    pieces: array[5, int8]
    last: int8


proc init*(s: var ColorStack) =
  for i in 0..4:
    s.pieces[i] = -1
  s.last = -1


proc `[]`*(s: ColorStack, i: Natural): Color =
  if i > s.last:
    raise newException(IndexDefect, "index " & $i & " is out of bounds.")
  result = Color(s.pieces[i])


proc `[]`*(s: ColorStack, i: BackwardsIndex): Color =
  if s.last == -1:
    raise newException(IndexDefect, "index out of bounds, the container is empty.") # matching stdlib again
  result = Color(s.pieces[s.last - int8(i) + 1])


proc `[]=`*(s: var ColorStack, i: Natural, v: Color) =
  if i > s.last:
    raise newException(IndexDefect, "index " & $i & " is out of bounds.")
  s.pieces[i] = int8(v)


proc `$`*(s: ColorStack): string =
  result.add("St@[")
  for i in 0 .. s.last:
    let c = Color(s.pieces[i])
    result.add($c)
    if i < s.last:
      result.add(", ")
  result.add("]")


proc high*(s: ColorStack): int8 =
  result = s.last


proc low*(s: ColorStack): int8 =
  result = case s.last
  of -1: 0 # a bit weird but it's how the stdlib seq works
  else: s.last


proc len*(s: ColorStack): int8 =
  result = s.last + 1


iterator items*(s: ColorStack): Color =
  for i in 0 .. s.last:
    yield Color(s[i])


iterator asInt*(s: ColorStack): int8 =
  for i in 0 .. s.last:
    yield s.pieces[i] # no conversion, should speed up hashing? maybe


iterator pairs*(s: ColorStack): auto =
  var count = 0
  for c in s:
    yield (count, c)
    inc count


proc add*(s: var ColorStack, c: Color) =
  let i = s.last + 1
  s.pieces[i] = int8(c) # will raise exception if out of bounds
  s.last = i


proc insert*(s: var ColorStack, c: Color, idx: Natural = 0) =
  for i in countdown(s.last, int8(idx)):
    swap(s.pieces[i], s.pieces[i + 1]) # will also raise exception if out of bounds
  s.pieces[idx] = int8(c)
  inc s.last


proc delete*(s: var ColorStack, idx: Natural) =
  if idx > s.last:
    raise newException(IndexDefect, "index " & $idx & " is out of bounds.")
  s.pieces[idx] = -1
  dec s.last
  for i in int8(idx) .. s.last:
    swap(s.pieces[i], s.pieces[i + 1])


proc find(s: ColorStack, c: Color): int8 =
  let needle = int(c)
  for i, v in s.pieces:
    if v == needle:
      return i
  return -1


proc moveSubstack*(src, dst: var ColorStack; start: Natural) =
  var count = 0 # have to track this separately apparently
  for idx in (int8(start) .. src.last):
    swap(src.pieces[idx], dst.pieces[dst.last + 1 + count])
    inc count
  dst.last += int8(count)
  src.last -= int8(count)


proc moveSubstackPre*(src, dst: var ColorStack; start: Natural) =
  let ssLen = src.last - start + 1 # length of substack
  for i in countdown(dst.last, 0):
    swap(dst.pieces[i], dst.pieces[i + ssLen])

  var count = 0
  for i in start .. src.last:
    swap(src.pieces[i], dst.pieces[count])
    inc count

  dst.last += int8(ssLen)
  src.last -= int8(ssLen)


proc display(s: ColorStack) =
  var p: seq[string]
  for i in s.pieces:
    if i == -1:
      p.add("none")
    else:
      p.add($Color(i))
  echo "pieces: @[", p.join(", "), "], last: ", s.last
  echo "len: ", s.len, "\n"