Nim/lib/pure/unicode.nim

#
#
#            Nim's Runtime Library
#        (c) Copyright 2012 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

## This module provides support to handle the Unicode UTF-8 encoding.
##
## There are no specialized ``insert``, ``delete``, ``add`` and ``contains``
## procedures for ``seq[Rune]`` in this module because the generic variants
## of these procedures in the system module already work with it.
##
## The current version is compatible with Unicode v12.0.0.
##
## **See also:**
## * `strutils module <strutils.html>`_
## * `unidecode module <unidecode.html>`_
## * `encodings module <encodings.html>`_

include "system/inclrtl"
import std/strbasics
template toOa(s: string): auto = s.toOpenArray(0, s.high)

proc substr(s: openArray[char] , first, last: int): string =
  # Copied substr from system
  let first = max(first, 0)
  let L = max(min(last, high(s)) - first + 1, 0)
  result = newString(L)
  for i in 0 .. L-1:
    result[i] = s[i+first]

type
  RuneImpl = int32 # underlying type of Rune
  Rune* = distinct RuneImpl ## \
    ## Type that can hold a single Unicode code point.
    ##
    ## A Rune may be composed with other Runes to a character on the screen.
    ## `RuneImpl` is the underlying type used to store Runes, currently `int32`.

template ones(n: untyped): untyped = ((1 shl n)-1)

proc runeLen*(s: openArray[char]): int {.rtl, extern: "nuc$1".} =
  ## Returns the number of runes of the string ``s``.
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeLen == 6
    ## note: a.len == 8

  result = 0
  var i = 0
  while i < len(s):
    if uint(s[i]) <= 127: inc(i)
    elif uint(s[i]) shr 5 == 0b110: inc(i, 2)
    elif uint(s[i]) shr 4 == 0b1110: inc(i, 3)
    elif uint(s[i]) shr 3 == 0b11110: inc(i, 4)
    elif uint(s[i]) shr 2 == 0b111110: inc(i, 5)
    elif uint(s[i]) shr 1 == 0b1111110: inc(i, 6)
    else: inc i
    inc(result)

proc runeLenAt*(s: openArray[char], i: Natural): int =
  ## Returns the number of bytes the rune starting at ``s[i]`` takes.
  ##
  ## See also:
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeLenAt(0) == 1
    doAssert a.runeLenAt(1) == 2

  if uint(s[i]) <= 127: result = 1
  elif uint(s[i]) shr 5 == 0b110: result = 2
  elif uint(s[i]) shr 4 == 0b1110: result = 3
  elif uint(s[i]) shr 3 == 0b11110: result = 4
  elif uint(s[i]) shr 2 == 0b111110: result = 5
  elif uint(s[i]) shr 1 == 0b1111110: result = 6
  else: result = 1

const replRune = Rune(0xFFFD)

template fastRuneAt*(s: openArray[char] or string, i: int, result: untyped, doInc = true) =
  ## Returns the rune ``s[i]`` in ``result``.
  ##
  ## If ``doInc == true`` (default), ``i`` is incremented by the number
  ## of bytes that have been processed.
  bind ones
  if uint(s[i]) <= 127:
    result = Rune(uint(s[i]))
    when doInc: inc(i)
  elif uint(s[i]) shr 5 == 0b110:
    # assert(uint(s[i+1]) shr 6 == 0b10)
    if i <= s.len - 2:
      result = Rune((uint(s[i]) and (ones(5))) shl 6 or
                    (uint(s[i+1]) and ones(6)))
      when doInc: inc(i, 2)
    else:
      result = replRune
      when doInc: inc(i)
  elif uint(s[i]) shr 4 == 0b1110:
    # assert(uint(s[i+1]) shr 6 == 0b10)
    # assert(uint(s[i+2]) shr 6 == 0b10)
    if i <= s.len - 3:
      result = Rune((uint(s[i]) and ones(4)) shl 12 or
                    (uint(s[i+1]) and ones(6)) shl 6 or
                    (uint(s[i+2]) and ones(6)))
      when doInc: inc(i, 3)
    else:
      result = replRune
      when doInc: inc(i)
  elif uint(s[i]) shr 3 == 0b11110:
    # assert(uint(s[i+1]) shr 6 == 0b10)
    # assert(uint(s[i+2]) shr 6 == 0b10)
    # assert(uint(s[i+3]) shr 6 == 0b10)
    if i <= s.len - 4:
      result = Rune((uint(s[i]) and ones(3)) shl 18 or
                    (uint(s[i+1]) and ones(6)) shl 12 or
                    (uint(s[i+2]) and ones(6)) shl 6 or
                    (uint(s[i+3]) and ones(6)))
      when doInc: inc(i, 4)
    else:
      result = replRune
      when doInc: inc(i)
  elif uint(s[i]) shr 2 == 0b111110:
    # assert(uint(s[i+1]) shr 6 == 0b10)
    # assert(uint(s[i+2]) shr 6 == 0b10)
    # assert(uint(s[i+3]) shr 6 == 0b10)
    # assert(uint(s[i+4]) shr 6 == 0b10)
    if i <= s.len - 5:
      result = Rune((uint(s[i]) and ones(2)) shl 24 or
                (uint(s[i+1]) and ones(6)) shl 18 or
                (uint(s[i+2]) and ones(6)) shl 12 or
                (uint(s[i+3]) and ones(6)) shl 6 or
                (uint(s[i+4]) and ones(6)))
      when doInc: inc(i, 5)
    else:
      result = replRune
      when doInc: inc(i)
  elif uint(s[i]) shr 1 == 0b1111110:
    # assert(uint(s[i+1]) shr 6 == 0b10)
    # assert(uint(s[i+2]) shr 6 == 0b10)
    # assert(uint(s[i+3]) shr 6 == 0b10)
    # assert(uint(s[i+4]) shr 6 == 0b10)
    # assert(uint(s[i+5]) shr 6 == 0b10)
    if i <= s.len - 6:
      result = Rune((uint(s[i]) and ones(1)) shl 30 or
                    (uint(s[i+1]) and ones(6)) shl 24 or
                    (uint(s[i+2]) and ones(6)) shl 18 or
                    (uint(s[i+3]) and ones(6)) shl 12 or
                    (uint(s[i+4]) and ones(6)) shl 6 or
                    (uint(s[i+5]) and ones(6)))
      when doInc: inc(i, 6)
    else:
      result = replRune
      when doInc: inc(i)
  else:
    result = Rune(uint(s[i]))
    when doInc: inc(i)

proc runeAt*(s: openArray[char], i: Natural): Rune =
  ## Returns the rune in ``s`` at **byte index** ``i``.
  ##
  ## See also:
  ## * `runeAtPos proc <#runeAtPos,string,int>`_
  ## * `runeStrAtPos proc <#runeStrAtPos,string,Natural>`_
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeAt(1) == "ñ".runeAt(0)
    doAssert a.runeAt(2) == "ñ".runeAt(1)
    doAssert a.runeAt(3) == "y".runeAt(0)
  fastRuneAt(s, i, result, false)

proc validateUtf8*(s: openArray[char]): int =
  ## Returns the position of the invalid byte in ``s`` if the string ``s`` does
  ## not hold valid UTF-8 data. Otherwise ``-1`` is returned.
  ##
  ## See also:
  ## * `toUTF8 proc <#toUTF8,Rune>`_
  ## * `$ proc <#$,Rune>`_ alias for `toUTF8`
  ## * `fastToUTF8Copy template <#fastToUTF8Copy.t,Rune,string,int>`_
  var i = 0
  let L = s.len
  while i < L:
    if uint(s[i]) <= 127:
      inc(i)
    elif uint(s[i]) shr 5 == 0b110:
      if uint(s[i]) < 0xc2: return i # Catch overlong ascii representations.
      if i+1 < L and uint(s[i+1]) shr 6 == 0b10: inc(i, 2)
      else: return i
    elif uint(s[i]) shr 4 == 0b1110:
      if i+2 < L and uint(s[i+1]) shr 6 == 0b10 and uint(s[i+2]) shr 6 == 0b10:
        inc i, 3
      else: return i
    elif uint(s[i]) shr 3 == 0b11110:
      if i+3 < L and uint(s[i+1]) shr 6 == 0b10 and
                     uint(s[i+2]) shr 6 == 0b10 and
                     uint(s[i+3]) shr 6 == 0b10:
        inc i, 4
      else: return i
    else:
      return i
  return -1

template fastToUTF8Copy*(c: Rune, s: var string, pos: int, doInc = true) =
  ## Copies UTF-8 representation of ``c`` into the preallocated string ``s``
  ## starting at position ``pos``.
  ##
  ## If ``doInc == true`` (default), ``pos`` is incremented
  ## by the number of bytes that have been processed.
  ##
  ## To be the most efficient, make sure ``s`` is preallocated
  ## with an additional amount equal to the byte length of ``c``.
  ##
  ## See also:
  ## * `validateUtf8 proc <#validateUtf8,string>`_
  ## * `toUTF8 proc <#toUTF8,Rune>`_
  ## * `$ proc <#$,Rune>`_ alias for `toUTF8`
  var i = RuneImpl(c)
  if i <=% 127:
    s.setLen(pos+1)
    s[pos+0] = chr(i)
    when doInc: inc(pos)
  elif i <=% 0x07FF:
    s.setLen(pos+2)
    s[pos+0] = chr((i shr 6) or 0b110_00000)
    s[pos+1] = chr((i and ones(6)) or 0b10_0000_00)
    when doInc: inc(pos, 2)
  elif i <=% 0xFFFF:
    s.setLen(pos+3)
    s[pos+0] = chr(i shr 12 or 0b1110_0000)
    s[pos+1] = chr(i shr 6 and ones(6) or 0b10_0000_00)
    s[pos+2] = chr(i and ones(6) or 0b10_0000_00)
    when doInc: inc(pos, 3)
  elif i <=% 0x001FFFFF:
    s.setLen(pos+4)
    s[pos+0] = chr(i shr 18 or 0b1111_0000)
    s[pos+1] = chr(i shr 12 and ones(6) or 0b10_0000_00)
    s[pos+2] = chr(i shr 6 and ones(6) or 0b10_0000_00)
    s[pos+3] = chr(i and ones(6) or 0b10_0000_00)
    when doInc: inc(pos, 4)
  elif i <=% 0x03FFFFFF:
    s.setLen(pos+5)
    s[pos+0] = chr(i shr 24 or 0b111110_00)
    s[pos+1] = chr(i shr 18 and ones(6) or 0b10_0000_00)
    s[pos+2] = chr(i shr 12 and ones(6) or 0b10_0000_00)
    s[pos+3] = chr(i shr 6 and ones(6) or 0b10_0000_00)
    s[pos+4] = chr(i and ones(6) or 0b10_0000_00)
    when doInc: inc(pos, 5)
  elif i <=% 0x7FFFFFFF:
    s.setLen(pos+6)
    s[pos+0] = chr(i shr 30 or 0b1111110_0)
    s[pos+1] = chr(i shr 24 and ones(6) or 0b10_0000_00)
    s[pos+2] = chr(i shr 18 and ones(6) or 0b10_0000_00)
    s[pos+3] = chr(i shr 12 and ones(6) or 0b10_0000_00)
    s[pos+4] = chr(i shr 6 and ones(6) or 0b10_0000_00)
    s[pos+5] = chr(i and ones(6) or 0b10_0000_00)
    when doInc: inc(pos, 6)
  else:
    discard # error, exception?

proc toUTF8*(c: Rune): string {.rtl, extern: "nuc$1".} =
  ## Converts a rune into its UTF-8 representation.
  ##
  ## See also:
  ## * `validateUtf8 proc <#validateUtf8,string>`_
  ## * `$ proc <#$,Rune>`_ alias for `toUTF8`
  ## * `utf8 iterator <#utf8.i,string>`_
  ## * `fastToUTF8Copy template <#fastToUTF8Copy.t,Rune,string,int>`_
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeAt(1).toUTF8 == "ñ"

  result = ""
  fastToUTF8Copy(c, result, 0, false)

proc add*(s: var string; c: Rune) =
  ## Adds a rune ``c`` to a string ``s``.
  runnableExamples:
    var s = "abc"
    let c = "ä".runeAt(0)
    s.add(c)
    doAssert s == "abcä"

  let pos = s.len
  fastToUTF8Copy(c, s, pos, false)

proc `$`*(rune: Rune): string =
  ## An alias for `toUTF8 <#toUTF8,Rune>`_.
  ##
  ## See also:
  ## * `validateUtf8 proc <#validateUtf8,string>`_
  ## * `fastToUTF8Copy template <#fastToUTF8Copy.t,Rune,string,int>`_
  rune.toUTF8

proc `$`*(runes: seq[Rune]): string =
  ## Converts a sequence of Runes to a string.
  ##
  ## See also:
  ## * `toRunes <#toRunes,string>`_ for a reverse operation
  runnableExamples:
    let
      someString = "öÑ"
      someRunes = toRunes(someString)
    doAssert $someRunes == someString

  result = ""
  for rune in runes:
    result.add rune

proc runeOffset*(s: openArray[char], pos: Natural, start: Natural = 0): int =
  ## Returns the byte position of rune
  ## at position ``pos`` in ``s`` with an optional start byte position.
  ## Returns the special value -1 if it runs out of the string.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeReverseOffset proc <#runeReverseOffset,string,Positive>`_
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeOffset(1) == 1
    doAssert a.runeOffset(3) == 4
    doAssert a.runeOffset(4) == 6

  var
    i = 0
    o = start
  while i < pos:
    o += runeLenAt(s, o)
    if o >= s.len:
      return -1
    inc i
  return o

proc runeReverseOffset*(s: openArray[char], rev: Positive): (int, int) =
  ## Returns a tuple with the byte offset of the
  ## rune at position ``rev`` in ``s``, counting
  ## from the end (starting with 1) and the total
  ## number of runes in the string.
  ##
  ## Returns a negative value for offset if there are too few runes in
  ## the string to satisfy the request.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeOffset proc <#runeOffset,string,Natural,Natural>`_
  var
    a = rev.int
    o = 0
    x = 0
  let times = 2*rev.int-s.runeLen # transformed from rev.int - a < s.runeLen - rev.int
  while o < s.len:
    let r = runeLenAt(s, o)
    o += r
    if a > times:
      x += r
    dec a
  result = if a > 0: (-a, rev.int-a) else: (x, -a+rev.int)

proc runeAtPos*(s: openArray[char], pos: int): Rune =
  ## Returns the rune at position ``pos``.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeAt proc <#runeAt,string,Natural>`_
  ## * `runeStrAtPos proc <#runeStrAtPos,string,Natural>`_
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  fastRuneAt(s, runeOffset(s, pos), result, false)

proc runeStrAtPos*(s: openArray[char], pos: Natural): string =
  ## Returns the rune at position ``pos`` as UTF8 String.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeAt proc <#runeAt,string,Natural>`_
  ## * `runeAtPos proc <#runeAtPos,string,int>`_
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  let o = runeOffset(s, pos)
  substr(s.toOpenArray(o,  (o+runeLenAt(s, o)-1)))

proc runeSubStr*(s: openArray[char], pos: int, len: int = int.high): string =
  ## Returns the UTF-8 substring starting at code point ``pos``
  ## with ``len`` code points.
  ##
  ## If ``pos`` or ``len`` is negative they count from
  ## the end of the string. If ``len`` is not given it means the longest
  ## possible string.
  runnableExamples:
    let s = "Hänsel  ««: 10,00€"
    doAssert(runeSubStr(s, 0, 2) == "Hä")
    doAssert(runeSubStr(s, 10, 1) == ":")
    doAssert(runeSubStr(s, -6) == "10,00€")
    doAssert(runeSubStr(s, 10) == ": 10,00€")
    doAssert(runeSubStr(s, 12, 5) == "10,00")
    doAssert(runeSubStr(s, -6, 3) == "10,")

  if pos < 0:
    let (o, rl) = runeReverseOffset(s, -pos)
    if len >= rl:
      result = s.substr(o, s.high)
    elif len < 0:
      let e = rl + len
      if e < 0:
        result = ""
      else:
        result = s.substr(o, runeOffset(s, e-(rl+pos), o)-1)
    else:
      result = s.substr(o, runeOffset(s, len, o)-1)
  else:
    let o = runeOffset(s, pos)
    if o < 0:
      result = ""
    elif len == int.high:
      result = s.substr(o, s.len-1)
    elif len < 0:
      let (e, rl) = runeReverseOffset(s, -len)
      discard rl
      if e <= 0:
        result = ""
      else:
        result = s.substr(o, e-1)
    else:
      var e = runeOffset(s, len, o)
      if e < 0:
        e = s.len
      result = s.substr(o, e-1)

proc `<=%`*(a, b: Rune): bool =
  ## Checks if code point of `a` is smaller or equal to code point of `b`.
  runnableExamples:
    let
      a = "ú".runeAt(0)
      b = "ü".runeAt(0)
    doAssert a <=% b
  return int(a) <=% int(b)

proc `<%`*(a, b: Rune): bool =
  ## Checks if code point of `a` is smaller than code point of `b`.
  runnableExamples:
    let
      a = "ú".runeAt(0)
      b = "ü".runeAt(0)
    doAssert a <% b
  return int(a) <% int(b)

proc `==`*(a, b: Rune): bool =
  ## Checks if two runes are equal.
  return int(a) == int(b)


include "includes/unicode_ranges"

proc binarySearch(c: RuneImpl, tab: openArray[int], len, stride: int): int =
  var n = len
  var t = 0
  while n > 1:
    var m = n div 2
    var p = t + m*stride
    if c >= tab[p]:
      t = p
      n = n-m
    else:
      n = m
  if n != 0 and c >= tab[t]:
    return t
  return -1

proc toLower*(c: Rune): Rune {.rtl, extern: "nuc$1".} =
  ## Converts ``c`` into lower case. This works for any rune.
  ##
  ## If possible, prefer ``toLower`` over ``toUpper``.
  ##
  ## See also:
  ## * `toUpper proc <#toUpper,Rune>`_
  ## * `toTitle proc <#toTitle,Rune>`_
  ## * `isLower proc <#isLower,Rune>`_
  var c = RuneImpl(c)
  var p = binarySearch(c, toLowerRanges, len(toLowerRanges) div 3, 3)
  if p >= 0 and c >= toLowerRanges[p] and c <= toLowerRanges[p+1]:
    return Rune(c + toLowerRanges[p+2] - 500)
  p = binarySearch(c, toLowerSinglets, len(toLowerSinglets) div 2, 2)
  if p >= 0 and c == toLowerSinglets[p]:
    return Rune(c + toLowerSinglets[p+1] - 500)
  return Rune(c)

proc toUpper*(c: Rune): Rune {.rtl, extern: "nuc$1".} =
  ## Converts ``c`` into upper case. This works for any rune.
  ##
  ## If possible, prefer ``toLower`` over ``toUpper``.
  ##
  ## See also:
  ## * `toLower proc <#toLower,Rune>`_
  ## * `toTitle proc <#toTitle,Rune>`_
  ## * `isUpper proc <#isUpper,Rune>`_
  var c = RuneImpl(c)
  var p = binarySearch(c, toUpperRanges, len(toUpperRanges) div 3, 3)
  if p >= 0 and c >= toUpperRanges[p] and c <= toUpperRanges[p+1]:
    return Rune(c + toUpperRanges[p+2] - 500)
  p = binarySearch(c, toUpperSinglets, len(toUpperSinglets) div 2, 2)
  if p >= 0 and c == toUpperSinglets[p]:
    return Rune(c + toUpperSinglets[p+1] - 500)
  return Rune(c)

proc toTitle*(c: Rune): Rune {.rtl, extern: "nuc$1".} =
  ## Converts ``c`` to title case.
  ##
  ## See also:
  ## * `toLower proc <#toLower,Rune>`_
  ## * `toUpper proc <#toUpper,Rune>`_
  ## * `isTitle proc <#isTitle,Rune>`_
  var c = RuneImpl(c)
  var p = binarySearch(c, toTitleSinglets, len(toTitleSinglets) div 2, 2)
  if p >= 0 and c == toTitleSinglets[p]:
    return Rune(c + toTitleSinglets[p+1] - 500)
  return Rune(c)

proc isLower*(c: Rune): bool {.rtl, extern: "nuc$1".} =
  ## Returns true if ``c`` is a lower case rune.
  ##
  ## If possible, prefer ``isLower`` over ``isUpper``.
  ##
  ## See also:
  ## * `toLower proc <#toLower,Rune>`_
  ## * `isUpper proc <#isUpper,Rune>`_
  ## * `isTitle proc <#isTitle,Rune>`_
  var c = RuneImpl(c)
  # Note: toUpperRanges is correct here!
  var p = binarySearch(c, toUpperRanges, len(toUpperRanges) div 3, 3)
  if p >= 0 and c >= toUpperRanges[p] and c <= toUpperRanges[p+1]:
    return true
  p = binarySearch(c, toUpperSinglets, len(toUpperSinglets) div 2, 2)
  if p >= 0 and c == toUpperSinglets[p]:
    return true

proc isUpper*(c: Rune): bool {.rtl, extern: "nuc$1".} =
  ## Returns true if ``c`` is a upper case rune.
  ##
  ## If possible, prefer ``isLower`` over ``isUpper``.
  ##
  ## See also:
  ## * `toUpper proc <#toUpper,Rune>`_
  ## * `isLower proc <#isLower,Rune>`_
  ## * `isTitle proc <#isTitle,Rune>`_
  ## * `isAlpha proc <#isAlpha,Rune>`_
  ## * `isWhiteSpace proc <#isWhiteSpace,Rune>`_
  var c = RuneImpl(c)
  # Note: toLowerRanges is correct here!
  var p = binarySearch(c, toLowerRanges, len(toLowerRanges) div 3, 3)
  if p >= 0 and c >= toLowerRanges[p] and c <= toLowerRanges[p+1]:
    return true
  p = binarySearch(c, toLowerSinglets, len(toLowerSinglets) div 2, 2)
  if p >= 0 and c == toLowerSinglets[p]:
    return true

proc isAlpha*(c: Rune): bool {.rtl, extern: "nuc$1".} =
  ## Returns true if ``c`` is an *alpha* rune (i.e., a letter).
  ##
  ## See also:
  ## * `isLower proc <#isLower,Rune>`_
  ## * `isTitle proc <#isTitle,Rune>`_
  ## * `isAlpha proc <#isAlpha,Rune>`_
  ## * `isWhiteSpace proc <#isWhiteSpace,Rune>`_
  ## * `isCombining proc <#isCombining,Rune>`_
  if isUpper(c) or isLower(c):
    return true
  var c = RuneImpl(c)
  var p = binarySearch(c, alphaRanges, len(alphaRanges) div 2, 2)
  if p >= 0 and c >= alphaRanges[p] and c <= alphaRanges[p+1]:
    return true
  p = binarySearch(c, alphaSinglets, len(alphaSinglets), 1)
  if p >= 0 and c == alphaSinglets[p]:
    return true

proc isTitle*(c: Rune): bool {.rtl, extern: "nuc$1".} =
  ## Returns true if ``c`` is a Unicode titlecase code point.
  ##
  ## See also:
  ## * `toTitle proc <#toTitle,Rune>`_
  ## * `isLower proc <#isLower,Rune>`_
  ## * `isUpper proc <#isUpper,Rune>`_
  ## * `isAlpha proc <#isAlpha,Rune>`_
  ## * `isWhiteSpace proc <#isWhiteSpace,Rune>`_
  return isUpper(c) and isLower(c)

proc isWhiteSpace*(c: Rune): bool {.rtl, extern: "nuc$1".} =
  ## Returns true if ``c`` is a Unicode whitespace code point.
  ##
  ## See also:
  ## * `isLower proc <#isLower,Rune>`_
  ## * `isUpper proc <#isUpper,Rune>`_
  ## * `isTitle proc <#isTitle,Rune>`_
  ## * `isAlpha proc <#isAlpha,Rune>`_
  var c = RuneImpl(c)
  var p = binarySearch(c, spaceRanges, len(spaceRanges) div 2, 2)
  if p >= 0 and c >= spaceRanges[p] and c <= spaceRanges[p+1]:
    return true

proc isCombining*(c: Rune): bool {.rtl, extern: "nuc$1".} =
  ## Returns true if ``c`` is a Unicode combining code unit.
  ##
  ## See also:
  ## * `isLower proc <#isLower,Rune>`_
  ## * `isUpper proc <#isUpper,Rune>`_
  ## * `isTitle proc <#isTitle,Rune>`_
  ## * `isAlpha proc <#isAlpha,Rune>`_
  var c = RuneImpl(c)

  # Optimized to return false immediately for ASCII
  return c >= 0x0300 and (c <= 0x036f or
    (c >= 0x1ab0 and c <= 0x1aff) or
    (c >= 0x1dc0 and c <= 0x1dff) or
    (c >= 0x20d0 and c <= 0x20ff) or
    (c >= 0xfe20 and c <= 0xfe2f))

template runeCheck(s, runeProc) =
  ## Common code for isAlpha and isSpace.
  result = if len(s) == 0: false else: true
  var
    i = 0
    rune: Rune
  while i < len(s) and result:
    fastRuneAt(s, i, rune, doInc = true)
    result = runeProc(rune) and result

proc isAlpha*(s: openArray[char]): bool {.noSideEffect,
  rtl, extern: "nuc$1Str".} =
  ## Returns true if ``s`` contains all alphabetic runes.
  runnableExamples:
    let a = "añyóng"
    doAssert a.isAlpha
  runeCheck(s, isAlpha)

proc isSpace*(s: openArray[char]): bool {.noSideEffect,
  rtl, extern: "nuc$1Str".} =
  ## Returns true if ``s`` contains all whitespace runes.
  runnableExamples:
    let a = "\t\l \v\r\f"
    doAssert a.isSpace
  runeCheck(s, isWhiteSpace)


template convertRune(s, runeProc) =
  ## Convert runes in ``s`` using ``runeProc`` as the converter.
  result = newString(len(s))
  var
    i = 0
    resultIndex = 0
    rune: Rune
  while i < len(s):
    fastRuneAt(s, i, rune, doInc = true)
    rune = runeProc(rune)
    fastToUTF8Copy(rune, result, resultIndex, doInc = true)

proc toUpper*(s: openArray[char]): string {.noSideEffect,
  rtl, extern: "nuc$1Str".} =
  ## Converts ``s`` into upper-case runes.
  runnableExamples:
    doAssert toUpper("abγ") == "ABΓ"
  convertRune(s, toUpper)

proc toLower*(s: openArray[char]): string {.noSideEffect,
  rtl, extern: "nuc$1Str".} =
  ## Converts ``s`` into lower-case runes.
  runnableExamples:
    doAssert toLower("ABΓ") == "abγ"
  convertRune(s, toLower)

proc swapCase*(s: openArray[char]): string {.noSideEffect,
  rtl, extern: "nuc$1".} =
  ## Swaps the case of runes in ``s``.
  ##
  ## Returns a new string such that the cases of all runes
  ## are swapped if possible.
  runnableExamples:
    doAssert swapCase("Αlpha Βeta Γamma") == "αLPHA βETA γAMMA"

  var
    i = 0
    resultIndex = 0
    rune: Rune
  result = newString(len(s))
  while i < len(s):
    fastRuneAt(s, i, rune)
    if rune.isUpper():
      rune = rune.toLower()
    elif rune.isLower():
      rune = rune.toUpper()
    fastToUTF8Copy(rune, result, resultIndex, doInc = true)

proc capitalize*(s: openArray[char]): string {.noSideEffect,
  rtl, extern: "nuc$1".} =
  ## Converts the first character of ``s`` into an upper-case rune.
  runnableExamples:
    doAssert capitalize("βeta") == "Βeta"

  if len(s) == 0:
    return ""
  var
    rune: Rune
    i = 0
  fastRuneAt(s, i, rune, doInc = true)
  result = $toUpper(rune) & substr(s.toOpenArray(i, s.high))

when not defined(nimHasEffectsOf):
  {.pragma: effectsOf.}

proc translate*(s: openArray[char], replacements: proc(key: string): string): string {.
  rtl, extern: "nuc$1", effectsOf: replacements.} =
  ## Translates words in a string using the ``replacements`` proc to substitute
  ## words inside ``s`` with their replacements.
  ##
  ## ``replacements`` is any proc that takes a word and returns
  ## a new word to fill it's place.
  runnableExamples:
    proc wordToNumber(s: string): string =
      case s
      of "one": "1"
      of "two": "2"
      else: s
    let a = "one two three four"
    doAssert a.translate(wordToNumber) == "1 2 three four"

  # Allocate memory for the new string based on the old one.
  # If the new string length is less than the old, no allocations
  # will be needed. If the new string length is greater than the
  # old, then maybe only one allocation is needed
  result = newStringOfCap(s.len)
  var
    index = 0
    lastIndex = 0
    wordStart = 0
    inWord = false
    rune: Rune

  while index < len(s):
    lastIndex = index
    fastRuneAt(s, index, rune)
    let whiteSpace = rune.isWhiteSpace()

    if whiteSpace and inWord:
      # If we've reached the end of a word
      let word = substr(s.toOpenArray(wordStart, lastIndex - 1))
      result.add(replacements(word))
      result.add($rune)
      inWord = false
    elif not whiteSpace and not inWord:
      # If we've hit a non space character and
      # are not currently in a word, track
      # the starting index of the word
      inWord = true
      wordStart = lastIndex
    elif whiteSpace:
      result.add($rune)

  if wordStart < len(s) and inWord:
    # Get the trailing word at the end
    let word = substr(s.toOpenArray(wordStart,  s.high))
    result.add(replacements(word))

proc title*(s: openArray[char]): string {.noSideEffect,
  rtl, extern: "nuc$1".} =
  ## Converts ``s`` to a unicode title.
  ##
  ## Returns a new string such that the first character
  ## in each word inside ``s`` is capitalized.
  runnableExamples:
    doAssert title("αlpha βeta γamma") == "Αlpha Βeta Γamma"

  var
    i = 0
    resultIndex = 0
    rune: Rune
  result = newString(len(s))
  var firstRune = true

  while i < len(s):
    fastRuneAt(s, i, rune)
    if not rune.isWhiteSpace() and firstRune:
      rune = rune.toUpper()
      firstRune = false
    elif rune.isWhiteSpace():
      firstRune = true
    fastToUTF8Copy(rune, result, resultIndex, doInc = true)


iterator runes*(s: openArray[char]): Rune =
  ## Iterates over any rune of the string ``s`` returning runes.
  var
    i = 0
    result: Rune
  while i < len(s):
    fastRuneAt(s, i, result, true)
    yield result

iterator utf8*(s: openArray[char]): string =
  ## Iterates over any rune of the string ``s`` returning utf8 values.
  ##
  ## See also:
  ## * `validateUtf8 proc <#validateUtf8,string>`_
  ## * `toUTF8 proc <#toUTF8,Rune>`_
  ## * `$ proc <#$,Rune>`_ alias for `toUTF8`
  ## * `fastToUTF8Copy template <#fastToUTF8Copy.t,Rune,string,int>`_
  var o = 0
  while o < s.len:
    let n = runeLenAt(s, o)
    yield substr(s.toOpenArray(o, (o+n-1)))
    o += n

proc toRunes*(s: openArray[char]): seq[Rune] =
  ## Obtains a sequence containing the Runes in ``s``.
  ##
  ## See also:
  ## * `$ proc <#$,Rune>`_ for a reverse operation
  runnableExamples:
    let a = toRunes("aáä")
    doAssert a == @["a".runeAt(0), "á".runeAt(0), "ä".runeAt(0)]

  result = newSeq[Rune]()
  for r in s.runes:
    result.add(r)

proc cmpRunesIgnoreCase*(a, b: openArray[char]): int {.rtl, extern: "nuc$1".} =
  ## Compares two UTF-8 strings and ignores the case. Returns:
  ##
  ## | 0 if a == b
  ## | < 0 if a < b
  ## | > 0 if a > b
  var i = 0
  var j = 0
  var ar, br: Rune
  while i < a.len and j < b.len:
    # slow path:
    fastRuneAt(a, i, ar)
    fastRuneAt(b, j, br)
    result = RuneImpl(toLower(ar)) - RuneImpl(toLower(br))
    if result != 0: return
  result = a.len - b.len

proc reversed*(s: openArray[char]): string =
  ## Returns the reverse of ``s``, interpreting it as runes.
  ##
  ## Unicode combining characters are correctly interpreted as well.
  runnableExamples:
    assert reversed("Reverse this!") == "!siht esreveR"
    assert reversed("先秦兩漢") == "漢兩秦先"
    assert reversed("as⃝df̅") == "f̅ds⃝a"
    assert reversed("a⃞b⃞c⃞") == "c⃞b⃞a⃞"

  var
    i = 0
    lastI = 0
    newPos = len(s) - 1
    blockPos = 0
    r: Rune

  template reverseUntil(pos) =
    var j = pos - 1
    while j > blockPos:
      result[newPos] = s[j]
      dec j
      dec newPos
    blockPos = pos - 1

  result = newString(len(s))

  while i < len(s):
    lastI = i
    fastRuneAt(s, i, r, true)
    if not isCombining(r):
      reverseUntil(lastI)

  reverseUntil(len(s))

proc graphemeLen*(s: openArray[char]; i: Natural): Natural =
  ## The number of bytes belonging to byte index ``s[i]``,
  ## including following combining code unit.
  runnableExamples:
    let a = "añyóng"
    doAssert a.graphemeLen(1) == 2 ## ñ
    doAssert a.graphemeLen(2) == 1
    doAssert a.graphemeLen(4) == 2 ## ó

  var j = i.int
  var r, r2: Rune
  if j < s.len:
    fastRuneAt(s, j, r, true)
    result = j-i
    while j < s.len:
      fastRuneAt(s, j, r2, true)
      if not isCombining(r2): break
      result = j-i

proc lastRune*(s: openArray[char]; last: int): (Rune, int) =
  ## Length of the last rune in ``s[0..last]``. Returns the rune and its length
  ## in bytes.
  if s[last] <= chr(127):
    result = (Rune(s[last]), 1)
  else:
    var L = 0
    while last-L >= 0 and uint(s[last-L]) shr 6 == 0b10: inc(L)
    var r: Rune
    fastRuneAt(s, last-L, r, false)
    result = (r, L+1)

proc size*(r: Rune): int {.noSideEffect.} =
  ## Returns the number of bytes the rune ``r`` takes.
  runnableExamples:
    let a = toRunes "aá"
    doAssert size(a[0]) == 1
    doAssert size(a[1]) == 2

  let v = r.uint32
  if v <= 0x007F'u32: result = 1
  elif v <= 0x07FF'u32: result = 2
  elif v <= 0xFFFF'u32: result = 3
  elif v <= 0x1FFFFF'u32: result = 4
  elif v <= 0x3FFFFFF'u32: result = 5
  elif v <= 0x7FFFFFFF'u32: result = 6
  else: result = 1

# --------- Private templates for different split separators -----------
proc stringHasSep(s: openArray[char], index: int, seps: openArray[Rune]): bool =
  var rune: Rune
  fastRuneAt(s, index, rune, false)
  return seps.contains(rune)

proc stringHasSep(s: openArray[char], index: int, sep: Rune): bool =
  var rune: Rune
  fastRuneAt(s, index, rune, false)
  return sep == rune

template splitCommon(s, sep, maxsplit: untyped) =
  ## Common code for split procedures.
  let
    sLen = len(s)
  var
    last = 0
    splits = maxsplit
  if sLen > 0:
    while last <= sLen:
      var first = last
      while last < sLen and not stringHasSep(s, last, sep):
        inc(last, runeLenAt(s, last))
      if splits == 0: last = sLen
      yield substr(s.toOpenArray(first, (last - 1)))
      if splits == 0: break
      dec(splits)
      inc(last, if last < sLen: runeLenAt(s, last) else: 1)

iterator split*(s: openArray[char], seps: openArray[Rune] = unicodeSpaces,
  maxsplit: int = -1): string =
  ## Splits the unicode string ``s`` into substrings using a group of separators.
  ##
  ## Substrings are separated by a substring containing only ``seps``.
  runnableExamples:
    import std/sequtils

    assert toSeq("hÃllo\lthis\lis an\texample\l是".split) ==
      @["hÃllo", "this", "is", "an", "example", "是"]

    # And the following code splits the same string using a sequence of Runes.
    assert toSeq(split("añyóng:hÃllo;是$example", ";:$".toRunes)) ==
      @["añyóng", "hÃllo", "是", "example"]

    # example with a `Rune` separator and unused one `;`:
    assert toSeq(split("ab是de:f:", ";:是".toRunes)) == @["ab", "de", "f", ""]

    # Another example that splits a string containing a date.
    let date = "2012-11-20T22:08:08.398990"

    assert toSeq(split(date, " -:T".toRunes)) ==
      @["2012", "11", "20", "22", "08", "08.398990"]

  splitCommon(s, seps, maxsplit)

iterator splitWhitespace*(s: openArray[char]): string =
  ## Splits a unicode string at whitespace runes.
  splitCommon(s, unicodeSpaces, -1)

template accResult(iter: untyped) =
  result = @[]
  for x in iter: add(result, x)

proc splitWhitespace*(s: openArray[char]): seq[string] {.noSideEffect,
  rtl, extern: "ncuSplitWhitespace".} =
  ## The same as the `splitWhitespace <#splitWhitespace.i,string>`_
  ## iterator, but is a proc that returns a sequence of substrings.
  accResult(splitWhitespace(s))

iterator split*(s: openArray[char], sep: Rune, maxsplit: int = -1): string =
  ## Splits the unicode string ``s`` into substrings using a single separator.
  ## Substrings are separated by the rune ``sep``.
  runnableExamples:
    import std/sequtils

    assert toSeq(split(";;hÃllo;this;is;an;;example;;;是", ";".runeAt(0))) ==
      @["", "", "hÃllo", "this", "is", "an", "", "example", "", "", "是"]

  splitCommon(s, sep, maxsplit)

proc split*(s: openArray[char], seps: openArray[Rune] = unicodeSpaces, maxsplit: int = -1):
    seq[string] {.noSideEffect, rtl, extern: "nucSplitRunes".} =
  ## The same as the `split iterator <#split.i,string,openArray[Rune],int>`_,
  ## but is a proc that returns a sequence of substrings.
  accResult(split(s, seps, maxsplit))

proc split*(s: openArray[char], sep: Rune, maxsplit: int = -1): seq[string] {.noSideEffect,
  rtl, extern: "nucSplitRune".} =
  ## The same as the `split iterator <#split.i,string,Rune,int>`_, but is a proc
  ## that returns a sequence of substrings.
  accResult(split(s, sep, maxsplit))

proc strip*(s: openArray[char], leading = true, trailing = true,
            runes: openArray[Rune] = unicodeSpaces): string {.noSideEffect,
            rtl, extern: "nucStrip".} =
  ## Strips leading or trailing ``runes`` from ``s`` and returns
  ## the resulting string.
  ##
  ## If ``leading`` is true (default), leading ``runes`` are stripped.
  ## If ``trailing`` is true (default), trailing ``runes`` are stripped.
  ## If both are false, the string is returned unchanged.
  runnableExamples:
    let a = "\táñyóng   "
    doAssert a.strip == "áñyóng"
    doAssert a.strip(leading = false) == "\táñyóng"
    doAssert a.strip(trailing = false) == "áñyóng   "

  var
    sI = 0          ## starting index into string ``s``
    eI = len(s) - 1 ## ending index into ``s``, where the last ``Rune`` starts
  if leading:
    var
      i = 0
      xI: int ## value of ``sI`` at the beginning of the iteration
      rune: Rune
    while i < len(s):
      xI = i
      fastRuneAt(s, i, rune)
      sI = i # Assume to start from next rune
      if not runes.contains(rune):
        sI = xI # Go back to where the current rune starts
        break
  if trailing:
    var
      i = eI
      xI: int
      rune: Rune
    while i >= 0:
      xI = i
      fastRuneAt(s, xI, rune)
      var yI = i - 1
      while yI >= 0:
        var
          yIend = yI
          pRune: Rune
        fastRuneAt(s, yIend, pRune)
        if yIend < xI: break
        i = yI
        rune = pRune
        dec(yI)
      if not runes.contains(rune):
        eI = xI - 1
        break
      dec(i)
  let newLen = eI - sI + 1
  result = newStringOfCap(newLen)
  if newLen > 0:
    result.add substr(s.toOpenArray(sI, eI))

proc repeat*(c: Rune, count: Natural): string {.noSideEffect,
  rtl, extern: "nucRepeatRune".} =
  ## Returns a string of ``count`` Runes ``c``.
  ##
  ## The returned string will have a rune-length of ``count``.
  runnableExamples:
    let a = "ñ".runeAt(0)
    doAssert a.repeat(5) == "ñññññ"

  let s = $c
  result = newStringOfCap(count * s.len)
  for i in 0 ..< count:
    result.add s

proc align*(s: openArray[char], count: Natural, padding = ' '.Rune): string {.
  noSideEffect, rtl, extern: "nucAlignString".} =
  ## Aligns a unicode string ``s`` with ``padding``, so that it has a rune-length
  ## of ``count``.
  ##
  ## ``padding`` characters (by default spaces) are added before ``s`` resulting in
  ## right alignment. If ``s.runelen >= count``, no spaces are added and ``s`` is
  ## returned unchanged. If you need to left align a string use the `alignLeft
  ## proc <#alignLeft,string,Natural>`_.
  runnableExamples:
    assert align("abc", 4) == " abc"
    assert align("a", 0) == "a"
    assert align("1232", 6) == "  1232"
    assert align("1232", 6, '#'.Rune) == "##1232"
    assert align("Åge", 5) == "  Åge"
    assert align("×", 4, '_'.Rune) == "___×"

  let sLen = s.runeLen
  if sLen < count:
    let padStr = $padding
    result = newStringOfCap(padStr.len * count)
    let spaces = count - sLen
    for i in 0 ..< spaces: result.add padStr
    result.add s
  else:
    result = s.substr

proc alignLeft*(s: openArray[char], count: Natural, padding = ' '.Rune): string {.
    noSideEffect.} =
  ## Left-aligns a unicode string ``s`` with ``padding``, so that it has a
  ## rune-length of ``count``.
  ##
  ## ``padding`` characters (by default spaces) are added after ``s`` resulting in
  ## left alignment. If ``s.runelen >= count``, no spaces are added and ``s`` is
  ## returned unchanged. If you need to right align a string use the `align
  ## proc <#align,string,Natural>`_.
  runnableExamples:
    assert alignLeft("abc", 4) == "abc "
    assert alignLeft("a", 0) == "a"
    assert alignLeft("1232", 6) == "1232  "
    assert alignLeft("1232", 6, '#'.Rune) == "1232##"
    assert alignLeft("Åge", 5) == "Åge  "
    assert alignLeft("×", 4, '_'.Rune) == "×___"
  let sLen = s.runeLen
  if sLen < count:
    let padStr = $padding
    result = newStringOfCap(s.len + (count - sLen) * padStr.len)
    result.add s
    for i in sLen ..< count:
      result.add padStr
  else:
    result = s.substr


proc runeLen*(s: string): int {.inline.} =
  ## Returns the number of runes of the string ``s``.
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeLen == 6
    ## note: a.len == 8
  runeLen(toOa(s))

proc runeLenAt*(s: string, i: Natural): int {.inline.} =
  ## Returns the number of bytes the rune starting at ``s[i]`` takes.
  ##
  ## See also:
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeLenAt(0) == 1
    doAssert a.runeLenAt(1) == 2
  runeLenAt(toOa(s), i)

proc runeAt*(s: string, i: Natural): Rune {.inline.} =
  ## Returns the rune in ``s`` at **byte index** ``i``.
  ##
  ## See also:
  ## * `runeAtPos proc <#runeAtPos,string,int>`_
  ## * `runeStrAtPos proc <#runeStrAtPos,string,Natural>`_
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeAt(1) == "ñ".runeAt(0)
    doAssert a.runeAt(2) == "ñ".runeAt(1)
    doAssert a.runeAt(3) == "y".runeAt(0)
  fastRuneAt(s, i, result, false)

proc validateUtf8*(s: string): int {.inline.} =
  ## Returns the position of the invalid byte in ``s`` if the string ``s`` does
  ## not hold valid UTF-8 data. Otherwise ``-1`` is returned.
  ##
  ## See also:
  ## * `toUTF8 proc <#toUTF8,Rune>`_
  ## * `$ proc <#$,Rune>`_ alias for `toUTF8`
  ## * `fastToUTF8Copy template <#fastToUTF8Copy.t,Rune,string,int>`_
  validateUtf8(toOa(s))

proc runeOffset*(s: string, pos: Natural, start: Natural = 0): int {.inline.} =
  ## Returns the byte position of rune
  ## at position ``pos`` in ``s`` with an optional start byte position.
  ## Returns the special value -1 if it runs out of the string.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeReverseOffset proc <#runeReverseOffset,string,Positive>`_
  runnableExamples:
    let a = "añyóng"
    doAssert a.runeOffset(1) == 1
    doAssert a.runeOffset(3) == 4
    doAssert a.runeOffset(4) == 6
  runeOffset(toOa(s), pos, start)

proc runeReverseOffset*(s: string, rev: Positive): (int, int) {.inline.} =
  ## Returns a tuple with the byte offset of the
  ## rune at position ``rev`` in ``s``, counting
  ## from the end (starting with 1) and the total
  ## number of runes in the string.
  ##
  ## Returns a negative value for offset if there are too few runes in
  ## the string to satisfy the request.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeOffset proc <#runeOffset,string,Natural,Natural>`_
  runeReverseOffset(toOa(s), rev)

proc runeAtPos*(s: string, pos: int): Rune {.inline.} =
  ## Returns the rune at position ``pos``.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeAt proc <#runeAt,string,Natural>`_
  ## * `runeStrAtPos proc <#runeStrAtPos,string,Natural>`_
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  fastRuneAt(toOa(s), runeOffset(s, pos), result, false)

proc runeStrAtPos*(s: string, pos: Natural): string {.inline.} =
  ## Returns the rune at position ``pos`` as UTF8 String.
  ##
  ## **Beware:** This can lead to unoptimized code and slow execution!
  ## Most problems can be solved more efficiently by using an iterator
  ## or conversion to a seq of Rune.
  ##
  ## See also:
  ## * `runeAt proc <#runeAt,string,Natural>`_
  ## * `runeAtPos proc <#runeAtPos,string,int>`_
  ## * `fastRuneAt template <#fastRuneAt.t,string,int,untyped>`_
  let o = runeOffset(s, pos)
  substr(s.toOpenArray(o, (o+runeLenAt(s, o)-1)))

proc runeSubStr*(s: string, pos: int, len: int = int.high): string {.inline.} =
  ## Returns the UTF-8 substring starting at code point ``pos``
  ## with ``len`` code points.
  ##
  ## If ``pos`` or ``len`` is negative they count from
  ## the end of the string. If ``len`` is not given it means the longest
  ## possible string.
  runnableExamples:
    let s = "Hänsel  ««: 10,00€"
    doAssert(runeSubStr(s, 0, 2) == "Hä")
    doAssert(runeSubStr(s, 10, 1) == ":")
    doAssert(runeSubStr(s, -6) == "10,00€")
    doAssert(runeSubStr(s, 10) == ": 10,00€")
    doAssert(runeSubStr(s, 12, 5) == "10,00")
    doAssert(runeSubStr(s, -6, 3) == "10,")
  runeSubStr(toOa(s), pos, len)


proc isAlpha*(s: string): bool {.noSideEffect, inline.} =
  ## Returns true if ``s`` contains all alphabetic runes.
  runnableExamples:
    let a = "añyóng"
    doAssert a.isAlpha
  isAlpha(toOa(s))

proc isSpace*(s: string): bool {.noSideEffect, inline.} =
  ## Returns true if ``s`` contains all whitespace runes.
  runnableExamples:
    let a = "\t\l \v\r\f"
    doAssert a.isSpace
  isSpace(toOa(s))


proc toUpper*(s: string): string {.noSideEffect, inline.} =
  ## Converts ``s`` into upper-case runes.
  runnableExamples:
    doAssert toUpper("abγ") == "ABΓ"
  toUpper(toOa(s))

proc toLower*(s: string): string {.noSideEffect, inline.} =
  ## Converts ``s`` into lower-case runes.
  runnableExamples:
    doAssert toLower("ABΓ") == "abγ"
  toLower(toOa(s))

proc swapCase*(s: string): string {.noSideEffect, inline.} =
  ## Swaps the case of runes in ``s``.
  ##
  ## Returns a new string such that the cases of all runes
  ## are swapped if possible.
  runnableExamples:
    doAssert swapCase("Αlpha Βeta Γamma") == "αLPHA βETA γAMMA"
  swapCase(toOa(s))

proc capitalize*(s: string): string {.noSideEffect.} =
  ## Converts the first character of ``s`` into an upper-case rune.
  runnableExamples:
    doAssert capitalize("βeta") == "Βeta"
  capitalize(toOa(s))


proc translate*(s: string, replacements: proc(key: string): string): string {.effectsOf: replacements, inline.} =
  ## Translates words in a string using the ``replacements`` proc to substitute
  ## words inside ``s`` with their replacements.
  ##
  ## ``replacements`` is any proc that takes a word and returns
  ## a new word to fill it's place.
  runnableExamples:
    proc wordToNumber(s: string): string =
      case s
      of "one": "1"
      of "two": "2"
      else: s
    let a = "one two three four"
    doAssert a.translate(wordToNumber) == "1 2 three four"
  translate(toOa(s), replacements)

proc title*(s: string): string {.noSideEffect, inline.} =
  ## Converts ``s`` to a unicode title.
  ##
  ## Returns a new string such that the first character
  ## in each word inside ``s`` is capitalized.
  runnableExamples:
    doAssert title("αlpha βeta γamma") == "Αlpha Βeta Γamma"
  title(toOa(s))


iterator runes*(s: string): Rune =
  ## Iterates over any rune of the string ``s`` returning runes.
  for rune in runes(toOa(s)):
    yield rune

iterator utf8*(s: string): string =
  ## Iterates over any rune of the string ``s`` returning utf8 values.
  ##
  ## See also:
  ## * `validateUtf8 proc <#validateUtf8,string>`_
  ## * `toUTF8 proc <#toUTF8,Rune>`_
  ## * `$ proc <#$,Rune>`_ alias for `toUTF8`
  ## * `fastToUTF8Copy template <#fastToUTF8Copy.t,Rune,string,int>`_
  for str in utf8(toOa(s)):
    yield str

proc toRunes*(s: string): seq[Rune] {.inline.} =
  ## Obtains a sequence containing the Runes in ``s``.
  ##
  ## See also:
  ## * `$ proc <#$,Rune>`_ for a reverse operation
  runnableExamples:
    let a = toRunes("aáä")
    doAssert a == @["a".runeAt(0), "á".runeAt(0), "ä".runeAt(0)]
  toRunes(toOa(s))

proc cmpRunesIgnoreCase*(a, b: string): int {.inline.} =
  ## Compares two UTF-8 strings and ignores the case. Returns:
  ##
  ## | 0 if a == b
  ## | < 0 if a < b
  ## | > 0 if a > b
  cmpRunesIgnoreCase(a.toOa(), b.toOa())

proc reversed*(s: string): string {.inline.} =
  ## Returns the reverse of ``s``, interpreting it as runes.
  ##
  ## Unicode combining characters are correctly interpreted as well.
  runnableExamples:
    assert reversed("Reverse this!") == "!siht esreveR"
    assert reversed("先秦兩漢") == "漢兩秦先"
    assert reversed("as⃝df̅") == "f̅ds⃝a"
    assert reversed("a⃞b⃞c⃞") == "c⃞b⃞a⃞"
  reversed(toOa(s))

proc graphemeLen*(s: string; i: Natural): Natural {.inline.} =
  ## The number of bytes belonging to byte index ``s[i]``,
  ## including following combining code unit.
  runnableExamples:
    let a = "añyóng"
    doAssert a.graphemeLen(1) == 2 ## ñ
    doAssert a.graphemeLen(2) == 1
    doAssert a.graphemeLen(4) == 2 ## ó
  graphemeLen(toOa(s), i)

proc lastRune*(s: string; last: int): (Rune, int) {.inline.} =
  ## Length of the last rune in ``s[0..last]``. Returns the rune and its length
  ## in bytes.
  lastRune(toOa(s), last)

iterator split*(s: string, seps: openArray[Rune] = unicodeSpaces,
  maxsplit: int = -1): string =
  ## Splits the unicode string ``s`` into substrings using a group of separators.
  ##
  ## Substrings are separated by a substring containing only ``seps``.
  runnableExamples:
    import std/sequtils

    assert toSeq("hÃllo\lthis\lis an\texample\l是".split) ==
      @["hÃllo", "this", "is", "an", "example", "是"]

    # And the following code splits the same string using a sequence of Runes.
    assert toSeq(split("añyóng:hÃllo;是$example", ";:$".toRunes)) ==
      @["añyóng", "hÃllo", "是", "example"]

    # example with a `Rune` separator and unused one `;`:
    assert toSeq(split("ab是de:f:", ";:是".toRunes)) == @["ab", "de", "f", ""]

    # Another example that splits a string containing a date.
    let date = "2012-11-20T22:08:08.398990"

    assert toSeq(split(date, " -:T".toRunes)) ==
      @["2012", "11", "20", "22", "08", "08.398990"]

  splitCommon(toOa(s), seps, maxsplit)

iterator splitWhitespace*(s: string): string =
  ## Splits a unicode string at whitespace runes.
  splitCommon(s.toOa(), unicodeSpaces, -1)


proc splitWhitespace*(s: string): seq[string] {.noSideEffect, inline.}=
  ## The same as the `splitWhitespace <#splitWhitespace.i,string>`_
  ## iterator, but is a proc that returns a sequence of substrings.
  accResult(splitWhitespace(toOa(s)))

iterator split*(s: string, sep: Rune, maxsplit: int = -1): string =
  ## Splits the unicode string ``s`` into substrings using a single separator.
  ## Substrings are separated by the rune ``sep``.
  runnableExamples:
    import std/sequtils

    assert toSeq(split(";;hÃllo;this;is;an;;example;;;是", ";".runeAt(0))) ==
      @["", "", "hÃllo", "this", "is", "an", "", "example", "", "", "是"]

  splitCommon(toOa(s), sep, maxsplit)

proc split*(s: string, seps: openArray[Rune] = unicodeSpaces, maxsplit: int = -1):
    seq[string] {.noSideEffect, inline.} =
  ## The same as the `split iterator <#split.i,string,openArray[Rune],int>`_,
  ## but is a proc that returns a sequence of substrings.
  accResult(split(toOa(s), seps, maxsplit))

proc split*(s: string, sep: Rune, maxsplit: int = -1): seq[string] {.noSideEffect, inline.} =
  ## The same as the `split iterator <#split.i,string,Rune,int>`_, but is a proc
  ## that returns a sequence of substrings.
  accResult(split(toOa(s), sep, maxsplit))

proc strip*(s: string, leading = true, trailing = true,
            runes: openArray[Rune] = unicodeSpaces): string {.noSideEffect, inline.} =
  ## Strips leading or trailing ``runes`` from ``s`` and returns
  ## the resulting string.
  ##
  ## If ``leading`` is true (default), leading ``runes`` are stripped.
  ## If ``trailing`` is true (default), trailing ``runes`` are stripped.
  ## If both are false, the string is returned unchanged.
  runnableExamples:
    let a = "\táñyóng   "
    doAssert a.strip == "áñyóng"
    doAssert a.strip(leading = false) == "\táñyóng"
    doAssert a.strip(trailing = false) == "áñyóng   "
  strip(toOa(s), leading, trailing, runes)


proc align*(s: string, count: Natural, padding = ' '.Rune): string {.noSideEffect, inline.} =
  ## Aligns a unicode string ``s`` with ``padding``, so that it has a rune-length
  ## of ``count``.
  ##
  ## ``padding`` characters (by default spaces) are added before ``s`` resulting in
  ## right alignment. If ``s.runelen >= count``, no spaces are added and ``s`` is
  ## returned unchanged. If you need to left align a string use the `alignLeft
  ## proc <#alignLeft,string,Natural>`_.
  runnableExamples:
    assert align("abc", 4) == " abc"
    assert align("a", 0) == "a"
    assert align("1232", 6) == "  1232"
    assert align("1232", 6, '#'.Rune) == "##1232"
    assert align("Åge", 5) == "  Åge"
    assert align("×", 4, '_'.Rune) == "___×"
  align(toOa(s), count, padding)

proc alignLeft*(s: string, count: Natural, padding = ' '.Rune): string {.noSideEffect, inline.} =
  ## Left-aligns a unicode string ``s`` with ``padding``, so that it has a
  ## rune-length of ``count``.
  ##
  ## ``padding`` characters (by default spaces) are added after ``s`` resulting in
  ## left alignment. If ``s.runelen >= count``, no spaces are added and ``s`` is
  ## returned unchanged. If you need to right align a string use the `align
  ## proc <#align,string,Natural>`_.
  runnableExamples:
    assert alignLeft("abc", 4) == "abc "
    assert alignLeft("a", 0) == "a"
    assert alignLeft("1232", 6) == "1232  "
    assert alignLeft("1232", 6, '#'.Rune) == "1232##"
    assert alignLeft("Åge", 5) == "Åge  "
    assert alignLeft("×", 4, '_'.Rune) == "×___"
  alignLeft(toOa(s), count, padding)