gen-paginator-v1.coffee

gen = (cur, all, chunk = 10) ->
  half = (chunk - 4) // 2

  ledge = Math.max(1  , cur - half)
  redge = Math.min(all, cur + half)

  ldiff = half - (cur - ledge) + ((ledge < half-1) && 2 || (ledge < half) && 1 || 0)
  rdiff = half - (redge - cur) + ((cur+half >= all) && 2 || (cur+half+1 == all) && 1 || 0)

  prev = 0
  return [1, ...[ledge-rdiff .. redge+ldiff], all]
    .filter (v) -> 0 < v <= all
    .reduce ((m, v) -> if m.indexOf(v) >= 0 then m else [...m, v]), []
    .reduce ((m, v) ->
      m.push('..')     if prev and v - prev >  2
      m.push(prev + 1) if prev and v - prev == 2
      m.push(v)
      prev = v
      return m
    ), []

gen-paginator-v2.coffee

generatePage = (cur, all = 35, chunkSize = 10) ->
  chunk = Math.ceil cur / chunkSize

  ledge = (chunk - 1) * chunkSize + 1
  ledge = all - chunkSize if all - ledge < chunkSize

  redge = chunk * chunkSize

  prev = 0

  return [1, ...[ledge .. redge], all]
    .filter (v) -> 0 < v <= all
    .reduce ((m, v) -> if m.indexOf(v) >= 0 then m else [...m, v]), []
    .reduce ((result, p) ->
      result.push '..' if prev and p - prev > 2
      result.push prev + 1 if prev and p - prev == 2
      result.push p
      prev = p
      return result
    ), []