import std/parseutils
import pkg/chronos

when not declared(parseDuration): # Odd code formatting to minimize diff v. mainLine
  const Whitespace = {' ', '\t', '\v', '\r', '\l', '\f'}

  func toLowerAscii(c: char): char =
    if c in {'A' .. 'Z'}:
      char(uint8(c) xor 0b0010_0000'u8)
    else:
      c

  func parseDuration*(s: string, size: var Duration): int =
    ## Parse a size qualified by simple time into `Duration`.
    ##
    runnableExamples:
      var res: Duration # caller must still know if 'b' refers to bytes|bits
      doAssert parseDuration("10H", res) == 3
      doAssert res == initDuration(hours = 10)
      doAssert parseDuration("64m", res) == 6
      doAssert res == initDuration(minutes = 64)
      doAssert parseDuration("7m/block", res) == 2 # '/' stops parse
      doAssert res == initDuration(minutes = 7) # 1 shl 30, forced binary metric
      doAssert parseDuration("3d", res) == 2 # '/' stops parse
      doAssert res == initDuration(days = 3) # 1 shl 30, forced binary metric

    const prefix = "s" & "mhdw" # byte|bit & lowCase metric-ish prefixes
    const timeScale = [1.0, 60.0, 3600.0, 86_400.0, 604_800.0]

    var number: float
    var scale = 1.0
    result = parseFloat(s, number)
    if number < 0: # While parseFloat accepts negatives ..
      result = 0 #.. we do not since sizes cannot be < 0
    else:
      let start = result # Save spot to maybe unwind white to EOS
      while result < s.len and s[result] in Whitespace:
        inc result
      if result < s.len: # Illegal starting char => unity
        if (let si = prefix.find(s[result].toLowerAscii); si >= 0):
          inc result # Now parse the scale
          scale = timeScale[si]
      else: # Unwind result advancement when there..
        result = start #..is no unit to the end of `s`.
      var sizeF = number * scale + 0.5 # Saturate to int64.high when too big
      size = seconds(int(sizeF))