import times

const zeroTime = fromUnix(0)
const ISO_8601_FULL_FORMAT = "yyyy:MM:dd'T'HH:mm:sszzz"

proc format*(ti: TimeInterval, fmt: string): string =
  let info = (fromUnix(0) + ti).utc
  return info.format(fmt)

# Will be deprecated in Nim 0.18.1 as it will exist in the standard times module.
proc `-`*(a, b: DateTime): TimeInterval =
  return seconds(cast[int](a.toTime - b.toTime))

proc `>`*(a, b: DateTime): bool =
  return a.toTime > b.toTime

proc `<`*(a, b: DateTime): bool =
  return a.toTime < b.toTime

proc `>=`*(a, b: DateTime): bool =
  return a.toTime >= b.toTime

proc `<=`*(a, b: DateTime): bool =
  return a.toTime <= b.toTime

proc `>`*(a, b: TimeInterval): bool =
  return (zeroTime + a) > (zeroTime + b)

proc `<`*(a, b: TimeInterval): bool =
  return (zeroTime + a) < (zeroTime + b)

proc `>=`*(a, b: TimeInterval): bool =
  return (zeroTime + a) >= (zeroTime + b)

proc `<=`*(a, b: TimeInterval): bool =
  return (zeroTime + a) <= (zeroTime + b)

proc between*(a, s, e: DateTime): bool =
  return a >= s and a < e

proc cmp*(a, b: DateTime): int =
  if b == a: return 0
  elif a > b: return 1
  else: return -1

proc startOfDay*(ti: DateTime): DateTime =
  result = ti
  result.hour = 0
  result.minute = 0
  result.second = 0

proc startOfWeek*(ti: DateTime, startDay = dMon): DateTime =
  var diff = (ti.weekday.ord - startDay.ord)
  if diff < 0: diff += 7
  return (ti - diff.days).startOfDay

proc parseIso8601*(val: string): DateTime =
  return val.parse(ISO_8601_FULL_FORMAT)

proc formatIso8601*(d: DateTime): string =
  return d.format(ISO_8601_FULL_FORMAT)

# This is a workaround needed due a bug in Nim's times.parse procedure.
# see: https://github.com/nim-lang/Nim/issues/4922
template fixedParse*(value, format: string): DateTime {.deprecated.} =
  parse(value, format)