cedartime.py

"""
This is a reference implementation for the proposed datetime RFC
for the Cedar Policy Language. The RFC is currently being discussed
at https://github.com/cedar-policy/rfcs/pull/80


>>> duration("1h")
3600000ms
>>> datetime("1970-01-01T00:00:00Z")
0ms
>>> datetime("1969-12-31T23:59:59Z")
-1000ms
>>> datetime("1970-01-01T00:00:00Z").offset(duration("1m"))
60000ms
>>> datetime("1970-01-01T00:00:00Z").offset(duration("-1m"))
-60000ms
>>> datetime("1980-01-01T00:00:00Z") > datetime("1970-01-01T00:00:00Z")
True
>>> datetime("1980-01-01T00:00:00Z") >= datetime("1970-01-01T00:00:00Z")
True
>>> datetime("1970-01-01T00:00:00Z") < datetime("1980-01-01T00:00:00Z")
True
>>> datetime("1969-12-31T23:59:59Z") < datetime("1970-01-01T00:00:00Z")
True
>>> datetime("1969-12-31T23:59:58Z") < datetime("1969-12-31T23:59:59Z")
True
>>> datetime("1970-01-01T00:00:01Z") < datetime("1969-12-31T23:59:59Z")
False
>>> datetime("1970-01-01T00:00:00Z") <= datetime("1980-01-01T00:00:00Z")
True
>>> datetime("1970-01-01T00:00:00Z") == datetime("1970-01-01T00:00:00Z")
True
>>> datetime("1970-01-01T00:00:00Z") != datetime("1980-01-01T00:00:00Z")
True
>>> datetime("1970-01-01T12:00:00Z").toDate() == datetime("1970-01-01T00:00:00Z")
True
>>> datetime("1970-01-01T12:00:00Z").toTime() == duration("12h")
True
>>> datetime("1970-01-01T00:00:00Z").durationSince(datetime("1970-01-01T00:00:00Z"))
0ms
>>> datetime("1970-01-01T00:00:00Z").durationSince(datetime("1970-01-01T00:00:01Z"))
-1000ms
>>> datetime("1969-12-31T23:59:59Z").durationSince(datetime("1970-01-01T00:00:00Z"))
-1000ms
>>> datetime("1969-12-31T23:59:58Z").durationSince(datetime("1969-12-31T23:59:59Z"))
-1000ms
>>> datetime("1970-01-01T00:00:01Z").durationSince(datetime("1969-12-31T23:59:59Z"))
2000ms
>>> datetime("1970-01-01T00:00:01Z").offset(datetime("1969-12-31T23:59:58Z").durationSince(datetime("1970-01-01T00:00:01Z"))) == datetime("1969-12-31T23:59:58Z")
True
>>> datetime("1970-01-01T00:00:01Z").offset(datetime("1970-01-01T00:00:03Z").durationSince(datetime("1970-01-01T00:00:01Z"))) == datetime("1970-01-01Z00:00:03Z")
True
>>> duration("1d") == duration("86400000ms")
True
>>> duration("1d") != duration("1d1ms")
True
>>> duration("2d") > duration("86400000ms")
True
>>> duration("2d") >= duration("86400000ms")
True
>>> duration("1d") < duration("2d")
True
>>> duration("1d") <= duration("2d")
True
>>> duration("1d").toMilliseconds()
86400000
>>> duration("1d").toSeconds()
86400
>>> duration("1d").toMinutes()
1440
>>> duration("1d").toHours()
24
>>> duration("1d").toDays()
1
"""

import datetime as rdt

def parseDuration(s):
    """
    Nu, where N is positive or negative integer, and u is one of:
       d, h, m, s, ms
    These are combined into a single string, and returned as milliseconds
    """
    totalMS = 0
    quantity = 0
    negative = False
    unit = ""
    i = 0
    while i < len(s):
        if s[i] == '-' and quantity == 0 and not negative:
            negative = True
            i += 1
        elif s[i].isdigit():
            quantity = (quantity * 10) + int(s[i])
            i += 1
        elif s[i] in "dhms":
            if s[i] == "m" and i+1 < len(s) and s[i+1] == "s":
                unit = "ms"
                i += 2
            else:
                unit = s[i]
                i += 1

            negate = -1 if negative else 1
            if unit == "ms":
                totalMS = totalMS + (quantity * negate)
            elif unit == "s":
                totalMS = totalMS + (quantity * 1000 * negate)
            elif unit == "m":
                totalMS = totalMS + (quantity * 60 * 1000 * negate)
            elif unit == "h":
                totalMS = totalMS + (quantity * 60 * 60 * 1000 * negate)
            elif unit == "d":
                totalMS = totalMS + (quantity * 24 * 60 * 60 * 1000 * negate)

            # reset
            quantity = 0
            negative = False
            unit = ""
        else:
            raise TypeError("not a valid duration string")
    return totalMS

class duration:
    def __init__(self, s):
        self.ms = parseDuration(s)
    def __gt__(self, other):
        return self.ms > other.ms
    def __ge__(self, other):
        return self.ms >= other.ms
    def __lt__(self, other):
        return self.ms < other.ms
    def __le__(self, other):
        return self.ms <= other.ms
    def __eq__(self, other):
        return self.ms == other.ms
    def __ne__(self, other):
        return self.ms != other.ms
    def toMilliseconds(self):
        return self.ms
    def toSeconds(self):
        return self.ms // 1000
    def toMinutes(self):
        return self.ms // (1000 * 60)
    def toHours(self):
        return self.ms // (1000 * 60 * 60)
    def toDays(self):
        return self.ms // (1000 * 60 * 60 * 24)
    def __repr__(self):
        return str(self.ms) + "ms"


class datetime:
    def __init__(self, s):
        self.ts = int(rdt.datetime.fromisoformat(s).timestamp() * 1000)
    def __gt__(self, other):
        return self.ts > other.ts
    def __ge__(self, other):
        return self.ts >= other.ts
    def __lt__(self, other):
        return self.ts < other.ts
    def __le__(self, other):
        return self.ts <= other.ts
    def __eq__(self, other):
        return self.ts == other.ts
    def __ne__(self, other):
        return self.ts != other.ts
    def durationSince(self, other):
        d = duration("0ms")
        d.ms = self.ts - other.ts
        return d
    def offset(self, dur):
        d = zerodate()
        d.ts = self.ts + dur.ms
        return d
    def toDate(self):
        d = zerodate()
        d.ts = self.ts - (self.ts % 86400000)
        return d
    def toTime(self):
        return self.durationSince(self.toDate())
    def __repr__(self):
        return str(self.ts) + "ms"

def zerodate():
    return datetime("1970-01-01T00:00:00Z")

if __name__ == "__main__":
    import doctest
    doctest.testmod()

    zero = datetime("1970-01-01T00:00:00Z")
    plus3 = datetime("1970-01-01T00:00:03Z")
    plus5 = datetime("1970-01-01T00:00:05Z")
    minus3 = datetime("1969-12-31T23:59:57Z")
    minus5 = datetime("1969-12-31T23:59:55Z")

    xs = [zero, plus3, plus5, minus3, minus5]
    ys = [zero, plus3, plus5, minus3, minus5]

    for x in xs:
        for y in ys:
            dur = x.durationSince(y)
            print(x, y, "durationSince:", dur, y.offset(dur) == x)