msgpack: support datetime interval arithmetic

Support datetime and interval arithmetic with the same rules as in
Tarantool [1].

Valid operations:
- tarantool.Datetime +  tarantool.Interval = tarantool.Datetime
- tarantool.Datetime -  tarantool.Datetime = tarantool.Interval
- tarantool.Interval +  tarantool.Interval = tarantool.Interval
- tarantool.Interval -  tarantool.Interval = tarantool.Interval

1. https://github.com/tarantool/tarantool/wiki/Datetime-Internals#interval-arithmetic

Closes #229

CHANGELOG.md

@@ -62,6 +62,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   is raised in this case.
 
 - Datetime interval type support and tarantool.Interval type (#229).
+- Datetime interval arithmetic support (#229).
 
 ### Changed
 - Bump msgpack requirement to 1.0.4 (PR #223).

tarantool/msgpack_ext/types/datetime.py

@@ -6,6 +6,8 @@
 import tarantool.msgpack_ext.types.timezones as tt_timezones
 from tarantool.error import MsgpackError, MsgpackWarning, warn
 
+from tarantool.msgpack_ext.types.interval import Interval, Adjust
+
 # https://www.tarantool.io/en/doc/latest/dev_guide/internals/msgpack_extensions/#the-datetime-type
 #
 # The datetime MessagePack representation looks like this:
@@ -45,8 +47,10 @@
 BYTEORDER = 'little'
 
 NSEC_IN_SEC = 1000000000
+NSEC_IN_MKSEC = 1000
 SEC_IN_MIN = 60
 MIN_IN_DAY = 60 * 24
+MONTH_IN_YEAR = 12
 
 
 def get_bytes_as_int(data, cursor, size):
@@ -209,6 +213,58 @@ def __init__(self, *args, tarantool_tzindex=None, **kwargs):
         self._tzoffset = tzoffset
         self._tzindex = tzindex
 
+    def __add__(self, other):
+        if not isinstance(other, Interval):
+            raise TypeError(f"unsupported operand type(s) for -: '{type(self)}' and '{type(other)}'")
+
+        self_ts = self._timestamp
+
+        # https://github.com/tarantool/tarantool/wiki/Datetime-Internals#date-adjustions-and-leap-years
+        months = other.year * MONTH_IN_YEAR + other.month
+
+        res = self_ts + pandas.DateOffset(months = months)
+
+        # pandas.DateOffset works like Adjust.Limit
+        if other.adjust == Adjust.Excess:
+            if self_ts.day > res.day:
+                res = res + pandas.DateOffset(days = self_ts.day - res.day)
+        elif other.adjust == Adjust.Last:
+            if self_ts.is_month_end:
+                # day replaces days
+                res = res.replace(day = res.days_in_month)
+
+        res = res + pandas.Timedelta(weeks = other.week,
+                                     days = other.day,
+                                     hours = other.hour,
+                                     minutes = other.minute,
+                                     seconds = other.second,
+                                     nanoseconds = other.nanosecond)
+
+        if self._tzindex != 0:
+            return Datetime(res, tarantool_tzindex=self._tzindex)
+        else:
+            return Datetime(res)
+
+    def __sub__(self, other):
+        if not isinstance(other, Datetime):
+            raise TypeError(f"unsupported operand type(s) for -: '{type(self)}' and '{type(other)}'")
+
+        self_ts = self._timestamp
+        other_ts = other._timestamp
+
+        self_nsec = self_ts.microsecond * NSEC_IN_MKSEC + self_ts.nanosecond
+        other_nsec = other_ts.microsecond * NSEC_IN_MKSEC + other_ts.nanosecond
+
+        return Interval(
+            year = self_ts.year - other_ts.year,
+            month = self_ts.month - other_ts.month,
+            day = self_ts.day - other_ts.day,
+            hour = self_ts.hour - other_ts.hour,
+            minute = self_ts.minute - other_ts.minute,
+            second = self_ts.second - other_ts.second,
+            nanosecond = self_nsec - other_nsec,
+        )
+
     def __eq__(self, other):
         if isinstance(other, Datetime):
             return self._timestamp == other._timestamp

tarantool/msgpack_ext/types/interval.py

@@ -102,6 +102,70 @@ def __init__(self, data=None, *, year=0, month=0, week=0,
             self.nanosecond = nanosecond
             self.adjust = adjust
 
+    def __add__(self, other):
+        if not isinstance(other, Interval):
+            raise TypeError(f"unsupported operand type(s) for +: '{type(self)}' and '{type(other)}'")
+
+        # Tarantool saves adjust of the first argument
+        #
+        # Tarantool 2.10.1-0-g482d91c66
+        #
+        # tarantool> dt1 = datetime.interval.new{year = 2, adjust='last'}
+        # ---
+        # ...
+        #
+        # tarantool> dt2 = datetime.interval.new{year = 1, adjust='excess'}
+        # ---
+        # ...
+        #
+        # tarantool> (dt1 + dt2).adjust
+        # ---
+        # - 'cdata<enum 112>: 2'
+        # ...
+
+        return Interval(
+            year = self.year + other.year,
+            month = self.month + other.month,
+            day = self.day + other.day,
+            hour = self.hour + other.hour,
+            minute = self.minute + other.minute,
+            second = self.second + other.second,
+            nanosecond = self.nanosecond + other.nanosecond,
+            adjust = self.adjust,
+        )
+
+    def __sub__(self, other):
+        if not isinstance(other, Interval):
+            raise TypeError(f"unsupported operand type(s) for -: '{type(self)}' and '{type(other)}'")
+
+        # Tarantool saves adjust of the first argument
+        #
+        # Tarantool 2.10.1-0-g482d91c66
+        #
+        # tarantool> dt1 = datetime.interval.new{year = 2, adjust='last'}
+        # ---
+        # ...
+        #
+        # tarantool> dt2 = datetime.interval.new{year = 1, adjust='excess'}
+        # ---
+        # ...
+        #
+        # tarantool> (dt1 - dt2).adjust
+        # ---
+        # - 'cdata<enum 112>: 2'
+        # ...
+
+        return Interval(
+            year = self.year - other.year,
+            month = self.month - other.month,
+            day = self.day - other.day,
+            hour = self.hour - other.hour,
+            minute = self.minute - other.minute,
+            second = self.second - other.second,
+            nanosecond = self.nanosecond - other.nanosecond,
+            adjust = self.adjust,
+        )
+
     def __eq__(self, other):
         if not isinstance(other, Interval):
             return False

test/suites/__init__.py

@@ -19,14 +19,16 @@
 from .test_uuid import TestSuite_UUID
 from .test_datetime import TestSuite_Datetime
 from .test_interval import TestSuite_Interval
+from .test_datetime_arithmetic import TestSuite_DatetimeArithmetic
 
 test_cases = (TestSuite_Schema_UnicodeConnection,
               TestSuite_Schema_BinaryConnection,
               TestSuite_Request, TestSuite_Protocol, TestSuite_Reconnect,
               TestSuite_Mesh, TestSuite_Execute, TestSuite_DBAPI,
               TestSuite_Encoding, TestSuite_Pool, TestSuite_Ssl,
               TestSuite_Decimal, TestSuite_UUID, TestSuite_Datetime,
-              TestSuite_Interval)
+              TestSuite_Interval, TestSuite_DatetimeArithmetic)
+
 
 def load_tests(loader, tests, pattern):
     suite = unittest.TestSuite()