Feature timewarp (#675)

* Implemented timewarp command

* Updated docs

* Added missing pytest mark

osxphotos/timezones.py

@@ -0,0 +1,56 @@
+"""Get list of valid timezones on macOS"""
+
+from typing import Union
+
+import Foundation
+import objc
+
+
+def known_timezone_names():
+    """Get list of valid timezones on macOS"""
+    return Foundation.NSTimeZone.knownTimeZoneNames()
+
+
+def format_offset_time(offset: int) -> str:
+    """Format offset time to exiftool format: -04:00"""
+    sign = "-" if offset < 0 else "+"
+    hours, remainder = divmod(abs(offset), 3600)
+    minutes, _ = divmod(remainder, 60)
+    return f"{sign}{hours:02d}:{minutes:02d}"
+
+
+class Timezone:
+    """Create Timezone object from either name (str) or offset from GMT (int)"""
+
+    def __init__(self, tz: Union[str, int]):
+        with objc.autorelease_pool():
+            if isinstance(tz, str):
+                self.timezone = Foundation.NSTimeZone.timeZoneWithName_(tz)
+                self._name = tz
+            elif isinstance(tz, int):
+                self.timezone = Foundation.NSTimeZone.timeZoneForSecondsFromGMT_(tz)
+                self._name = self.timezone.name()
+            else:
+                raise TypeError("Timezone must be a string or an int")
+
+    @property
+    def name(self) -> str:
+        return self._name
+
+    @property
+    def offset(self) -> int:
+        return self.timezone.secondsFromGMT()
+
+    @property
+    def offset_str(self) -> str:
+        return format_offset_time(self.offset)
+
+    @property
+    def abbreviation(self) -> str:
+        return self.timezone.abbreviation()
+
+    def __str__(self):
+        return self.name
+
+    def __repr__(self):
+        return self.name