Dragging an event across the month grid wrote the date of the cell it
landed on into the event's stored start. Those are the same date only
while the event's time zone is the reader's.
An event kept in Asia/Tokyo at 15:00 is drawn to a reader in Phoenix at
23:00 the previous evening. Dropped on the 11th, it was written as the
11th in Tokyo -- which is the 10th on screen. It went where its own
calendar said rather than where the pointer did, one day short, every
time.
Moving by the difference between the two local days instead moves it
exactly as far as the hand did, and adding whole days to a stored wall
clock leaves the time of day alone without touching the zone -- so the
frame the rest of this path is careful about is still not crossed.
Found by giving the mock an event in a zone that is not the machine's.
Every other fixture used the machine's own, which cannot tell a correct
conversion from no conversion at all: the case that works is the one the
fixtures were all testing.
The calendar could only be edited through the editor, so moving a meeting
half an hour meant opening a dialog, changing two fields and saving. Every
other surface a finger or a pointer drives already answers to a drag.
In the day and week grids an event moves by dragging it and changes length
by dragging its bottom edge, snapping to fifteen minutes. In the month
grid it moves to another day and keeps the time it had, because a month
cell is a day and nothing finer -- changing the hour as well would answer
a question nobody asked.
It goes through the same path a menu edit takes. A recurring event is
asked which dates it means, and the answer runs through runScoped, so a
date the server will only change as part of a whole series offers that
rather than failing.
Three things do not offer a drag, and the reasons are checked in one place
so no grid has to remember all three: a read-only calendar, an event with
no calendar, and a birthday -- which is derived from a contact and has
nothing on the server to move. The reserved classes the swipe gesture was
told to keep out of are exactly the ones that are draggable here, which is
what that reservation was for.
Invitations are not sent. A drag is a scheduling gesture, and mailing
every guest on each nudge of a block is not what the hand was asking for;
a change that should go out with notice goes through the editor.
The new time is computed in the event's own frame rather than through an
instant. Working it out from the reader's local hours and then
re-expressing it in the event's zone converts twice, and the two do not
cancel: caught in the browser, where an event moved two hours the first
time it was dragged in the month grid and then sat still, because after
that its stored time and the reader's agreed. Parsing the stored string
into its parts and adding minutes to those touches no zone at all, and a
resize sends only a duration, so the question does not arise there either.
jcoffey-dev