Whitespace issue in parser

[dcastro]

Clarification and motivation

At the moment, the parser only recognizes time references if:

• they're immediately at the beginning of the message: "9am"
• or after a space: "I can't go today, let's try 9am tomorrow instead"

This is implemented here:

tzbot/src/TzBot/Parser.hs

Lines 274 to 275 in 0f58a50

	-- time reference can be either at the beginning or after a space
	. (Whitespace :)

tzbot/src/TzBot/Parser.hs

Line 445 in 0f58a50

_ <- space

tzbot/src/TzBot/Parser.hs

Lines 339 to 340 in 0f58a50

	-- no space here before `timeRefGroupParser` requires a space before the contents
	secondGroup <- timeRefGroupParser

The rationale is to avoid parsing things like "The product ID is AEH9AM" as "9AM".

However, there can be situations where a legitimate time reference is not actually preceded by a space:

>>> parseTimeRefs "How about Mike's suggestion (9am tomorrow)?"
[]

We should be able to parse these.

[dcastro]

Here's a real-world example:

Notice how (5 pm MSK, 4 pm CET) was incorrectly interpreted as MSK, 4 pm. The 5 pm part was ignored because it was not preceded by a whitespace.

[dcastro]

Yes another real-world example:

it will be at 11 AM CEST (9 AM UTC+0, 12 PM MSK)

The bot parsed UTC+0, 12 PM