[Calculator][ux] Add paste support

Spaces is not invalid characters, and our Calculator's engine could handle it.
Our engine is very powerful, and we don't use half od its possibilities, eg matrix, units etc.

In my opinion changing pasted formula will be very frustrating for user, because user never will know what was removed from his formula.

My proposal is to paste everything, without modification, and then user could correct that.

I would like to avoid situation, when user receive wrong result, because we modified formula.

Yeah, I'm sorry for that bad example of using spaces.

While I agree that I'd like the app to accept any input and let the user deal with any of its issues, the calculator app is already very restrictive when it comes to letting users type stuff using a keyboard. If you want to input "sin(" for example, you have to press the "s" key. If you because you're used to it type in "sin" instead, you will end up with "sin(" and "i" being inserted.
Furthermore, there are a lot of other character combinations which are not allowed by the engine. Let's say you type in "5*2.234" but want to change it to "5*2.2+3.4" for whatever reason and start by trying to insert the dot after the "3", the calculator app won't let you. And there are many examples like this one.
That's why I believe we should, even if it's just for consistency, filter the user's input. Otherwise it will be very confusing for everyone. You can't filter the input at one place and then decide not to do it somewhere else.

Thanks a lot for your reply, James. However, there's still something missing. Should we notify the user when he pastes invalid content? Or should we simply insert as much as possible?

(In my opinion the latter would be superior in those cases when there aren't any downsides to filtering the input, while the former would be preferable when the pasted string is seriously broken and we can only insert a small part of it.)

There are many issues with pasting support.
Fo example, user should paste only formula in engine format, example:
2*2/2

and it will be converted to:
2x2÷2

If user accidentely paste
2x2÷2
then to what it will be converted:
222 ?

How user should notice if he paste wrong formula?
He didn't have even have chance to correct it.

@Bartosz I did consider this when writing my implementation. All display texts will be converted back to their internal representation. Don't worry regarding this aspect.

Fix committed into lp:ubuntu-calculator-app at revision 228, scheduled for release in ubuntu-calculator-app, milestone Unknown

I changed the bug status for this to Triaged again in the ubuntu-calculator-app project as we still need support for touch devices and to "In Progress" in Ubuntu UX as the following has yet to be answered (post #3):

"Should we notify the user when he pastes invalid content? Or should we simply insert as much as possible?

(In my opinion the latter would be superior in those cases when there aren't any downsides to filtering the input, while the former would be preferable when the pasted string is seriously broken and we can only insert a small part of it.)"

I would like to propose, to notify user about bad paste, by "flash light" of the Formula Input Field.

I will be similar as we already have for entering incorrect formula (try to type "5*******").
I would like to "light" whole Formula Input Field, because sometimes the whole pasted text is wrong (because user make mistake), and we should notify user about that fact.

Fix committed into lp:ubuntu-calculator-app at revision 235, scheduled for release in ubuntu-calculator-app, milestone Unknown

@Bartosz, that makes sense to me. Let's file a bug report. :)

By the way, I finally fixed the remaining issue: https://code.launchpad.net/~nikwen/ubuntu-calculator-app/bracket-paste-fix/+merge/279368

Here's the bug report for that issue: https://bugs.launchpad.net/ubuntu-calculator-app/+bug/1522161

Furthermore, I filed the following one: https://bugs.launchpad.net/ubuntu-calculator-app/+bug/1522162