DatePicker. Fix today circle

[alexzhirkevich]

Proposed Changes

1. Fix one more bug from Kotlinx datetime CalendarModel (support date picker on darwin and web) #717 🥲.
   Today time millis should be at the midnight.
   Added the last test from Android that checks the equality of legacy and new models. Forgot to do it in the first PR.
   Prostite brakodela 🙏

2. Use narrow weekdays format instead of short (as in non-legacy model on Android).
   It should be more consistent with Android 26+ (see screenshots from fixed issue).
   Also removed hardcoded weekdays names as all platforms have localized ones.

3. Replace input format building with existing function from common (missed that it already exists). It should be more stable for unusual locales.

4. atStartOfDay can produce non-midnight time. Some calendar model methods require midnight and some start of day. Aligned all methods with the newer android implementation

Testing

Test: EqualityOfCalendarModelsTest. This should protect from other bugs i believe

Issues Fixed

Fixes: JetBrains/compose-multiplatform#3591

[m-sasha]

@alexzhirkevich I started investigating before I noticed your PR.

Today time millis should be at the start of day.

Indeed, this seems to be the problem.

[m-sasha]

https://kotlinlang.org/api/kotlinx-datetime/kotlinx-datetime/kotlinx.datetime/at-start-of-day-in.html says atStartOfDay isn't necessarily at midnight, and we do want midnight here because of how isToday is computed:

val dateInMillis = month.startUtcTimeMillis + (dayNumber * MillisecondsIn24Hours)
val isToday = dateInMillis == today.utcTimeMillis

that's why I suggested to use atTime(0,0).

[m-sasha]

Or maybe both will be wrong, that is neither will match dateInMillis? I'm not sure. The way isToday is computed looks bad to me.

But Android uses

utcTimeMillis = systemLocalDate.atTime(LocalTime.MIDNIGHT)
                    .atZone(utcTimeZoneId).toInstant().toEpochMilli()

so maybe it's better to stick with that, unless you're sure atStartOfDayIn is correct.

[alexzhirkevich]

Hmm, this is what CalendarModel interface comments (from canonical date method) says about it:

compose-multiplatform-core/compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/CalendarModel.kt

Lines 94 to 95 in 8f57b8c

	* The returned date will hold milliseconds value that represent the start of the day, which may
	* be different than the one provided to this function.

So it does not exactly say it needs to be 00:00, but start of day 🤔

Maybe today method should behave differently

---

Newer android calendar model takes it at midnight, lets do the same
(but canonical date it takes at start of day 🥲🔫)

[alexzhirkevich]

Aligned all methods with the Android implementation

[m-sasha]

@alexzhirkevich Would you like me to merge this?

[alexzhirkevich]

@alexzhirkevich Would you like me to merge this?

Yep if everything looks good to you