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* ⬆️ Updated deps
* 💥 Upgraded to Polymer 3.x
* ✅ Fixed demo's and tests

✅ Trying to fix broken tests

…ve Intl

…nt type

`calendar` method does not taken `showWeekNumber` into account
when `firstDayOfWeek` > 0. Also, updated method to render calendar
with `repeat` and `cache`.

Updated UI based on latest Material design datepicker on latest Android.
`rollup` has been added for simple build for UI implementation.

Added implementation logics for any year, month, and date selection.
Added UI implementation for selected year and date as well as
today's date.

Calendar can now display week numbers on the extreme left as labels for
each calendar week by toggling `showWeekNumber` property. Minor CSS
tweaks to ensure only clickable elements such as date on the calendar to
show pointer cursor when hovering. `theme` property has been removed as
it is no longer relevant when the design is based on Material Design 2.

Noticed slow rendering on full calendar. After series of debugging,
it is quite surprising to find out that running `Intl.DateTimeFormat`
every single time with varying `locale` can cause a disastrous perf hit
especially in initializing them in each loop. By running them once then
passing the cached functions into the loops, the execution time to
render a full calendar now takes < 1ms as compared to > 100ms
before the patch.

Implemented dragging feature for touch-enabled devices with
`Pointer Events` and animating calendar with `Web Animations`.
Minor perf improvements has been made to render **ONLY** one calendar
when button is clicked to navigate between months, then on next frame
(or idle frame if supported natively) re-render all calendars.
`Intl` initialization can be slow in rendering calendar, passing
the necessary functions can be done at higher level so that functions
are cached and reused with lesser overhead, thus faster rendering.

`Pointer Events` does not work as expected on touch mobile devices.
There is a limitation when tracking happens on wider range. Hence, drop
the API in favor of Polymer's Gestures API for better compatibility.
Minor UI and animation enhancements applied to match that of on Android.

Upgraded to `lit-html@1.0.0-rc.1` and `lit-element@0.6.5` for v1.0 RC
which just released today.

Further improved perf in re-rendering on slower devices by fixing broken
tracking implementation. Now, re-rendering works properly as expected,
even on hovering which has been added in this patch as well for desktop.

Optimized calendar rendering performs slightly better due to micro-opts.
But the enhancement was broken when `showWeekNumber` is set. Additional
fix has been applied to ensure that week number **ONLY** renders when
the current date is still within the date range of the current month in
each iteration during rendering. Also, `GestureEventListeners` mixin is
not mandatory thus removed due to `PropertyEffects` overhead in
rendering. Simple demo with timestamp has been added for reference use.

Blink requires defined width when updating `transform` property of an
element else it will trigger layout on every frame thus caused drop in
perf. By setting fixed width via `getBoundingClientRect` before tracking
starts, it temporarily updates the element and its parent element that
are responsible for smoother tracking to have fixed width. Critical bug
has been discovered in `calendar` module where week number shows up on
empty last row of a calendar. A temporary fix has been included to make
sure calendar renders correctly as of now but it will be revisited.

* Removed `debugger` keyword
* Minor fix in tracking function to reset flags

* Rewrote `calendar.ts` with just ` for-loop to do the job. Feel free to
  submit optimization PR to improve the perf.
* Minor code re-ordering for maintainability and readability.
* Removed other test scripts which are no longer in use.

* Added missing `TSLint` config and fixed all linting issues.
* Added `rollup` build for production/ publish.

Redundant execution happens when `_selectedView` property has different
value. A year list does not need anything from a calendar, however,
tasks to render a calendar still runs regardless. By moving all logics
to related method can help reduce unnecessary computation in different
view.

* WIP - to use `pointer-tracker` instead of Polymer Gestures API.
* Refactored to use `query` decorator.
* Upgraded deps.

* Disabled calendar day greys out now.
* Fixed an issue where unwanted re-rendering triggers on unselectable
  calendar day or weekday label.
* Fixed `Pointer Events` API does not work on touch devices by adding
  `touch-action: none` on draggable element. For more details on the
  issue, see GoogleChromeLabs/pointer-tracker#1.
* Updated selected and focused state of selectable calendar day.

* Dropping all Polymer elements in favor of `mwc-*` elements but yet to
  be released. At least for now, keeping the element lightweight and
  fast is top priority.
* Moved focus of calendar table to its container.

* Navigating between calendar's month can be achieved with keyboard.
* WIP - to add keyboard support for navigating years in year list.

* Added support for `value` just like how native datepicker works.
  Invalid date input will not update any date internally.
* `yearList` already has keyboard support so no extra work is needed.

* Introduced `landscape` attribute to set calendar to view in landscape
  mode.
* Introduced `startView` attribute to set initial view when
  the datepicker first renders.
* Due to the addition of `startView` breaks the implementation of
  updating `_totalDraggableDistance`, it has been fixed by moving the
  implementation to `updated` method with condition check.
* Added CSS styling for calendar in landscape mode.
* ⚡️ Identified an issue where `::after` pseudo-elements can trigger
  paint when the calendar container is in its dragging phase. An
  optimized solution for triggering lesser paint is by promoting certain
  layers to its own layer to reduce paint caused by its inner children
  elements, and removed all `::after` pseudo-elements in all calendar in
  initial render and only render the pseudo-element when needed, e.g.
  hovering and updating focused date. The improvement is phenomenal on
  low-end devices.
* Refactored code to leverage `translate3d` for dragging/ tracking
  draggable element and removed the use of `left` CSS property to center
  too long calendar container.
* [TIL]: Custom getter and setter methods for `value` and `startView`
  can be achieved by combination of `property` decorator and custom
  getter and setter methods. Without the use `property` decorator,
  `lit-element` will not be able to keep track of the
  attribute-to-property mapping and performs updates accordingly
  whenever its value changes via attribute or property. However,
  duplicate declarations of properties is prohibited in TypeScript.
  `// @ts-ignore` can be used to bypass the checking.

* Added `datepicker-first-updated` event to include 1st focusable
  element so that outside world can make use of this event to do more
  stuff.
* Removed not-so-useful `keydown` event on calendar.
* Minor code refactoring.

* Refactored code to return `null` when a calendar has its first day
  larger than `max` or its last day smaller than `min`. When a calendar
  returns `null`, no rendering will take place for that month.
* Month selector button will not render for disabled calendar. It
  restores when the left (first) and right (last) calendars are not
  disabled calendars (all calendar days fall in between valid date
  range).
* Dragging functionality aborts when it attempts to happen on an
  out-of-bound calendar, that is, all calendar days are smaller than
  `min` or larger than `max`. A disabled calendar will not get rendered.

* Removed time zone detail of a `max` date. A date in the format of
  `yyyy-MM-dd` suffices to convert to a Date object with timezone offset
  relative to UTC time. UTC time is the de facto way of ensuring that
  local timezone offset will not affect the final outcome of a selected
  date and it can be consumed safely from a browser to a backend server
  that is in different timezone.
* Added additional condition check to ensure that 1st day of the current
  visible/ focusing month will be focused when a keyboard event fires.
  The value of month or full year in a `_selectedDate` could be altered
  by user's input without actually updating `_focusedDate` thus renders
  `_focusedDate` could be an out-of-bound date. This change will bring
  the focus back to currently visible/ focusing month when the user
  chooses to interact with that calendar again.

* `TouchEvent` does not work as well as that of Chrome on Firefox.
  It's not that straightforward to do tracking anymore if that is the
  case plus `pointer-tracker` also has problem on Firefox.

* Fixed bug where flickering occurs when calendars re-render with new
  `_selectedDate` value after Web Animations ends on unsupported
  browsers such as Edge. Simple workaround for that is to set `fill` to
  `both` but this will break on other evergreen browsers. A flag is
  added to fix this minor issue with polyfill and native implementation.

* Minor CSS update to set `line-height: 0` for element that has no text.

* Finally, a simple `Tracker` class has been made for the element. It
  works on almost all tested browsers including notorious Firefox.

Congrats on Rollup's v1.0 release! It's been a great year with such
amazing build tool.

Finally got some time to implement yet another important piece of the
element which is the dialog version. It has been a tough lesson for me
to get some stuffs to work as expected. `Web Animations` is used in this
case for animations basically but the weird behavior from both the
native supported browsers and the polyfill created different end
results. Thanks to a simple polyfill for browsers like Chrome lacks
native supported for the `Promise`d version that exposes a property
named `finished`. By loading polyfill just because of that, it breaks
all the animations on Chrome but it worked fine on other browsers. BTW,
Firefox is the only browser that shipped a working Web Animations on its
stable version.

Another new update is that `rollup` might be redundant for creating
libraries. `TypeScript`'s own CLI suffice to do the compilation since
bundling is not needed for `lit-element` based components.

Upgraded Rollup plugins that supports Rollup v1.

Minor CSS update including `border-radius` and improved animations when
opening/ closing dialog.

Removed `finished` polyfill for Chrome or browsers that natively
supported Web Animations. A simple solution for that is to wrap the
`onfinish` event handler with a Promise like so:

  new Promise(yay => (fadeInAnimation.onfinish = yay)).then(...)

This has been a technique used while developing the datepicker. Totally
forgotten about that and now this one-liner solution is once back again
for the dialog's animations.

Also worth to document this down later. `web-animations-next-lite` is
the recommended polyfill for better cross platform compatibility. It
works perfectly on Edge, Firefox, and Chrome (all tested). Yet to do a
testing on Safari. It's TP version supports native Web Animations behind
experimental flag. The main issue in other polyfill version is that
`fill` is causing discrepancies after applying polyfills. On Edge,
animated element will be set to the previous state forever and never get
reset for subsequent animation to take place. In the case of datepicker,
tracking logic that moves the calendar basically does nothing on
subsequent runs.

Added support for focus trap with `noFocusTrap` property. Focus
management does not work well on Firefox when `overflow-y: auto` is set.
This still needs to verify if this is a bug.

Improved accessibility on datepicker dialog based on WAI-ARIA specs.

Minor code refactoring and cleanup.

Removed Rollup in favor of TypeScript compiler for building library.
LitElement user should build or bundle their own projects with bundler
like Rollup to reduce the files shipped to end users.

The latest update introduces [Constructible Stylesheets][cs-url] via
`static get styles()`. All codes have been refactored to use that for
declaring styles with shareable styles. However this blocks TS
compilation due to unsupported types of the new API which has yet to be
implemented into browsers except being enabled by default in latest
Chrome Canary 73. To learn more about the issue, please visit
lit/lit-element#428.

[cs-url]: https://www.chromestatus.com/feature/5394843094220800

Latest `lit-element` has fixed a known issue where missing types are not
exported thus breaks TS compilation for many users. To learn more about
the issue, please visit lit/lit-element#428.

`@material/mwc-button` has been updated to latest `lit-element` too.
Reinstalled to make the buttons work again!

Tried Karma but it has limited support for TypeScript, switched back to
WCT.

Upgraded LitElement to latest RC with fixes in `static get styles()`.

Minor code cleanup.

Adding unit tests for <AppDatepicker> element.

Improved project structure and config files to build for testing and
publishing.

To ensure datetime consistency between the local browsers and the
datepicker, input date value can be a local datetime but it needs to
convert to UTC within the datepicker by picking just the date values
with `get*` methods instead of `getUTC*` methods.

FWIW, `get*` might return something unexpected in certain time zones
but that is acceptable since the datepicker is relying on what the
browser tells what it is.

Fixes tests to ensure all datetime values within the datepicker is
always in UTC time so `timeZone: UTC` is needed when doing a strict
comparison.

Also, added `_formatters` property to keep track of all kinds of date
formatters depending on value of `locale`.

Refactor year list with idiomatic JS and that requires polyfill for
newly added `Array.prototype.keys`.

All items in year list view now rendered with formatted year according
to the value of `locale`.

Changed `year` to `yearList` as one of the start/ selected views.

Fixes IE11-only CSS hacks that is broken on other browsers. Now it works
on IE11 and other browsers.

✅ Added more tests for year list view.

KNOWN ISSUES:-

- `disabledDays` and `disabledDates` are not supported.

Fixes an issue where polyfill.io no longer works as expected to load
necessary polyfills via feature detections or UA detection. A quick
patch is to replace modern features with compatible codes to ensure
Chrome 41 is able to load and run the datepicker without any issues.

`pointerup` -> `click` event listener on scrim of
`<AppDatepickerDialog>`.

Due to andyearnshaw/Intl.js/issues/256, the Intl polyfill has to be
pinned at v1.2.4. It breaks on Safari 9 and using older version should
fix the broken tests.

SauceLabs runs certain browsers on a machine that returns a different
locale other than `en-US`. By defaulting to `en-US` for the tests should
resolve the issues.

Remove latest Node.js to reduce the number of testing environments as
SauceLabs timed out quite frequently as this might the cause of it.

Run both Chrome and Firefox on CI but skips Firefox when testing on
local machine. Run tests on other browsers via SauceLabs.

Fixes more bugs after adding more tests to perfecting the datepicker.

Fixes a local date bug when different timezones are taken into account.
Now there is a conversion for input date that reads local date reported
from the browser locally and UTC date is used internally. The datepicker
deals with UTC date to render the calendar and selected date is output
as UTC date as well in the format of `yyyy-MM-dd`. The fix has been
tested and it works so far in affected timezone (PST).

Upgrades `lit-element` to latest version - RC5 as of this commit.

Stripping all LTR marks on output of Intl.DateTimeFormatter on older
browsers: IE11, Edge < 18 to ensure cross-browsers compatibility and
consistency since LTR mark is no longer part of the output in modern
browsers.

Removes `window-size` flag in WCT configuration file.

Adds a couple of IE11 only fixes via CSS hacks or conventional CSS.

Updates broken tests after adding IE11 fixes. To learn more, please see
#128 which details all the bugs that experienced
while building this project.