Late sunsets give incorrect date for time zone

[tal]

I'm getting an issue with putting in a date that is after midnight UTC but before midnight local. It returns a solar instance for the following day. I've tried passing in a custom calendar but that doesn't seem to fix the issue. I'll continue working on it but for now here's a test I wrote to recreate this failure case.

	func testLateTimeCorrectReturnDate() {
		let lateTime = Date(timeIntervalSince1970: 1499130000) // After midnight UTC, before midnight in DC.
		let city = cities.first(where: { $0.name == "Washington, D. C." })!
		
		let calendar: Calendar = {
			var calendar = Calendar.current
			calendar.timeZone = TimeZone(identifier: "EST")!
			return calendar
		}()
		
		guard let solar = Solar(for: lateTime, latitude: city.latitude, longitude: city.longitude) else {
			XCTFail("Cannot get solar")
			return
		}
		
		let sameDate = calendar.compare(lateTime, to: solar.sunset!, toGranularity: .day)
		
		XCTAssertTrue(sameDate == .orderedSame, "The sunset given \(solar.sunset!) is not same day as given date \(lateTime)")
	}

[ceeK]

Hi Tal! Thanks for the report and including a test, super helpful! Apologies for the delay.

I've had a look at your test and as far as I can tell it seems to be working as expected, in that it always returns a UTC date that you have to format 🤔 maybe I am misunderstanding though. I've added a little debug code to the bottom of your test. Can you check my logic:

func testLateTimeCorrectReturnDate() {
        let lateTime = Date(timeIntervalSince1970: 1499130000) // Tuesday, 4 July 2017 01:00:00 UTC
        let city = cities.first(where: { $0.name == "Washington, D. C." })!
        
        let calendar: Calendar = {
            var calendar = Calendar.current
            calendar.timeZone = TimeZone(identifier: "EST")!
            return calendar
        }()
        
        guard let solar = Solar(for: lateTime, latitude: city.latitude, longitude: city.longitude) else {
            XCTFail("Cannot get solar")
            return
        }
        
        let sameDate = calendar.compare(lateTime, to: solar.sunset!, toGranularity: .day)
        
        XCTAssertTrue(sameDate == .orderedSame, "The sunset given \(solar.sunset!) is not same day as given date \(lateTime)")
        
        let dateFormatter = DateFormatter()
        dateFormatter.dateStyle = .full
        dateFormatter.timeStyle = .full
        dateFormatter.timeZone = TimeZone(identifier: "EST")!
        let string = dateFormatter.string(from: solar.sunset!)
        print("Date: \(string)")
    }

This outputs Date: Tuesday, July 4, 2017 at 7:36:56 PM GMT-05:00. I've had a look this reference website and can see that the local sunset is July 4th 8:36pm GMT-04:00 (EDT). This looks to me that it's producing the correct sunset date given the 1 hour DST difference between EST and EDT.

After running your pull request test and checking Solar's date, I get:
2017-07-04 00:37:07 +0000. The timezone here is UTC, so when we format this date to EST we actually get a date on 2017-07-03.

Tell me if I'm missing something! 🙈