TimeZoneUtils.swift

import Foundation

// Create TimeZone instance from UTC offset string like "-07:30"
extension TimeZone {
    
    private static let refZoneString = "+0000"
    
    private static var _offsetTimezoneDateFormatter: DateFormatter!
    static var offsetTimezoneDateFormatter: DateFormatter {
        if let _offsetTimezoneDateFormatter = _offsetTimezoneDateFormatter {
            return _offsetTimezoneDateFormatter
        }
        _offsetTimezoneDateFormatter = DateFormatter()
        _offsetTimezoneDateFormatter.dateFormat = "Z"
        return _offsetTimezoneDateFormatter
    }
    
    private static let refUTCDate = offsetTimezoneDateFormatter.date(from: refZoneString)
    
    
    init?(UTCOffsetString ofs: String) {
        guard let refDate = TimeZone.refUTCDate,
            let date = TimeZone.offsetTimezoneDateFormatter.date(from: ofs) else {
                return nil
        }
        
        if let offsetInSec = Calendar.current.dateComponents([.second], from: date, to: refDate).second {
            self.init(secondsFromGMT: offsetInSec)
        } else {
            return nil
        }
    }
}

let tz = TimeZone.init(UTCOffsetString: "-07:30")
print(tz?.identifier ?? "unknown")

// Prints GMT-0730