// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

import Foundation

extension Date {
    var isGoZeroTime: Bool {
        return self == GoZeroTime
    }
}

// GoZeroTime is a Date instance that matches Go's time.Time zero value. It's
// explicitly created using Go's zero value (0001-01-01, 00:00:00 UTC), since
// using an offset from the Unix epoch (1970-01-01, 00:00:00 UTC) does not work
// as expected on macOS 10.13.
let GoZeroTimeString = "0001-01-01T00:00:00Z"
let GoZeroTime = ISO8601DateFormatter().date(from: GoZeroTimeString)!

extension String {
    func iso8601Date() -> Date? {
        let iso8601DateFormatter = {
            ISO8601DateFormatter()
        }()
        
        let iso8601DateFormatterFractionalSeconds: ISO8601DateFormatter = {
            let dateFormatter = ISO8601DateFormatter()
            dateFormatter.formatOptions.insert(.withFractionalSeconds)
            return dateFormatter
        }()
        
        // Fractional seconds are optional in RFC3339 as generated by Go/control,
        // but Foundation date formatters do not parse dates with and without
        // fractional seconds without specifying the option to look for them.
        if let date = iso8601DateFormatterFractionalSeconds.date(from: self) {
            return date
        }
        if let date = iso8601DateFormatter.date(from: self) {
            return date
        }
        return nil
    }
}