PostgreSQLData+Date.swift

extension Date: PostgreSQLDataConvertible {
    /// See `PostgreSQLDataConvertible`.
    public static func convertFromPostgreSQLData(_ data: PostgreSQLData) throws -> Date {
        switch data.storage {
        case .text(let value):
            switch data.type {
            case .timestamp: return try value.parseDate(format:  "yyyy-MM-dd HH:mm:ss")
            case .date: return try value.parseDate(format:  "yyyy-MM-dd")
            case .time: return try value.parseDate(format:  "HH:mm:ss")
            default: throw PostgreSQLError.decode(Date.self, from: data)
            }
        case .binary(let value):
            switch data.type {
            case .timestamp, .timestamptz:
                let microseconds = value.as(Int64.self, default: 0).bigEndian
                let seconds = Double(microseconds) / Double(_microsecondsPerSecond)
                return Date(timeInterval: seconds, since: _psqlDateStart)
            case .time, .timetz: throw PostgreSQLError.decode(Date.self, from: data)
            case .date:
                let days = value.as(Int32.self, default: 0).bigEndian
                let seconds = Int64(days) * _secondsInDay
                return Date(timeInterval: Double(seconds), since: _psqlDateStart)
            default: throw PostgreSQLError.decode(Date.self, from: data)
            }
        case .null: throw PostgreSQLError.decode(Date.self, from: data)
        }
    }

    /// See `PostgreSQLDataConvertible`.
    public func convertToPostgreSQLData() throws -> PostgreSQLData {
        return PostgreSQLData(.timestamp, binary: Data.of(Int64(self.timeIntervalSince(_psqlDateStart) * Double(_microsecondsPerSecond)).bigEndian))
    }
}

// MARK: Private

private let _microsecondsPerSecond: Int64 = 1_000_000
private let _secondsInDay: Int64 = 24 * 60 * 60
private let _psqlDateStart = Date(timeIntervalSince1970: 946_684_800) // values are stored as seconds before or after midnight 2000-01-01

private extension String {
    /// Parses a Date from this string with the supplied date format.
    func parseDate(format: String) throws -> Date {
        let formatter = DateFormatter()
        if contains(".") {
            formatter.dateFormat = format + ".SSSSSS"
        } else {
            formatter.dateFormat = format
        }
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        guard let date = formatter.date(from: self) else {
            throw PostgreSQLError(identifier: "date", reason: "Malformed date: \(self)")
        }
        return date
    }
}