DnsUpdater/Sources/App/Model/DomainState.swift

import Foundation

struct DomainState: Codable {

    /// The date of the last successful update
    let date: Date

    /// The last registered addresses
    let addresses: Set<String>

    /**
     Number of successive errors signaled by the server.

     Needed to prevent excessive requests and being flagged as abuse.
     */
    let serverErrorCount: Int

    /**
     Number of errors on the client side.

     Errors here will not force the algorithm to back off.
     */
    let clientErrorCount: Int

    /**
     The time to wait before the next update attempt
     */
    let currentWaitPeriod: TimeInterval

    let lastResult: DNSChangeResponse

    init(date: Date, addresses: Set<String>, serverErrorCount: Int, clientErrorCount: Int, currentWaitPeriod: TimeInterval, lastResult: DNSChangeResponse) {
        self.date = date
        self.addresses = addresses
        self.serverErrorCount = serverErrorCount
        self.clientErrorCount = clientErrorCount
        self.currentWaitPeriod = currentWaitPeriod
        self.lastResult = lastResult
    }

    init(initial date: Date) {
        self.date = date
        self.addresses = []
        self.serverErrorCount = 0
        self.clientErrorCount = 0
        self.currentWaitPeriod = 0
        self.lastResult = .success
    }

    var nextUpdate: Date {
        date.addingTimeInterval(currentWaitPeriod)
    }


    private static let formatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        formatter.timeStyle = .short
        return formatter
    }()

    func logEntry(domain: String) -> String {
        "\(domain);\(DomainState.formatter.string(from: date));\(addressList);\(serverErrorCount);\(clientErrorCount);\(currentWaitPeriod);\(lastResult.rawValue)"
    }

    var addressList: String {
        addresses.sortedList
    }

    func needsUpdate(at now: Date, to addresses: Set<String>) -> Bool {
        guard now >= nextUpdate else {
            return false
        }
        return !self.addresses.subtracting(addresses).isEmpty
    }

    func updated(_ now: Date, from result: DNSChangeResponse, expecting addresses: Set<String>) -> DomainState {
        let addresses = result.isSuccessStatus ? addresses : self.addresses
        let serverError = result.isServerError ? serverErrorCount + 1 : 0
        let clientError = result.isClientError ? clientErrorCount + 1 : 0
        let waitTime = result.delayTime(previous: currentWaitPeriod)
        return .init(
            date: now,
            addresses: addresses,
            serverErrorCount: serverError,
            clientErrorCount: clientError,
            currentWaitPeriod: waitTime,
            lastResult: result)
    }
}

extension DomainState: Equatable {

    static func == (lhs: DomainState, rhs: DomainState) -> Bool {
        lhs.date == rhs.date &&
        lhs.addresses == rhs.addresses &&
        lhs.clientErrorCount == rhs.clientErrorCount &&
        lhs.serverErrorCount == rhs.serverErrorCount &&
        lhs.currentWaitPeriod == rhs.currentWaitPeriod &&
        lhs.lastResult == rhs.lastResult
    }
}