import Foundation

struct DNSUpdater {

    private let log: Log

    private let files: Files

    init(configurationFileUrl: URL) throws {
        let files = try Files(configurationFileURL: configurationFileUrl)
        self.log = Log(logLevel: files.configuration.logLevel)
        self.files = files
        log.debug("Starting DNS updater")
        log.debug("    Last update file: \(files.configuration.lastUpdateFilePath)")
        log.debug("            Log file: \(files.configuration.logFilePath)")
    }

    func performDnsUpdateIfNeeded(log: Log) async throws {
        let now = Date()

        let configuration = try files.loadDomainConfiguration()
        log.debug("Running DNS updater")
        log.debug("             Domains: \(configuration.domains.sortedList)")
        log.debug("                IPv4: \(configuration.useIPv4 ? "yes" : "no")")
        log.debug("                IPv6: \(configuration.useIPv6 ? "yes" : "no")")


        let oldState = try files.loadLastState()
        oldState.print(to: log)

        var newState = oldState
        newState.state = .nominal
        newState.domainStates = oldState.domainStates.filter { (domain, _) in
            guard configuration.domains.contains(domain) else {
                log.info("Removing state of domain \(domain)")
                return false
            }
            return true
        }

        guard !configuration.domains.isEmpty else {
            log.warning("No domains configured")
            newState.state = .noDomainConfigured
            try files.save(lastState: newState)
            return
        }
        var currentIPs: Set<String> = []

        let ipChecker = IPAddressCheck()
        if configuration.useIPv4 {
            do {
                let ipV4 = try await ipChecker.determineIPv4()
                currentIPs.insert(ipV4)
            } catch {
                log.error(error.localizedDescription)
                newState.state = .missingIPv4
            }
        }
        if configuration.useIPv6 {
            do {
                let ipV6 = try ipChecker.determineIPv6()
                currentIPs.insert(ipV6)
            } catch {
                log.error(error.localizedDescription)
                newState.state = .missingIPv6
            }
        }

        guard !currentIPs.isEmpty else {
            log.warning("No addresses available to update")
            newState.state = .missingAddresses
            try files.save(lastState: newState)
            return
        }

        let domainsNeedingUpdate = updates(from: newState.domainStates, with: currentIPs, for: configuration.domains)

        guard !domainsNeedingUpdate.isEmpty else {
            log.info("No update needed")
            return
        }
        log.info("Updating \(domainsNeedingUpdate.list) to \(currentIPs.sortedList)")

        let updatedDomains = await updateStratoEntry(
            domains: domainsNeedingUpdate,
            addresses: currentIPs,
            password: configuration.password)

        var updates = [String : DomainState]()

        for (domain, response) in updatedDomains {
            log.debug("\(domain): \(response)")
            let old = newState.domainStates[domain] ?? .init(initial: now)
            let new = old.updated(now, from: response, expecting: currentIPs)
            updates[domain] = new
            newState.domainStates[domain] = new

            if response.isServerError {
                newState.state = .serverError
            }
            if response.isClientError && newState.state != .serverError {
                newState.state = .clientError
            }
        }

        if newState != oldState {
            do {
                try files.save(lastState: newState)
                log.debug("State updated")
            } catch {
                log.error(error.localizedDescription)
            }
        }

        if !updates.isEmpty {
            try files.addLogEntry(changedDomains: updates)
            log.debug("Log updated")
        }
    }


    private func updates(from lastState: [String : DomainState], with currentIPs: Set<String>, for domains: Set<String>) -> [String] {
        let now = Date()
        // Add all new domains
        var updates = domains.subtracting(lastState.keys)
        for (domain, state) in lastState {
            guard state.needsUpdate(at: now, to: currentIPs) else {
                continue
            }
            updates.insert(domain)
        }
        return updates.sorted()
    }

    private func updateStratoEntry(domains: [String], addresses: Set<String>, password: String) async -> [String : DNSChangeResponse] {

        func fail(_ error: DNSChangeResponse) -> [String : DNSChangeResponse] {
            domains.reduce(into: [:]) { $0[$1] = error }
        }

        func unknown(_ message: String) -> [String : DNSChangeResponse] {
            fail(.unknown(message))
        }

        guard let domain = domains.first else {
            return fail(.success)
        }
        let domainList = domains.joined(separator: ",")
        let addressList = addresses.sorted().joined(separator: ",")

        let url = "https://dyndns.strato.com/nic/update?hostname=\(domainList)&myip=\(addressList)"

        var request = URLRequest(url: URL(string: url)!)
        request.httpMethod = "GET"

        let auth = "\(domain):\(password)".data(using: .utf8)!.base64EncodedString()
        request.setValue("Basic \(auth)", forHTTPHeaderField: "Authorization")
        request.setValue("CH DNS Updater 1.0", forHTTPHeaderField: "User-Agent")

        let data: Data
        let response: URLResponse
        do {
            (data, response) = try await URLSession.shared.data(for: request)
        } catch {
            return unknown("Request failed (\(error.localizedDescription.singleLined))")
        }
        let httpResponse = response as! HTTPURLResponse
        guard httpResponse.statusCode == 200 else {
            return unknown("Response \(httpResponse.statusCode)")
        }
        guard let responseBody = String(data: data, encoding: .utf8) else {
            return fail(.noResponseString)
        }
        let domainResults = responseBody
            .components(separatedBy: "\n")
            .compactMap { $0.trimmed.nonEmpty }

        guard domainResults.count == domains.count else {
            return unknown("Result count mismatch: \(domainResults.count) != \(domains.count)")
        }
        return (0..<domains.count).reduce(into: [:]) { dict, index in
            dict[domains[index]] = DNSChangeResponse(line: domainResults[index], expecting: addresses)
        }
    }
}