//
//  PushManagerImpl.swift
//  PushNotifications
//
//  Created by Shadowfacts on 4/7/24.
//

import UIKit
import UserAccounts
import CryptoKit

class PushManagerImpl: _PushManager {
    private let endpoint: URL
    
    var enabled: Bool {
        true
    }
    
    private var apnsEnvironment: String {
        #if DEBUG
        "development"
        #else
        "release"
        #endif
    }
    
    private var remoteNotificationsRegistrationContinuation: CheckedContinuation<Data, any Error>?
    
    private let defaults = UserDefaults(suiteName: "group.space.vaccor.Tusker")!
    private(set) var proxyRegistration: PushProxyRegistration? {
        get {
            if let dict = defaults.dictionary(forKey: "PushProxyRegistration") as? [String: String],
               let registration = PushProxyRegistration(defaultsDict: dict) {
                return registration
            } else {
                return nil
            }
        }
        set {
            defaults.setValue(newValue?.defaultsDict, forKey: "PushProxyRegistration")
        }
    }
    private(set) var subscriptions: [PushSubscription] {
        get {
            if let array = defaults.array(forKey: "PushSubscriptions") as? [[String: Any]] {
                return array.compactMap(PushSubscription.init(defaultsDict:))
            } else {
                return []
            }
        }
        set {
            defaults.setValue(newValue.map(\.defaultsDict), forKey: "PushSubscriptions")
        }
    }
    
    init(endpoint: URL) {
        self.endpoint = endpoint
    }
    
    func createSubscription(account: UserAccountInfo) throws -> PushSubscription {
        guard let proxyRegistration else {
            throw CreateSubscriptionError.notRegisteredWithProxy
        }
        if let existing = pushSubscription(account: account) {
            return existing
        }
        let key = P256.KeyAgreement.PrivateKey()
        var authSecret = Data(count: 16)
        let res = authSecret.withUnsafeMutableBytes { ptr in
            SecRandomCopyBytes(kSecRandomDefault, 16, ptr.baseAddress!)
        }
        guard res == errSecSuccess else {
            throw CreateSubscriptionError.generatingAuthSecret(res)
        }
        let subscription = PushSubscription(
            accountID: account.id,
            endpoint: endpointURL(registration: proxyRegistration, accountID: account.id),
            secretKey: key,
            authSecret: authSecret,
            alerts: [],
            policy: .all
        )
        subscriptions.append(subscription)
        return subscription
    }
    
    private func endpointURL(registration: PushProxyRegistration, accountID: String) -> URL {
        var endpoint = URLComponents(url: registration.endpoint, resolvingAgainstBaseURL: false)!
        endpoint.queryItems = endpoint.queryItems ?? []
        endpoint.queryItems!.append(URLQueryItem(name: "ctx", value: accountID))
        return endpoint.url!
    }
    
    func removeSubscription(account: UserAccountInfo) {
        subscriptions.removeAll { $0.accountID == account.id }
    }
    
    func updateSubscription(account: UserAccountInfo, alerts: PushSubscription.Alerts, policy: PushSubscription.Policy) {
        guard let index = subscriptions.firstIndex(where: { $0.accountID == account.id }) else {
            return
        }
        var copy = subscriptions[index]
        copy.alerts = alerts
        copy.policy = policy
        subscriptions[index] = copy
    }
    
    func pushSubscription(account: UserAccountInfo) -> PushSubscription? {
        subscriptions.first { $0.accountID == account.id }
    }
    
    func register(transactionID: UInt64) async throws -> PushProxyRegistration {
        guard remoteNotificationsRegistrationContinuation == nil else {
            throw PushRegistrationError.alreadyRegistering
        }
        let deviceToken = try await getDeviceToken().hexEncodedString()
        PushManager.logger.debug("Got device token: \(deviceToken)")
        let registration: PushProxyRegistration
        do {
            registration = try await register(deviceToken: deviceToken)
            PushManager.logger.debug("Got endpoint: \(registration.endpoint)")
        } catch {
            PushManager.logger.error("Proxy registration failed: \(String(describing: error))")
            throw PushRegistrationError.registeringWithProxy(error)
        }
        proxyRegistration = registration
        return registration
    }
    
    func unregister() async throws {
        guard let proxyRegistration else {
            return
        }
        var url = URLComponents(url: endpoint, resolvingAgainstBaseURL: false)!
        url.path = "/app/v1/registrations/\(proxyRegistration.id)"
        var request = URLRequest(url: url.url!)
        request.httpMethod = "DELETE"
        let (data, resp) = try await URLSession.shared.data(for: request)
        let status = (resp as! HTTPURLResponse).statusCode
        if (200...299).contains(status) {
            self.proxyRegistration = nil
            PushManager.logger.debug("Unregistered from proxy")
        } else {
            PushManager.logger.error("Unregistering: unexpected status \(status)")
            let error = (try? JSONDecoder().decode(ProxyRegistrationError.self, from: data)) ?? ProxyRegistrationError(error: "Unknown error", fields: nil)
            throw PushRegistrationError.unregistering(error)
        }
    }
    
    func updateIfNecessary(updateSubscription: @escaping (PushSubscription) async -> Bool) async {
        guard let proxyRegistration else {
            return
        }
        PushManager.logger.debug("Push proxy registration: \(proxyRegistration.id, privacy: .public)")
        do {
            let token = try await getDeviceToken().hexEncodedString()
            guard token != proxyRegistration.deviceToken else {
                // already up-to-date, nothing to do
                return
            }
            let newRegistration = try await update(registration: proxyRegistration, deviceToken: token)
            self.proxyRegistration = newRegistration
            if proxyRegistration.endpoint != newRegistration.endpoint {
                self.subscriptions = await AsyncSequenceAdaptor(wrapping: self.subscriptions).map {
                    var copy = $0
                    copy.endpoint = await self.endpointURL(registration: newRegistration, accountID: $0.accountID)
                    if await updateSubscription(copy) {
                        return copy
                    } else {
                        return $0
                    }
                }.reduce(into: [], { partialResult, el in
                    partialResult.append(el)
                })
            }
        } catch {
            PushManager.logger.error("Failed to update push registration: \(String(describing: error), privacy: .public)")
            PushManager.captureError?(error)
        }
    }
    
    private func getDeviceToken() async throws -> Data {
        defer {
            remoteNotificationsRegistrationContinuation = nil
        }
        return try await withCheckedThrowingContinuation { continuation in
            remoteNotificationsRegistrationContinuation = continuation
            UIApplication.shared.registerForRemoteNotifications()
        }
    }
    
    func didRegisterForRemoteNotifications(deviceToken: Data) {
        remoteNotificationsRegistrationContinuation?.resume(returning: deviceToken)
    }
    
    func didFailToRegisterForRemoteNotifications(error: any Error) {
        remoteNotificationsRegistrationContinuation?.resume(throwing: PushRegistrationError.registeringForRemoteNotifications(error))
    }
    
    private func register(deviceToken: String) async throws -> PushProxyRegistration {
        var url = URLComponents(url: endpoint, resolvingAgainstBaseURL: false)!
        url.path = "/app/v1/registrations"
        var request = URLRequest(url: url.url!)
        request.httpMethod = "POST"
        request.setValue("application/json", forHTTPHeaderField: "content-type")
        request.httpBody = try! JSONEncoder().encode(PushRegistrationParams(transactionID: "TODO", environment: apnsEnvironment, deviceToken: deviceToken, pushVersion: 1))
        let (data, resp) = try await URLSession.shared.data(for: request)
        let status = (resp as! HTTPURLResponse).statusCode
        guard (200...299).contains(status) else {
            PushManager.logger.error("Registering: unexpected status \(status)")
            let error = (try? JSONDecoder().decode(ProxyRegistrationError.self, from: data)) ?? ProxyRegistrationError(error: "Unknown error", fields: [])
            throw error
        }
        return try JSONDecoder().decode(PushProxyRegistration.self, from: data)
    }
    
    private func update(registration: PushProxyRegistration, deviceToken: String) async throws -> PushProxyRegistration {
        var url = URLComponents(url: endpoint, resolvingAgainstBaseURL: false)!
        url.path = "/app/v1/registrations/\(registration.id)"
        var request = URLRequest(url: url.url!)
        request.httpMethod = "PUT"
        request.setValue("application/json", forHTTPHeaderField: "content-type")
        request.httpBody = try! JSONEncoder().encode(PushUpdateParams(environment: apnsEnvironment, deviceToken: deviceToken, pushVersion: 1))
        let (data, resp) = try await URLSession.shared.data(for: request)
        let status = (resp as! HTTPURLResponse).statusCode
        guard (200...299).contains(status) else {
            PushManager.logger.error("Updating: unexpected status \(status)")
            let error = (try? JSONDecoder().decode(ProxyRegistrationError.self, from: data)) ?? ProxyRegistrationError(error: "Unknown error", fields: [])
            throw error
        }
        return try JSONDecoder().decode(PushProxyRegistration.self, from: data)
    }
}

enum PushRegistrationError: LocalizedError {
    case alreadyRegistering
    case registeringForRemoteNotifications(any Error)
    case registeringWithProxy(any Error)
    case unregistering(any Error)
    
    var errorDescription: String? {
        switch self {
        case .alreadyRegistering:
            "Already registering"
        case .registeringForRemoteNotifications(let error):
            "Remote notifications: \(error.localizedDescription)"
        case .registeringWithProxy(let error):
            "Proxy: \(error.localizedDescription)"
        case .unregistering(let error):
            "Unregistering: \(error.localizedDescription)"
        }
    }
}

struct ProxyRegistrationError: LocalizedError, Decodable {
    let error: String
    let fields: [Field]?
    
    var errorDescription: String? {
        if let fields,
           !fields.isEmpty {
            error + ": " + fields.map { "\($0.key): \($0.reason)" }.joined(separator: ", ")
        } else {
            error
        }
    }
    
    struct Field: Decodable {
        let key: String
        let reason: String
    }
}

enum CreateSubscriptionError: LocalizedError {
    case notRegisteredWithProxy
    case generatingAuthSecret(OSStatus)
    
    var errorDescription: String? {
        switch self {
        case .notRegisteredWithProxy:
            "Not registered with proxy"
        case .generatingAuthSecret(let code):
            "Generating auth secret: \(code)"
        }
    }
}

private struct PushRegistrationParams: Encodable {
    let transactionID: String
    let environment: String
    let deviceToken: String
    let pushVersion: Int
    
    enum CodingKeys: String, CodingKey {
        case transactionID = "transaction_id"
        case environment
        case deviceToken = "device_token"
        case pushVersion = "push_version"
    }
}

private struct PushUpdateParams: Encodable {
    let environment: String
    let deviceToken: String
    let pushVersion: Int
    
    enum CodingKeys: String, CodingKey {
        case environment
        case deviceToken = "device_token"
        case pushVersion = "push_version"
    }
}

private extension Data {
    func hexEncodedString() -> String {
        String(unsafeUninitializedCapacity: count * 2) { buffer in
            let chars = Array("0123456789ABCDEF".utf8)
            for (i, x) in enumerated() {
                let (upper, lower) = x.quotientAndRemainder(dividingBy: 16)
                buffer[i * 2] = chars[Int(upper)]
                buffer[i * 2 + 1] = chars[Int(lower)]
            }
            return count * 2
        }
    }
}

private struct AsyncSequenceAdaptor<S: Sequence>: AsyncSequence {
    typealias Element = S.Element
    
    let base: S
    
    init(wrapping base: S) {
        self.base = base
    }
    
    func makeAsyncIterator() -> AsyncIterator {
        AsyncIterator(base: base.makeIterator())
    }
    
    struct AsyncIterator: AsyncIteratorProtocol {
        var base: S.Iterator
        
        mutating func next() async -> Element? {
            base.next()
        }
    }
}