//
//  Request.swift
//  Befund
//
//  Created by Irakli Abetschkhrischwili on 15.05.22.
//  Copyright © 2022 MVZ Dr. Stein und Kollegen. All rights reserved.

import Foundation
import UIKit
import Combine
import CryptoKit


extension SecTrust {

    var isSelfSigned: Bool? {
        guard SecTrustGetCertificateCount(self) == 1 else {
            return false
        }
        guard let cert = SecTrustGetCertificateAtIndex(self, 0) else {
            return nil
        }
        return cert.isSelfSigned
    }
}

extension SecCertificate {

    var isSelfSigned: Bool? {
        guard
            let subject = SecCertificateCopyNormalizedSubjectSequence(self),
            let issuer = SecCertificateCopyNormalizedIssuerSequence(self)
        else {
            return nil
        }
        return subject == issuer
    }
}

extension Core
{

    enum RequestError: Error
    {
        case HANDLED_ERROR(msg: String)
        case UNEXPECTED_ERROR(msg: String)
    }
    
    @MainActor
    public class EncryptedResponse
    {
        var settings: Core.Models.Settings
        var descriptor: String
        var contentObject: Any
        var controller: String
        var action: String
        var requestType: Core.Models.Request.EncryptedRequest.Types
        
        private var _publicKey: Core.Models.Response.PublicKey? = nil
        private var _keyPair: Core.Security.Curve25519.KeyPair? = nil
        
        public init(settings: Core.Models.Settings, descriptor: String, contentObject: Any, controller: String, action: String, requestType: Core.Models.Request.EncryptedRequest.Types) {
            self.settings = settings
            self.descriptor = descriptor
            self.contentObject = contentObject
            self.controller = controller
            self.action = action
            self.requestType = requestType
        }
        
        private var host: Core.Https.Servers{
            get {
                return settings.labor?.host ?? .DEVELOPMENT
            }
        }
        
        private var keyPair: Core.Security.Curve25519.KeyPair {
            get {
                if(_keyPair == nil){
                    _keyPair = Core.Security.Curve25519.GenerateKeyPair()
                }
                return _keyPair!
            }
        }
        
        private var postRequest: HttpsAsync.Request.PostEncryptedRequestAsync{
            get {
                return HttpsAsync.Request.PostEncryptedRequestAsync()
            }
        }
        
        private var publicKey: Core.Models.Response.PublicKey? {
            get async throws {
                if (_publicKey == nil)
                {
                    _publicKey = try await postRequest.getPublicKey(host: host, _keyPair: keyPair)
                }
                return _publicKey
            }
        }
        
        public var sharedKey: CryptoKit.SymmetricKey? {
            get async throws{
                return try await keyPair.GetSharedKey(peerPublicKeyBase64: publicKey?.key)
            }
        }
        
        public var response: Core.Models.Response.EncryptedResponse? {
            get async throws {
                let _shared = try await sharedKey
                if(_shared != nil)
                {
                    let encryptedRequest = Core.Models.Request.EncryptedRequest(descriptor: descriptor, contentObject: contentObject, requestType: requestType, key: _shared!)

                    let encryptedResponse = try await postRequest.getEncryptedResponse(host: host, controller: controller, action: action, _request: encryptedRequest, serverPublicKey: publicKey, _keyPair: keyPair)
                    
                    return encryptedResponse

                }
                else
                {
                    return nil
                }

            }
        }
    }
    
    public struct HttpsAsync
    {
        public class Request
        {
            /**
             * Low Level Header protector
             */
            private static let HeaderSecureHash: String = "3HzKQw/&>*VH^?cAR{Qd5pP~6w(V5%aZ";
            private static let HeaderValueSecureHash: String = "7*R3P!f:sC4Q8XS:@*J/z:4/sS;V3GnM";
                        
            /**
             * Sends EncryptedRequest to the server in async mode and calls callback(onSucces or onError)
             */
            @MainActor
            public class PostEncryptedRequestAsync: NSObject, URLSessionDelegate
            {
                /**
                 * Runs encrypted request async and calls ether onSuccess or onError callback
                 *
                 * @param host - host of the server s. Servers enum
                 * @param controller - controller of request
                 * @param action - action of request
                 * @param _request - encrypted request that contains descriptor, request object and hmac
                 * @param serverPublicKey - Exchanged server public key from the first request
                 * @param _keyPair - Curve25519 KeyPair (Private & Public Keys)
                 */
                func getEncryptedResponse(host: Https.Servers, controller: String, action: String, _request: Core.Models.Request.EncryptedRequest, serverPublicKey: Core.Models.Response.PublicKey?, _keyPair: Core.Security.Curve25519.KeyPair? = nil) async throws -> Core.Models.Response.EncryptedResponse
                {
                    var (data,response) : (Data, URLResponse)
                    let keyPair = PrepareKeyPair(_keyPair: _keyPair)
                    do
                    {                        
                        let request = try PrepareURLRequest(host: host, controller: controller, action: action, _request: _request, keyPair: keyPair)
                        
                        let s = URLSession(configuration: URLSessionConfiguration.default, delegate: self, delegateQueue: nil)
                        (data,response) = try await s.data(for: request)
                    }
                    catch
                    {
                        throw RequestError.UNEXPECTED_ERROR(msg: error.localizedDescription)
                    }

                    let httpR = response as? HTTPURLResponse
                    if (httpR != nil)
                    {
                            if (httpR?.statusCode == 429)
                            {
                                AppDelegate.Session.Maintenance = false
                                AppDelegate.Session.MaintenanceNotified = false
                                throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "ERROR_TOO_MANY_REQUESTS"))
                            }
                            else if (httpR?.statusCode == 503)
                            {
                                AppDelegate.Session.Maintenance = true
                                throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "MSG_MAINTENANCE"))
                            }
                            else
                            {
                                AppDelegate.Session.Maintenance = false
                                AppDelegate.Session.MaintenanceNotified = false
                                if(!Core.Https.Request.validServerHeaders(server: httpR!))
                                {
                                    throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "ERROR_INVALID_RESPONSE"))
                                }
                                else
                                {
                                    let encrR = try JSONDecoder().decode(Core.Models.Response.EncryptedResponse.self, from: data)
                                    let symKey = keyPair.GetSharedKey(peerPublicKeyBase64: serverPublicKey?.key!)
                                    if(Core.Https.Request.validServerSignature(server: httpR!, encryptedResponse: encrR, deriveKey: symKey!))
                                    {
                                        return encrR
                                    }
                                    else
                                    {
                                        throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "ERROR_INVALID_RESPONSE"))
                                    }
                                }
                            }
                    }
                    else
                    {
                        throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "ERROR_INVALID_RESPONSE"))
                    }

                }
                
                @MainActor
                func getPublicKey(host: Https.Servers, _keyPair: Core.Security.Curve25519.KeyPair? = nil) async throws -> Core.Models.Response.PublicKey
                {
                    var (data,response) : (Data, URLResponse)
                    do
                    {
                        let keyPair = PrepareKeyPair(_keyPair: _keyPair)
                        
                        let request = try PrepareURLRequest(host: host, controller: "exchange", action: "key", _request: nil, keyPair: keyPair)
                        
                        let s = URLSession(configuration: URLSessionConfiguration.default, delegate: self, delegateQueue: nil)
                        (data,response) = try await s.data(for: request)
                    }
                    catch
                    {
                        throw RequestError.UNEXPECTED_ERROR(msg: error.localizedDescription)
                    }

                    let httpR = response as? HTTPURLResponse
                    if(httpR != nil)
                    {
                            
                            if (httpR!.statusCode == 429)
                            {
                                AppDelegate.Session.Maintenance = false
                                AppDelegate.Session.MaintenanceNotified = false
                                throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "ERROR_TOO_MANY_REQUESTS"))
                            }
                            else if (httpR!.statusCode == 503)
                            {
                                AppDelegate.Session.Maintenance = true
                                throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "MSG_MAINTENANCE"))
                            }
                            else
                            {
                                AppDelegate.Session.Maintenance = false
                                AppDelegate.Session.MaintenanceNotified = false
                                if(!Core.Https.Request.validServerHeaders(server: httpR!))
                                {
                                    throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "ERROR_INVALID_RESPONSE"))
                                }
                                else
                                {
                                    let publicKey = try JSONDecoder().decode(Core.Models.Response.PublicKey.self, from: data)
                                    return publicKey
                                }
                            }
                    }
                    else
                    {
                        throw RequestError.HANDLED_ERROR(msg: Core.Lang.Get(key: "ERROR_INVALID_RESPONSE"))
                    }

                }
                
                nonisolated public func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {
#if DEBUG
                    // Accept all certificates
                    let urlCredential = URLCredential(trust: challenge.protectionSpace.serverTrust!)
                    completionHandler(.useCredential, urlCredential)
#else
                    completionHandler(.performDefaultHandling, nil)
#endif
                }
                                
                private func PrepareKeyPair(_keyPair: Core.Security.Curve25519.KeyPair? = nil) -> Core.Security.Curve25519.KeyPair
                {
                    var keyPair = _keyPair;
                    
                    if(keyPair == nil)
                    {
                        keyPair = Security.Curve25519.GenerateKeyPair()
                    }
                    
                    return keyPair!
                }
                
                private func PrepareURLRequest(host: Https.Servers, controller: String, action: String, _request: Core.Models.Request.EncryptedRequest?, keyPair: Core.Security.Curve25519.KeyPair) throws -> URLRequest
                {
                    
                    let strURL = Core.Https.Request.wellFormedControllerAction(host: host, controller: controller, action: action)
                    let url = URL(string: strURL)!
                    var request = URLRequest(url: url)
                    
                    request.httpMethod = "POST"
                    request.setValue(host.rawValue, forHTTPHeaderField: "Host")
                    request.setValue("BefundApp", forHTTPHeaderField: "User-Agent")
                    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
                    request.setValue(Security.AES.Encrypt(value: HeaderValueSecureHash, deriveKey: SymmetricKey(data: Security.AES.GetKey(password: HeaderSecureHash))), forHTTPHeaderField: "Client-Hash")
                    request.setValue(keyPair.PublicKey, forHTTPHeaderField: "Client-Key")
                    if(_request == nil)
                    {
                        request.httpBody = try JSONEncoder().encode(Core.Models.Request.KeyExchange())
                    }
                    else
                    {
                        request.setValue(keyPair.SigningPublicKey, forHTTPHeaderField: "Client-Signature-Key")
                        request.setValue(keyPair.GetSignature(signingValue: (_request!.encrypted_content != nil ? _request!.encrypted_content : _request!.descriptor)!), forHTTPHeaderField: "Client-Signature")
                        
                        request.httpBody = try JSONEncoder().encode(_request)
                    }
                    
                    return request
                }
                
            }
        }
    }
}