//
//  AES.swift
//  Befund
//
//  Created by Irakli Abetschkhrischwili on 29.04.22.
//  Copyright © 2022 MVZ Dr. Stein und Kollegen. All rights reserved.

import Foundation
import CryptoKit

extension Core.Security
{
    public class AES
    {
        public static let PGS_ENCRYPT_PARTIAL_KEY = "wA6j@x.CcmM>~5Ss^C_!#,zch)$YsDsd59,::>dW#F`@U]Ye5ETZcMT7}&+#*!%z"
        /**
         * Encrypts string with password (string)
         *
         * @param value - string value that should be encrypted
         * @param password - string password that should be used for encryption(max. 32 bytes)
         * @return - returns encrypted base64 string
         */
        static func Encrypt(value: String, password: String) -> String?
        {
            var result: String? = nil
            
            do
            {
                let key = SymmetricKey(data: GetKey(password: password))
                let data = value.data(using: .utf8)
                
                if(data != nil)
                {
                    let encrypted = try CryptoKit.AES.GCM.seal(data!, using: key)
                    result = encrypted.combined!.base64EncodedString()
                }
            }
            catch
            {
                Core.Log.Error(err: error, namespace: "Core.Security.AES", method: "Encrypt(string, string)")
            }
            
            return result
        }
        
        /**
         * Encrypts string with key
         *
         * @param value - string value that should be encrypted
         * @param deriveKey - shared deriveKey that should be used for encryption(max. 32 bytes)
         * @return - returns encrypted base64 string
         */
        static func Encrypt(value: String, deriveKey: CryptoKit.SymmetricKey) -> String?
        {
            var result: String? = nil
            
            do
            {
                let data = value.data(using: .utf8)
                
                if(data != nil)
                {
                    let encrypted = try CryptoKit.AES.GCM.seal(data!, using: deriveKey)
                    result = Base64.ToBase64String(data: encrypted.combined!)
                }
            }
            catch
            {
                Core.Log.Error(err: error, namespace: "Core.Security.AES", method: "Encrypt(String, SymmetricKey)")
            }
            
            return result
        }
        
        /**
         * Decrypts encrypted base64 string with key
         *
         * @param value - base64 string that should be decrypted
         * @param deriveKey - key that should be used for the decryption(max. 32 bytes)
         * @return
         */
        static func Decrypt(value: String, deriveKey: CryptoKit.SymmetricKey) -> String?
        {
            var result: String? = nil
            
            do
            {
                let data = Data(base64Encoded: value)
                
                if(data != nil)
                {
                    let sealedData = try CryptoKit.AES.GCM.SealedBox(combined: data!)
                    let decryptedData = try CryptoKit.AES.GCM.open(sealedData, using: deriveKey)
                    result = String(data: decryptedData, encoding: .utf8)
                }
            }
            catch
            {
                result = nil
            }
           
            return result
        }
        
        /**
         * Decrypts encrypted base64 string with password(string)
         *
         * @param value - base64 string that should be decrypted
         * @param password - string password that should be used for the decryption(max. 32 bytes)
         * @return
         */
        static func Decrypt(value: String, password: String) -> String?
        {
            var result: String? = nil
            
            do
            {
                let key = SymmetricKey(data: GetKey(password: password))
                let data = Data(base64Encoded: value)
                
                if(data != nil)
                {
                    let sealedData = try CryptoKit.AES.GCM.SealedBox(combined: data!)
                    let decryptedData = try CryptoKit.AES.GCM.open(sealedData, using:key)
                    result = String(data: decryptedData, encoding: .utf8)
                }
            }
            catch let error
            {
                Core.Log.Error(err: error, namespace: "AES", method: "Decrypt")
                result = nil
            }
           
            return result
        }
        
        /**
         * Converts the text passed password to the 32 byte array
         *
         * @param password - Text based password
         * @return returns password as byte array
         */
        static func GetKey(password: String) -> Data
        {
            if(password.count < 32)
            {
                return password.padding(toLength: 32, withPad: "@", startingAt: 0).data(using: .ascii)!
            }
            else if(password.count > 32)
            {
                return MD5.Encrypt(value: password).data(using: .ascii)!
            }
            else
            {
                return password.data(using: .ascii)!
            }
        }
    }
}