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Repositories/ContactRepository.cs

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+using Microsoft.Win32;
+using System;
+using System.Runtime;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace ContactsApp
+{
+    public class ContactRepository : IContactRepository
+    {
+        List<Contact> Contacts = new ();
+
+
+        public void AddContact(Contact contact)
+        {
+            CheckUnique(contact);
+            Contacts.Add(contact);
+        }
+
+        public void UpdateContact(Guid id, Contact contact)
+        {
+            CheckUnique(contact);
+            Contact previous = GetContactById(id);
+            if (previous == null)
+            {
+                Contacts.Add(contact);
+                return;
+            }
+            
+            previous.Name = contact.Name;
+            previous.Email = contact.Email;
+            previous.Phone = contact.Phone;
+        }
+
+        public void DeleteContact(Guid id)
+        {
+            var contact = GetContactById(id);
+            if (contact == null)
+                return;
+            Contacts.Remove(contact);
+        }
+
+        public Contact GetContactById(Guid id)
+        {
+            return Contacts.Find(x => x.Id == id);
+        }
+        public void LoadJSON(string json)
+        {
+            var list = JsonSerializer.Deserialize<List<Contact>>(json);
+            Contacts.AddRange(list);
+        }
+        public string SaveJSON()
+        {
+            return JsonSerializer.Serialize(Contacts, new JsonSerializerOptions { WriteIndented = true });
+        }
+
+        public IEnumerable<Contact> GetAll() => Contacts;
+        private void CheckUnique(Contact contact)
+        {
+            if (Contacts.FirstOrDefault(x => x.Equals(contact)) != null)
+                throw new Exception("Такой контакт уже есть");
+        }
+    }
+}