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diff --git a/src/DevHive.Services/Services/UserService.cs b/src/DevHive.Services/Services/UserService.cs
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+using AutoMapper;
+using DevHive.Services.Options;
+using DevHive.Services.Models.Identity.User;
+using System.Threading.Tasks;
+using DevHive.Data.Models;
+using System;
+using System.IdentityModel.Tokens.Jwt;
+using System.Security.Claims;
+using Microsoft.IdentityModel.Tokens;
+using System.Text;
+using System.Collections.Generic;
+using DevHive.Common.Models.Identity;
+using DevHive.Services.Interfaces;
+using DevHive.Data.Interfaces.Repositories;
+using System.Linq;
+using DevHive.Common.Models.Misc;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Identity;
+
+namespace DevHive.Services.Services
+{
+	public class UserService : IUserService
+	{
+		private readonly IUserRepository _userRepository;
+		private readonly IRoleRepository _roleRepository;
+		private readonly ILanguageRepository _languageRepository;
+		private readonly ITechnologyRepository _technologyRepository;
+		private readonly UserManager<User> _userManager;
+		private readonly RoleManager<Role> _roleManager;
+		private readonly IMapper _userMapper;
+		private readonly JWTOptions _jwtOptions;
+		private readonly ICloudService _cloudService;
+
+		public UserService(IUserRepository userRepository,
+			ILanguageRepository languageRepository,
+			IRoleRepository roleRepository,
+			ITechnologyRepository technologyRepository,
+			UserManager<User> userManager,
+			RoleManager<Role> roleManager,
+			IMapper mapper,
+			JWTOptions jwtOptions,
+			ICloudService cloudService)
+		{
+			this._userRepository = userRepository;
+			this._roleRepository = roleRepository;
+			this._userMapper = mapper;
+			this._jwtOptions = jwtOptions;
+			this._languageRepository = languageRepository;
+			this._technologyRepository = technologyRepository;
+			this._userManager = userManager;
+			this._roleManager = roleManager;
+			this._cloudService = cloudService;
+		}
+
+		#region Authentication
+		/// <summary>
+        /// Adds a new user to the database with the values from the given model.
+		/// Returns a JSON Web Token (that can be used for authorization)
+        /// </summary>
+		public async Task<TokenModel> LoginUser(LoginServiceModel loginModel)
+		{
+			if (!await this._userRepository.DoesUsernameExistAsync(loginModel.UserName))
+				throw new ArgumentException("Invalid username!");
+
+			User user = await this._userRepository.GetByUsernameAsync(loginModel.UserName);
+
+			if (user.PasswordHash != PasswordModifications.GeneratePasswordHash(loginModel.Password))
+				throw new ArgumentException("Incorrect password!");
+
+			return new TokenModel(WriteJWTSecurityToken(user.Id, user.UserName, user.Roles));
+		}
+
+		/// <summary>
+        /// Returns a new JSON Web Token (that can be used for authorization) for the given user
+        /// </summary>
+		public async Task<TokenModel> RegisterUser(RegisterServiceModel registerModel)
+		{
+			if (await this._userRepository.DoesUsernameExistAsync(registerModel.UserName))
+				throw new ArgumentException("Username already exists!");
+
+			if (await this._userRepository.DoesEmailExistAsync(registerModel.Email))
+				throw new ArgumentException("Email already exists!");
+
+			User user = this._userMapper.Map<User>(registerModel);
+			user.PasswordHash = PasswordModifications.GeneratePasswordHash(registerModel.Password);
+			user.ProfilePicture = new ProfilePicture() { PictureURL = "/assets/images/feed/profile-pic.png" };
+
+			// Make sure the default role exists
+			//TODO: Move when project starts
+			if (!await this._roleRepository.DoesNameExist(Role.DefaultRole))
+				await this._roleRepository.AddAsync(new Role { Name = Role.DefaultRole });
+
+			user.Roles.Add(await this._roleRepository.GetByNameAsync(Role.DefaultRole));
+
+			IdentityResult userResult = await this._userManager.CreateAsync(user);
+			User createdUser = await this._userRepository.GetByUsernameAsync(registerModel.UserName);
+
+			if (!userResult.Succeeded)
+				throw new ArgumentException("Unable to create a user");
+
+			return new TokenModel(WriteJWTSecurityToken(createdUser.Id, createdUser.UserName, createdUser.Roles));
+		}
+		#endregion
+
+		#region Read
+		public async Task<UserServiceModel> GetUserById(Guid id)
+		{
+			User user = await this._userRepository.GetByIdAsync(id) ??
+				throw new ArgumentException("User does not exist!");
+
+			return this._userMapper.Map<UserServiceModel>(user);
+		}
+
+		public async Task<UserServiceModel> GetUserByUsername(string username)
+		{
+			User user = await this._userRepository.GetByUsernameAsync(username) ??
+				throw new ArgumentException("User does not exist!");
+
+			return this._userMapper.Map<UserServiceModel>(user);
+		}
+		#endregion
+
+		#region Update
+		public async Task<UserServiceModel> UpdateUser(UpdateUserServiceModel updateUserServiceModel)
+		{
+			await this.ValidateUserOnUpdate(updateUserServiceModel);
+
+			User currentUser = await this._userRepository.GetByIdAsync(updateUserServiceModel.Id);
+			await this.PopulateUserModel(currentUser, updateUserServiceModel);
+
+			if (updateUserServiceModel.Friends.Count() > 0)
+				await this.CreateRelationToFriends(currentUser, updateUserServiceModel.Friends.ToList());
+			else
+				currentUser.Friends.Clear();
+
+			IdentityResult result = await this._userManager.UpdateAsync(currentUser);
+
+			if (!result.Succeeded)
+				throw new InvalidOperationException("Unable to edit user!");
+
+			User newUser = await this._userRepository.GetByIdAsync(currentUser.Id);
+			return this._userMapper.Map<UserServiceModel>(newUser);
+		}
+
+		/// <summary>
+        /// Uploads the given picture and assigns it's link to the user in the database
+        /// </summary>
+		public async Task<ProfilePictureServiceModel> UpdateProfilePicture(UpdateProfilePictureServiceModel updateProfilePictureServiceModel)
+		{
+			User user = await this._userRepository.GetByIdAsync(updateProfilePictureServiceModel.UserId);
+
+			if (!string.IsNullOrEmpty(user.ProfilePicture.PictureURL))
+			{
+				bool success = await _cloudService.RemoveFilesFromCloud(new List<string> { user.ProfilePicture.PictureURL });
+				if (!success)
+					throw new InvalidCastException("Could not delete old profile picture!");
+			}
+
+			string fileUrl = (await this._cloudService.UploadFilesToCloud(new List<IFormFile> { updateProfilePictureServiceModel.Picture }))[0] ??
+				throw new ArgumentNullException("Unable to upload profile picture to cloud");
+
+			bool successful = await this._userRepository.UpdateProfilePicture(updateProfilePictureServiceModel.UserId, fileUrl);
+
+			if (!successful)
+				throw new InvalidOperationException("Unable to change profile picture!");
+
+			return new ProfilePictureServiceModel() { ProfilePictureURL = fileUrl };
+		}
+		#endregion
+
+		#region Delete
+		public async Task<bool> DeleteUser(Guid id)
+		{
+			if (!await this._userRepository.DoesUserExistAsync(id))
+				throw new ArgumentException("User does not exist!");
+
+			User user = await this._userRepository.GetByIdAsync(id);
+			IdentityResult result = await this._userManager.DeleteAsync(user);
+
+			return result.Succeeded;
+		}
+		#endregion
+
+		#region Validations
+		/// <summary>
+        /// Checks whether the given user, gotten by the "id" property,
+		/// is the same user as the one in the token (uness the user in the token has the admin role)
+		/// and the roles in the token are the same as those in the user, gotten by the id in the token
+        /// </summary>
+		public async Task<bool> ValidJWT(Guid id, string rawTokenData)
+		{
+			// There is authorization name in the beginning, i.e. "Bearer eyJh..."
+			var jwt = new JwtSecurityTokenHandler().ReadJwtToken(rawTokenData.Remove(0, 7));
+
+			Guid jwtUserID = new Guid(this.GetClaimTypeValues("ID", jwt.Claims).First());
+			List<string> jwtRoleNames = this.GetClaimTypeValues("role", jwt.Claims);
+
+			User user = await this._userRepository.GetByIdAsync(jwtUserID)
+				?? throw new ArgumentException("User does not exist!");
+
+			/* Check if user is trying to do something to himself, unless he's an admin */
+
+			/* Check roles */
+			if (!jwtRoleNames.Contains(Role.AdminRole))
+				if (user.Id != id)
+					return false;
+
+			// Check if jwt contains all user roles (if it doesn't, jwt is either old or tampered with)
+			foreach (var role in user.Roles)
+			{
+				if (!jwtRoleNames.Contains(role.Name))
+					return false;
+			}
+
+			// Check if jwt contains only roles of user
+			if (jwtRoleNames.Count != user.Roles.Count)
+				return false;
+
+			return true;
+		}
+
+		/// <summary>
+        /// Returns all values from a given claim type
+        /// </summary>
+		private List<string> GetClaimTypeValues(string type, IEnumerable<Claim> claims)
+		{
+			List<string> toReturn = new();
+
+			foreach (var claim in claims)
+				if (claim.Type == type)
+					toReturn.Add(claim.Value);
+
+			return toReturn;
+		}
+
+		/// <summary>
+        /// Checks whether the user in the model exists
+		/// and whether the username in the model is already taken.
+		/// If the check fails (is false), it throws an exception, otherwise nothing happens
+        /// </summary>
+		private async Task ValidateUserOnUpdate(UpdateUserServiceModel updateUserServiceModel)
+		{
+			if (!await this._userRepository.DoesUserExistAsync(updateUserServiceModel.Id))
+				throw new ArgumentException("User does not exist!");
+
+			if (updateUserServiceModel.Friends.Any(x => x.UserName == updateUserServiceModel.UserName))
+				throw new ArgumentException("You cant add yourself as a friend(sry, bro)!");
+
+			if (!this._userRepository.DoesUserHaveThisUsername(updateUserServiceModel.Id, updateUserServiceModel.UserName)
+					&& await this._userRepository.DoesUsernameExistAsync(updateUserServiceModel.UserName))
+				throw new ArgumentException("Username already exists!");
+
+			List<string> usernames = new();
+			foreach (var friend in updateUserServiceModel.Friends)
+				usernames.Add(friend.UserName);
+
+			if (!await this._userRepository.ValidateFriendsCollectionAsync(usernames))
+				throw new ArgumentException("One or more friends do not exist!");
+		}
+
+		/// <summary>
+        /// Return a new JSON Web Token, containing the user id, username and roles.
+		/// Tokens have an expiration time of 7 days.
+        /// </summary>
+		private string WriteJWTSecurityToken(Guid userId, string username, HashSet<Role> roles)
+		{
+			byte[] signingKey = Encoding.ASCII.GetBytes(_jwtOptions.Secret);
+			HashSet<Claim> claims = new()
+			{
+				new Claim("ID", $"{userId}"),
+				new Claim("Username", username)
+			};
+
+			foreach (var role in roles)
+			{
+				claims.Add(new Claim(ClaimTypes.Role, role.Name));
+			}
+
+			SecurityTokenDescriptor tokenDescriptor = new()
+			{
+				Subject = new ClaimsIdentity(claims),
+				Expires = DateTime.Today.AddDays(7),
+				SigningCredentials = new SigningCredentials(
+					new SymmetricSecurityKey(signingKey),
+					SecurityAlgorithms.HmacSha512Signature)
+			};
+
+			JwtSecurityTokenHandler tokenHandler = new();
+			SecurityToken token = tokenHandler.CreateToken(tokenDescriptor);
+			return tokenHandler.WriteToken(token);
+		}
+		#endregion
+
+		#region Misc
+		public async Task<TokenModel> SuperSecretPromotionToAdmin(Guid userId)
+		{
+			User user = await this._userRepository.GetByIdAsync(userId) ??
+				throw new ArgumentException("User does not exist! Can't promote shit in this country...");
+
+			if (!await this._roleRepository.DoesNameExist(Role.AdminRole))
+			{
+				Role adminRole = new()
+				{
+					Name = Role.AdminRole
+				};
+				adminRole.Users.Add(user);
+
+				await this._roleRepository.AddAsync(adminRole);
+			}
+
+			Role admin = await this._roleManager.FindByNameAsync(Role.AdminRole);
+
+			user.Roles.Add(admin);
+			await this._userManager.UpdateAsync(user);
+
+			User newUser = await this._userRepository.GetByIdAsync(userId);
+
+			return new TokenModel(WriteJWTSecurityToken(newUser.Id, newUser.UserName, newUser.Roles));
+		}
+
+		private async Task PopulateUserModel(User user, UpdateUserServiceModel updateUserServiceModel)
+		{
+			user.UserName = updateUserServiceModel.UserName;
+			user.FirstName = updateUserServiceModel.FirstName;
+			user.LastName = updateUserServiceModel.LastName;
+			user.Email = updateUserServiceModel.Email;
+
+			//Do NOT allow a user to change his roles, unless he is an Admin
+			bool isAdmin = await this._userManager.IsInRoleAsync(user, Role.AdminRole);
+
+			if (isAdmin)
+			{
+				HashSet<Role> roles = new();
+				foreach (var role in updateUserServiceModel.Roles)
+				{
+					Role returnedRole = await this._roleRepository.GetByNameAsync(role.Name) ??
+						throw new ArgumentException($"Role {role.Name} does not exist!");
+
+					roles.Add(returnedRole);
+				}
+				user.Roles = roles;
+			}
+
+			HashSet<Language> languages = new();
+			int languagesCount = updateUserServiceModel.Languages.Count;
+			for (int i = 0; i < languagesCount; i++)
+			{
+				Language language = await this._languageRepository.GetByNameAsync(updateUserServiceModel.Languages.ElementAt(i).Name) ??
+					throw new ArgumentException("Invalid language name!");
+
+				languages.Add(language);
+			}
+			user.Languages = languages;
+
+			/* Fetch Technologies and replace model's*/
+			HashSet<Technology> technologies = new();
+			int technologiesCount = updateUserServiceModel.Technologies.Count;
+			for (int i = 0; i < technologiesCount; i++)
+			{
+				Technology technology = await this._technologyRepository.GetByNameAsync(updateUserServiceModel.Technologies.ElementAt(i).Name) ??
+					throw new ArgumentException("Invalid technology name!");
+
+				technologies.Add(technology);
+			}
+			user.Technologies = technologies;
+		}
+
+		private async Task CreateRelationToFriends(User user, List<UpdateFriendServiceModel> friends)
+		{
+			foreach (var friend in friends)
+			{
+				User amigo = await this._userRepository.GetByUsernameAsync(friend.UserName);
+
+				user.Friends.Add(amigo);
+				amigo.Friends.Add(user);
+
+				await this._userManager.UpdateAsync(amigo);
+			}
+		}
+		#endregion
+	}
+}