using System.Security.Cryptography;
using System.Text;
using FlowAPI.Application.DTOs.User;
using FlowAPI.Application.Interfaces;
using FlowAPI.Domain.Entities;
using Microsoft.Extensions.Configuration;

namespace FlowAPI.Application.Services
{
    public class UserService : IUserService
    {
        private readonly IUserRepository _repo;
        private readonly ITokenService _tokenService;
        private readonly IConfiguration _config;
        private readonly IAchievementService _achievementService;

        public UserService(IUserRepository repo, ITokenService tokenService, IConfiguration config, IAchievementService achievementService)
        {
            _repo = repo;
            _tokenService = tokenService;
            _config = config;
            _achievementService = achievementService;
        }

        public async Task<IEnumerable<UserResponseDto>> GetAllAsync()
        {
            var users = await _repo.GetAllAsync();
            return users.Select(MapToDto);
        }

        public async Task<UserResponseDto?> GetByIdAsync(Guid id)
        {
            var user = await _repo.GetByIdAsync(id);
            return user is null ? null : MapToDto(user);
        }

        public async Task<AuthResponseDto> RegisterAsync(CreateUserDto dto)
        {
            var existing = await _repo.GetByEmailAsync(dto.Email);
            if (existing is not null)
                throw new InvalidOperationException("User with this email already exists.");

            var user = new User
            {
                Id = Guid.NewGuid(),
                Email = dto.Email,
                PasswordHash = HashPassword(dto.Password),
                DisplayName = dto.DisplayName,
                CreatedAt = DateTime.UtcNow
            };

            var created = await _repo.CreateAsync(user);
            return new AuthResponseDto 
            { 
                User = MapToDto(created),
                Token = _tokenService.CreateToken(created)
            };
        }

        public async Task<AuthResponseDto?> LoginAsync(LoginDto dto)
        {
            var user = await _repo.GetByEmailAsync(dto.Email);
            if (user is null || string.IsNullOrEmpty(user.PasswordHash) || user.PasswordHash != HashPassword(dto.Password))
                return null;

            return new AuthResponseDto 
            { 
                User = MapToDto(user),
                Token = _tokenService.CreateToken(user)
            };
        }

        public async Task<AuthResponseDto> GoogleLoginAsync(GoogleLoginDto dto)
        {
            var settings = new Google.Apis.Auth.GoogleJsonWebSignature.ValidationSettings
            {
                Audience = new List<string> { _config["Google:ClientId"]! }
            };

            var payload = await Google.Apis.Auth.GoogleJsonWebSignature.ValidateAsync(dto.IdToken, settings);

            var user = await _repo.GetByEmailAsync(payload.Email);

            if (user == null)
            {
                user = new User
                {
                    Id = Guid.NewGuid(),
                    Email = payload.Email,
                    DisplayName = payload.Name,
                    CreatedAt = DateTime.UtcNow,
                    PasswordHash = "" // No password for Google users
                };
                user = await _repo.CreateAsync(user);
            }

            return new AuthResponseDto
            {
                User = MapToDto(user),
                Token = _tokenService.CreateToken(user)
            };
        }

        public async Task<UserResponseDto?> UpdateAsync(Guid id, UpdateUserDto dto)
        {
            var user = await _repo.GetByIdAsync(id);
            if (user is null) return null;

            bool isAvatarUpdated = dto.AvatarUrl is not null && user.AvatarUrl != dto.AvatarUrl;

            if (dto.DisplayName is not null) user.DisplayName = dto.DisplayName;
            if (dto.IsPremium.HasValue) user.IsPremium = dto.IsPremium.Value;
            if (dto.AvatarUrl is not null) user.AvatarUrl = dto.AvatarUrl;
            if (dto.SubscriptionTier is not null)
            {
                user.SubscriptionTier = dto.SubscriptionTier;
                user.IsPremium = dto.SubscriptionTier != "Free";
            }
            if (!string.IsNullOrEmpty(dto.Password)) user.PasswordHash = HashPassword(dto.Password);

            var updated = await _repo.UpdateAsync(user);

            if (isAvatarUpdated)
            {
                await _achievementService.ProcessEventAsync(id, "AvatarUploaded");
            }

            return MapToDto(updated);
        }

        public async Task<bool> DeleteAsync(Guid id)
        {
            return await _repo.DeleteAsync(id);
        }

        private static string HashPassword(string password)
        {
            var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(password));
            return Convert.ToBase64String(bytes);
        }

        private static UserResponseDto MapToDto(User user) => new()
        {
            Id = user.Id,
            Email = user.Email,
            DisplayName = user.DisplayName,
            IsPremium = user.IsPremium,
            AvatarUrl = user.AvatarUrl,
            CreatedAt = user.CreatedAt,
            SubscriptionTier = user.SubscriptionTier,
            DailyAiGenerationsCount = user.DailyAiGenerationsCount
        };
    }
}