using System.Security.Cryptography;
using Azaion.Common;
using Azaion.Common.Database;
using Azaion.Common.Entities;
using Azaion.Common.Extensions;
using Azaion.Common.Requests;
using LinqToDB;
using Npgsql;

namespace Azaion.Services;

public interface IUserService
{
    Task RegisterUser(RegisterUserRequest request, CancellationToken ct = default);
    Task<RegisterDeviceResponse> RegisterDevice(CancellationToken ct = default);
    Task<User> ValidateUser(LoginRequest request, CancellationToken ct = default);
    Task<User?> GetByEmail(string? email, CancellationToken ct = default);
    Task UpdateQueueOffsets(string email, UserQueueOffsets queueOffsets, CancellationToken ct = default);
    Task<IEnumerable<User>> GetUsers(string? searchEmail, RoleEnum? searchRole, CancellationToken ct = default);
    Task ChangeRole(string email, RoleEnum newRole, CancellationToken ct = default);
    Task SetEnableStatus(string email, bool isEnabled, CancellationToken ct = default);
    Task RemoveUser(string email, CancellationToken ct = default);
}

public class UserService(IDbFactory dbFactory, ICache cache) : IUserService
{
    private const string DeviceEmailPrefix    = "azj-";
    private const string DeviceEmailDomain    = "@azaion.com";
    private const int    SerialNumberStart    = 4; // index of NNNN inside "azj-NNNN..." (length of DeviceEmailPrefix)
    private const int    SerialNumberLength   = 4;
    private const int    DevicePasswordBytes  = 16; // hex-encoded → 32 chars

    public async Task RegisterUser(RegisterUserRequest request, CancellationToken ct = default)
    {
        try
        {
            await dbFactory.RunAdmin(async db =>
            {
                await db.InsertAsync(new User
                {
                    Id = Guid.NewGuid(),
                    Email = request.Email,
                    PasswordHash = request.Password.ToHash(),
                    Role = request.Role,
                    CreatedAt = DateTime.UtcNow,
                    IsEnabled = true
                }, token: ct);
            });
        }
        catch (PostgresException ex) when (ex.SqlState == PostgresErrorCodes.UniqueViolation)
        {
            throw new BusinessException(ExceptionEnum.EmailExists);
        }
    }

    public async Task<RegisterDeviceResponse> RegisterDevice(CancellationToken ct = default)
    {
        var (serial, email) = await NextDeviceIdentity(ct);
        var password = Convert.ToHexString(RandomNumberGenerator.GetBytes(DevicePasswordBytes)).ToLowerInvariant();

        await RegisterUser(new RegisterUserRequest
        {
            Email    = email,
            Password = password,
            Role     = RoleEnum.CompanionPC
        }, ct);

        return new RegisterDeviceResponse
        {
            Serial   = serial,
            Email    = email,
            Password = password
        };
    }

    private async Task<(string Serial, string Email)> NextDeviceIdentity(CancellationToken ct) =>
        await dbFactory.Run(async db =>
        {
            var lastEmail = await db.Users
                .Where(u => u.Role == RoleEnum.CompanionPC)
                .OrderByDescending(u => u.CreatedAt)
                .Select(u => u.Email)
                .FirstOrDefaultAsync(token: ct);

            var nextNumber = 0;
            if (!string.IsNullOrEmpty(lastEmail) && lastEmail.Length >= SerialNumberStart + SerialNumberLength)
            {
                var serialPart = lastEmail.Substring(SerialNumberStart, SerialNumberLength);
                if (int.TryParse(serialPart, out var current))
                    nextNumber = current + 1;
            }

            var serial = $"{DeviceEmailPrefix}{nextNumber.ToString($"D{SerialNumberLength}")}";
            var email  = $"{serial}{DeviceEmailDomain}";
            return (serial, email);
        });

    public async Task<User?> GetByEmail(string? email, CancellationToken ct = default)
    {
        if (string.IsNullOrWhiteSpace(email)) throw new ArgumentNullException(nameof(email));

        return await cache.GetFromCacheAsync(User.GetCacheKey(email),
            async () => await dbFactory.Run(async db =>
                await db.Users.FirstOrDefaultAsync(x => x.Email == email, ct)));
    }


    public async Task<User> ValidateUser(LoginRequest request, CancellationToken ct = default) =>
        await dbFactory.Run(async db =>
        {
            var user = await db.Users.FirstOrDefaultAsync(x => x.Email == request.Email, token: ct);
            if (user == null)
                throw new BusinessException(ExceptionEnum.NoEmailFound);

            if (request.Password.ToHash() != user.PasswordHash)
                throw new BusinessException(ExceptionEnum.WrongPassword);

            if (!user.IsEnabled)
                throw new BusinessException(ExceptionEnum.UserDisabled);

            return user;
        });


    public async Task UpdateQueueOffsets(string email, UserQueueOffsets queueOffsets, CancellationToken ct = default)
    {
        await dbFactory.RunAdmin(async db =>
        {
            var userConfig = await db.Users.Where(x => x.Email == email).Select(x => x.UserConfig).FirstOrDefaultAsync(token: ct);
            userConfig ??= new UserConfig();
            userConfig.QueueOffsets = queueOffsets;

            await db.Users.UpdateAsync(x => x.Email == email,
                u => new User
                {
                    UserConfig = userConfig
                }, token: ct);
        });
        cache.Invalidate(User.GetCacheKey(email));
    }

    public async Task<IEnumerable<User>> GetUsers(string? searchEmail, RoleEnum? searchRole, CancellationToken ct) =>
        await dbFactory.Run(async db =>
            await db.Users
                .WhereIf(!string.IsNullOrEmpty(searchEmail),
                    u => u.Email.ToLower().Contains(searchEmail!.ToLower()))
                .WhereIf(searchRole != null,
                    u => u.Role == searchRole)
                .ToListAsync(token: ct));

    public async Task ChangeRole(string email, RoleEnum newRole, CancellationToken ct = default)
    {
        await dbFactory.RunAdmin(async db =>
            await db.Users.UpdateAsync(x => x.Email == email, u => new User
            {
                Role = newRole
            }, ct));
    }

    public async Task SetEnableStatus(string email, bool isEnabled, CancellationToken ct = default)
    {
        await dbFactory.RunAdmin(async db =>
            await db.Users.UpdateAsync(x => x.Email == email, u => new User
            {
                IsEnabled = isEnabled
            }, ct));
    }


    public async Task RemoveUser(string email, CancellationToken ct = default)
    {
        await dbFactory.RunAdmin(async db =>
            await db.Users.DeleteAsync(x => x.Email == email, ct));
    }
}