using System.Security.Cryptography;
using Azaion.Common;
using Azaion.Common.Configs;
using Azaion.Common.Database;
using Azaion.Common.Entities;
using Azaion.Common.Extensions;
using Azaion.Common.Requests;
using LinqToDB;
using Microsoft.Extensions.Options;
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<User?> GetById(Guid userId, 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,
    IAuditLog auditLog,
    IOptions<AuthConfig> authConfig) : IUserService
{
    private readonly AuthConfig _auth = authConfig.Value;

    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 = Security.HashPassword(request.Password),
                    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?> GetById(Guid userId, CancellationToken ct = default) =>
        await dbFactory.Run(async db => await db.Users.FirstOrDefaultAsync(x => x.Id == userId, token: ct));


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

        if (user == null)
            throw new BusinessException(ExceptionEnum.NoEmailFound);

        // AZ-537 AC-3 — active lockout takes precedence over the password check; even
        // a correct password is rejected with 423 Locked until the lockout expires.
        if (user.LockoutUntil is { } until && until > DateTime.UtcNow)
        {
            var remaining = (int)Math.Ceiling((until - DateTime.UtcNow).TotalSeconds);
            throw new BusinessException(ExceptionEnum.AccountLocked, Math.Max(remaining, 1));
        }

        // AZ-537 AC-2 — per-account sliding-window rate limit. Counts only failed
        // logins in the recent window so legitimate retries after success aren't punished.
        var recentFailures = await auditLog.CountRecentFailedLogins(
            user.Email, _auth.RateLimit.PerAccountWindowSeconds, ct);
        if (recentFailures >= _auth.RateLimit.PerAccountPermitLimit)
            throw new BusinessException(ExceptionEnum.LoginRateLimited, _auth.RateLimit.PerAccountWindowSeconds);

        var verify = Security.VerifyPassword(request.Password, user.PasswordHash);
        if (!verify.Valid)
        {
            await RegisterFailedLogin(user, ct);
            throw new BusinessException(ExceptionEnum.WrongPassword);
        }

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

        await RegisterSuccessfulLogin(user, request.Password, verify.NeedsRehash, ct);
        return user;
    }

    // Lazy migration of legacy SHA-384 hashes (and future Argon2 param upgrades).
    // Conditional on the original hash to avoid clobbering a concurrent rehash from
    // a parallel login of the same account.
    private async Task RegisterSuccessfulLogin(User user, string plaintext, bool rehash, CancellationToken ct)
    {
        var newHash = rehash ? Security.HashPassword(plaintext) : null;
        var oldHash = user.PasswordHash;

        await dbFactory.RunAdmin(async db =>
        {
            if (newHash != null)
            {
                await db.Users.UpdateAsync(
                    u => u.Id == user.Id && u.PasswordHash == oldHash,
                    u => new User
                    {
                        PasswordHash     = newHash,
                        FailedLoginCount = 0,
                        LockoutUntil     = null
                    },
                    token: ct);
            }
            else
            {
                await db.Users.UpdateAsync(
                    u => u.Id == user.Id,
                    u => new User
                    {
                        FailedLoginCount = 0,
                        LockoutUntil     = null
                    },
                    token: ct);
            }
        });

        if (newHash != null)
            user.PasswordHash = newHash;
        user.FailedLoginCount = 0;
        user.LockoutUntil     = null;
        cache.Invalidate(User.GetCacheKey(user.Email));

        await auditLog.RecordLoginSuccess(user.Email, ct);
    }

    private async Task RegisterFailedLogin(User user, CancellationToken ct)
    {
        await auditLog.RecordLoginFailed(user.Email, ct);

        var newCount    = user.FailedLoginCount + 1;
        var triggersLock = newCount >= _auth.Lockout.MaxAttempts;
        DateTime? newLockoutUntil = triggersLock
            ? DateTime.UtcNow.AddSeconds(_auth.Lockout.DurationSeconds)
            : user.LockoutUntil;

        await dbFactory.RunAdmin(async db =>
            await db.Users.UpdateAsync(
                u => u.Id == user.Id,
                u => new User
                {
                    FailedLoginCount = newCount,
                    LockoutUntil     = newLockoutUntil
                },
                token: ct));

        cache.Invalidate(User.GetCacheKey(user.Email));

        if (triggersLock)
        {
            await auditLog.RecordLoginLockout(user.Email, ct);
            // Promote a wrong-password into a lockout response so the caller learns the
            // account is locked the moment the threshold is crossed.
            throw new BusinessException(ExceptionEnum.AccountLocked, _auth.Lockout.DurationSeconds);
        }
    }

    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));
    }
}