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);

    /// <summary>
    /// AZ-557 — shared failure-accounting path for MFA-side failures. Mirrors what the
    /// password-side path in <see cref="ValidateUser"/> does on a wrong-password event:
    /// records the appropriate audit row, increments <c>failed_login_count</c>,
    /// crosses-the-threshold trips <c>lockout_until</c>, and signals lockout by throwing
    /// <see cref="BusinessException"/> with <see cref="ExceptionEnum.InvalidCredentials"/>
    /// + <see cref="BusinessException.RetryAfterSeconds"/>. Callers (e.g.,
    /// <c>MfaService.VerifyForLogin</c>) MUST handle the throw branch and rethrow their
    /// own opaque error if the threshold was not crossed.
    /// </summary>
    Task RegisterMfaFailedLogin(User user, 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));

        // AZ-556 — unknown email: equalize timing with a dummy Argon2id verify so a
        // wall-clock observer can't distinguish "no such email" from "wrong password".
        // No counter to increment (there is no row), so this path skips lockout
        // accounting entirely; the audit row preserves the attempted email for SecOps.
        if (user == null)
        {
            Security.VerifyDummy(request.Password);
            await auditLog.RecordLoginFailedUnknownEmail(request.Email, ct);
            throw new BusinessException(ExceptionEnum.InvalidCredentials);
        }

        // AZ-537 AC-3 — active lockout takes precedence over the password check; even
        // a correct password is rejected until the lockout expires. AZ-556 collapses
        // the response code to `InvalidCredentials` while keeping the Retry-After
        // header so legitimate clients can self-throttle.
        if (user.LockoutUntil is { } until && until > DateTime.UtcNow)
        {
            var remaining = (int)Math.Ceiling((until - DateTime.UtcNow).TotalSeconds);
            throw new BusinessException(ExceptionEnum.InvalidCredentials, Math.Max(remaining, 1));
        }

        // AZ-537 AC-2 — per-account sliding-window rate limit. Counts only failure
        // events in the recent window (login_failed + mfa_login_failed per AZ-557) so
        // legitimate retries after a success aren't punished.
        var recentFailures = await auditLog.CountRecentFailedLogins(
            user.Email, _auth.RateLimit.PerAccountWindowSeconds, ct);
        if (recentFailures >= _auth.RateLimit.PerAccountPermitLimit)
            throw new BusinessException(ExceptionEnum.InvalidCredentials, _auth.RateLimit.PerAccountWindowSeconds);

        // AZ-556 F-AUTH-3 — disabled-account check moved BEFORE password verify. An
        // attacker who knows the password of a disabled account no longer learns that
        // fact via a distinct error code (or via the missing-Argon2id timing tell).
        // Still run the dummy verify so the wall-clock equalises against a real
        // wrong-password branch.
        if (!user.IsEnabled)
        {
            Security.VerifyDummy(request.Password);
            await auditLog.RecordLoginFailedDisabled(user.Email, ct);
            throw new BusinessException(ExceptionEnum.InvalidCredentials);
        }

        var verify = Security.VerifyPassword(request.Password, user.PasswordHash);
        if (!verify.Valid)
        {
            // RegisterFailedLogin may itself throw InvalidCredentials + Retry-After
            // when the threshold trips; otherwise we fall through and throw the
            // non-Retry-After variant below.
            await RegisterFailedLogin(user, ct);
            throw new BusinessException(ExceptionEnum.InvalidCredentials);
        }

        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 Task RegisterFailedLogin(User user, CancellationToken ct) =>
        RegisterFailedLoginCore(user, FailureKind.Password, ct);

    public Task RegisterMfaFailedLogin(User user, CancellationToken ct = default) =>
        RegisterFailedLoginCore(user, FailureKind.Mfa, ct);

    // AZ-557 — single accounting path shared by the password-side (`ValidateUser`) and
    // the MFA-side (`MfaService.VerifyForLogin`) failure branches. The audit row type
    // diverges (`login_failed` vs `mfa_login_failed`) so SecOps can analyse the two
    // categories separately, but the counter / lockout / Retry-After semantics are
    // identical. On lockout-trip we throw `InvalidCredentials` + Retry-After so the
    // caller can rethrow its opaque wire response without losing the cooldown hint.
    private async Task RegisterFailedLoginCore(User user, FailureKind kind, CancellationToken ct)
    {
        if (kind == FailureKind.Password)
            await auditLog.RecordLoginFailed(user.Email, ct);
        else
            await auditLog.RecordMfaLoginFailed(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);
            // AZ-556 — promote a threshold-crossing failure into the unified lockout
            // response. The caller sees `InvalidCredentials` + Retry-After regardless
            // of whether the threshold was crossed by a password or an MFA attempt.
            throw new BusinessException(ExceptionEnum.InvalidCredentials, _auth.Lockout.DurationSeconds);
        }
    }

    private enum FailureKind
    {
        Password,
        Mfa,
    }

    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));
    }
}