using System.Security.Cryptography;
using System.Text;
using MiaoJiZhang.Domain.Entities;
using MiaoJiZhang.Infrastructure.Persistence;
using Microsoft.EntityFrameworkCore;

namespace MiaoJiZhang.Api.Services;

public sealed record AdminPrincipal(
    long UserId,
    long SessionId,
    string Username,
    string Role,
    bool MustChangePassword);

public sealed record AdminLoginResult(AdminPrincipal Principal, string CsrfToken);

public static class AdminRequestContext
{
    public const string PrincipalKey = "miaoji.admin.principal";
    public const string AuditUsernameKey = "miaoji.admin.audit.username";

    public static AdminPrincipal? Principal(HttpContext context) =>
        context.Items.TryGetValue(PrincipalKey, out var value)
            ? value as AdminPrincipal
            : null;
}

public sealed class AdminSessionService(
    AppDbContext db,
    IConfiguration configuration,
    IWebHostEnvironment environment)
{
    public const string CookieName = "miaoji_admin_session";
    public const string CsrfHeader = "X-CSRF-Token";
    private static readonly TimeSpan IdleLifetime = TimeSpan.FromHours(8);
    private static readonly TimeSpan AbsoluteLifetime = TimeSpan.FromDays(7);
    private static readonly TimeSpan LockoutLifetime = TimeSpan.FromMinutes(15);

    public async Task<AdminLoginResult?> LoginAsync(
        HttpContext context,
        string username,
        string password,
        CancellationToken ct)
    {
        var normalizedUsername = username.Trim();
        context.Items[AdminRequestContext.AuditUsernameKey] = normalizedUsername;
        var user = await db.AdminUsers.FirstOrDefaultAsync(
            item => item.Username == normalizedUsername,
            ct);
        var now = DateTime.UtcNow;
        if (user is null || !user.IsActive ||
            user.LockedUntil.HasValue && user.LockedUntil.Value > now)
        {
            BCrypt.Net.BCrypt.Verify(password, DummyPasswordHash());
            return null;
        }

        if (!BCrypt.Net.BCrypt.Verify(password, user.PasswordHash))
        {
            user.FailedLoginCount++;
            if (user.FailedLoginCount >= 5)
            {
                user.FailedLoginCount = 0;
                user.LockedUntil = now.Add(LockoutLifetime);
            }
            user.UpdatedAt = now;
            await db.SaveChangesAsync(ct);
            return null;
        }

        user.FailedLoginCount = 0;
        user.LockedUntil = null;
        user.LastLoginAt = now;
        user.UpdatedAt = now;
        var rawToken = NewToken();
        var csrfToken = NewToken();
        var session = new AdminSession
        {
            AdminUser = user,
            TokenHash = Hash(rawToken),
            CsrfTokenHash = Hash(csrfToken),
            AuthVersion = user.AuthVersion,
            ExpiresAt = now.Add(IdleLifetime),
            AbsoluteExpiresAt = now.Add(AbsoluteLifetime),
            LastSeenAt = now,
            IpAddress = ClientIp(context),
            UserAgent = Trim(context.Request.Headers.UserAgent.ToString(), 300),
            CreatedAt = now,
        };
        db.AdminSessions.Add(session);
        await db.SaveChangesAsync(ct);
        WriteCookie(context, rawToken, session.AbsoluteExpiresAt);

        var principal = ToPrincipal(user, session);
        context.Items[AdminRequestContext.PrincipalKey] = principal;
        return new AdminLoginResult(principal, csrfToken);
    }

    public async Task<(AdminPrincipal Principal, string CsrfToken)?> AuthenticateAsync(
        HttpContext context,
        bool validateCsrf,
        CancellationToken ct)
    {
        if (!context.Request.Cookies.TryGetValue(CookieName, out var token) ||
            string.IsNullOrWhiteSpace(token))
            return null;

        var tokenHash = Hash(token);
        var now = DateTime.UtcNow;
        var session = await db.AdminSessions
            .Include(item => item.AdminUser)
            .FirstOrDefaultAsync(item => item.TokenHash == tokenHash, ct);
        if (session is null || session.RevokedAt.HasValue ||
            session.ExpiresAt <= now || session.AbsoluteExpiresAt <= now ||
            !session.AdminUser.IsActive ||
            session.AuthVersion != session.AdminUser.AuthVersion)
        {
            DeleteCookie(context);
            return null;
        }

        var csrfToken = context.Request.Headers[CsrfHeader].FirstOrDefault();
        if (validateCsrf && (string.IsNullOrWhiteSpace(csrfToken) ||
            !CryptographicOperations.FixedTimeEquals(
                Encoding.ASCII.GetBytes(Hash(csrfToken)),
                Encoding.ASCII.GetBytes(session.CsrfTokenHash))))
        {
            return null;
        }

        if (now - session.LastSeenAt >= TimeSpan.FromMinutes(5))
        {
            session.LastSeenAt = now;
            session.ExpiresAt = Min(now.Add(IdleLifetime), session.AbsoluteExpiresAt);
            await db.SaveChangesAsync(ct);
        }
        var principal = ToPrincipal(session.AdminUser, session);
        context.Items[AdminRequestContext.PrincipalKey] = principal;
        return (principal, csrfToken ?? string.Empty);
    }

    public async Task<string> RotateCsrfAsync(long sessionId, CancellationToken ct)
    {
        var session = await db.AdminSessions.FindAsync([sessionId], ct) ??
            throw new InvalidOperationException("管理会话不存在");
        var token = NewToken();
        session.CsrfTokenHash = Hash(token);
        await db.SaveChangesAsync(ct);
        return token;
    }

    public async Task LogoutAsync(HttpContext context, long sessionId, CancellationToken ct)
    {
        var session = await db.AdminSessions.FindAsync([sessionId], ct);
        if (session is not null && !session.RevokedAt.HasValue)
        {
            session.RevokedAt = DateTime.UtcNow;
            await db.SaveChangesAsync(ct);
        }
        DeleteCookie(context);
    }

    public async Task RevokeOtherSessionsAsync(
        long userId,
        long currentSessionId,
        int authVersion,
        CancellationToken ct)
    {
        var now = DateTime.UtcNow;
        await db.AdminSessions
            .Where(item => item.AdminUserId == userId && item.Id != currentSessionId &&
                !item.RevokedAt.HasValue)
            .ExecuteUpdateAsync(setters => setters.SetProperty(item => item.RevokedAt, now), ct);
        var current = await db.AdminSessions.FindAsync([currentSessionId], ct);
        if (current is not null) current.AuthVersion = authVersion;
    }

    public static string HashPassword(string password) =>
        BCrypt.Net.BCrypt.HashPassword(password, workFactor: 12);

    public static bool IsSafeMethod(string method) =>
        HttpMethods.IsGet(method) || HttpMethods.IsHead(method) || HttpMethods.IsOptions(method);

    private void WriteCookie(HttpContext context, string token, DateTime expiresAt) =>
        context.Response.Cookies.Append(CookieName, token, CookieOptions(context, expiresAt));

    private void DeleteCookie(HttpContext context) =>
        context.Response.Cookies.Delete(CookieName, CookieOptions(context, DateTime.UtcNow.AddDays(-1)));

    private CookieOptions CookieOptions(HttpContext context, DateTime expiresAt) => new()
    {
        HttpOnly = true,
        Secure = configuration.GetValue<bool?>("Admin:CookieSecure") ??
            (!environment.IsDevelopment() || context.Request.IsHttps),
        SameSite = SameSiteMode.Strict,
        Path = "/api/admin",
        IsEssential = true,
        Expires = expiresAt,
    };

    private static AdminPrincipal ToPrincipal(AdminUser user, AdminSession session) =>
        new(user.Id, session.Id, user.Username, user.Role, user.MustChangePassword);

    private static DateTime Min(DateTime left, DateTime right) => left <= right ? left : right;
    private static string NewToken() => Convert.ToBase64String(RandomNumberGenerator.GetBytes(32))
        .TrimEnd('=').Replace('+', '-').Replace('/', '_');
    private static string Hash(string value) =>
        Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(value))).ToLowerInvariant();
    private static string? ClientIp(HttpContext context) =>
        Trim(context.Connection.RemoteIpAddress?.ToString(), 64);
    private static string? Trim(string? value, int length) =>
        string.IsNullOrEmpty(value) ? null : value.Length <= length ? value : value[..length];

    private static string DummyPasswordHash() =>
        "$2a$12$1i3L4fD4PrM9xMVzKDnwoO.nGsRoW6u9Q9tT6A4vPi04QoV9S3Mca";
}