/* ========================================================================
 * Copyright (c) 2005-2026 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
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 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
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 *
 * The above copyright notice and this permission notice shall be
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 * OTHER DEALINGS IN THE SOFTWARE.
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 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Options;
using Opc.Ua.Gds.Server.Hosting;
using Opc.Ua.Identity;

namespace Opc.Ua.Gds.Server.Identity
{
    /// <summary>
    /// In-memory AuthorizationService provider that delegates token
    /// signing to an <see cref="ITokenIssuer"/>.
    /// </summary>
    public sealed class InMemoryAccessTokenProvider : IAccessTokenProvider
    {
        private static readonly char[] s_scopeSeparators = [' ', ',', ';', '\r', '\n', '\t'];
        private readonly AuthorizationServiceOptions m_options;
        private readonly ConcurrentDictionary<Guid, RequestRecord> m_requests = new();

        private readonly ConcurrentDictionary<string, IssuedTokenRecord> m_issuedTokens =
            new(StringComparer.Ordinal);

        private readonly ConcurrentDictionary<string, DateTime> m_revokedTokens =
            new(StringComparer.Ordinal);

        /// <summary>
        /// Creates an in-memory token provider.
        /// </summary>
        public InMemoryAccessTokenProvider(
            ITokenIssuer tokenIssuer,
            IOptions<AuthorizationServiceOptions> options)
        {
            TokenIssuer = tokenIssuer ?? throw new ArgumentNullException(nameof(tokenIssuer));
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }
            m_options = options.Value ?? throw new ArgumentNullException(nameof(options));
        }

        /// <summary>
        /// Creates an in-memory token provider for tests and direct hosting.
        /// </summary>
        public InMemoryAccessTokenProvider(
            ITokenIssuer tokenIssuer,
            AuthorizationServiceOptions options)
            : this(tokenIssuer, Options.Create(options))
        {
        }

        /// <summary>
        /// Gets the signer used by this provider.
        /// </summary>
        internal ITokenIssuer TokenIssuer { get; }

        /// <inheritdoc/>
        [Obsolete("Use StartRequestTokenAsync + FinishRequestTokenAsync for Part 12 v1.05 compliance.")]
        public async ValueTask<string> RequestAccessTokenAsync(
            UserIdentityToken identityToken,
            string resourceId,
            CancellationToken ct = default)
        {
            ValidateAudience(resourceId);
            string[] scopes = NormalizeScopes(m_options.DefaultScopes);
            AccessToken token = await IssueAsync(
                GetSubject(identityToken, null),
                resourceId,
                scopes,
                [],
                ct)
                .ConfigureAwait(false);
            using (token)
            {
                return Encoding.UTF8.GetString(token.TokenData.ToArray());
            }
        }

        /// <inheritdoc/>
        public ValueTask<(ByteString serviceData, Guid requestId)> StartRequestTokenAsync(
            string resourceId,
            string policyId,
            ByteString requestorData,
            CancellationToken ct = default)
        {
            return StartRequestTokenAsync(resourceId, policyId, requestorData, null, ct);
        }

        /// <summary>
        /// Begins a token request for the supplied session identity.
        /// </summary>
        public ValueTask<(ByteString serviceData, Guid requestId)> StartRequestTokenAsync(
            string resourceId,
            string policyId,
            ByteString requestorData,
            IUserIdentity? callerIdentity,
            CancellationToken ct = default)
        {
            ct.ThrowIfCancellationRequested();
            ValidateAudience(resourceId);
            string[] scopes = DecodeScopes(requestorData);
            if (scopes.Length == 0)
            {
                scopes = NormalizeScopes(m_options.DefaultScopes);
            }

            var requestId = Guid.NewGuid();
            m_requests[requestId] = new RequestRecord(
                resourceId,
                policyId ?? string.Empty,
                scopes,
                callerIdentity?.DisplayName ?? string.Empty,
                DateTime.UtcNow.AddMinutes(5));

            return new ValueTask<(ByteString serviceData, Guid requestId)>((ByteString.Empty, requestId));
        }

        /// <inheritdoc/>
        public async ValueTask<AccessTokenResult> FinishRequestTokenAsync(
            Guid requestId,
            ArrayOf<string> requestedRoles,
            UserIdentityToken userIdentityToken,
            SignatureData userTokenSignature,
            CancellationToken ct = default)
        {
            ct.ThrowIfCancellationRequested();
            if (!m_requests.TryRemove(requestId, out RequestRecord? request))
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadInvalidArgument,
                    "Unknown or expired AuthorizationService token request id.");
            }

            if (request.ExpiresAtUtc < DateTime.UtcNow)
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadTimeout,
                    "AuthorizationService token request expired.");
            }

            string[] roles = requestedRoles.IsEmpty
                ? []
                : [.. requestedRoles.ToArray()!.Where(role => !string.IsNullOrWhiteSpace(role))];
            string subject = GetSubject(userIdentityToken, request.Subject);
            AccessToken token = await IssueAsync(
                subject,
                request.ResourceId,
                request.Scopes,
                roles,
                ct)
                .ConfigureAwait(false);

            string? refreshToken = null;
            DateTime refreshExpiry = DateTime.MinValue;
            if (m_options.EnableRefreshTokens)
            {
                refreshToken = CreateRefreshToken();
                refreshExpiry = DateTime.UtcNow + m_options.DefaultRefreshTokenLifetime;
                m_issuedTokens[refreshToken] = new IssuedTokenRecord(
                    subject,
                    request.ResourceId,
                    [.. request.Scopes],
                    [.. roles],
                    refreshExpiry);
            }

            using (token)
            {
                return new AccessTokenResult
                {
                    AccessToken = Encoding.UTF8.GetString(token.TokenData.ToArray()),
                    AccessTokenExpiryTime = token.ExpiresAt,
                    RefreshToken = refreshToken,
                    RefreshTokenExpiryTime = refreshExpiry,
                    TokenType = "JWT",
                    PolicyId = string.IsNullOrEmpty(request.PolicyId) ? "jwt" : request.PolicyId,
                    AccessTokenBytes = token.TokenData.ToArray()
                };
            }
        }

        /// <inheritdoc/>
        /// <remarks>
        /// Refresh tokens are single-use and bound to their original resource id. An attempted
        /// use with a different resource id is treated as misuse and revokes that refresh token.
        /// </remarks>
        public async ValueTask<AccessTokenResult> RefreshTokenAsync(
            string resourceId,
            string currentRefreshToken,
            CancellationToken ct = default)
        {
            ct.ThrowIfCancellationRequested();

            if (!m_options.EnableRefreshTokens)
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadNotSupported,
                    "AuthorizationService refresh tokens are disabled.");
            }

            if (string.IsNullOrEmpty(resourceId))
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadInvalidArgument,
                    "Resource id is required.");
            }
            if (string.IsNullOrEmpty(currentRefreshToken))
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadInvalidArgument,
                    "Refresh token is required.");
            }

            PruneRevokedTokens();

            if (m_revokedTokens.ContainsKey(currentRefreshToken))
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadIdentityTokenRejected,
                    "Refresh token has already been used.");
            }

            if (!m_issuedTokens.TryRemove(currentRefreshToken, out IssuedTokenRecord? record))
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadIdentityTokenRejected,
                    "Unknown refresh token.");
            }

            if (record.ExpiresAtUtc < DateTime.UtcNow)
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadTimeout,
                    "Refresh token has expired.");
            }

            if (!string.Equals(record.ResourceId, resourceId, StringComparison.Ordinal))
            {
                m_revokedTokens[currentRefreshToken] = record.ExpiresAtUtc;
                throw ServiceResultException.Create(
                    StatusCodes.BadInvalidArgument,
                    "Refresh token is bound to a different resource.");
            }

            m_revokedTokens[currentRefreshToken] = record.ExpiresAtUtc;
            ValidateAudience(resourceId);

            AccessToken token = await IssueAsync(
                record.Subject,
                record.ResourceId,
                record.Scopes,
                record.Roles,
                ct)
                .ConfigureAwait(false);

            string newRefreshToken = CreateRefreshToken();
            DateTime newRefreshExpiry = DateTime.UtcNow + m_options.DefaultRefreshTokenLifetime;
            m_issuedTokens[newRefreshToken] = new IssuedTokenRecord(
                record.Subject,
                record.ResourceId,
                [.. record.Scopes],
                [.. record.Roles],
                newRefreshExpiry);

            using (token)
            {
                return new AccessTokenResult
                {
                    AccessToken = Encoding.UTF8.GetString(token.TokenData.ToArray()),
                    AccessTokenExpiryTime = token.ExpiresAt,
                    RefreshToken = newRefreshToken,
                    RefreshTokenExpiryTime = newRefreshExpiry,
                    TokenType = "JWT",
                    PolicyId = "jwt",
                    AccessTokenBytes = token.TokenData.ToArray()
                };
            }
        }

        private ValueTask<AccessToken> IssueAsync(
            string subject,
            string audience,
            string[] scopes,
            string[] roles,
            CancellationToken ct)
        {
            var additionalClaims = new Dictionary<string, object?>(StringComparer.Ordinal);
            if (roles.Length != 0)
            {
                additionalClaims["roles"] = roles;
            }

            return TokenIssuer.IssueAsync(
                new TokenIssuanceRequest(
                    subject,
                    audience,
                    scopes,
                    additionalClaims,
                    m_options.DefaultTokenLifetime),
                ct);
        }

        private void ValidateAudience(string resourceId)
        {
            if (string.IsNullOrEmpty(resourceId))
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadInvalidArgument,
                    "AuthorizationService resource id must be supplied.");
            }

            if (m_options.AllowedAudiences.Count != 0 &&
                !m_options.AllowedAudiences.Contains(resourceId, StringComparer.Ordinal))
            {
                throw ServiceResultException.Create(
                    StatusCodes.BadUserAccessDenied,
                    "AuthorizationService audience is not allowed.");
            }
        }

        private static string GetSubject(UserIdentityToken? identityToken, string? fallback)
        {
            if (identityToken is UserNameIdentityToken userName && !string.IsNullOrEmpty(userName.UserName))
            {
                return userName.UserName;
            }
            if (identityToken is X509IdentityToken x509 && x509.CertificateData.Length != 0)
            {
                return Convert.ToBase64String(x509.CertificateData.ToArray());
            }
            if (!string.IsNullOrEmpty(fallback))
            {
                return fallback!;
            }
            if (!string.IsNullOrEmpty(identityToken?.PolicyId))
            {
                return identityToken!.PolicyId!;
            }
            return "anonymous";
        }

        private static string[] DecodeScopes(ByteString requestorData)
        {
            if (requestorData.Length == 0)
            {
                return [];
            }

            string text = Encoding.UTF8.GetString(requestorData.ToArray());
            return [.. text
                .Split(s_scopeSeparators, StringSplitOptions.RemoveEmptyEntries)
                .Where(scope => !string.IsNullOrWhiteSpace(scope))
                .Distinct(StringComparer.Ordinal)];
        }

        private static string[] NormalizeScopes(IEnumerable<string> scopes)
        {
            return [.. scopes
                .Where(scope => !string.IsNullOrWhiteSpace(scope))
                .Distinct(StringComparer.Ordinal)];
        }

        private static string CreateRefreshToken()
        {
            byte[] bytes = new byte[32];
            using (var generator = RandomNumberGenerator.Create())
            {
                generator.GetBytes(bytes);
            }
            return Utils.ToHexString(bytes);
        }

        private void PruneRevokedTokens()
        {
            DateTime now = DateTime.UtcNow;
            foreach (KeyValuePair<string, DateTime> entry in m_revokedTokens)
            {
                if (entry.Value < now)
                {
                    m_revokedTokens.TryRemove(entry.Key, out _);
                }
            }
        }

        private sealed record RequestRecord(
            string ResourceId,
            string PolicyId,
            string[] Scopes,
            string Subject,
            DateTime ExpiresAtUtc);

        private sealed record IssuedTokenRecord(
            string Subject,
            string ResourceId,
            string[] Scopes,
            string[] Roles,
            DateTime ExpiresAtUtc);
    }
}