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 * 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
 * restriction, including without limitation the rights to use,
 * 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
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
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 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Threading;
using System.Threading.Tasks;

namespace Opc.Ua.Identity
{
    /// <summary>
    /// Helper APIs for materializing client user identities from endpoint policies.
    /// </summary>
    public static class ClientIdentityProviderExtensions
    {
        /// <summary>
        /// Selects a matching user-token policy and asks <paramref name="provider"/> to create an identity.
        /// </summary>
        /// <exception cref="ArgumentNullException">
        /// Thrown when <paramref name="endpointDescription"/> or <paramref name="messageContext"/> is <c>null</c>.
        /// </exception>
        public static ValueTask<IUserIdentity> AcquireIdentityAsync(
            this IClientIdentityProvider provider,
            EndpointDescription endpointDescription,
            IServiceMessageContext messageContext,
            CancellationToken ct = default)
        {
            if (endpointDescription == null)
            {
                throw new ArgumentNullException(nameof(endpointDescription));
            }
            if (messageContext == null)
            {
                throw new ArgumentNullException(nameof(messageContext));
            }

            var context = new IdentitySelectionContext(
                endpointDescription,
                endpointDescription.UserIdentityTokens.ToArray() ?? [],
                messageContext);
            return provider.AcquireIdentityAsync(context, ct);
        }

        /// <summary>
        /// Selects a matching user-token policy and asks <paramref name="provider"/> to create an identity.
        /// </summary>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="provider"/> is <c>null</c>.</exception>
        public static async ValueTask<IUserIdentity> AcquireIdentityAsync(
            this IClientIdentityProvider provider,
            IdentitySelectionContext context,
            CancellationToken ct = default)
        {
            if (provider == null)
            {
                throw new ArgumentNullException(nameof(provider));
            }

            UserTokenPolicy identityPolicy = provider.SelectUserTokenPolicy(context);
            IUserIdentity identity = await provider
                .GetIdentityAsync(identityPolicy, context, ct)
                .ConfigureAwait(false);
            identity.TokenHandler.Token.PolicyId = identityPolicy.PolicyId;
            return identity;
        }

        /// <summary>
        /// Selects the best offered user-token policy for <paramref name="provider"/>.
        /// </summary>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="provider"/> is <c>null</c>.</exception>
        /// <exception cref="ServiceResultException">
        /// Thrown with <see cref="StatusCodes.BadIdentityTokenRejected"/> when the endpoint offers no
        /// user-token policy that the provider can satisfy.
        /// </exception>
        public static UserTokenPolicy SelectUserTokenPolicy(
            this IClientIdentityProvider provider,
            IdentitySelectionContext context)
        {
            if (provider == null)
            {
                throw new ArgumentNullException(nameof(provider));
            }

            string tokenSecurityPolicyUri =
                context.EndpointDescription.SecurityPolicyUri ?? SecurityPolicies.None;
            UserTokenPolicy? sameEncryptionAlgorithm = null;
            UserTokenPolicy? unspecifiedSecPolicy = null;

            foreach (UserTokenPolicy policy in context.OfferedPolicies)
            {
                if (!provider.CanSatisfy(policy, context))
                {
                    continue;
                }

                if (policy.TokenType == UserTokenType.Anonymous ||
                    string.Equals(
                        policy.SecurityPolicyUri,
                        tokenSecurityPolicyUri,
                        StringComparison.Ordinal))
                {
                    return policy;
                }

                if (string.IsNullOrEmpty(policy.SecurityPolicyUri))
                {
                    unspecifiedSecPolicy ??= policy;
                }
                else if (HasSameEncryptionAlgorithm(
                    policy.SecurityPolicyUri!,
                    tokenSecurityPolicyUri))
                {
                    sameEncryptionAlgorithm ??= policy;
                }
            }

            return sameEncryptionAlgorithm ??
                unspecifiedSecPolicy ??
                    throw ServiceResultException.Create(
                        StatusCodes.BadIdentityTokenRejected,
                        "Endpoint does not offer a user token policy that can be satisfied by the identity provider.");
        }

        private static bool HasSameEncryptionAlgorithm(
            string policySecurityPolicyUri,
            string tokenSecurityPolicyUri)
        {
            return CryptoUtils.IsEccPolicy(policySecurityPolicyUri) ==
                CryptoUtils.IsEccPolicy(tokenSecurityPolicyUri);
        }
    }
}