/*
 * Licensed under the Apache License, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)
 * See https://github.com/openiddict/openiddict-core for more information concerning
 * the license and the contributors participating to this project.
 */

using System.Collections.Immutable;
using System.Diagnostics;
using System.Security.Claims;
using System.Security.Cryptography;
using System.Text;
using System.Text.Encodings.Web;
using System.Text.Json;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.WebUtilities;
using Microsoft.Extensions.Caching.Distributed;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Microsoft.IdentityModel.JsonWebTokens;
using Microsoft.IdentityModel.Tokens;
using Microsoft.Net.Http.Headers;
using static OpenIddict.Server.AspNetCore.OpenIddictServerAspNetCoreConstants;
using JsonWebTokenTypes = OpenIddict.Server.AspNetCore.OpenIddictServerAspNetCoreConstants.JsonWebTokenTypes;

namespace OpenIddict.Server.AspNetCore;

public static partial class OpenIddictServerAspNetCoreHandlers
{
    public static class Authentication
    {
        public static ImmutableArray<OpenIddictServerHandlerDescriptor> DefaultHandlers { get; } = ImmutableArray.Create(
            /*
             * Authorization request extraction:
             */
            ExtractGetOrPostRequest<ExtractAuthorizationRequestContext>.Descriptor,
            RestoreCachedRequestParameters.Descriptor,
            CacheRequestParameters.Descriptor,

            /*
             * Authorization request handling:
             */
            EnablePassthroughMode<HandleAuthorizationRequestContext, RequireAuthorizationEndpointPassthroughEnabled>.Descriptor,

            /*
             * Authorization response processing:
             */
            RemoveCachedRequest.Descriptor,
            AttachHttpResponseCode<ApplyAuthorizationResponseContext>.Descriptor,
            AttachCacheControlHeader<ApplyAuthorizationResponseContext>.Descriptor,
            ProcessFormPostResponse.Descriptor,
            ProcessQueryResponse.Descriptor,
            ProcessFragmentResponse.Descriptor,
            ProcessPassthroughErrorResponse<ApplyAuthorizationResponseContext, RequireAuthorizationEndpointPassthroughEnabled>.Descriptor,
            ProcessStatusCodePagesErrorResponse<ApplyAuthorizationResponseContext>.Descriptor,
            ProcessLocalErrorResponse<ApplyAuthorizationResponseContext>.Descriptor);

        /// <summary>
        /// Contains the logic responsible of restoring cached requests from the request_id, if specified.
        /// Note: this handler is not used when the OpenID Connect request is not initially handled by ASP.NET Core.
        /// </summary>
        public class RestoreCachedRequestParameters : IOpenIddictServerHandler<ExtractAuthorizationRequestContext>
        {
            private readonly IDistributedCache _cache;

            public RestoreCachedRequestParameters() => throw new InvalidOperationException(SR.GetResourceString(SR.ID0116));

            public RestoreCachedRequestParameters(IDistributedCache cache!!)
                => _cache = cache;

            /// <summary>
            /// Gets the default descriptor definition assigned to this handler.
            /// </summary>
            public static OpenIddictServerHandlerDescriptor Descriptor { get; }
                = OpenIddictServerHandlerDescriptor.CreateBuilder<ExtractAuthorizationRequestContext>()
                    .AddFilter<RequireHttpRequest>()
                    .AddFilter<RequireAuthorizationRequestCachingEnabled>()
                    .UseSingletonHandler<RestoreCachedRequestParameters>()
                    .SetOrder(ExtractGetOrPostRequest<ExtractAuthorizationRequestContext>.Descriptor.Order + 1_000)
                    .SetType(OpenIddictServerHandlerType.BuiltIn)
                    .Build();

            /// <inheritdoc/>
            public async ValueTask HandleAsync(ExtractAuthorizationRequestContext context!!)
            {
                Debug.Assert(context.Request is not null, SR.GetResourceString(SR.ID4008));

                // If a request_id parameter can be found in the authorization request,
                // restore the complete authorization request from the distributed cache.

                if (string.IsNullOrEmpty(context.Request.RequestId))
                {
                    return;
                }

                // Note: the cache key is always prefixed with a specific marker
                // to avoid collisions with the other types of cached payloads.
                var token = await _cache.GetStringAsync(Cache.AuthorizationRequest + context.Request.RequestId);
                if (token is null || !context.Options.JsonWebTokenHandler.CanReadToken(token))
                {
                    context.Logger.LogInformation(SR.GetResourceString(SR.ID6146), Parameters.RequestId);

                    context.Reject(
                        error: Errors.InvalidRequest,
                        description: SR.FormatID2052(Parameters.RequestId),
                        uri: SR.FormatID8000(SR.ID2052));

                    return;
                }

                var parameters = context.Options.TokenValidationParameters.Clone();
                parameters.ValidIssuer ??= context.Issuer?.AbsoluteUri;
                parameters.ValidAudience = context.Issuer?.AbsoluteUri;
                parameters.ValidTypes = new[] { JsonWebTokenTypes.Private.AuthorizationRequest };

                var result = await context.Options.JsonWebTokenHandler.ValidateTokenAsync(token, parameters);
                if (!result.IsValid)
                {
                    context.Logger.LogInformation(SR.GetResourceString(SR.ID6146), Parameters.RequestId);

                    context.Reject(
                        error: Errors.InvalidRequest,
                        description: SR.FormatID2052(Parameters.RequestId),
                        uri: SR.FormatID8000(SR.ID2052));

                    return;
                }

                using var document = JsonDocument.Parse(
                    Base64UrlEncoder.Decode(((JsonWebToken) result.SecurityToken).InnerToken.EncodedPayload));
                if (document.RootElement.ValueKind is not JsonValueKind.Object)
                {
                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0117));
                }

                // Restore the authorization request parameters from the serialized payload.
                foreach (var parameter in document.RootElement.EnumerateObject())
                {
                    // Avoid overriding the current request parameters.
                    if (context.Request.HasParameter(parameter.Name))
                    {
                        continue;
                    }

                    context.Request.SetParameter(parameter.Name, parameter.Value.Clone());
                }
            }
        }

        /// <summary>
        /// Contains the logic responsible of caching authorization requests, if applicable.
        /// Note: this handler is not used when the OpenID Connect request is not initially handled by ASP.NET Core.
        /// </summary>
        public class CacheRequestParameters : IOpenIddictServerHandler<ExtractAuthorizationRequestContext>
        {
            private readonly IDistributedCache _cache;
            private readonly IOptionsMonitor<OpenIddictServerAspNetCoreOptions> _options;

            public CacheRequestParameters() => throw new InvalidOperationException(SR.GetResourceString(SR.ID0116));

            public CacheRequestParameters(
                IDistributedCache cache,
                IOptionsMonitor<OpenIddictServerAspNetCoreOptions> options!!)
            {
                _cache = cache;
                _options = options;
            }

            /// <summary>
            /// Gets the default descriptor definition assigned to this handler.
            /// </summary>
            public static OpenIddictServerHandlerDescriptor Descriptor { get; }
                = OpenIddictServerHandlerDescriptor.CreateBuilder<ExtractAuthorizationRequestContext>()
                    .AddFilter<RequireHttpRequest>()
                    .AddFilter<RequireAuthorizationRequestCachingEnabled>()
                    .UseSingletonHandler<CacheRequestParameters>()
                    .SetOrder(RestoreCachedRequestParameters.Descriptor.Order + 1_000)
                    .SetType(OpenIddictServerHandlerType.BuiltIn)
                    .Build();

            /// <inheritdoc/>
            public async ValueTask HandleAsync(ExtractAuthorizationRequestContext context!!)
            {
                Debug.Assert(context.Request is not null, SR.GetResourceString(SR.ID4008));

                // This handler only applies to ASP.NET Core requests. If the HTTP context cannot be resolved,
                // this may indicate that the request was incorrectly processed by another server stack.
                var request = context.Transaction.GetHttpRequest() ??
                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0114));

                // Don't cache the request if the request doesn't include any parameter.
                // If a request_id parameter can be found in the authorization request,
                // ignore the following logic to prevent an infinite redirect loop.
                if (context.Request.Count == 0 || !string.IsNullOrEmpty(context.Request.RequestId))
                {
                    return;
                }

                // Generate a 256-bit request identifier using a crypto-secure random number generator.
                var data = new byte[256 / 8];

#if SUPPORTS_STATIC_RANDOM_NUMBER_GENERATOR_METHODS
                RandomNumberGenerator.Fill(data);
#else
                using var generator = RandomNumberGenerator.Create();
                generator.GetBytes(data);
#endif

                context.Request.RequestId = Base64UrlEncoder.Encode(data);

                // Store the serialized authorization request parameters in the distributed cache.
                var token = context.Options.JsonWebTokenHandler.CreateToken(new SecurityTokenDescriptor
                {
                    Audience = context.Issuer?.AbsoluteUri,
                    Claims = context.Request.GetParameters().ToDictionary(
                        parameter => parameter.Key,
                        parameter => parameter.Value.Value),
                    EncryptingCredentials = context.Options.EncryptionCredentials.First(),
                    Issuer = context.Issuer?.AbsoluteUri,
                    SigningCredentials = context.Options.SigningCredentials.First(),
                    Subject = new ClaimsIdentity(),
                    TokenType = JsonWebTokenTypes.Private.AuthorizationRequest
                });

                // Note: the cache key is always prefixed with a specific marker
                // to avoid collisions with the other types of cached payloads.
                await _cache.SetStringAsync(Cache.AuthorizationRequest + context.Request.RequestId,
                    token, _options.CurrentValue.AuthorizationRequestCachingPolicy);

                // Create a new GET authorization request containing only the request_id parameter.
                var address = QueryHelpers.AddQueryString(
                    uri: request.Scheme + Uri.SchemeDelimiter + request.Host + request.PathBase + request.Path,
                    name: Parameters.RequestId,
                    value: context.Request.RequestId);

                request.HttpContext.Response.Redirect(address);

                // Mark the response as handled to skip the rest of the pipeline.
                context.HandleRequest();
            }
        }

        /// <summary>
        /// Contains the logic responsible of removing cached authorization requests from the distributed cache.
        /// Note: this handler is not used when the OpenID Connect request is not initially handled by ASP.NET Core.
        /// </summary>
        public class RemoveCachedRequest : IOpenIddictServerHandler<ApplyAuthorizationResponseContext>
        {
            private readonly IDistributedCache _cache;

            public RemoveCachedRequest() => throw new InvalidOperationException(SR.GetResourceString(SR.ID0116));

            public RemoveCachedRequest(IDistributedCache cache!!)
                => _cache = cache;

            /// <summary>
            /// Gets the default descriptor definition assigned to this handler.
            /// </summary>
            public static OpenIddictServerHandlerDescriptor Descriptor { get; }
                = OpenIddictServerHandlerDescriptor.CreateBuilder<ApplyAuthorizationResponseContext>()
                    .AddFilter<RequireHttpRequest>()
                    .AddFilter<RequireAuthorizationRequestCachingEnabled>()
                    .UseSingletonHandler<RemoveCachedRequest>()
                    .SetOrder(int.MinValue + 100_000)
                    .SetType(OpenIddictServerHandlerType.BuiltIn)
                    .Build();

            /// <inheritdoc/>
            public ValueTask HandleAsync(ApplyAuthorizationResponseContext context!!)
            {
                if (string.IsNullOrEmpty(context.Request?.RequestId))
                {
                    return default;
                }

                // Note: the ApplyAuthorizationResponse event is called for both successful
                // and errored authorization responses but discrimination is not necessary here,
                // as the authorization request must be removed from the distributed cache in both cases.

                // Note: the cache key is always prefixed with a specific marker
                // to avoid collisions with the other types of cached payloads.
                return new(_cache.RemoveAsync(Cache.AuthorizationRequest + context.Request.RequestId));
            }
        }

        /// <summary>
        /// Contains the logic responsible of processing authorization responses using the form_post response mode.
        /// Note: this handler is not used when the OpenID Connect request is not initially handled by ASP.NET Core.
        /// </summary>
        public class ProcessFormPostResponse : IOpenIddictServerHandler<ApplyAuthorizationResponseContext>
        {
            private readonly HtmlEncoder _encoder;

            public ProcessFormPostResponse(HtmlEncoder encoder)
                => _encoder = encoder;

            /// <summary>
            /// Gets the default descriptor definition assigned to this handler.
            /// </summary>
            public static OpenIddictServerHandlerDescriptor Descriptor { get; }
                = OpenIddictServerHandlerDescriptor.CreateBuilder<ApplyAuthorizationResponseContext>()
                    .AddFilter<RequireHttpRequest>()
                    .UseSingletonHandler<ProcessFormPostResponse>()
                    .SetOrder(50_000)
                    .SetType(OpenIddictServerHandlerType.BuiltIn)
                    .Build();

            /// <inheritdoc/>
            public async ValueTask HandleAsync(ApplyAuthorizationResponseContext context!!)
            {
                // This handler only applies to ASP.NET Core requests. If the HTTP context cannot be resolved,
                // this may indicate that the request was incorrectly processed by another server stack.
                var response = context.Transaction.GetHttpRequest()?.HttpContext.Response ??
                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0114));

                if (string.IsNullOrEmpty(context.RedirectUri) ||
                   !string.Equals(context.ResponseMode, ResponseModes.FormPost, StringComparison.Ordinal))
                {
                    return;
                }

                context.Logger.LogInformation(SR.GetResourceString(SR.ID6147), context.RedirectUri, context.Response);

                using var buffer = new MemoryStream();
                using var writer = new StreamWriter(buffer);

                writer.WriteLine("<!doctype html>");
                writer.WriteLine("<html>");
                writer.WriteLine("<body>");

                // While the redirect_uri parameter should be guarded against unknown values,
                // it's still safer to encode it to avoid cross-site scripting attacks
                // if the authorization server has a relaxed policy concerning redirect URIs.
                writer.WriteLine($@"<form name=""form"" method=""post"" action=""{_encoder.Encode(context.RedirectUri)}"">");

                // Note: while initially not allowed by the core OAuth 2.0 specification, multiple parameters
                // with the same name are used by derived drafts like the OAuth 2.0 token exchange specification.
                // For consistency, multiple parameters with the same name are also supported by this endpoint.
                foreach (var (key, value) in
                    from parameter in context.Response.GetParameters()
                    let values = (string?[]?) parameter.Value
                    where values is not null
                    from value in values
                    where !string.IsNullOrEmpty(value)
                    select (parameter.Key, Value: value))
                {
                    writer.WriteLine($@"<input type=""hidden"" name=""{_encoder.Encode(key)}"" value=""{_encoder.Encode(value)}"" />");
                }

                writer.WriteLine(@"<noscript>Click here to finish the authorization process: <input type=""submit"" /></noscript>");
                writer.WriteLine("</form>");
                writer.WriteLine("<script>document.form.submit();</script>");
                writer.WriteLine("</body>");
                writer.WriteLine("</html>");
                writer.Flush();

                response.StatusCode = 200;
                response.ContentLength = buffer.Length;
                response.ContentType = "text/html;charset=UTF-8";

                response.Headers[HeaderNames.CacheControl] = "no-cache";
                response.Headers[HeaderNames.Pragma] = "no-cache";
                response.Headers[HeaderNames.Expires] = "-1";

                buffer.Seek(offset: 0, loc: SeekOrigin.Begin);
                await buffer.CopyToAsync(response.Body, 4096);

                context.HandleRequest();
            }
        }

        /// <summary>
        /// Contains the logic responsible of processing authorization responses using the query response mode.
        /// Note: this handler is not used when the OpenID Connect request is not initially handled by ASP.NET Core.
        /// </summary>
        public class ProcessQueryResponse : IOpenIddictServerHandler<ApplyAuthorizationResponseContext>
        {
            /// <summary>
            /// Gets the default descriptor definition assigned to this handler.
            /// </summary>
            public static OpenIddictServerHandlerDescriptor Descriptor { get; }
                = OpenIddictServerHandlerDescriptor.CreateBuilder<ApplyAuthorizationResponseContext>()
                    .AddFilter<RequireHttpRequest>()
                    .UseSingletonHandler<ProcessQueryResponse>()
                    .SetOrder(ProcessFormPostResponse.Descriptor.Order + 1_000)
                    .SetType(OpenIddictServerHandlerType.BuiltIn)
                    .Build();

            /// <inheritdoc/>
            public ValueTask HandleAsync(ApplyAuthorizationResponseContext context!!)
            {
                // This handler only applies to ASP.NET Core requests. If the HTTP context cannot be resolved,
                // this may indicate that the request was incorrectly processed by another server stack.
                var response = context.Transaction.GetHttpRequest()?.HttpContext.Response ??
                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0114));

                if (string.IsNullOrEmpty(context.RedirectUri) ||
                   !string.Equals(context.ResponseMode, ResponseModes.Query, StringComparison.Ordinal))
                {
                    return default;
                }

                context.Logger.LogInformation(SR.GetResourceString(SR.ID6148), context.RedirectUri, context.Response);

                // Note: while initially not allowed by the core OAuth 2.0 specification, multiple parameters
                // with the same name are used by derived drafts like the OAuth 2.0 token exchange specification.
                // For consistency, multiple parameters with the same name are also supported by this endpoint.

#if SUPPORTS_MULTIPLE_VALUES_IN_QUERYHELPERS
                var location = QueryHelpers.AddQueryString(context.RedirectUri,
                    from parameter in context.Response.GetParameters()
                    let values = (string?[]?) parameter.Value
                    where values is not null
                    from value in values
                    where !string.IsNullOrEmpty(value)
                    select KeyValuePair.Create(parameter.Key, value));
#else
                var location = context.RedirectUri;

                foreach (var (key, value) in
                    from parameter in context.Response.GetParameters()
                    let values = (string?[]?) parameter.Value
                    where values is not null
                    from value in values
                    where !string.IsNullOrEmpty(value)
                    select (parameter.Key, Value: value))
                {
                    location = QueryHelpers.AddQueryString(location, key, value);
                }
#endif
                response.Redirect(location);
                context.HandleRequest();

                return default;
            }
        }

        /// <summary>
        /// Contains the logic responsible of processing authorization responses using the fragment response mode.
        /// Note: this handler is not used when the OpenID Connect request is not initially handled by ASP.NET Core.
        /// </summary>
        public class ProcessFragmentResponse : IOpenIddictServerHandler<ApplyAuthorizationResponseContext>
        {
            /// <summary>
            /// Gets the default descriptor definition assigned to this handler.
            /// </summary>
            public static OpenIddictServerHandlerDescriptor Descriptor { get; }
                = OpenIddictServerHandlerDescriptor.CreateBuilder<ApplyAuthorizationResponseContext>()
                    .AddFilter<RequireHttpRequest>()
                    .UseSingletonHandler<ProcessFragmentResponse>()
                    .SetOrder(ProcessQueryResponse.Descriptor.Order + 1_000)
                    .SetType(OpenIddictServerHandlerType.BuiltIn)
                    .Build();

            /// <inheritdoc/>
            public ValueTask HandleAsync(ApplyAuthorizationResponseContext context!!)
            {
                // This handler only applies to ASP.NET Core requests. If the HTTP context cannot be resolved,
                // this may indicate that the request was incorrectly processed by another server stack.
                var response = context.Transaction.GetHttpRequest()?.HttpContext.Response ??
                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0114));

                if (string.IsNullOrEmpty(context.RedirectUri) ||
                   !string.Equals(context.ResponseMode, ResponseModes.Fragment, StringComparison.Ordinal))
                {
                    return default;
                }

                context.Logger.LogInformation(SR.GetResourceString(SR.ID6149), context.RedirectUri, context.Response);

                var builder = new StringBuilder(context.RedirectUri);

                // Note: while initially not allowed by the core OAuth 2.0 specification, multiple parameters
                // with the same name are used by derived drafts like the OAuth 2.0 token exchange specification.
                // For consistency, multiple parameters with the same name are also supported by this endpoint.
                foreach (var (key, value) in
                    from parameter in context.Response.GetParameters()
                    let values = (string?[]?) parameter.Value
                    where values is not null
                    from value in values
                    where !string.IsNullOrEmpty(value)
                    select (parameter.Key, Value: value))
                {
                    builder.Append(Contains(builder, '#') ? '&' : '#')
                           .Append(Uri.EscapeDataString(key))
                           .Append('=')
                           .Append(Uri.EscapeDataString(value));
                }

                response.Redirect(builder.ToString());
                context.HandleRequest();

                return default;

                static bool Contains(StringBuilder builder, char delimiter)
                {
                    for (var index = 0; index < builder.Length; index++)
                    {
                        if (builder[index] == delimiter)
                        {
                            return true;
                        }
                    }

                    return false;
                }
            }
        }
    }
}