// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Collections.Concurrent;
using System.Diagnostics.CodeAnalysis;

namespace Microsoft.Extensions.DependencyInjection.ServiceLookup
{
    internal sealed class CallSiteValidator : CallSiteVisitor<CallSiteValidator.CallSiteValidatorState, Type?>
    {
        // Keys are services being resolved via GetService, values - first scoped service in their call site tree
        private readonly ConcurrentDictionary<ServiceCacheKey, Type?> _scopedServices = new ConcurrentDictionary<ServiceCacheKey, Type?>();

        public void ValidateCallSite(ServiceCallSite callSite) => VisitCallSite(callSite, default);

        public void ValidateResolution(ServiceCallSite callSite, IServiceScope scope, IServiceScope rootScope)
        {
            if (ReferenceEquals(scope, rootScope)
                && _scopedServices.TryGetValue(callSite.Cache.Key, out Type? scopedService)
                && scopedService != null)
            {
                Type serviceType = callSite.ServiceType;
                if (serviceType == scopedService)
                {
                    throw new InvalidOperationException(
                        SR.Format(SR.DirectScopedResolvedFromRootException, callSite.ServiceType,
                            nameof(ServiceLifetime.Scoped).ToLowerInvariant()));
                }

                throw new InvalidOperationException(
                    SR.Format(SR.ScopedResolvedFromRootException,
                        callSite.ServiceType,
                        scopedService,
                        nameof(ServiceLifetime.Scoped).ToLowerInvariant()));
            }
        }

        protected override Type? VisitCallSite(ServiceCallSite callSite, CallSiteValidatorState argument)
        {
            // First, check if we have encountered this call site before to prevent visiting call site trees that have already been visited
            // If firstScopedServiceInCallSiteTree is null there are no scoped dependencies in this service's call site tree
            // If firstScopedServiceInCallSiteTree has a value, it contains the first scoped service in this service's call site tree
            if (!_scopedServices.TryGetValue(callSite.Cache.Key, out Type? firstScopedServiceInCallSiteTree))
            {
                // This call site wasn't cached yet, walk the tree
                firstScopedServiceInCallSiteTree = base.VisitCallSite(callSite, argument);

                // Cache the result
                _scopedServices[callSite.Cache.Key] = firstScopedServiceInCallSiteTree;
            }

            // If there is a scoped service in the call site tree, make sure we are not resolving it from a singleton
            if (firstScopedServiceInCallSiteTree != null && argument.Singleton != null)
            {
                throw new InvalidOperationException(SR.Format(SR.ScopedInSingletonException,
                    callSite.ServiceType,
                    argument.Singleton.ServiceType,
                    nameof(ServiceLifetime.Scoped).ToLowerInvariant(),
                    nameof(ServiceLifetime.Singleton).ToLowerInvariant()
                    ));
            }

            return firstScopedServiceInCallSiteTree;
        }

        protected override Type? VisitConstructor(ConstructorCallSite constructorCallSite, CallSiteValidatorState state)
        {
            Type? result = null;
            foreach (ServiceCallSite parameterCallSite in constructorCallSite.ParameterCallSites)
            {
                Type? scoped = VisitCallSite(parameterCallSite, state);
                result ??= scoped;
            }
            return result;
        }

        protected override Type? VisitIEnumerable(IEnumerableCallSite enumerableCallSite,
            CallSiteValidatorState state)
        {
            Type? result = null;
            foreach (ServiceCallSite serviceCallSite in enumerableCallSite.ServiceCallSites)
            {
                Type? scoped = VisitCallSite(serviceCallSite, state);
                result ??= scoped;
            }
            return result;
        }

        protected override Type? VisitRootCache(ServiceCallSite singletonCallSite, CallSiteValidatorState state)
        {
            state.Singleton = singletonCallSite;
            return VisitCallSiteMain(singletonCallSite, state);
        }

        protected override Type? VisitScopeCache(ServiceCallSite scopedCallSite, CallSiteValidatorState state)
        {
            // We are fine with having ServiceScopeService requested by singletons
            if (scopedCallSite.ServiceType == typeof(IServiceScopeFactory))
            {
                return null;
            }

            VisitCallSiteMain(scopedCallSite, state);
            return scopedCallSite.ServiceType;
        }

        protected override Type? VisitConstant(ConstantCallSite constantCallSite, CallSiteValidatorState state) => null;

        protected override Type? VisitServiceProvider(ServiceProviderCallSite serviceProviderCallSite, CallSiteValidatorState state) => null;

        protected override Type? VisitFactory(FactoryCallSite factoryCallSite, CallSiteValidatorState state) => null;

        internal struct CallSiteValidatorState
        {
            [DisallowNull]
            public ServiceCallSite? Singleton { get; set; }
        }
    }
}