src/Epam.GraphQL/Configuration/Implementations/Fields/UnionQueryField.cs

// Copyright © 2020 EPAM Systems, Inc. All Rights Reserved. All information contained herein is, and remains the
// property of EPAM Systems, Inc. and/or its suppliers and is protected by international intellectual
// property law. Dissemination of this information or reproduction of this material is strictly forbidden,
// unless prior written permission is obtained from EPAM Systems, Inc

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Epam.GraphQL.Builders.Loader;
using Epam.GraphQL.Configuration.Implementations.Descriptors;
using Epam.GraphQL.Configuration.Implementations.Fields.Helpers;
using Epam.GraphQL.Configuration.Implementations.Fields.ResolvableFields;
using Epam.GraphQL.Diagnostics;
using Epam.GraphQL.Helpers;

namespace Epam.GraphQL.Configuration.Implementations.Fields
{
    internal static class UnionQueryField
    {
        public static UnionQueryField<TExecutionContext> Create<TLastElementType, TExecutionContext>(
            IInlinedChainConfigurationContext configurationContext,
            BaseObjectGraphTypeConfigurator<object, TExecutionContext> parent,
            string name,
            Action<IInlineObjectBuilder<TLastElementType, TExecutionContext>>? build)
        {
            return new UnionQueryField<TExecutionContext>(configurationContext, parent, name, typeof(TLastElementType), CreateTypeResolver(build, configurationContext));
        }

        public static Func<UnionFieldBase<object, TExecutionContext>, IGraphTypeDescriptor<TExecutionContext>> CreateTypeResolver<TLastElementType, TExecutionContext>(
            Action<IInlineObjectBuilder<TLastElementType, TExecutionContext>>? build,
            IInlinedChainConfigurationContext configurationContext)
        {
            return field => field.Parent.GetGraphQLTypeDescriptor(field, build, configurationContext);
        }
    }

    internal class UnionQueryField<TExecutionContext> :
        UnionFieldBase<object, TExecutionContext>,
        IUnionableRootField<TExecutionContext>
    {
        public UnionQueryField(
            IChainConfigurationContext configurationContext,
            BaseObjectGraphTypeConfigurator<object, TExecutionContext> parent,
            string name,
            Type unionType,
            Func<UnionFieldBase<object, TExecutionContext>, IGraphTypeDescriptor<TExecutionContext>> graphTypeFactory)
            : base(configurationContext, parent, name, unionType, graphTypeFactory)
        {
        }

        private UnionQueryField(
            IChainConfigurationContext configurationContext,
            BaseObjectGraphTypeConfigurator<object, TExecutionContext> parent,
            string name,
            Type unionType,
            Func<UnionFieldBase<object, TExecutionContext>, IGraphTypeDescriptor<TExecutionContext>> graphTypeFactory,
            UnionGraphTypeDescriptor<TExecutionContext> unionGraphType)
            : base(
                configurationContext,
                parent,
                name,
                unionType,
                graphTypeFactory,
                unionGraphType)
        {
        }

        public IVoid Resolve<TReturnType>(Func<TExecutionContext, TReturnType> resolve, Action<IInlineObjectBuilder<TReturnType, TExecutionContext>>? build)
        {
            var resolver = ResolvedFieldResolverFactory.Create(
                Resolvers.ConvertFieldResolver(resolve));
            return Parent.ApplyResolvedField<TReturnType>(
                ConfigurationContext.Chain<TReturnType>(nameof(Resolve))
                    .Argument(resolve)
                    .OptionalArgument(build),
                this,
                GraphType,
                resolver);
        }

        public IVoid Resolve<TReturnType>(Func<TExecutionContext, Task<TReturnType>> resolve, Action<IInlineObjectBuilder<TReturnType, TExecutionContext>>? build)
        {
            var resolver = ResolvedFieldResolverFactory.Create(
                Resolvers.ConvertFieldResolver(resolve));
            return Parent.ApplyResolvedField<TReturnType>(
                ConfigurationContext.Chain<TReturnType>(nameof(Resolve))
                    .Argument(resolve)
                    .OptionalArgument(build),
                this,
                GraphType,
                resolver);
        }

        public IVoid Resolve<TReturnType>(Func<TExecutionContext, IEnumerable<TReturnType>> resolve, Action<IInlineObjectBuilder<TReturnType, TExecutionContext>>? build)
        {
            var resolver = ResolvedFieldResolverFactory.Create(
                Resolvers.ConvertFieldResolver(resolve));

            return Parent.ApplyResolvedField<IEnumerable<TReturnType>>(
                ConfigurationContext.Chain<TReturnType>(nameof(Resolve))
                    .Argument(resolve)
                    .OptionalArgument(build),
                this,
                GraphType.MakeListDescriptor(),
                resolver);
        }

        public IVoid Resolve<TReturnType>(Func<TExecutionContext, Task<IEnumerable<TReturnType>>> resolve, Action<IInlineObjectBuilder<TReturnType, TExecutionContext>>? build)
        {
            var resolver = ResolvedFieldResolverFactory.Create(
                Resolvers.ConvertFieldResolver(resolve));

            return Parent.ApplyResolvedField<IEnumerable<TReturnType>>(
                ConfigurationContext.Chain<TReturnType>(nameof(Resolve))
                    .Argument(resolve)
                    .OptionalArgument(build),
                this,
                GraphType.MakeListDescriptor(),
                resolver);
        }

        public IUnionableRootField<TExecutionContext> AsUnionOf<TLastElementType>(Action<IInlineObjectBuilder<TLastElementType, TExecutionContext>>? build)
        {
            return And(build);
        }

        public IUnionableRootField<TExecutionContext> And<TLastElementType>(Action<IInlineObjectBuilder<TLastElementType, TExecutionContext>>? build)
        {
            var configurationContext = ConfigurationContext.Chain<TLastElementType>(nameof(And)).OptionalArgument(build);
            var unionField = new UnionQueryField<TExecutionContext>(
                configurationContext,
                Parent,
                Name,
                typeof(TLastElementType),
                UnionMutationField.CreateTypeResolver(build, configurationContext),
                UnionGraphType);
            return ApplyField(unionField);
        }

        public IUnionableRootField<TExecutionContext> AsUnionOf<TEnumerable, TLastElementType>(Action<IInlineObjectBuilder<TLastElementType, TExecutionContext>>? build)
            where TEnumerable : IEnumerable<TLastElementType>
        {
            return And<TEnumerable, TLastElementType>(build);
        }

        public IUnionableRootField<TExecutionContext> And<TEnumerable, TLastElementType>(Action<IInlineObjectBuilder<TLastElementType, TExecutionContext>>? build)
            where TEnumerable : IEnumerable<TLastElementType>
        {
            return And(build);
        }
    }
}