using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Semmle.Extraction.CSharp.Populators;

namespace Semmle.Extraction.CSharp.Entities
{
    internal class NamedType : Type<INamedTypeSymbol>
    {
        private NamedType(Context cx, INamedTypeSymbol init, bool constructUnderlyingTupleType)
            : base(cx, init)
        {
            typeArgumentsLazy = new Lazy<Type[]>(() => Symbol.TypeArguments.Select(t => Create(cx, t)).ToArray());
            this.constructUnderlyingTupleType = constructUnderlyingTupleType;
        }

        public static NamedType Create(Context cx, INamedTypeSymbol type) =>
            NamedTypeFactory.Instance.CreateEntityFromSymbol(cx, type);

        /// <summary>
        /// Creates a named type entity from a tuple type. Unlike <see cref="Create"/>, this
        /// will create an entity for the underlying `System.ValueTuple` struct.
        /// For example, `(int, string)` will result in an entity for `System.ValueTuple&lt;int, string&gt;`.
        /// </summary>
        public static NamedType CreateNamedTypeFromTupleType(Context cx, INamedTypeSymbol type) =>
            UnderlyingTupleTypeFactory.Instance.CreateEntity(cx, (new SymbolEqualityWrapper(type), typeof(TupleType)), type);

        public override bool NeedsPopulation => base.NeedsPopulation || Symbol.TypeKind == TypeKind.Error;

        public override void Populate(TextWriter trapFile)
        {
            if (Symbol.TypeKind == TypeKind.Error)
            {
                UnknownType.Create(Context); // make sure this exists so we can use it in `TypeRef::getReferencedType`
                Context.ExtractionContext.MissingType(Symbol.ToString()!, Context.FromSource);
                return;
            }

            if (UsesTypeRef)
                trapFile.typeref_type((NamedTypeRef)TypeRef, this);

            if (Symbol.IsGenericType)
            {
                if (Symbol.IsBoundNullable())
                {
                    // An instance of Nullable<T>
                    trapFile.nullable_underlying_type(this, TypeArguments[0].TypeRef);
                }
                else if (Symbol.IsReallyUnbound())
                {
                    for (var i = 0; i < Symbol.TypeParameters.Length; ++i)
                    {
                        TypeParameter.Create(Context, Symbol.TypeParameters[i]);
                        var param = Symbol.TypeParameters[i];
                        var typeParameter = TypeParameter.Create(Context, param);
                        trapFile.type_parameters(typeParameter, i, this);
                    }
                }
                else
                {
                    var unbound = constructUnderlyingTupleType
                        ? CreateNamedTypeFromTupleType(Context, Symbol.ConstructedFrom)
                        : Type.Create(Context, Symbol.ConstructedFrom);
                    trapFile.constructed_generic(this, unbound.TypeRef);

                    for (var i = 0; i < TypeArguments.Length; ++i)
                    {
                        trapFile.type_arguments(TypeArguments[i].TypeRef, i, this);
                    }
                }
            }

            PopulateType(trapFile, constructUnderlyingTupleType);

            if (Symbol.EnumUnderlyingType is not null)
            {
                trapFile.enum_underlying_type(this, Type.Create(Context, Symbol.EnumUnderlyingType).TypeRef);
            }

            // Class location
            if (!Symbol.IsGenericType || Symbol.IsReallyUnbound())
            {
                foreach (var l in Locations)
                    trapFile.type_location(this, l);
            }

            if (Symbol.IsAnonymousType)
            {
                trapFile.anonymous_types(this);
            }
        }

        private readonly Lazy<Type[]> typeArgumentsLazy;
        private readonly bool constructUnderlyingTupleType;

        public Type[] TypeArguments => typeArgumentsLazy.Value;

        public override IEnumerable<Type> TypeMentions => TypeArguments;

        public override IEnumerable<Location> Locations
        {
            get
            {
                foreach (var l in GetLocations(Symbol))
                    yield return Context.CreateLocation(l);

                if (Symbol.DeclaringSyntaxReferences.Any())
                    yield return Assembly.CreateOutputAssembly(Context);
            }
        }

        private static IEnumerable<Microsoft.CodeAnalysis.Location> GetLocations(INamedTypeSymbol type)
        {
            return type.Locations
                .Where(l => l.IsInMetadata)
                .Concat(type.DeclaringSyntaxReferences
                    .Select(loc => loc.GetSyntax())
                    .OfType<CSharpSyntaxNode>()
                    .Select(l => l.FixedLocation())
                );
        }

        public override Microsoft.CodeAnalysis.Location? ReportingLocation => GetLocations(Symbol).BestOrDefault();

        private bool IsAnonymousType() => Symbol.IsAnonymousType || Symbol.Name.Contains("__AnonymousType");

        public override void WriteId(EscapingTextWriter trapFile)
        {
            if (IsAnonymousType())
            {
                trapFile.Write('*');
            }
            else
            {
                Symbol.BuildTypeId(Context, trapFile, Symbol, constructUnderlyingTupleType);
                trapFile.Write(";type");
            }
        }

        public sealed override void WriteQuotedId(EscapingTextWriter trapFile)
        {
            if (IsAnonymousType())
                trapFile.Write('*');
            else
                base.WriteQuotedId(trapFile);
        }

        private class NamedTypeFactory : CachedEntityFactory<INamedTypeSymbol, NamedType>
        {
            public static NamedTypeFactory Instance { get; } = new NamedTypeFactory();

            public override NamedType Create(Context cx, INamedTypeSymbol init) => new NamedType(cx, init, false);
        }

        private class UnderlyingTupleTypeFactory : CachedEntityFactory<INamedTypeSymbol, NamedType>
        {
            public static UnderlyingTupleTypeFactory Instance { get; } = new UnderlyingTupleTypeFactory();

            public override NamedType Create(Context cx, INamedTypeSymbol init) => new NamedType(cx, init, true);
        }

        // Do not create typerefs of constructed generics as they are always in the current trap file.
        // Create typerefs for constructed error types in case they are fully defined elsewhere.
        // We cannot use `!this.NeedsPopulation` because this would not be stable as it would depend on
        // the assembly that was being extracted at the time.
        private bool UsesTypeRef =>
            Symbol.TypeKind == TypeKind.Error ||
            SymbolEqualityComparer.Default.Equals(Symbol.OriginalDefinition, Symbol);

        public override Type TypeRef => UsesTypeRef ? (Type)NamedTypeRef.Create(Context, Symbol) : this;
    }

    internal class NamedTypeRef : Type<INamedTypeSymbol>
    {
        private readonly Type referencedType;

        public NamedTypeRef(Context cx, INamedTypeSymbol symbol) : base(cx, symbol)
        {
            referencedType = Type.Create(cx, symbol);
        }

        public static NamedTypeRef Create(Context cx, INamedTypeSymbol type) =>
            // We need to use a different cache key than `type` to avoid mixing up
            // `NamedType`s and `NamedTypeRef`s
            NamedTypeRefFactory.Instance.CreateEntity(cx, (typeof(NamedTypeRef), new SymbolEqualityWrapper(type)), type);

        private class NamedTypeRefFactory : CachedEntityFactory<INamedTypeSymbol, NamedTypeRef>
        {
            public static NamedTypeRefFactory Instance { get; } = new NamedTypeRefFactory();

            public override NamedTypeRef Create(Context cx, INamedTypeSymbol init) => new NamedTypeRef(cx, init);
        }

        public override bool NeedsPopulation => true;

        public override void WriteId(EscapingTextWriter trapFile)
        {
            trapFile.WriteSubId(referencedType);
            trapFile.Write(";typeRef");
        }

        public override void Populate(TextWriter trapFile)
        {
            trapFile.typerefs(this, Symbol.Name);
        }
    }
}
