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

#pragma warning disable 618 // CurrencyWrapper is obsolete

using System;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Dynamic;
using System.Linq.Expressions;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace Microsoft.CSharp.RuntimeBinder.ComInterop
{
    internal static class ComBinderHelpers
    {
        internal static bool PreferPut(Type type, bool holdsNull)
        {
            Debug.Assert(type != null);

            if (type.IsValueType
                || type.IsArray
                || type == typeof(string)
                || type == typeof(DBNull)
                || holdsNull
                || type == typeof(System.Reflection.Missing)
                || type == typeof(CurrencyWrapper))
            {
                return true;
            }

            return false;
        }

        internal static bool IsByRef(DynamicMetaObject mo)
        {
            return mo.Expression is ParameterExpression pe && pe.IsByRef;
        }

        [RequiresUnreferencedCode(Binder.TrimmerWarning)]
        internal static bool IsStrongBoxArg(DynamicMetaObject o)
        {
            Type t = o.LimitType;
            return t.IsGenericType && t.GetGenericTypeDefinition() == typeof(StrongBox<>);
        }

        // This helper prepares arguments for COM binding by transforming ByVal StrongBox arguments
        // into ByRef expressions that represent the argument's Value fields.
        [RequiresUnreferencedCode(Binder.TrimmerWarning)]
        internal static bool[] ProcessArgumentsForCom(ref DynamicMetaObject[] args)
        {
            Debug.Assert(args != null);

            DynamicMetaObject[] newArgs = new DynamicMetaObject[args.Length];
            bool[] isByRefArg = new bool[args.Length];

            for (int i = 0; i < args.Length; i++)
            {
                DynamicMetaObject curArgument = args[i];

                // set new arg infos to their original values or set default ones
                // we will do this fixup early so that we can assume we always have
                // arginfos in COM binder.
                if (IsByRef(curArgument))
                {
                    newArgs[i] = curArgument;
                    isByRefArg[i] = true;
                }
                else
                {
                    if (IsStrongBoxArg(curArgument))
                    {
                        BindingRestrictions restrictions = curArgument.Restrictions.Merge(
                            GetTypeRestrictionForDynamicMetaObject(curArgument)
                        );

                        // we have restricted this argument to LimitType so we can convert and conversion will be trivial cast.
                        Expression boxedValueAccessor = Expression.Field(
                            Helpers.Convert(
                                curArgument.Expression,
                                curArgument.LimitType
                            ),
                            curArgument.LimitType.GetField("Value")
                        );

                        IStrongBox value = curArgument.Value as IStrongBox;
                        object boxedValue = value?.Value;

                        newArgs[i] = new DynamicMetaObject(
                            boxedValueAccessor,
                            restrictions,
                            boxedValue
                        );

                        isByRefArg[i] = true;
                    }
                    else
                    {
                        newArgs[i] = curArgument;
                        isByRefArg[i] = false;
                    }
                }
            }

            args = newArgs;
            return isByRefArg;
        }

        internal static BindingRestrictions GetTypeRestrictionForDynamicMetaObject(DynamicMetaObject obj)
        {
            if (obj.Value == null && obj.HasValue)
            {
                //If the meta object holds a null value, create an instance restriction for checking null
                return BindingRestrictions.GetInstanceRestriction(obj.Expression, null);
            }
            return BindingRestrictions.GetTypeRestriction(obj.Expression, obj.LimitType);
        }
    }
}