// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System.Diagnostics;
using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.PooledObjects;
 
namespace Microsoft.CodeAnalysis.CSharp
{
    internal sealed partial class LocalRewriter
    {
        public override BoundNode VisitFromEndIndexExpression(BoundFromEndIndexExpression node)
        {
            Debug.Assert(node.MethodOpt != null);
 
            NamedTypeSymbol booleanType = _compilation.GetSpecialType(SpecialType.System_Boolean);
            BoundExpression fromEnd = MakeLiteral(node.Syntax, ConstantValue.Create(true), booleanType);
 
            BoundExpression operand = VisitExpression(node.Operand);
 
            if (NullableNeverHasValue(operand))
            {
                operand = new BoundDefaultExpression(operand.Syntax, operand.Type!.GetNullableUnderlyingType());
            }
 
            operand = NullableAlwaysHasValue(operand) ?? operand;
 
            if (!node.Type.IsNullableType())
            {
                return new BoundObjectCreationExpression(node.Syntax, node.MethodOpt, operand, fromEnd);
            }
 
            ArrayBuilder<BoundExpression> sideeffects = ArrayBuilder<BoundExpression>.GetInstance();
            ArrayBuilder<LocalSymbol> locals = ArrayBuilder<LocalSymbol>.GetInstance();
 
            // operand.HasValue
            operand = CaptureExpressionInTempIfNeeded(operand, sideeffects, locals);
            BoundExpression condition = MakeOptimizedHasValue(operand.Syntax, operand);
 
            // new Index(operand, fromEnd: true)
            BoundExpression boundOperandGetValueOrDefault = MakeOptimizedGetValueOrDefault(operand.Syntax, operand);
            BoundExpression indexCreation = new BoundObjectCreationExpression(node.Syntax, node.MethodOpt, boundOperandGetValueOrDefault, fromEnd);
 
            // new Nullable(new Index(operand, fromEnd: true))
            BoundExpression consequence = ConvertToNullable(node.Syntax, node.Type, indexCreation);
 
            // default
            BoundExpression alternative = new BoundDefaultExpression(node.Syntax, node.Type);
 
            // operand.HasValue ? new Nullable(new Index(operand, fromEnd: true)) : default
            BoundExpression conditionalExpression = RewriteConditionalOperator(
                syntax: node.Syntax,
                rewrittenCondition: condition,
                rewrittenConsequence: consequence,
                rewrittenAlternative: alternative,
                constantValueOpt: null,
                rewrittenType: node.Type,
                isRef: false);
 
            return new BoundSequence(
                syntax: node.Syntax,
                locals: locals.ToImmutableAndFree(),
                sideEffects: sideeffects.ToImmutableAndFree(),
                value: conditionalExpression,
                type: node.Type);
        }
 
        private BoundExpression ConvertToNullable(SyntaxNode syntax, TypeSymbol targetNullableType, BoundExpression underlyingValue)
        {
            Debug.Assert(targetNullableType.IsNullableType());
            Debug.Assert(TypeSymbol.Equals(targetNullableType.GetNullableUnderlyingType(), underlyingValue.Type, TypeCompareKind.AllIgnoreOptions));
 
            if (!TryGetNullableMethod(syntax, targetNullableType, SpecialMember.System_Nullable_T__ctor, out MethodSymbol nullableCtor))
            {
                return BadExpression(syntax, targetNullableType, underlyingValue);
            }
 
            return new BoundObjectCreationExpression(syntax, nullableCtor, underlyingValue);
        }
    }
}