// 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.
 
#nullable disable
 
using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Debugging;
using Microsoft.CodeAnalysis.ErrorReporting;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
 
namespace Microsoft.CodeAnalysis.CSharp.Debugging;
 
internal static class DataTipInfoGetter
{
    internal static async Task<DebugDataTipInfo> GetInfoAsync(Document document, int position, CancellationToken cancellationToken)
    {
        try
        {
            var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
            if (root == null)
            {
                return default;
            }
 
            var token = root.FindToken(position);
 
            if (token.Parent is not ExpressionSyntax expression)
            {
                return token.IsKind(SyntaxKind.IdentifierToken)
                    ? new DebugDataTipInfo(token.Span, text: null)
                    : default;
            }
 
            if (expression is LiteralExpressionSyntax)
            {
                // If the user hovers over a literal, give them a DataTip for the type of the literal they're hovering
                // over. Partial semantics should always be sufficient because the (unconverted) type of a literal can
                // always easily be determined.
                document = document.WithFrozenPartialSemantics(cancellationToken);
                var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
                var type = semanticModel.GetTypeInfo(expression, cancellationToken).Type;
                return type == null
                    ? default
                    : new DebugDataTipInfo(expression.Span, type.ToNameDisplayString());
            }
 
            if (expression.IsRightSideOfDotOrArrow())
            {
                var curr = expression.GetRootConditionalAccessExpression() ?? expression;
                if (curr == expression)
                {
                    // NB: Parent.Span, not Span as below.
                    return new DebugDataTipInfo(expression.Parent.Span, text: null);
                }
 
                // NOTE: There may not be an ExpressionSyntax corresponding to the range we want.
                // For example, for input a?.$$B?.C, we want span [|a?.B|]?.C.
                return new DebugDataTipInfo(TextSpan.FromBounds(curr.SpanStart, expression.Span.End), text: null);
            }
 
            // NOTE(cyrusn): This behavior is to mimic what we did in Dev10, I'm not sure if it's
            // necessary or not.
            if (expression is InvocationExpressionSyntax invocation)
            {
                expression = invocation.Expression;
            }
 
            string textOpt = null;
            if (expression is TypeSyntax typeSyntax && typeSyntax.IsVar)
            {
                // If the user is hovering over 'var', then pass back the full type name that 'var'
                // binds to.
                var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
                var type = semanticModel.GetTypeInfo(typeSyntax, cancellationToken).Type;
                if (type != null)
                {
                    textOpt = type.ToNameDisplayString();
                }
            }
 
            return new DebugDataTipInfo(expression.Span, textOpt);
        }
        catch (Exception e) when (FatalError.ReportAndCatchUnlessCanceled(e, cancellationToken))
        {
            return default;
        }
    }
}