// 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;
using System.Composition;
using System.Threading;
using Microsoft.CodeAnalysis.BraceCompletion;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.BraceCompletion;

/// <summary>
/// Brace completion service used for completing curly braces inside interpolated strings.
/// In other curly brace completion scenarios the <see cref="CurlyBraceCompletionService"/> should be used.
/// </summary>
[ExportBraceCompletionService(LanguageNames.CSharp), Shared]
[method: ImportingConstructor]
[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
internal sealed class InterpolationBraceCompletionService() : AbstractCSharpBraceCompletionService
{
    protected override char OpeningBrace => CurlyBrace.OpenCharacter;
    protected override char ClosingBrace => CurlyBrace.CloseCharacter;

    public override bool AllowOverType(BraceCompletionContext context, CancellationToken cancellationToken)
        => AllowOverTypeWithValidClosingToken(context);

    /// <summary>
    /// Only return this service as valid when we're typing curly braces inside an interpolated string.
    /// Otherwise curly braces should be completed using the <see cref="CurlyBraceCompletionService"/>
    /// </summary>
    public override bool CanProvideBraceCompletion(char brace, int openingPosition, ParsedDocument document, CancellationToken cancellationToken)
        => OpeningBrace == brace && IsPositionInInterpolationContext(document, openingPosition);

    protected override bool IsValidOpenBraceTokenAtPosition(SourceText text, SyntaxToken token, int position)
        => IsValidOpeningBraceToken(token) && token.SpanStart == position;

    protected override bool IsValidOpeningBraceToken(SyntaxToken token)
        => token.IsKind(SyntaxKind.OpenBraceToken) && token.Parent.IsKind(SyntaxKind.Interpolation);

    protected override bool IsValidClosingBraceToken(SyntaxToken token)
        => token.IsKind(SyntaxKind.CloseBraceToken);

    /// <summary>
    /// Returns true when the input position could be starting an interpolation expression if a curly brace was typed.
    /// </summary>
    public static bool IsPositionInInterpolationContext(ParsedDocument document, int position)
    {
        // First, check to see if the character to the left of the position is an open curly.
        // If it is, we shouldn't complete because the user may be trying to escape a curly.
        // E.g. they are trying to type $"{{"
        if (CouldEscapePreviousOpenBrace('{', position, document.Text))
        {
            return false;
        }

        var token = document.Root.FindTokenOnLeftOfPosition(position);
        if (!token.Span.IntersectsWith(position))
        {
            return false;
        }

        // We can be starting an interpolation expression if we're inside an interpolated string.
        return token.Parent.IsKind(SyntaxKind.InterpolatedStringExpression) || token.Parent.IsParentKind(SyntaxKind.InterpolatedStringExpression);
    }
}