﻿// 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.Collections.Generic;
using System.Composition;
using System.Diagnostics;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Highlighting;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.KeywordHighlighting.KeywordHighlighters
{
    [ExportHighlighter(LanguageNames.CSharp), Shared]
    internal class LoopHighlighter : AbstractKeywordHighlighter
    {
        [ImportingConstructor]
        [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
        public LoopHighlighter()
        {
        }

        protected override bool IsHighlightableNode(SyntaxNode node)
            => node.IsContinuableConstruct();

        protected override void AddHighlightsForNode(
            SyntaxNode node, List<TextSpan> spans, CancellationToken cancellationToken)
        {
            switch (node)
            {
                case DoStatementSyntax doStatement:
                    HighlightDoStatement(doStatement, spans);
                    break;
                case ForStatementSyntax forStatement:
                    HighlightForStatement(forStatement, spans);
                    break;
                case CommonForEachStatementSyntax forEachStatement:
                    HighlightForEachStatement(forEachStatement, spans);
                    break;
                case WhileStatementSyntax whileStatement:
                    HighlightWhileStatement(whileStatement, spans);
                    break;
            }

            HighlightRelatedKeywords(node, spans, highlightBreaks: true, highlightContinues: true);
        }

        private static void HighlightDoStatement(DoStatementSyntax statement, List<TextSpan> spans)
        {
            spans.Add(statement.DoKeyword.Span);
            spans.Add(statement.WhileKeyword.Span);
            spans.Add(EmptySpan(statement.SemicolonToken.Span.End));
        }

        private static void HighlightForStatement(ForStatementSyntax statement, List<TextSpan> spans)
            => spans.Add(statement.ForKeyword.Span);

        private static void HighlightForEachStatement(CommonForEachStatementSyntax statement, List<TextSpan> spans)
            => spans.Add(statement.ForEachKeyword.Span);

        private static void HighlightWhileStatement(WhileStatementSyntax statement, List<TextSpan> spans)
            => spans.Add(statement.WhileKeyword.Span);

        /// <summary>
        /// Finds all breaks and continues that are a child of this node, and adds the appropriate spans to the spans list.
        /// </summary>
        private static void HighlightRelatedKeywords(SyntaxNode node, List<TextSpan> spans,
            bool highlightBreaks, bool highlightContinues)
        {
            Debug.Assert(highlightBreaks || highlightContinues);

            if (highlightBreaks && node is BreakStatementSyntax breakStatement)
            {
                spans.Add(breakStatement.BreakKeyword.Span);
                spans.Add(EmptySpan(breakStatement.SemicolonToken.Span.End));
            }
            else if (highlightContinues && node is ContinueStatementSyntax continueStatement)
            {
                spans.Add(continueStatement.ContinueKeyword.Span);
                spans.Add(EmptySpan(continueStatement.SemicolonToken.Span.End));
            }
            else
            {
                foreach (var child in node.ChildNodes())
                {
                    var highlightBreaksForChild = highlightBreaks && !child.IsBreakableConstruct();
                    var highlightContinuesForChild = highlightContinues && !child.IsContinuableConstruct();

                    // Only recurse if we have anything to do
                    if (highlightBreaksForChild || highlightContinuesForChild)
                    {
                        HighlightRelatedKeywords(child, spans, highlightBreaksForChild, highlightContinuesForChild);
                    }
                }
            }
        }
    }
}
