// 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.Collections.Immutable;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis.CodeStyle;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.LanguageService;

namespace Microsoft.CodeAnalysis.NewLines.ConsecutiveStatementPlacement
{
    internal abstract class AbstractConsecutiveStatementPlacementDiagnosticAnalyzer<TExecutableStatementSyntax>
        : AbstractBuiltInCodeStyleDiagnosticAnalyzer
        where TExecutableStatementSyntax : SyntaxNode
    {
        private readonly ISyntaxFacts _syntaxFacts;

        protected AbstractConsecutiveStatementPlacementDiagnosticAnalyzer(ISyntaxFacts syntaxFacts)
            : base(IDEDiagnosticIds.ConsecutiveStatementPlacementDiagnosticId,
                   EnforceOnBuildValues.ConsecutiveStatementPlacement,
                   CodeStyleOptions2.AllowStatementImmediatelyAfterBlock,
                   new LocalizableResourceString(
                       nameof(AnalyzersResources.Blank_line_required_between_block_and_subsequent_statement), AnalyzersResources.ResourceManager, typeof(AnalyzersResources)))
        {
            _syntaxFacts = syntaxFacts;
        }

        protected abstract bool IsBlockLikeStatement(SyntaxNode node);
        protected abstract Location GetDiagnosticLocation(SyntaxNode block);

        public sealed override DiagnosticAnalyzerCategory GetAnalyzerCategory()
            => DiagnosticAnalyzerCategory.SyntaxTreeWithoutSemanticsAnalysis;

        protected sealed override void InitializeWorker(AnalysisContext context)
            => context.RegisterSyntaxTreeAction(AnalyzeSyntaxTree);

        private void AnalyzeSyntaxTree(SyntaxTreeAnalysisContext context)
        {
            var option = context.GetAnalyzerOptions().AllowStatementImmediatelyAfterBlock;
            if (option.Value)
                return;

            Recurse(context, option.Notification.Severity, context.GetAnalysisRoot(findInTrivia: false), context.CancellationToken);
        }

        private void Recurse(SyntaxTreeAnalysisContext context, ReportDiagnostic severity, SyntaxNode node, CancellationToken cancellationToken)
        {
            if (node.ContainsDiagnostics && node.GetDiagnostics().Any(d => d.Severity == DiagnosticSeverity.Error))
                return;

            if (IsBlockLikeStatement(node))
                ProcessBlockLikeStatement(context, severity, node);

            foreach (var child in node.ChildNodesAndTokens())
            {
                if (!context.ShouldAnalyzeSpan(child.FullSpan))
                    continue;

                if (child.IsNode)
                    Recurse(context, severity, child.AsNode()!, cancellationToken);
            }
        }

        private void ProcessBlockLikeStatement(SyntaxTreeAnalysisContext context, ReportDiagnostic severity, SyntaxNode block)
        {
            // Don't examine broken blocks.
            var endToken = block.GetLastToken();
            if (endToken.IsMissing)
                return;

            // If the close brace itself doesn't have a newline, then ignore this.  This is a case of series of
            // statements on the same line.
            if (!endToken.TrailingTrivia.Any())
                return;

            if (!_syntaxFacts.IsEndOfLineTrivia(endToken.TrailingTrivia.Last()))
                return;

            // Grab whatever comes after the close brace.  If it's not the start of a statement, ignore it.
            var nextToken = endToken.GetNextToken();
            var nextTokenContainingStatement = nextToken.Parent?.FirstAncestorOrSelf<TExecutableStatementSyntax>();
            if (nextTokenContainingStatement == null)
                return;

            if (nextToken != nextTokenContainingStatement.GetFirstToken())
                return;

            // There has to be at least a blank line between the end of the block and the start of the next statement.

            foreach (var trivia in nextToken.LeadingTrivia)
            {
                // If there's a blank line between the brace and the next token, we're all set.
                if (_syntaxFacts.IsEndOfLineTrivia(trivia))
                    return;

                if (_syntaxFacts.IsWhitespaceTrivia(trivia))
                    continue;

                // got something that wasn't whitespace.  Bail out as we don't want to place any restrictions on this code.
                return;
            }

            context.ReportDiagnostic(DiagnosticHelper.Create(
                this.Descriptor,
                GetDiagnosticLocation(block),
                severity,
                additionalLocations: ImmutableArray.Create(nextToken.GetLocation()),
                properties: null));
        }
    }
}
