// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Immutable;
using System.Linq;
using Analyzer.Utilities;
using Analyzer.Utilities.Extensions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Operations;

namespace Microsoft.NetCore.Analyzers.Tasks
{
    using static MicrosoftNetCoreAnalyzersResources;

    /// <summary>
    /// CA2008: <inheritdoc cref="DoNotCreateTasksWithoutPassingATaskSchedulerTitle"/>
    /// </summary>
    [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
    public sealed class DoNotCreateTasksWithoutPassingATaskSchedulerAnalyzer : DiagnosticAnalyzer
    {
        internal const string RuleId = "CA2008";

        internal static readonly DiagnosticDescriptor Rule = DiagnosticDescriptorHelper.Create(
            RuleId,
            CreateLocalizableResourceString(nameof(DoNotCreateTasksWithoutPassingATaskSchedulerTitle)),
            CreateLocalizableResourceString(nameof(DoNotCreateTasksWithoutPassingATaskSchedulerMessage)),
            DiagnosticCategory.Reliability,
            RuleLevel.CandidateForRemoval,     // Superseded by VS threading analyzers
            description: CreateLocalizableResourceString(nameof(DoNotCreateTasksWithoutPassingATaskSchedulerDescription)),
            isPortedFxCopRule: false,
            isDataflowRule: false);

        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(Rule);

        public sealed override void Initialize(AnalysisContext context)
        {
            context.EnableConcurrentExecution();
            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);

            context.RegisterCompilationStartAction(compilationContext =>
            {
                // Check if TPL is available before actually doing the searches
                var taskType = compilationContext.Compilation.GetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemThreadingTasksTask);
                var taskFactoryType = compilationContext.Compilation.GetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemThreadingTasksTaskFactory);
                var taskSchedulerType = compilationContext.Compilation.GetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemThreadingTasksTaskScheduler);
                if (taskType == null || taskFactoryType == null || taskSchedulerType == null)
                {
                    return;
                }

                compilationContext.RegisterOperationAction(operationContext =>
                {
                    var invocation = (IInvocationOperation)operationContext.Operation;
                    if (invocation.TargetMethod == null)
                    {
                        return;
                    }

                    if (!IsMethodOfInterest(invocation.TargetMethod, taskType, taskFactoryType))
                    {
                        return;
                    }

                    // We want to ensure that all overloads called are explicitly taking a task scheduler
                    if (invocation.TargetMethod.Parameters.Any(p => p.Type.Equals(taskSchedulerType)))
                    {
                        return;
                    }

                    operationContext.ReportDiagnostic(invocation.CreateDiagnostic(Rule, invocation.TargetMethod.Name));
                }, OperationKind.Invocation);
            });
        }

        private static bool IsMethodOfInterest(IMethodSymbol methodSymbol, INamedTypeSymbol taskType, INamedTypeSymbol taskFactoryType)
        {
            // Check if it's a method of Task or a derived type (for Task<T>)
            if ((taskType.Equals(methodSymbol.ContainingType) ||
                 taskType.Equals(methodSymbol.ContainingType.BaseType)) &&
                methodSymbol.Name == "ContinueWith")
            {
                return true;
            }

            if (methodSymbol.ContainingType.Equals(taskFactoryType) &&
                methodSymbol.Name == "StartNew")
            {
                return true;
            }

            return false;
        }
    }
}