// 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.Collections.Generic;
using System.Collections.Immutable;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeActions.WorkspaceServices;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.AddMissingReference
{
    internal class AddMissingReferenceCodeAction : CodeAction
    {
        private readonly Project _project;
        private readonly ProjectReference? _projectReferenceToAdd;
        private readonly AssemblyIdentity _missingAssemblyIdentity;
 
        public override string Title { get; }
 
        /// <summary>
        /// This code action only works by adding references.  As such, it requires a non document change (and is
        /// thus restricted in which hosts it can run).
        /// </summary>
        public override ImmutableArray<string> Tags => RequiresNonDocumentChangeTags;
 
        public AddMissingReferenceCodeAction(Project project, string title, ProjectReference? projectReferenceToAdd, AssemblyIdentity missingAssemblyIdentity)
        {
            _project = project;
            Title = title;
            _projectReferenceToAdd = projectReferenceToAdd;
            _missingAssemblyIdentity = missingAssemblyIdentity;
        }
 
        public static async Task<CodeAction> CreateAsync(Project project, AssemblyIdentity missingAssemblyIdentity, CancellationToken cancellationToken)
        {
            var dependencyGraph = project.Solution.GetProjectDependencyGraph();
 
            // We want to find a project that generates this assembly, if one so exists. We therefore 
            // search all projects that our project with an error depends on. We want to do this for
            // complicated and evil scenarios like this one:
            //
            //     C -> B -> A
            //
            //     A'
            //
            // Where, for some insane reason, A and A' are two projects that both emit an assembly 
            // by the same name. So imagine we are using a type in B from C, and we are missing a 
            // reference to A.dll. Both A and A' are candidates, but we know we can throw out A'
            // since whatever type from B we are using that's causing the error, we know that type 
            // isn't referencing A'. Put another way: this code action adds a reference, but should 
            // never change the transitive closure of project references that C has.
            //
            // Doing this filtering also means we get to check less projects (good), and ensures that
            // whatever project reference we end up adding won't add a circularity (also good.)
            foreach (var candidateProjectId in dependencyGraph.GetProjectsThatThisProjectTransitivelyDependsOn(project.Id))
            {
                var candidateProject = project.Solution.GetRequiredProject(candidateProjectId);
                if (candidateProject.SupportsCompilation &&
                    string.Equals(missingAssemblyIdentity.Name, candidateProject.AssemblyName, StringComparison.OrdinalIgnoreCase))
                {
                    // The name matches, so let's see if the full identities are equal. 
                    var compilation = await candidateProject.GetRequiredCompilationAsync(cancellationToken).ConfigureAwait(false);
                    if (missingAssemblyIdentity.Equals(compilation.Assembly.Identity))
                    {
                        // It matches, so just add a reference to this
                        return new AddMissingReferenceCodeAction(project,
                            string.Format(FeaturesResources.Add_project_reference_to_0, candidateProject.Name),
                            new ProjectReference(candidateProjectId), missingAssemblyIdentity);
                    }
                }
            }
 
            // No matching project, so metadata reference
            var description = string.Format(FeaturesResources.Add_reference_to_0, missingAssemblyIdentity.GetDisplayName());
            return new AddMissingReferenceCodeAction(project, description, null, missingAssemblyIdentity);
        }
 
        protected override Task<IEnumerable<CodeActionOperation>> ComputeOperationsAsync(CancellationToken cancellationToken)
        {
            // If we have a project reference to add, then add it
            if (_projectReferenceToAdd != null)
            {
                // note: no need to post process since we are just adding a project reference and not making any code changes.
                return Task.FromResult(SpecializedCollections.SingletonEnumerable<CodeActionOperation>(
                    new ApplyChangesOperation(_project.AddProjectReference(_projectReferenceToAdd).Solution)));
            }
            else
            {
                // We didn't have any project, so we need to try adding a metadata reference
                var factoryService = _project.Solution.Services.GetRequiredService<IAddMetadataReferenceCodeActionOperationFactoryWorkspaceService>();
                var operation = factoryService.CreateAddMetadataReferenceOperation(_project.Id, _missingAssemblyIdentity);
                return Task.FromResult(SpecializedCollections.SingletonEnumerable(operation));
            }
        }
    }
}