Add dotnet nuget why command

src/NuGet.Core/NuGet.CommandLine.XPlat/Commands/WhyCommand/DependencyGraphFinder.cs

@@ -0,0 +1,300 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+#nullable enable
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using NuGet.ProjectModel;
+
+namespace NuGet.CommandLine.XPlat
+{
+    internal static class DependencyGraphFinder
+    {
+        /// <summary>
+        /// Finds all dependency graphs for a given project.
+        /// </summary>
+        /// <param name="assetsFile">Assets file for the project.</param>
+        /// <param name="targetPackage">The package we want the dependency paths for.</param>
+        /// <param name="userInputFrameworks">List of target framework aliases.</param>
+        /// <returns>
+        /// Dictionary mapping target framework aliases to their respective dependency graphs.
+        /// Returns null if the project does not have a dependency on the target package.
+        /// </returns>
+        public static Dictionary<string, List<DependencyNode>?>? GetAllDependencyGraphsForTarget(
+            LockFile assetsFile,
+            string targetPackage,
+            List<string> userInputFrameworks)
+        {
+            var dependencyGraphPerFramework = new Dictionary<string, List<DependencyNode>?>(assetsFile.Targets.Count);
+            bool doesProjectHaveDependencyOnPackage = false;
+
+            // get all top-level package and project references for the project, categorized by target framework alias
+            Dictionary<string, List<string>> topLevelReferencesByFramework = GetTopLevelPackageAndProjectReferences(assetsFile, userInputFrameworks);
+
+            if (topLevelReferencesByFramework.Count > 0)
+            {
+                foreach (var (targetFrameworkAlias, topLevelReferences) in topLevelReferencesByFramework)
+                {
+                    LockFileTarget? target = assetsFile.GetTarget(targetFrameworkAlias, runtimeIdentifier: null);
+
+                    // get all package libraries for the framework
+                    IList<LockFileTargetLibrary>? packageLibraries = target?.Libraries;
+
+                    // if the project has a dependency on the target package, get the dependency graph
+                    if (packageLibraries?.Any(l => l?.Name?.Equals(targetPackage, StringComparison.OrdinalIgnoreCase) == true) == true)
+                    {
+                        doesProjectHaveDependencyOnPackage = true;
+                        dependencyGraphPerFramework.Add(targetFrameworkAlias,
+                                                        GetDependencyGraphForTargetPerFramework(topLevelReferences, packageLibraries, targetPackage));
+                    }
+                    else
+                    {
+                        dependencyGraphPerFramework.Add(targetFrameworkAlias, null);
+                    }
+                }
+            }
+
+            return doesProjectHaveDependencyOnPackage
+                ? dependencyGraphPerFramework
+                : null;
+        }
+
+        /// <summary>
+        /// Finds all dependency paths from the top-level packages to the target package for a given framework.
+        /// </summary>
+        /// <param name="topLevelReferences">All top-level package and project references for the framework.</param>
+        /// <param name="packageLibraries">All package libraries for the framework.</param>
+        /// <param name="targetPackage">The package we want the dependency paths for.</param>
+        /// <returns>
+        /// List of all top-level package nodes in the dependency graph.
+        /// </returns>
+        private static List<DependencyNode>? GetDependencyGraphForTargetPerFramework(
+            List<string> topLevelReferences,
+            IList<LockFileTargetLibrary> packageLibraries,
+            string targetPackage)
+        {
+            List<DependencyNode>? dependencyGraph = null;
+
+            // hashset tracking every package node that we've traversed
+            var visited = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            // dictionary tracking all package nodes that have been added to the graph, mapped to their DependencyNode objects
+            var dependencyNodes = new Dictionary<string, DependencyNode>(StringComparer.OrdinalIgnoreCase);
+            // dictionary mapping all packageIds to their resolved version
+            Dictionary<string, string> versions = GetAllResolvedVersions(packageLibraries);
+
+            foreach (var topLevelReference in topLevelReferences)
+            {
+                // use depth-first search to find dependency paths from the top-level package to the target package
+                DependencyNode? topLevelNode = FindDependencyPathForTarget(topLevelReference, packageLibraries, visited, dependencyNodes, versions, targetPackage);
+
+                if (topLevelNode != null)
+                {
+                    dependencyGraph ??= [];
+                    dependencyGraph.Add(topLevelNode);
+                }
+            }
+
+            return dependencyGraph;
+        }
+
+        /// <summary>
+        /// Traverses the dependency graph for a given top-level package, looking for a path to the target package.
+        /// </summary>
+        /// <param name="topLevelPackage">Top-level package.</param>
+        /// <param name="packageLibraries">All package libraries for a given framework.</param>
+        /// <param name="visited">HashSet tracking every package node that we've traversed.</param>
+        /// <param name="dependencyNodes">Dictionary tracking all packageIds that were added to the graph, mapped to their DependencyNode objects.</param>
+        /// <param name="versions">Dictionary mapping packageIds to their resolved versions.</param>
+        /// <param name="targetPackage">The package we want the dependency paths for.</param>
+        /// <returns>
+        /// The top-level package node in the dependency graph (if a path was found), or null (if no path was found).
+        /// </returns>
+        private static DependencyNode? FindDependencyPathForTarget(
+            string topLevelPackage,
+            IList<LockFileTargetLibrary> packageLibraries,
+            HashSet<string> visited,
+            Dictionary<string, DependencyNode> dependencyNodes,
+            Dictionary<string, string> versions,
+            string targetPackage)
+        {
+            var stack = new Stack<StackDependencyData>();
+            stack.Push(new StackDependencyData(topLevelPackage, null));
+
+            while (stack.Count > 0)
+            {
+                var currentPackageData = stack.Pop();
+                var currentPackageId = currentPackageData.Id;
+
+                // if we reach the target node, or if we've already traversed this node and found dependency paths, add it to the graph
+                if (currentPackageId.Equals(targetPackage, StringComparison.OrdinalIgnoreCase)
+                    || dependencyNodes.ContainsKey(currentPackageId))
+                {
+                    AddToGraph(currentPackageData, dependencyNodes, versions);
+                    continue;
+                }
+
+                // if we have already traversed this node's children, continue
+                if (visited.Contains(currentPackageId))
+                {
+                    continue;
+                }
+
+                visited.Add(currentPackageId);
+
+                // get all dependencies for the current package
+                var dependencies = packageLibraries?.FirstOrDefault(i => i?.Name?.Equals(currentPackageId, StringComparison.OrdinalIgnoreCase) == true)?.Dependencies;
+
+                if (dependencies?.Count > 0)
+                {
+                    // push all the dependencies onto the stack
+                    foreach (var dependency in dependencies)
+                    {
+                        stack.Push(new StackDependencyData(dependency.Id, currentPackageData));
+                    }
+                }
+            }
+
+            return dependencyNodes.ContainsKey(topLevelPackage)
+                ? dependencyNodes[topLevelPackage]
+                : null;
+        }
+
+        /// <summary>
+        /// Adds a dependency path to the graph, starting from the target package and traversing up to the top-level package.
+        /// </summary>
+        /// <param name="targetPackageData">Target node data. This stores parent references, so it can be used to construct the dependency graph
+        /// up to the top-level package.</param>
+        /// <param name="dependencyNodes">Dictionary tracking all packageIds that were added to the graph, mapped to their DependencyNode objects.</param>
+        /// <param name="versions">Dictionary mapping packageIds to their resolved versions.</param>
+        private static void AddToGraph(
+            StackDependencyData targetPackageData,
+            Dictionary<string, DependencyNode> dependencyNodes,
+            Dictionary<string, string> versions)
+        {
+            // first, we traverse the target's parents, listing the packages in the path from the target to the top-level package
+            var dependencyPath = new List<string> { targetPackageData.Id };
+            StackDependencyData? current = targetPackageData.Parent;
+
+            while (current != null)
+            {
+                dependencyPath.Add(current.Id);
+                current = current.Parent;
+            }
+
+            // then, we traverse this list from the target package to the top-level package, initializing/updating their dependency nodes as needed
+            for (int i = 0; i < dependencyPath.Count; i++)
+            {
+                string currentPackageId = dependencyPath[i];
+
+                if (!dependencyNodes.ContainsKey(currentPackageId))
+                {
+                    dependencyNodes.Add(currentPackageId, new DependencyNode(currentPackageId, versions[currentPackageId]));
+                }
+
+                if (i > 0)
+                {
+                    var childNode = dependencyNodes[dependencyPath[i - 1]];
+                    dependencyNodes[currentPackageId].Children.Add(childNode);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Get all top-level package and project references for the given project.
+        /// </summary>
+        /// <param name="assetsFile">Assets file for the project.</param>
+        /// <param name="userInputFrameworks">List of target framework aliases.</param>
+        /// <returns>
+        /// Dictionary mapping the project's target framework aliases to their respective top-level package and project references.
+        /// </returns>
+        private static Dictionary<string, List<string>> GetTopLevelPackageAndProjectReferences(
+            LockFile assetsFile,
+            List<string> userInputFrameworks)
+        {
+            var topLevelReferences = new Dictionary<string, List<string>>();
+
+            var targetAliases = assetsFile.PackageSpec.RestoreMetadata.OriginalTargetFrameworks;
+
+            // filter the targets to the set of targets that the user has specified
+            if (userInputFrameworks?.Count > 0)
+            {
+                targetAliases = targetAliases.Where(f => userInputFrameworks.Contains(f)).ToList();
+            }
+
+            // we need to match top-level project references to their target library entries using their paths,
+            // so we will store all project reference paths in a dictionary here
+            var projectLibraries = assetsFile.Libraries.Where(l => l.Type == "project");
+            var projectLibraryPathToName = new Dictionary<string, string>(projectLibraries.Count());
+            var projectDirectoryPath = Path.GetDirectoryName(assetsFile.PackageSpec.FilePath);
+
+            if (projectDirectoryPath != null)
+            {
+                foreach (var library in projectLibraries)
+                {
+                    projectLibraryPathToName.Add(Path.GetFullPath(library.Path, projectDirectoryPath), library.Name);
+                }
+            }
+
+            // get all top-level references for each target alias
+            foreach (string targetAlias in targetAliases)
+            {
+                topLevelReferences.Add(targetAlias, []);
+
+                // top-level packages
+                TargetFrameworkInformation? targetFrameworkInformation = assetsFile.PackageSpec.TargetFrameworks.FirstOrDefault(tfi => tfi.TargetAlias.Equals(targetAlias, StringComparison.OrdinalIgnoreCase));
+                if (targetFrameworkInformation != default)
+                {
+                    var topLevelPackages = targetFrameworkInformation.Dependencies.Select(d => d.Name);
+                    topLevelReferences[targetAlias].AddRange(topLevelPackages);
+                }
+
+                // top-level projects
+                ProjectRestoreMetadataFrameworkInfo? restoreMetadataFrameworkInfo = assetsFile.PackageSpec.RestoreMetadata.TargetFrameworks.FirstOrDefault(tfi => tfi.TargetAlias.Equals(targetAlias, StringComparison.OrdinalIgnoreCase));
+                if (restoreMetadataFrameworkInfo != default)
+                {
+                    var topLevelProjectPaths = restoreMetadataFrameworkInfo.ProjectReferences.Select(p => p.ProjectPath);
+                    foreach (var projectPath in topLevelProjectPaths)
+                    {
+                        topLevelReferences[targetAlias].Add(projectLibraryPathToName[projectPath]);
+                    }
+                }
+            }
+
+            return topLevelReferences;
+        }
+
+        /// <summary>
+        /// Adds all resolved versions of packages to a dictionary.
+        /// </summary>
+        /// <param name="packageLibraries">All package libraries for a given framework.</param>
+        private static Dictionary<string, string> GetAllResolvedVersions(IList<LockFileTargetLibrary> packageLibraries)
+        {
+            var versions = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+
+            foreach (var package in packageLibraries)
+            {
+                if (package?.Name != null && package?.Version != null)
+                {
+                    versions.Add(package.Name, package.Version.ToNormalizedString());
+                }
+            }
+
+            return versions;
+        }
+
+        private class StackDependencyData
+        {
+            public string Id { get; set; }
+            public StackDependencyData? Parent { get; set; }
+
+            public StackDependencyData(string currentId, StackDependencyData? parentDependencyData)
+            {
+                Id = currentId;
+                Parent = parentDependencyData;
+            }
+        }
+    }
+}