// 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.Generic;
using System.Collections.Immutable;
using System.IO;
using System.Linq;
using Microsoft.CodeAnalysis.Collections;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.UnusedReferences.ProjectAssets;

// This class will read the dependency heirarchy from the project.assets.json file. The format of this file
// is subject to change and in the future this information will be provided by an API.  See https://github.com/dotnet/roslyn/issues/50054
internal static partial class ProjectAssetsReader
{
    // NuGet will include entries to keep empty folders from being removed. These entries can be ignored.
    private const string NuGetEmptyFileName = "_._";

    /// <summary>
    /// Enhances references with the assemblies they bring into the compilation and their dependency hierarchy.
    /// </summary>
    public static ImmutableArray<ReferenceInfo> AddDependencyHierarchies(
        ImmutableArray<ReferenceInfo> projectReferences,
        ProjectAssetsFile? projectAssets)
    {
        if (projectAssets is null ||
            projectAssets.Version != 3)
        {
            return [];
        }

        if (projectAssets.Targets is null ||
            projectAssets.Targets.Count == 0)
        {
            return [];
        }

        if (projectAssets.Libraries is null ||
            projectAssets.Libraries.Count == 0)
        {
            return [];
        }

        // We keep a list of references that were automatically added by SDKs or other sources so that we can ignore them
        // since they can't be removed even if they were unused.
        var autoReferences = projectAssets.Project?.Frameworks?.Values
            .Where(framework => framework.Dependencies != null)
            .SelectMany(framework => framework.Dependencies!.Keys.Where(key => framework.Dependencies[key].AutoReferenced))
            .Distinct()
            .ToImmutableHashSet();
        autoReferences ??= [];

        // Targets contain a hashmap of Libraries keyed by `{LibraryName}/{LibraryVersion}` we need to split these keys
        // and create a mapping of LibraryName to the complete library key.
        var targetLibraryKeys = projectAssets.Targets
            .ToImmutableDictionary(t => t.Key, t => t.Value.ToImmutableDictionary(l => l.Key.Split('/')[0], l => l.Key));

        var builtReferences = new Dictionary<string, ReferenceInfo?>();

        var references = projectReferences
            .Select(projectReference => EnhanceReference(projectAssets, projectReference, autoReferences, targetLibraryKeys, builtReferences))
            .WhereNotNull()
            .ToImmutableArray();

        return references;
    }

    private static ReferenceInfo? EnhanceReference(
        ProjectAssetsFile projectAssets,
        ReferenceInfo referenceInfo,
        ImmutableHashSet<string> autoReferences,
        ImmutableDictionary<string, ImmutableDictionary<string, string>> targetLibraryKeys,
        Dictionary<string, ReferenceInfo?> builtReferences)
    {
        var referenceName = referenceInfo.ReferenceType == ReferenceType.Project
            ? Path.GetFileNameWithoutExtension(referenceInfo.ItemSpecification)
            : referenceInfo.ItemSpecification;

        if (autoReferences.Contains(referenceName))
        {
            return null;
        }

        var reference = BuildReference(projectAssets, referenceName, referenceInfo.TreatAsUsed, targetLibraryKeys, builtReferences);

        // Since the reference being enhanced was provided by the Project System we should always return an
        // enhanced reference with its original ItemSpecification. The project assets file typically works with
        // full paths, however project reference typically are relative. This ensures that when changes are
        // persisted back by the Project System, it will match the specification it is expecting.
        return reference?.WithItemSpecification(referenceInfo.ItemSpecification);
    }

    private static ReferenceInfo? BuildReference(
        ProjectAssetsFile projectAssets,
        string referenceName,
        bool treatAsUsed,
        ImmutableDictionary<string, ImmutableDictionary<string, string>> targetLibraryKeys,
        Dictionary<string, ReferenceInfo?> builtReferences)
    {
        var dependencyNames = new HashSet<string>();
        var compilationAssemblies = ImmutableArray.CreateBuilder<string>();
        var referenceType = ReferenceType.Unknown;
        var itemSpecification = referenceName;

        var packagesPath = projectAssets.Project?.Restore?.PackagesPath ?? string.Empty;

        RoslynDebug.AssertNotNull(projectAssets.Targets);
        RoslynDebug.AssertNotNull(projectAssets.Libraries);

        foreach (var (targetName, libraryKeys) in targetLibraryKeys)
        {
            if (!libraryKeys.TryGetValue(referenceName, out var key) ||
                !projectAssets.Libraries.TryGetValue(key, out var library))
            {
                continue;
            }

            var target = projectAssets.Targets[targetName];
            var targetLibrary = target[key];

            referenceType = targetLibrary.Type switch
            {
                "package" => ReferenceType.Package,
                "project" => ReferenceType.Project,
                _ => ReferenceType.Assembly
            };

            if (referenceType == ReferenceType.Project &&
                library.Path is not null)
            {
                // Project references are keyed by their filename but the
                // item specification should be the path to the project file
                // with Windows-style directory separators.
                itemSpecification = library.Path.Replace('/', '\\');
            }

            if (targetLibrary.Dependencies != null)
            {
                dependencyNames.AddRange(targetLibrary.Dependencies.Keys);
            }

            if (targetLibrary.Compile != null)
            {
                foreach (var assemblyPath in targetLibrary.Compile.Keys)
                {
                    if (!assemblyPath.EndsWith(NuGetEmptyFileName))
                    {
                        compilationAssemblies.Add(Path.GetFullPath(Path.Combine(packagesPath, library.Path ?? "", assemblyPath)));
                    }
                }
            }
        }

        if (referenceType == ReferenceType.Unknown)
        {
            return null;
        }

        if (referenceType == ReferenceType.Package && itemSpecification == ".NETStandard.Library")
        {
            // Referencing .NETStandard.Library brings along references to a number of common .NET libraries
            // for which the .NET SDK already brings into the compilation. This makes it very easy for
            // the parent reference to be considered transitively used.
            return null;
        }

        if (builtReferences.TryGetValue(itemSpecification, out var builtReference))
        {
            return builtReference;
        }

        var dependencies = dependencyNames
            .Select(dependency => BuildReference(projectAssets, dependency, treatAsUsed: false, targetLibraryKeys, builtReferences))
            .WhereNotNull()
            .ToImmutableArray();

        var reference = new ReferenceInfo(referenceType, itemSpecification, treatAsUsed, compilationAssemblies.ToImmutable(), dependencies);

        builtReferences.Add(reference.ItemSpecification, reference);

        return reference;
    }
}