using Semmle.Util;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Semmle.Extraction.CSharp.Standalone;
using System.Threading.Tasks;
using System.Collections.Concurrent;
using System.Text;
using System.Security.Cryptography;

namespace Semmle.BuildAnalyser
{
    /// <summary>
    /// The output of a build analysis.
    /// </summary>
    internal interface IBuildAnalysis
    {
        /// <summary>
        /// Full filepaths of external references.
        /// </summary>
        IEnumerable<string> ReferenceFiles { get; }

        /// <summary>
        /// Full filepaths of C# source files from project files.
        /// </summary>
        IEnumerable<string> ProjectSourceFiles { get; }

        /// <summary>
        /// Full filepaths of C# source files in the filesystem.
        /// </summary>
        IEnumerable<string> AllSourceFiles { get; }

        /// <summary>
        /// The assembly IDs which could not be resolved.
        /// </summary>
        IEnumerable<string> UnresolvedReferences { get; }

        /// <summary>
        /// List of source files referenced by projects but
        /// which were not found in the filesystem.
        /// </summary>
        IEnumerable<string> MissingSourceFiles { get; }
    }

    /// <summary>
    /// Main implementation of the build analysis.
    /// </summary>
    internal sealed class BuildAnalysis : IBuildAnalysis, IDisposable
    {
        private readonly AssemblyCache assemblyCache;
        private readonly IProgressMonitor progressMonitor;
        private readonly IDictionary<string, bool> usedReferences = new ConcurrentDictionary<string, bool>();
        private readonly IDictionary<string, bool> sources = new ConcurrentDictionary<string, bool>();
        private readonly IDictionary<string, string> unresolvedReferences = new ConcurrentDictionary<string, string>();
        private int failedProjects, succeededProjects;
        private readonly string[] allSources;
        private int conflictedReferences = 0;

        /// <summary>
        /// Performs a C# build analysis.
        /// </summary>
        /// <param name="options">Analysis options from the command line.</param>
        /// <param name="progress">Display of analysis progress.</param>
        public BuildAnalysis(Options options, IProgressMonitor progress)
        {
            var startTime = DateTime.Now;

            progressMonitor = progress;
            var sourceDir = new DirectoryInfo(options.SrcDir);

            progressMonitor.FindingFiles(options.SrcDir);

            allSources = sourceDir.GetFiles("*.cs", SearchOption.AllDirectories)
                .Select(d => d.FullName)
                .Where(d => !options.ExcludesFile(d))
                .ToArray();

            var dllDirNames = options.DllDirs.Select(Path.GetFullPath).ToList();
            packageDirectory = new TemporaryDirectory(ComputeTempDirectory(sourceDir.FullName));

            if (options.UseNuGet)
            {
                try
                {
                    var nuget = new NugetPackages(sourceDir.FullName, packageDirectory);
                    nuget.InstallPackages(progressMonitor);
                }
                catch (FileNotFoundException)
                {
                    progressMonitor.MissingNuGet();
                }
            }

            // Find DLLs in the .Net Framework
            if (options.ScanNetFrameworkDlls)
            {
                var runtimeLocation = Runtime.GetRuntime(options.UseSelfContainedDotnet);
                progressMonitor.Log(Util.Logging.Severity.Debug, $"Runtime location selected: {runtimeLocation}");
                dllDirNames.Add(runtimeLocation);
            }

            // These files can sometimes prevent `dotnet restore` from working correctly.
            using (new FileRenamer(sourceDir.GetFiles("global.json", SearchOption.AllDirectories)))
            using (new FileRenamer(sourceDir.GetFiles("Directory.Build.props", SearchOption.AllDirectories)))
            {
                var solutions = options.SolutionFile is not null ?
                        new[] { options.SolutionFile } :
                        sourceDir.GetFiles("*.sln", SearchOption.AllDirectories).Select(d => d.FullName);

                if (options.UseNuGet)
                {
                    RestoreSolutions(solutions);
                }
                dllDirNames.Add(packageDirectory.DirInfo.FullName);
                assemblyCache = new BuildAnalyser.AssemblyCache(dllDirNames, progress);
                AnalyseSolutions(solutions);

                foreach (var filename in assemblyCache.AllAssemblies.Select(a => a.Filename))
                    UseReference(filename);
            }

            ResolveConflicts();

            if (options.UseMscorlib)
            {
                UseReference(typeof(object).Assembly.Location);
            }

            // Output the findings
            foreach (var r in usedReferences.Keys)
            {
                progressMonitor.ResolvedReference(r);
            }

            foreach (var r in unresolvedReferences)
            {
                progressMonitor.UnresolvedReference(r.Key, r.Value);
            }

            progressMonitor.Summary(
                AllSourceFiles.Count(),
                ProjectSourceFiles.Count(),
                MissingSourceFiles.Count(),
                ReferenceFiles.Count(),
                UnresolvedReferences.Count(),
                conflictedReferences,
                succeededProjects + failedProjects,
                failedProjects,
                DateTime.Now - startTime);
        }

        /// <summary>
        /// Computes a unique temp directory for the packages associated
        /// with this source tree. Use a SHA1 of the directory name.
        /// </summary>
        /// <param name="srcDir"></param>
        /// <returns>The full path of the temp directory.</returns>
        private static string ComputeTempDirectory(string srcDir)
        {
            var bytes = Encoding.Unicode.GetBytes(srcDir);

            using var sha1 = SHA1.Create();
            var sha = sha1.ComputeHash(bytes);
            var sb = new StringBuilder();
            foreach (var b in sha.Take(8))
                sb.AppendFormat("{0:x2}", b);

            return Path.Combine(Path.GetTempPath(), "GitHub", "packages", sb.ToString());
        }

        /// <summary>
        /// Resolves conflicts between all of the resolved references.
        /// If the same assembly name is duplicated with different versions,
        /// resolve to the higher version number.
        /// </summary>
        private void ResolveConflicts()
        {
            var sortedReferences = new List<AssemblyInfo>();
            foreach (var usedReference in usedReferences)
            {
                try
                {
                    var assemblyInfo = assemblyCache.GetAssemblyInfo(usedReference.Key);
                    sortedReferences.Add(assemblyInfo);
                }
                catch (AssemblyLoadException)
                {
                    progressMonitor.Log(Util.Logging.Severity.Warning, $"Could not load assembly information from {usedReference.Key}");
                }
            }

            sortedReferences = sortedReferences.OrderBy(r => r.Version).ToList();

            var finalAssemblyList = new Dictionary<string, AssemblyInfo>();

            // Pick the highest version for each assembly name
            foreach (var r in sortedReferences)
                finalAssemblyList[r.Name] = r;

            // Update the used references list
            usedReferences.Clear();
            foreach (var r in finalAssemblyList.Select(r => r.Value.Filename))
                UseReference(r);

            // Report the results
            foreach (var r in sortedReferences)
            {
                var resolvedInfo = finalAssemblyList[r.Name];
                if (resolvedInfo.Version != r.Version)
                {
                    progressMonitor.ResolvedConflict(r.Id, resolvedInfo.Id);
                    ++conflictedReferences;
                }
            }
        }

        /// <summary>
        /// Store that a particular reference file is used.
        /// </summary>
        /// <param name="reference">The filename of the reference.</param>
        private void UseReference(string reference)
        {
            usedReferences[reference] = true;
        }

        /// <summary>
        /// Store that a particular source file is used (by a project file).
        /// </summary>
        /// <param name="sourceFile">The source file.</param>
        private void UseSource(FileInfo sourceFile)
        {
            sources[sourceFile.FullName] = sourceFile.Exists;
        }

        /// <summary>
        /// The list of resolved reference files.
        /// </summary>
        public IEnumerable<string> ReferenceFiles => this.usedReferences.Keys;

        /// <summary>
        /// The list of source files used in projects.
        /// </summary>
        public IEnumerable<string> ProjectSourceFiles => sources.Where(s => s.Value).Select(s => s.Key);

        /// <summary>
        /// All of the source files in the source directory.
        /// </summary>
        public IEnumerable<string> AllSourceFiles => allSources;

        /// <summary>
        /// List of assembly IDs which couldn't be resolved.
        /// </summary>
        public IEnumerable<string> UnresolvedReferences => this.unresolvedReferences.Select(r => r.Key);

        /// <summary>
        /// List of source files which were mentioned in project files but
        /// do not exist on the file system.
        /// </summary>
        public IEnumerable<string> MissingSourceFiles => sources.Where(s => !s.Value).Select(s => s.Key);

        /// <summary>
        /// Record that a particular reference couldn't be resolved.
        /// Note that this records at most one project file per missing reference.
        /// </summary>
        /// <param name="id">The assembly ID.</param>
        /// <param name="projectFile">The project file making the reference.</param>
        private void UnresolvedReference(string id, string projectFile)
        {
            unresolvedReferences[id] = projectFile;
        }

        private readonly TemporaryDirectory packageDirectory;

        /// <summary>
        /// Reads all the source files and references from the given list of projects.
        /// </summary>
        /// <param name="projectFiles">The list of projects to analyse.</param>
        private void AnalyseProjectFiles(IEnumerable<FileInfo> projectFiles)
        {
            foreach (var proj in projectFiles)
                AnalyseProject(proj);
        }

        private void AnalyseProject(FileInfo project)
        {
            if (!project.Exists)
            {
                progressMonitor.MissingProject(project.FullName);
                return;
            }

            try
            {
                var csProj = new Extraction.CSharp.CsProjFile(project);

                foreach (var @ref in csProj.References)
                {
                    try
                    {
                        var resolved = assemblyCache.ResolveReference(@ref);
                        UseReference(resolved.Filename);
                    }
                    catch (AssemblyLoadException)
                    {
                        UnresolvedReference(@ref, project.FullName);
                    }
                }

                foreach (var src in csProj.Sources)
                {
                    // Make a note of which source files the projects use.
                    // This information doesn't affect the build but is dumped
                    // as diagnostic output.
                    UseSource(new FileInfo(src));
                }

                ++succeededProjects;
            }
            catch (Exception ex)  // lgtm[cs/catch-of-all-exceptions]
            {
                ++failedProjects;
                progressMonitor.FailedProjectFile(project.FullName, ex.Message);
            }

        }

        private void Restore(string projectOrSolution)
        {
            int exit;
            try
            {
                exit = DotNet.RestoreToDirectory(projectOrSolution, packageDirectory.DirInfo.FullName);
            }
            catch (FileNotFoundException)
            {
                exit = 2;
            }

            switch (exit)
            {
                case 0:
                case 1:
                    // No errors
                    break;
                default:
                    progressMonitor.CommandFailed("dotnet", $"restore \"{projectOrSolution}\"", exit);
                    break;
            }
        }

        public void RestoreSolutions(IEnumerable<string> solutions)
        {
            Parallel.ForEach(solutions, new ParallelOptions { MaxDegreeOfParallelism = 4 }, Restore);
        }

        public void AnalyseSolutions(IEnumerable<string> solutions)
        {
            Parallel.ForEach(solutions, new ParallelOptions { MaxDegreeOfParallelism = 4 }, solutionFile =>
            {
                try
                {
                    var sln = new SolutionFile(solutionFile);
                    progressMonitor.AnalysingSolution(solutionFile);
                    AnalyseProjectFiles(sln.Projects.Select(p => new FileInfo(p)).Where(p => p.Exists));
                }
                catch (Microsoft.Build.Exceptions.InvalidProjectFileException ex)
                {
                    progressMonitor.FailedProjectFile(solutionFile, ex.BaseMessage);
                }
            });
        }

        public void Dispose()
        {
            packageDirectory?.Dispose();
        }
    }
}