path: root/LibGit2Sharp/Repository.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text.RegularExpressions;
using LibGit2Sharp.Core;
using LibGit2Sharp.Core.Handles;
using LibGit2Sharp.Handlers;

namespace LibGit2Sharp
{
    /// <summary>
    /// A Repository is the primary interface into a git repository
    /// </summary>
    [DebuggerDisplay("{DebuggerDisplay,nq}")]
    public sealed class Repository : IRepository
    {
        private readonly bool isBare;
        private readonly BranchCollection branches;
        private readonly CommitLog commits;
        private readonly Lazy<Configuration> config;
        private readonly RepositorySafeHandle handle;
        private readonly Index index;
        private readonly ReferenceCollection refs;
        private readonly TagCollection tags;
        private readonly StashCollection stashes;
        private readonly Lazy<RepositoryInformation> info;
        private readonly Diff diff;
        private readonly NoteCollection notes;
        private readonly Lazy<ObjectDatabase> odb;
        private readonly Lazy<Network> network;
        private readonly Stack<IDisposable> toCleanup = new Stack<IDisposable>();
        private readonly Ignore ignore;
        private readonly SubmoduleCollection submodules;
        private static readonly Lazy<string> versionRetriever = new Lazy<string>(RetrieveVersion);
        private readonly Lazy<PathCase> pathCase;

        /// <summary>
        /// Initializes a new instance of the <see cref="Repository"/> class, providing ooptional behavioral overrides through <paramref name="options"/> parameter.
        /// <para>For a standard repository, <paramref name="path"/> should either point to the ".git" folder or to the working directory. For a bare repository, <paramref name="path"/> should directly point to the repository folder.</para>
        /// </summary>
        /// <param name="path">
        /// The path to the git repository to open, can be either the path to the git directory (for non-bare repositories this
        /// would be the ".git" folder inside the working directory) or the path to the working directory.
        /// </param>
        /// <param name="options">
        /// Overrides to the way a repository is opened.
        /// </param>
        public Repository(string path, RepositoryOptions options = null)
        {
            Ensure.ArgumentNotNullOrEmptyString(path, "path");

            try
            {
                handle = Proxy.git_repository_open(path);
                RegisterForCleanup(handle);

                isBare = Proxy.git_repository_is_bare(handle);

                Func<Index> indexBuilder = () => new Index(this);

                string configurationGlobalFilePath = null;
                string configurationXDGFilePath = null;
                string configurationSystemFilePath = null;

                if (options != null)
                {
                    bool isWorkDirNull = string.IsNullOrEmpty(options.WorkingDirectoryPath);
                    bool isIndexNull = string.IsNullOrEmpty(options.IndexPath);

                    if (isBare && (isWorkDirNull ^ isIndexNull))
                    {
                        throw new ArgumentException(
                            "When overriding the opening of a bare repository, both RepositoryOptions.WorkingDirectoryPath an RepositoryOptions.IndexPath have to be provided.");
                    }

                    isBare = false;

                    if (!isIndexNull)
                    {
                        indexBuilder = () => new Index(this, options.IndexPath);
                    }

                    if (!isWorkDirNull)
                    {
                        Proxy.git_repository_set_workdir(handle, options.WorkingDirectoryPath);
                    }

                    configurationGlobalFilePath = options.GlobalConfigurationLocation;
                    configurationXDGFilePath = options.XdgConfigurationLocation;
                    configurationSystemFilePath = options.SystemConfigurationLocation;
                }

                if (!isBare)
                {
                    index = indexBuilder();
                }

                commits = new CommitLog(this);
                refs = new ReferenceCollection(this);
                branches = new BranchCollection(this);
                tags = new TagCollection(this);
                stashes = new StashCollection(this);
                info = new Lazy<RepositoryInformation>(() => new RepositoryInformation(this, isBare));
                config =
                    new Lazy<Configuration>(
                        () =>
                        RegisterForCleanup(new Configuration(this, configurationGlobalFilePath, configurationXDGFilePath,
                                                             configurationSystemFilePath)));
                odb = new Lazy<ObjectDatabase>(() => new ObjectDatabase(this));
                diff = new Diff(this);
                notes = new NoteCollection(this);
                ignore = new Ignore(this);
                network = new Lazy<Network>(() => new Network(this));
                pathCase = new Lazy<PathCase>(() => new PathCase(this));
                submodules = new SubmoduleCollection(this);

                EagerlyLoadTheConfigIfAnyPathHaveBeenPassed(options);
            }
            catch
            {
                CleanupDisposableDependencies();
                throw;
            }
        }

        /// <summary>
        /// Check if parameter <paramref name="path"/> leads to a valid git repository.
        /// </summary>
        /// <param name="path">
        /// The path to the git repository to check, can be either the path to the git directory (for non-bare repositories this
        /// would be the ".git" folder inside the working directory) or the path to the working directory.
        /// </param>
        /// <returns>True if a repository can be resolved through this path; false otherwise</returns>
        static public bool IsValid(string path)
        {
            Ensure.ArgumentNotNullOrEmptyString(path, "path");

            try
            {
                Proxy.git_repository_open_ext(path, RepositoryOpenFlags.NoSearch, null);
            }
            catch (RepositoryNotFoundException)
            {
                return false;
            }

            return true;
        }

        private void EagerlyLoadTheConfigIfAnyPathHaveBeenPassed(RepositoryOptions options)
        {
            if (options == null)
            {
                return;
            }

            if (options.GlobalConfigurationLocation == null &&
                options.XdgConfigurationLocation == null &&
                options.SystemConfigurationLocation == null)
            {
                return;
            }

            // Dirty hack to force the eager load of the configuration
            // without Resharper pestering about useless code

            if (!Config.HasConfig(ConfigurationLevel.Local))
            {
                throw new InvalidOperationException("Unexpected state.");
            }
        }

        internal RepositorySafeHandle Handle
        {
            get { return handle; }
        }

        /// <summary>
        /// Shortcut to return the branch pointed to by HEAD
        /// </summary>
        public Branch Head
        {
            get
            {
                Reference reference = Refs.Head;

                if (reference == null)
                {
                    throw new LibGit2SharpException("Corrupt repository. The 'HEAD' reference is missing.");
                }

                if (reference is SymbolicReference)
                {
                    return new Branch(this, reference);
                }

                return new DetachedHead(this, reference);
            }
        }

        /// <summary>
        /// Provides access to the configuration settings for this repository.
        /// </summary>
        public Configuration Config
        {
            get { return config.Value; }
        }

        /// <summary>
        /// Gets the index.
        /// </summary>
        public Index Index
        {
            get
            {
                if (isBare)
                {
                    throw new BareRepositoryException("Index is not available in a bare repository.");
                }

                return index;
            }
        }

        /// <summary>
        /// Manipulate the currently ignored files.
        /// </summary>
        public Ignore Ignore
        {
            get
            {
                return ignore;
            }
        }

        /// <summary>
        /// Provides access to network functionality for a repository.
        /// </summary>
        public Network Network
        {
            get
            {
                return network.Value;
            }
        }

        /// <summary>
        /// Gets the database.
        /// </summary>
        public ObjectDatabase ObjectDatabase
        {
            get
            {
                return odb.Value;
            }
        }

        /// <summary>
        /// Lookup and enumerate references in the repository.
        /// </summary>
        public ReferenceCollection Refs
        {
            get { return refs; }
        }

        /// <summary>
        /// Lookup and enumerate commits in the repository.
        /// Iterating this collection directly starts walking from the HEAD.
        /// </summary>
        public IQueryableCommitLog Commits
        {
            get { return commits; }
        }

        /// <summary>
        /// Lookup and enumerate branches in the repository.
        /// </summary>
        public BranchCollection Branches
        {
            get { return branches; }
        }

        /// <summary>
        /// Lookup and enumerate tags in the repository.
        /// </summary>
        public TagCollection Tags
        {
            get { return tags; }
        }

        ///<summary>
        /// Lookup and enumerate stashes in the repository.
        ///</summary>
        public StashCollection Stashes
        {
            get { return stashes; }
        }

        /// <summary>
        /// Provides high level information about this repository.
        /// </summary>
        public RepositoryInformation Info
        {
            get { return info.Value; }
        }

        /// <summary>
        /// Provides access to diffing functionalities to show changes between the working tree and the index or a tree, changes between the index and a tree, changes between two trees, or changes between two files on disk.
        /// </summary>
        public Diff Diff
        {
            get { return diff; }
        }

        /// <summary>
        /// Lookup notes in the repository.
        /// </summary>
        public NoteCollection Notes
        {
            get { return notes; }
        }

        /// <summary>
        /// Submodules in the repository.
        /// </summary>
        public SubmoduleCollection Submodules
        {
            get { return submodules; }
        }

        #region IDisposable Members

        /// <summary>
        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
        /// </summary>
        public void Dispose()
        {
            Dispose(true);
        }

        /// <summary>
        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
        /// </summary>
        private void Dispose(bool disposing)
        {
            CleanupDisposableDependencies();
        }

        #endregion

        /// <summary>
        /// Initialize a repository at the specified <paramref name="path"/>.
        /// </summary>
        /// <param name="path">The path to the working folder when initializing a standard ".git" repository. Otherwise, when initializing a bare repository, the path to the expected location of this later.</param>
        /// <param name="isBare">true to initialize a bare repository. False otherwise, to initialize a standard ".git" repository.</param>
        /// <returns>The path to the created repository.</returns>
        public static string Init(string path, bool isBare = false)
        {
            Ensure.ArgumentNotNullOrEmptyString(path, "path");

            using (RepositorySafeHandle repo = Proxy.git_repository_init_ext(null, path, isBare))
            {
                FilePath repoPath = Proxy.git_repository_path(repo);
                return repoPath.Native;
            }
        }

        /// <summary>
        /// Initialize a repository by explictly setting the path to both the working directory and the git directory.
        /// </summary>
        /// <param name="workingDirectoryPath">The path to the working directory.</param>
        /// <param name="gitDirectoryPath">The path to the git repository to be created.</param>
        /// <returns>The path to the created repository.</returns>
        public static string Init(string workingDirectoryPath, string gitDirectoryPath)
        {
            Ensure.ArgumentNotNullOrEmptyString(workingDirectoryPath, "workingDirectoryPath");
            Ensure.ArgumentNotNullOrEmptyString(gitDirectoryPath, "gitDirectoryPath");

            // When being passed a relative workdir path, libgit2 will evaluate it from the
            // path to the repository. We pass a fully rooted path in order for the LibGit2Sharp caller
            // to pass a path relatively to his current directory.
            string wd = Path.GetFullPath(workingDirectoryPath);

            // TODO: Shouldn't we ensure that the working folder isn't under the gitDir?

            using (RepositorySafeHandle repo = Proxy.git_repository_init_ext(wd, gitDirectoryPath, false))
            {
                FilePath repoPath = Proxy.git_repository_path(repo);
                return repoPath.Native;
            }
        }

        /// <summary>
        /// Try to lookup an object by its <see cref="ObjectId"/>. If no matching object is found, null will be returned.
        /// </summary>
        /// <param name="id">The id to lookup.</param>
        /// <returns>The <see cref="GitObject"/> or null if it was not found.</returns>
        public GitObject Lookup(ObjectId id)
        {
            return LookupInternal(id, GitObjectType.Any, null);
        }

        /// <summary>
        /// Try to lookup an object by its sha or a reference canonical name. If no matching object is found, null will be returned.
        /// </summary>
        /// <param name="objectish">A revparse spec for the object to lookup.</param>
        /// <returns>The <see cref="GitObject"/> or null if it was not found.</returns>
        public GitObject Lookup(string objectish)
        {
            return Lookup(objectish, GitObjectType.Any, LookUpOptions.None);
        }

        /// <summary>
        /// Try to lookup an object by its <see cref="ObjectId"/> and <see cref="ObjectType"/>. If no matching object is found, null will be returned.
        /// </summary>
        /// <param name="id">The id to lookup.</param>
        /// <param name="type">The kind of GitObject being looked up</param>
        /// <returns>The <see cref="GitObject"/> or null if it was not found.</returns>
        public GitObject Lookup(ObjectId id, ObjectType type)
        {
            return LookupInternal(id, type.ToGitObjectType(), null);
        }

        /// <summary>
        /// Try to lookup an object by its sha or a reference canonical name and <see cref="ObjectType"/>. If no matching object is found, null will be returned.
        /// </summary>
        /// <param name="objectish">A revparse spec for the object to lookup.</param>
        /// <param name="type">The kind of <see cref="GitObject"/> being looked up</param>
        /// <returns>The <see cref="GitObject"/> or null if it was not found.</returns>
        public GitObject Lookup(string objectish, ObjectType type)
        {
            return Lookup(objectish, type.ToGitObjectType(), LookUpOptions.None);
        }

        internal GitObject LookupInternal(ObjectId id, GitObjectType type, FilePath knownPath)
        {
            Ensure.ArgumentNotNull(id, "id");

            using (GitObjectSafeHandle obj = Proxy.git_object_lookup(handle, id, type))
            {
                if (obj == null)
                {
                    return null;
                }

                return GitObject.BuildFrom(this, id, Proxy.git_object_type(obj), knownPath);
            }
        }

        private static string PathFromRevparseSpec(string spec)
        {
            if (spec.StartsWith(":/", StringComparison.Ordinal))
            {
                return null;
            }

            if (Regex.IsMatch(spec, @"^:.*:"))
            {
                return null;
            }

            var m = Regex.Match(spec, @"[^@^ ]*:(.*)");
            return (m.Groups.Count > 1) ? m.Groups[1].Value : null;
        }

        internal GitObject Lookup(string objectish, GitObjectType type, LookUpOptions lookUpOptions)
        {
            Ensure.ArgumentNotNullOrEmptyString(objectish, "commitOrBranchSpec");

            GitObject obj;
            using (GitObjectSafeHandle sh = Proxy.git_revparse_single(handle, objectish))
            {
                if (sh == null)
                {
                    if (lookUpOptions.HasFlag(LookUpOptions.ThrowWhenNoGitObjectHasBeenFound))
                    {
                        Ensure.GitObjectIsNotNull(null, objectish);
                    }

                    return null;
                }

                GitObjectType objType = Proxy.git_object_type(sh);

                if (type != GitObjectType.Any && objType != type)
                {
                    return null;
                }

                obj = GitObject.BuildFrom(this, Proxy.git_object_id(sh), objType, PathFromRevparseSpec(objectish));
            }

            if (lookUpOptions.HasFlag(LookUpOptions.DereferenceResultToCommit))
            {
                return obj.DereferenceToCommit(
                    lookUpOptions.HasFlag(LookUpOptions.ThrowWhenCanNotBeDereferencedToACommit));
            }

            return obj;
        }

        internal Commit LookupCommit(string committish)
        {
            return (Commit)Lookup(committish, GitObjectType.Any,
                LookUpOptions.ThrowWhenNoGitObjectHasBeenFound |
                LookUpOptions.DereferenceResultToCommit |
                LookUpOptions.ThrowWhenCanNotBeDereferencedToACommit);
        }

        /// <summary>
        /// Probe for a git repository.
        /// <para>The lookup start from <paramref name="startingPath"/> and walk upward parent directories if nothing has been found.</para>
        /// </summary>
        /// <param name="startingPath">The base path where the lookup starts.</param>
        /// <returns>The path to the git repository.</returns>
        public static string Discover(string startingPath)
        {
            FilePath discoveredPath = Proxy.git_repository_discover(startingPath);

            if (discoveredPath == null)
            {
                return null;
            }

            return discoveredPath.Native;
        }

        /// <summary>
        /// Clone with specified options.
        /// </summary>
        /// <param name="sourceUrl">URI for the remote repository</param>
        /// <param name="workdirPath">Local path to clone into</param>
        /// <param name="options"><see cref="CloneOptions"/> controlling clone behavior</param>
        /// <returns>The path to the created repository.</returns>
        public static string Clone(string sourceUrl, string workdirPath,
            CloneOptions options = null)
        {
            options = options ?? new CloneOptions();

            using (GitCheckoutOptsWrapper checkoutOptionsWrapper = new GitCheckoutOptsWrapper(options))
            {
                var gitCheckoutOptions = checkoutOptionsWrapper.Options;

                var remoteCallbacks = new RemoteCallbacks(null, options.OnTransferProgress, null, options.Credentials);
                var gitRemoteCallbacks = remoteCallbacks.GenerateCallbacks();

                var cloneOpts = new GitCloneOptions
                {
                    Version = 1,
                    Bare = options.IsBare ? 1 : 0,
                    CheckoutOpts = gitCheckoutOptions,
                    RemoteCallbacks = gitRemoteCallbacks,
                };

                FilePath repoPath;
                using (RepositorySafeHandle repo = Proxy.git_clone(sourceUrl, workdirPath, ref cloneOpts))
                {
                    repoPath = Proxy.git_repository_path(repo);
                }

                return repoPath.Native;
            }
        }

        /// <summary>
        /// Find where each line of a file originated.
        /// </summary>
        /// <param name="path">Path of the file to blame.</param>
        /// <param name="options">Specifies optional parameters; if null, the defaults are used.</param>
        /// <returns>The blame for the file.</returns>
        public BlameHunkCollection Blame(string path, BlameOptions options = null)
        {
            return new BlameHunkCollection(this, Handle, path, options ?? new BlameOptions());
        }

        /// <summary>
        /// Checkout the specified <see cref="Branch"/>, reference or SHA.
        /// <para>
        ///   If the committishOrBranchSpec parameter resolves to a branch name, then the checked out HEAD will
        ///   will point to the branch. Otherwise, the HEAD will be detached, pointing at the commit sha.
        /// </para>
        /// </summary>
        /// <param name="committishOrBranchSpec">A revparse spec for the commit or branch to checkout.</param>
        /// <param name="options"><see cref="CheckoutOptions"/> controlling checkout behavior.</param>
        /// <param name="signature">Identity for use when updating the reflog.</param>
        /// <returns>The <see cref="Branch"/> that was checked out.</returns>
        public Branch Checkout(string committishOrBranchSpec, CheckoutOptions options, Signature signature = null)
        {
            Ensure.ArgumentNotNullOrEmptyString(committishOrBranchSpec, "committishOrBranchSpec");
            Ensure.ArgumentNotNull(options, "options");

            var handles = Proxy.git_revparse_ext(Handle, committishOrBranchSpec);
            if (handles == null)
            {
                Ensure.GitObjectIsNotNull(null, committishOrBranchSpec);
            }

            var objH = handles.Item1;
            var refH = handles.Item2;
            GitObject obj;
            try
            {
                if (!refH.IsInvalid)
                {
                    var reference = Reference.BuildFromPtr<Reference>(refH, this);
                    if (reference.IsLocalBranch())
                    {
                        Branch branch = Branches[reference.CanonicalName];
                        return Checkout(branch, options, signature);
                    }
                }

                obj = GitObject.BuildFrom(this, Proxy.git_object_id(objH), Proxy.git_object_type(objH),
                                              PathFromRevparseSpec(committishOrBranchSpec));
            }
            finally
            {
                objH.Dispose();
                refH.Dispose();
            }

            Commit commit = obj.DereferenceToCommit(true);
            Checkout(commit.Tree, options, commit.Id.Sha, committishOrBranchSpec, signature);

            return Head;
        }

        /// <summary>
        /// Checkout the tip commit of the specified <see cref="Branch"/> object. If this commit is the
        /// current tip of the branch, will checkout the named branch. Otherwise, will checkout the tip commit
        /// as a detached HEAD.
        /// </summary>
        /// <param name="branch">The <see cref="Branch"/> to check out.</param>
        /// <param name="options"><see cref="CheckoutOptions"/> controlling checkout behavior.</param>
        /// <param name="signature">Identity for use when updating the reflog.</param>
        /// <returns>The <see cref="Branch"/> that was checked out.</returns>
        public Branch Checkout(Branch branch, CheckoutOptions options, Signature signature = null)
        {
            Ensure.ArgumentNotNull(branch, "branch");
            Ensure.ArgumentNotNull(options, "options");

            // Make sure this is not an unborn branch.
            if (branch.Tip == null)
            {
                throw new UnbornBranchException(
                    string.Format(CultureInfo.InvariantCulture,
                    "The tip of branch '{0}' is null. There's nothing to checkout.", branch.Name));
            }

            if (!branch.IsRemote && !(branch is DetachedHead) &&
                string.Equals(Refs[branch.CanonicalName].TargetIdentifier, branch.Tip.Id.Sha,
                StringComparison.OrdinalIgnoreCase))
            {
                Checkout(branch.Tip.Tree, options, branch.CanonicalName, branch.Name, signature);
            }
            else
            {
                Checkout(branch.Tip.Tree, options, branch.Tip.Id.Sha, branch.Name, signature);
            }

            return Head;
        }

        /// <summary>
        /// Checkout the specified <see cref="LibGit2Sharp.Commit"/>.
        /// <para>
        ///   Will detach the HEAD and make it point to this commit sha.
        /// </para>
        /// </summary>
        /// <param name="commit">The <see cref="LibGit2Sharp.Commit"/> to check out.</param>
        /// <param name="options"><see cref="CheckoutOptions"/> controlling checkout behavior.</param>
        /// <param name="signature">Identity for use when updating the reflog.</param>
        /// <returns>The <see cref="Branch"/> that was checked out.</returns>
        public Branch Checkout(Commit commit, CheckoutOptions options, Signature signature = null)
        {
            Ensure.ArgumentNotNull(commit, "commit");
            Ensure.ArgumentNotNull(options, "options");

            Checkout(commit.Tree, options, commit.Id.Sha, commit.Id.Sha, signature);

            return Head;
        }

        /// <summary>
        /// Internal implementation of Checkout that expects the ID of the checkout target
        /// to already be in the form of a canonical branch name or a commit ID.
        /// </summary>
        /// <param name="tree">The <see cref="Tree"/> to checkout.</param>
        /// <param name="checkoutOptions"><see cref="CheckoutOptions"/> controlling checkout behavior.</param>
        /// <param name="headTarget">Target for the new HEAD.</param>
        /// <param name="refLogHeadSpec">The spec which will be written as target in the reflog.</param>
        /// <param name="signature">Identity for use when updating the reflog.</param>
        private void Checkout(
            Tree tree,
            CheckoutOptions checkoutOptions,
            string headTarget, string refLogHeadSpec, Signature signature)
        {
            var previousHeadName = Info.IsHeadDetached ? Head.Tip.Sha : Head.Name;

            CheckoutTree(tree, null, checkoutOptions);

            Refs.UpdateTarget("HEAD", headTarget, signature,
                string.Format(
                    CultureInfo.InvariantCulture,
                    "checkout: moving from {0} to {1}", previousHeadName, refLogHeadSpec));
        }

        /// <summary>
        /// Checkout the specified tree.
        /// </summary>
        /// <param name="tree">The <see cref="Tree"/> to checkout.</param>
        /// <param name="paths">The paths to checkout.</param>
        /// <param name="opts">Collection of parameters controlling checkout behavior.</param>
        private void CheckoutTree(
            Tree tree,
            IList<string> paths,
            IConvertableToGitCheckoutOpts opts)
        {

            using(GitCheckoutOptsWrapper checkoutOptionsWrapper = new GitCheckoutOptsWrapper(opts, ToFilePaths(paths)))
            {
                var options = checkoutOptionsWrapper.Options;
                Proxy.git_checkout_tree(Handle, tree.Id, ref options);
            }
        }

        /// <summary>
        /// Sets the current <see cref="Head"/> to the specified commit and optionally resets the <see cref="Index"/> and
        /// the content of the working tree to match.
        /// </summary>
        /// <param name="resetMode">Flavor of reset operation to perform.</param>
        /// <param name="commit">The target commit object.</param>
        /// <param name="signature">Identity for use when updating the reflog.</param>
        /// <param name="logMessage">Message to use when updating the reflog.</param>
        public void Reset(ResetMode resetMode, Commit commit, Signature signature = null, string logMessage = null)
        {
            Ensure.ArgumentNotNull(commit, "commit");

            if (logMessage == null)
            {
                logMessage = string.Format(
                    CultureInfo.InvariantCulture,
                    "reset: moving to {0}", commit.Sha);
            }

            Proxy.git_reset(handle, commit.Id, resetMode, signature.OrDefault(Config), logMessage);
        }

        /// <summary>
        /// Updates specifed paths in the index and working directory with the versions from the specified branch, reference, or SHA.
        /// <para>
        /// This method does not switch branches or update the current repository HEAD.
        /// </para>
        /// </summary>
        /// <param name = "committishOrBranchSpec">A revparse spec for the commit or branch to checkout paths from.</param>
        /// <param name="paths">The paths to checkout. Will throw if null is passed in. Passing an empty enumeration results in nothing being checked out.</param>
        /// <param name="checkoutOptions">Collection of parameters controlling checkout behavior.</param>
        public void CheckoutPaths(string committishOrBranchSpec, IEnumerable<string> paths, CheckoutOptions checkoutOptions = null)
        {
            Ensure.ArgumentNotNullOrEmptyString(committishOrBranchSpec, "committishOrBranchSpec");
            Ensure.ArgumentNotNull(paths, "paths");

            // If there are no paths, then there is nothing to do.
            if (!paths.Any())
            {
                return;
            }

            Commit commit = LookupCommit(committishOrBranchSpec);
            CheckoutTree(commit.Tree, paths.ToList(), checkoutOptions ?? new CheckoutOptions());
        }

        /// <summary>
        /// Replaces entries in the <see cref="Repository.Index"/> with entries from the specified commit.
        /// </summary>
        /// <param name="commit">The target commit object.</param>
        /// <param name="paths">The list of paths (either files or directories) that should be considered.</param>
        /// <param name="explicitPathsOptions">
        /// If set, the passed <paramref name="paths"/> will be treated as explicit paths.
        /// Use these options to determine how unmatched explicit paths should be handled.
        /// </param>
        public void Reset(Commit commit, IEnumerable<string> paths = null, ExplicitPathsOptions explicitPathsOptions = null)
        {
            if (Info.IsBare)
            {
                throw new BareRepositoryException("Reset is not allowed in a bare repository");
            }

            Ensure.ArgumentNotNull(commit, "commit");

            var changes = Diff.Compare<TreeChanges>(commit.Tree, DiffTargets.Index, paths, explicitPathsOptions);
            Index.Reset(changes);
        }

        /// <summary>
        /// Stores the content of the <see cref="Repository.Index"/> as a new <see cref="LibGit2Sharp.Commit"/> into the repository.
        /// The tip of the <see cref="Repository.Head"/> will be used as the parent of this new Commit.
        /// Once the commit is created, the <see cref="Repository.Head"/> will move forward to point at it.
        /// </summary>
        /// <param name="message">The description of why a change was made to the repository.</param>
        /// <param name="author">The <see cref="Signature"/> of who made the change.</param>
        /// <param name="committer">The <see cref="Signature"/> of who added the change to the repository.</param>
        /// <param name="options">The <see cref="CommitOptions"/> that specify the commit behavior.</param>
        /// <returns>The generated <see cref="LibGit2Sharp.Commit"/>.</returns>
        public Commit Commit(string message, Signature author, Signature committer, CommitOptions options = null)
        {
            if (options == null)
            {
                options = new CommitOptions();
            }

            bool isHeadOrphaned = Info.IsHeadUnborn;

            if (options.AmendPreviousCommit && isHeadOrphaned)
            {
                throw new UnbornBranchException("Can not amend anything. The Head doesn't point at any commit.");
            }

            var treeId = Proxy.git_tree_create_fromindex(Index);
            var tree = this.Lookup<Tree>(treeId);

            var parents = RetrieveParentsOfTheCommitBeingCreated(options.AmendPreviousCommit).ToList();

            if (parents.Count == 1 && !options.AllowEmptyCommit)
            {
                var treesame = parents[0].Tree.Id.Equals(treeId);
                var amendMergeCommit = options.AmendPreviousCommit && !isHeadOrphaned && Head.Tip.Parents.Count() > 1;

                if (treesame && !amendMergeCommit)
                {
                    throw new EmptyCommitException(
                        options.AmendPreviousCommit ?
                        String.Format(CultureInfo.InvariantCulture,
                            "Amending this commit would produce a commit that is identical to its parent (id = {0})", parents[0].Id) :
                        "No changes; nothing to commit.");
                }
            }

            Commit result = ObjectDatabase.CreateCommit(author, committer, message, tree, parents, options.PrettifyMessage, options.CommentaryChar);

            Proxy.git_repository_state_cleanup(handle);

            var logMessage = BuildCommitLogMessage(result, options.AmendPreviousCommit, isHeadOrphaned, parents.Count > 1);
            UpdateHeadAndTerminalReference(result, logMessage);

            return result;
        }

        private static string BuildCommitLogMessage(Commit commit, bool amendPreviousCommit, bool isHeadOrphaned, bool isMergeCommit)
        {
            string kind = string.Empty;
            if (isHeadOrphaned)
            {
                kind = " (initial)";
            }
            else if (amendPreviousCommit)
            {
                kind = " (amend)";
            }
            else if (isMergeCommit)
            {
                kind = " (merge)";
            }

            return string.Format(CultureInfo.InvariantCulture, "commit{0}: {1}", kind, commit.MessageShort);
        }

        private void UpdateHeadAndTerminalReference(Commit commit, string reflogMessage)
        {
            Reference reference = Refs.Head;

            while (true) //TODO: Implement max nesting level
            {
                if (reference is DirectReference)
                {
                    Refs.UpdateTarget(reference, commit.Id, commit.Committer, reflogMessage);
                    return;
                }

                var symRef = (SymbolicReference) reference;

                reference = symRef.Target;

                if (reference == null)
                {
                    Refs.Add(symRef.TargetIdentifier, commit.Id, commit.Committer, reflogMessage);
                    return;
                }
            }
        }

        private IEnumerable<Commit> RetrieveParentsOfTheCommitBeingCreated(bool amendPreviousCommit)
        {
            if (amendPreviousCommit)
            {
                return Head.Tip.Parents;
            }

            if (Info.IsHeadUnborn)
            {
                return Enumerable.Empty<Commit>();
            }

            var parents = new List<Commit> { Head.Tip };

            if (Info.CurrentOperation == CurrentOperation.Merge)
            {
                parents.AddRange(MergeHeads.Select(mh => mh.Tip));
            }

            return parents;
        }

        /// <summary>
        /// Clean the working tree by removing files that are not under version control.
        /// </summary>
        public void RemoveUntrackedFiles()
        {
            var options = new GitCheckoutOpts
            {
                version = 1,
                checkout_strategy = CheckoutStrategy.GIT_CHECKOUT_REMOVE_UNTRACKED
                                     | CheckoutStrategy.GIT_CHECKOUT_ALLOW_CONFLICTS,
            };

            Proxy.git_checkout_index(Handle, new NullGitObjectSafeHandle(), ref options);
        }

        private void CleanupDisposableDependencies()
        {
            while (toCleanup.Count > 0)
            {
                toCleanup.Pop().SafeDispose();
            }
        }

        internal T RegisterForCleanup<T>(T disposable) where T : IDisposable
        {
            toCleanup.Push(disposable);
            return disposable;
        }

        /// <summary>
        /// Gets the current LibGit2Sharp version.
        /// <para>
        ///   The format of the version number is as follows:
        ///   <para>Major.Minor.Patch-LibGit2Sharp_abbrev_hash-libgit2_abbrev_hash (x86|amd64 - features)</para>
        /// </para>
        /// </summary>
        public static string Version
        {
            get { return versionRetriever.Value; }
        }

        private static string RetrieveVersion()
        {
            Assembly assembly = typeof(Repository).Assembly;

            Version version = assembly.GetName().Version;

            string libgit2Hash = ReadContentFromResource(assembly, "libgit2_hash.txt");
            string libgit2sharpHash = ReadContentFromResource(assembly, "libgit2sharp_hash.txt");
            string features = GlobalSettings.Features().ToString();

            return string.Format(
                CultureInfo.InvariantCulture,
                "{0}-{1}-{2} ({3} - {4})",
                version.ToString(3),
                libgit2sharpHash.Substring(0, 7),
                libgit2Hash.Substring(0, 7),
                NativeMethods.ProcessorArchitecture,
                features);
        }

        private static string ReadContentFromResource(Assembly assembly, string partialResourceName)
        {
            string name = string.Format(CultureInfo.InvariantCulture, "LibGit2Sharp.{0}", partialResourceName);
            using (var sr = new StreamReader(assembly.GetManifestResourceStream(name)))
            {
                return sr.ReadLine();
            }
        }

        /// <summary>
        /// Merges changes from commit into the branch pointed at by HEAD.
        /// </summary>
        /// <param name="commit">The commit to merge into the branch pointed at by HEAD.</param>
        /// <param name="merger">The <see cref="Signature"/> of who is performing the merge.</param>
        /// <param name="options">Specifies optional parameters controlling merge behavior; if null, the defaults are used.</param>
        /// <returns>The <see cref="MergeResult"/> of the merge.</returns>
        public MergeResult Merge(Commit commit, Signature merger, MergeOptions options = null)
        {
            Ensure.ArgumentNotNull(commit, "commit");
            Ensure.ArgumentNotNull(merger, "merger");

            options = options ?? new MergeOptions();

            using (GitMergeHeadHandle mergeHeadHandle = Proxy.git_merge_head_from_id(Handle, commit.Id.Oid))
            {
                return Merge(new[] { mergeHeadHandle }, merger, options);
            }
        }

        /// <summary>
        /// Merges changes from branch into the branch pointed at by HEAD.
        /// </summary>
        /// <param name="branch">The branch to merge into the branch pointed at by HEAD.</param>
        /// <param name="merger">The <see cref="Signature"/> of who is performing the merge.</param>
        /// <param name="options">Specifies optional parameters controlling merge behavior; if null, the defaults are used.</param>
        /// <returns>The <see cref="MergeResult"/> of the merge.</returns>
        public MergeResult Merge(Branch branch, Signature merger, MergeOptions options = null)
        {
            Ensure.ArgumentNotNull(branch, "branch");
            Ensure.ArgumentNotNull(merger, "merger");

            options = options ?? new MergeOptions();

            using (ReferenceSafeHandle referencePtr = Refs.RetrieveReferencePtr(branch.CanonicalName))
            using (GitMergeHeadHandle mergeHeadHandle = Proxy.git_merge_head_from_ref(Handle, referencePtr))
            {
                return Merge(new[] { mergeHeadHandle }, merger, options);
            }
        }

        /// <summary>
        /// Merges changes from the commit into the branch pointed at by HEAD.
        /// </summary>
        /// <param name="committish">The commit to merge into the branch pointed at by HEAD.</param>
        /// <param name="merger">The <see cref="Signature"/> of who is performing the merge.</param>
        /// <param name="options">Specifies optional parameters controlling merge behavior; if null, the defaults are used.</param>
        /// <returns>The <see cref="MergeResult"/> of the merge.</returns>
        public MergeResult Merge(string committish, Signature merger, MergeOptions options = null)
        {
            Ensure.ArgumentNotNull(committish, "committish");
            Ensure.ArgumentNotNull(merger, "merger");

            options = options ?? new MergeOptions();

            Commit commit = LookupCommit(committish);
            return Merge(commit, merger, options);
        }

        /// <summary>
        /// Merge the current fetch heads into the branch pointed at by HEAD.
        /// </summary>
        /// <param name="merger">The <see cref="Signature"/> of who is performing the merge.</param>
        /// <param name="options">Specifies optional parameters controlling merge behavior; if null, the defaults are used.</param>
        /// <returns>The <see cref="MergeResult"/> of the merge.</returns>
        internal MergeResult MergeFetchHeads(Signature merger, MergeOptions options)
        {
            Ensure.ArgumentNotNull(merger, "merger");

            options = options ?? new MergeOptions();

            // The current FetchHeads that are marked for merging.
            FetchHead[] fetchHeads = Network.FetchHeads.Where(fetchHead => fetchHead.ForMerge).ToArray();

            if (fetchHeads.Length == 0)
            {
                throw new LibGit2SharpException("Remote ref to merge from was not fetched.");
            }

            GitMergeHeadHandle[] mergeHeadHandles = fetchHeads.Select(fetchHead =>
                Proxy.git_merge_head_from_fetchhead(Handle, fetchHead.RemoteCanonicalName, fetchHead.Url, fetchHead.Target.Id.Oid)).ToArray();

            try
            {
                // Perform the merge.
                return Merge(mergeHeadHandles, merger, options);
            }
            finally
            {
                // Cleanup.
                foreach (GitMergeHeadHandle mergeHeadHandle in mergeHeadHandles)
                {
                    mergeHeadHandle.Dispose();
                }
            }
        }

        /// <summary>
        /// Revert the specified commit.
        /// </summary>
        /// <param name="commit">The <see cref="Commit"/> to revert.</param>
        /// <param name="reverter">The <see cref="Signature"/> of who is performing the revert.</param>
        /// <param name="options"><see cref="RevertOptions"/> controlling revert behavior.</param>
        /// <returns>The result of the revert.</returns>
        public RevertResult Revert(Commit commit, Signature reverter, RevertOptions options = null)
        {
            Ensure.ArgumentNotNull(commit, "commit");
            Ensure.ArgumentNotNull(reverter, "reverter");

            options = options ?? new RevertOptions();

            RevertResult result = null;

            using (GitCheckoutOptsWrapper checkoutOptionsWrapper = new GitCheckoutOptsWrapper(options))
            {
                var mergeOptions = new GitMergeOpts
                {
                    Version = 1,
                    MergeFileFavorFlags = options.MergeFileFavor,
                    MergeTreeFlags = options.FindRenames ? GitMergeTreeFlags.GIT_MERGE_TREE_FIND_RENAMES :
                                                           GitMergeTreeFlags.GIT_MERGE_TREE_NORMAL,
                    RenameThreshold = (uint)options.RenameThreshold,
                    TargetLimit = (uint)options.TargetLimit,
                };

                GitRevertOpts gitRevertOpts = new GitRevertOpts()
                {
                    Mainline = (uint)options.Mainline,
                    MergeOpts = mergeOptions,

                    CheckoutOpts = checkoutOptionsWrapper.Options,
                };

                Proxy.git_revert(handle, commit.Id.Oid, gitRevertOpts);

                if (Index.IsFullyMerged)
                {
                    Commit revertCommit = null;
                    if (options.CommitOnSuccess)
                    {
                        revertCommit = this.Commit(Info.Message, author: reverter, committer: reverter);
                    }

                    result = new RevertResult(RevertStatus.Reverted, revertCommit);
                }
                else
                {
                    result = new RevertResult(RevertStatus.Conflicts);
                }
            }

            return result;
        }

        /// <summary>
        /// Cherry-picks the specified commit.
        /// </summary>
        /// <param name="commit">The <see cref="Commit"/> to cherry-pick.</param>
        /// <param name="committer">The <see cref="Signature"/> of who is performing the cherry pick.</param>
        /// <param name="options"><see cref="CherryPickOptions"/> controlling cherry pick behavior.</param>
        /// <returns>The result of the cherry pick.</returns>
        public CherryPickResult CherryPick(Commit commit, Signature committer, CherryPickOptions options = null)
        {
            Ensure.ArgumentNotNull(commit, "commit");
            Ensure.ArgumentNotNull(committer, "committer");

            options = options ?? new CherryPickOptions();

            CherryPickResult result = null;

            using (GitCheckoutOptsWrapper checkoutOptionsWrapper = new GitCheckoutOptsWrapper(options))
            {
                var mergeOptions = new GitMergeOpts
                {
                    Version = 1,
                    MergeFileFavorFlags = options.MergeFileFavor,
                    MergeTreeFlags = options.FindRenames ? GitMergeTreeFlags.GIT_MERGE_TREE_FIND_RENAMES :
                                                           GitMergeTreeFlags.GIT_MERGE_TREE_NORMAL,
                    RenameThreshold = (uint)options.RenameThreshold,
                    TargetLimit = (uint)options.TargetLimit,
                };

                GitCherryPickOptions gitCherryPickOpts = new GitCherryPickOptions()
                {
                    Mainline = (uint)options.Mainline,
                    MergeOpts = mergeOptions,

                    CheckoutOpts = checkoutOptionsWrapper.Options,
                };

                Proxy.git_cherry_pick(handle, commit.Id.Oid, gitCherryPickOpts);

                if (Index.IsFullyMerged)
                {
                    Commit cherryPickCommit = null;
                    if (options.CommitOnSuccess)
                    {
                        cherryPickCommit = this.Commit(Info.Message, commit.Author, committer);
                    }

                    result = new CherryPickResult(CherryPickStatus.CherryPicked, cherryPickCommit);
                }
                else
                {
                    result = new CherryPickResult(CherryPickStatus.Conflicts);
                }
            }

            return result;
        }

        /// <summary>
        /// Internal implementation of merge.
        /// </summary>
        /// <param name="mergeHeads">Merge heads to operate on.</param>
        /// <param name="merger">The <see cref="Signature"/> of who is performing the merge.</param>
        /// <param name="options">Specifies optional parameters controlling merge behavior; if null, the defaults are used.</param>
        /// <returns>The <see cref="MergeResult"/> of the merge.</returns>
        private MergeResult Merge(GitMergeHeadHandle[] mergeHeads, Signature merger, MergeOptions options)
        {
            GitMergeAnalysis mergeAnalysis;
            GitMergePreference mergePreference;

            Proxy.git_merge_analysis(Handle, mergeHeads, out mergeAnalysis, out mergePreference);

            MergeResult mergeResult = null;

            if ((mergeAnalysis & GitMergeAnalysis.GIT_MERGE_ANALYSIS_UP_TO_DATE) == GitMergeAnalysis.GIT_MERGE_ANALYSIS_UP_TO_DATE)
            {
                return new MergeResult(MergeStatus.UpToDate);
            }

            switch(options.FastForwardStrategy)
            {
                case FastForwardStrategy.Default:
                    if (mergeAnalysis.HasFlag(GitMergeAnalysis.GIT_MERGE_ANALYSIS_FASTFORWARD))
                    {
                        if (mergeHeads.Length != 1)
                        {
                            // We should not reach this code unless there is a bug somewhere.
                            throw new LibGit2SharpException("Unable to perform Fast-Forward merge with mith multiple merge heads.");
                        }

                        mergeResult = FastForwardMerge(mergeHeads[0], merger, options);
                    }
                    else if (mergeAnalysis.HasFlag(GitMergeAnalysis.GIT_MERGE_ANALYSIS_NORMAL))
                    {
                        mergeResult = NormalMerge(mergeHeads, merger, options);
                    }
                    break;
                case FastForwardStrategy.FastForwardOnly:
                    if (mergeAnalysis.HasFlag(GitMergeAnalysis.GIT_MERGE_ANALYSIS_FASTFORWARD))
                    {
                        if (mergeHeads.Length != 1)
                        {
                            // We should not reach this code unless there is a bug somewhere.
                            throw new LibGit2SharpException("Unable to perform Fast-Forward merge with mith multiple merge heads.");
                        }

                        mergeResult = FastForwardMerge(mergeHeads[0], merger, options);
                    }
                    else
                    {
                        // TODO: Maybe this condition should rather be indicated through the merge result
                        //       instead of throwing an exception.
                        throw new NonFastForwardException("Cannot perform fast-forward merge.");
                    }
                    break;
                case FastForwardStrategy.NoFastFoward:
                    if (mergeAnalysis.HasFlag(GitMergeAnalysis.GIT_MERGE_ANALYSIS_NORMAL))
                    {
                        mergeResult = NormalMerge(mergeHeads, merger, options);
                    }
                    break;
                default:
                    throw new NotImplementedException(
                        string.Format(CultureInfo.InvariantCulture, "Unknown fast forward strategy: {0}", mergeAnalysis));
            }

            if (mergeResult == null)
            {
                throw new NotImplementedException(
                    string.Format(CultureInfo.InvariantCulture, "Unknown merge analysis: {0}", options.FastForwardStrategy));
            }

            return mergeResult;
        }

        /// <summary>
        /// Perform a normal merge (i.e. a non-fast-forward merge).
        /// </summary>
        /// <param name="mergeHeads">The merge head handles to merge.</param>
        /// <param name="merger">The <see cref="Signature"/> of who is performing the merge.</param>
        /// <param name="options">Specifies optional parameters controlling merge behavior; if null, the defaults are used.</param>
        /// <returns>The <see cref="MergeResult"/> of the merge.</returns>
        private MergeResult NormalMerge(GitMergeHeadHandle[] mergeHeads, Signature merger, MergeOptions options)
        {
            MergeResult mergeResult;

            var mergeOptions = new GitMergeOpts
                {
                    Version = 1,
                    MergeFileFavorFlags = options.MergeFileFavor,
                    MergeTreeFlags = options.FindRenames ? GitMergeTreeFlags.GIT_MERGE_TREE_FIND_RENAMES :
                                                           GitMergeTreeFlags.GIT_MERGE_TREE_NORMAL,
                    RenameThreshold = (uint) options.RenameThreshold,
                    TargetLimit = (uint) options.TargetLimit,
                };

            using (GitCheckoutOptsWrapper checkoutOptionsWrapper = new GitCheckoutOptsWrapper(options))
            {
                var checkoutOpts = checkoutOptionsWrapper.Options;

                Proxy.git_merge(Handle, mergeHeads, mergeOptions, checkoutOpts);
            }

            if (Index.IsFullyMerged)
            {
                Commit mergeCommit = null;
                if (options.CommitOnSuccess)
                {
                    // Commit the merge
                    mergeCommit = Commit(Info.Message, author: merger, committer: merger);
                }

                mergeResult = new MergeResult(MergeStatus.NonFastForward, mergeCommit);
            }
            else
            {
                mergeResult = new MergeResult(MergeStatus.Conflicts);
            }

            return mergeResult;
        }

        /// <summary>
        /// Perform a fast-forward merge.
        /// </summary>
        /// <param name="mergeHead">The merge head handle to fast-forward merge.</param>
        /// <param name="merger">The <see cref="Signature"/> of who is performing the merge.</param>
        /// <param name="options">Options controlling merge behavior.</param>
        /// <returns>The <see cref="MergeResult"/> of the merge.</returns>
        private MergeResult FastForwardMerge(GitMergeHeadHandle mergeHead, Signature merger, MergeOptions options)
        {
            ObjectId id = Proxy.git_merge_head_id(mergeHead);
            Commit fastForwardCommit = (Commit) Lookup(id, ObjectType.Commit);
            Ensure.GitObjectIsNotNull(fastForwardCommit, id.Sha);

            CheckoutTree(fastForwardCommit.Tree, null, options);

            var reference = Refs.Head.ResolveToDirectReference();

            // TODO: This reflog entry could be more specific
            string refLogEntry = string.Format(
                CultureInfo.InvariantCulture, "merge {0}: Fast-forward", fastForwardCommit.Sha);

            if (reference == null)
            {
                // Reference does not exist, create it.
                Refs.Add(Refs.Head.TargetIdentifier, fastForwardCommit.Id, merger, refLogEntry);
            }
            else
            {
                // Update target reference.
                Refs.UpdateTarget(reference, fastForwardCommit.Id.Sha, merger, refLogEntry);
            }

            return new MergeResult(MergeStatus.FastForward, fastForwardCommit);
        }

        /// <summary>
        /// Gets the references to the tips that are currently being merged.
        /// </summary>
        internal IEnumerable<MergeHead> MergeHeads
        {
            get
            {
                int i = 0;
                return Proxy.git_repository_mergehead_foreach(Handle,
                    commitId => new MergeHead(this, commitId, i++));
            }
        }

        internal StringComparer PathComparer
        {
            get { return pathCase.Value.Comparer; }
        }

        internal bool PathStartsWith(string path, string value)
        {
            return pathCase.Value.StartsWith(path, value);
        }

        internal FilePath[] ToFilePaths(IEnumerable<string> paths)
        {
            if (paths == null)
            {
                return null;
            }

            var filePaths = new List<FilePath>();

            foreach (string path in paths)
            {
                if (string.IsNullOrEmpty(path))
                {
                    throw new ArgumentException("At least one provided path is either null or empty.", "paths");
                }

                filePaths.Add(this.BuildRelativePathFrom(path));
            }

            if (filePaths.Count == 0)
            {
                throw new ArgumentException("No path has been provided.", "paths");
            }

            return filePaths.ToArray();
        }

        private string DebuggerDisplay
        {
            get
            {
                return string.Format(CultureInfo.InvariantCulture,
                    "{0} = \"{1}\"",
                    Info.IsBare ? "Gitdir" : "Workdir",
                    Info.IsBare ? Info.Path : Info.WorkingDirectory);
            }
        }
    }
}