#include "git-utils.hh"
#include "input-accessor.hh"
#include "cache.hh"

#include <boost/core/span.hpp>

#include <git2/blob.h>
#include <git2/commit.h>
#include <git2/describe.h>
#include <git2/errors.h>
#include <git2/global.h>
#include <git2/object.h>
#include <git2/refs.h>
#include <git2/remote.h>
#include <git2/repository.h>
#include <git2/status.h>
#include <git2/tree.h>

#include <unordered_set>
#include <queue>

namespace std {

template<> struct hash<git_oid>
{
    size_t operator()(const git_oid & oid) const
    {
        return * (size_t *) oid.id;
    }
};

}

std::ostream & operator << (std::ostream & str, const git_oid & oid)
{
    str << git_oid_tostr_s(&oid);
    return str;
}

bool operator == (const git_oid & oid1, const git_oid & oid2)
{
    return git_oid_equal(&oid1, &oid2);
}

namespace nix {

// Some wrapper types that ensure that the git_*_free functions get called.
template<auto del>
struct Deleter
{
    template <typename T>
    void operator()(T * p) const { del(p); };
};

typedef std::unique_ptr<git_repository, Deleter<git_repository_free>> Repository;
typedef std::unique_ptr<git_tree_entry, Deleter<git_tree_entry_free>> TreeEntry;
typedef std::unique_ptr<git_tree, Deleter<git_tree_free>> Tree;
typedef std::unique_ptr<git_treebuilder, Deleter<git_treebuilder_free>> TreeBuilder;
typedef std::unique_ptr<git_blob, Deleter<git_blob_free>> Blob;
typedef std::unique_ptr<git_object, Deleter<git_object_free>> Object;
typedef std::unique_ptr<git_commit, Deleter<git_commit_free>> Commit;
typedef std::unique_ptr<git_reference, Deleter<git_reference_free>> Reference;
typedef std::unique_ptr<git_describe_result, Deleter<git_describe_result_free>> DescribeResult;
typedef std::unique_ptr<git_status_list, Deleter<git_status_list_free>> StatusList;
typedef std::unique_ptr<git_remote, Deleter<git_remote_free>> Remote;

// A helper to ensure that we don't leak objects returned by libgit2.
template<typename T>
struct Setter
{
    T & t;
    typename T::pointer p = nullptr;

    Setter(T & t) : t(t) { }

    ~Setter() { if (p) t = T(p); }

    operator typename T::pointer * () { return &p; }
};

Hash toHash(const git_oid & oid)
{
    #ifdef GIT_EXPERIMENTAL_SHA256
    assert(oid.type == GIT_OID_SHA1);
    #endif
    Hash hash(htSHA1);
    memcpy(hash.hash, oid.id, hash.hashSize);
    return hash;
}

static void initLibGit2()
{
    if (git_libgit2_init() < 0)
        throw Error("initialising libgit2: %s", git_error_last()->message);
}

git_oid hashToOID(const Hash & hash)
{
    git_oid oid;
    if (git_oid_fromstr(&oid, hash.gitRev().c_str()))
        throw Error("cannot convert '%s' to a Git OID", hash.gitRev());
    return oid;
}

Object lookupObject(git_repository * repo, const git_oid & oid)
{
    Object obj;
    if (git_object_lookup(Setter(obj), repo, &oid, GIT_OBJECT_ANY)) {
        auto err = git_error_last();
        throw Error("getting Git object '%s': %s", oid, err->message);
    }
    return obj;
}

template<typename T>
T peelObject(git_repository * repo, git_object * obj, git_object_t type)
{
    T obj2;
    if (git_object_peel((git_object * *) (typename T::pointer *) Setter(obj2), obj, type)) {
        auto err = git_error_last();
        throw Error("peeling Git object '%s': %s", git_object_id(obj), err->message);
    }
    return obj2;
}

int statusCallbackTrampoline(const char * path, unsigned int statusFlags, void * payload)
{
    return (*((std::function<int(const char * path, unsigned int statusFlags)> *) payload))(path, statusFlags);
}

struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
{
    CanonPath path;
    Repository repo;

    GitRepoImpl(CanonPath _path, bool create, bool bare)
        : path(std::move(_path))
    {
        initLibGit2();

        if (pathExists(path.abs())) {
            if (git_repository_open(Setter(repo), path.c_str()))
                throw Error("opening Git repository '%s': %s", path, git_error_last()->message);
        } else {
            if (git_repository_init(Setter(repo), path.c_str(), bare))
                throw Error("creating Git repository '%s': %s", path, git_error_last()->message);
        }
    }

    operator git_repository * ()
    {
        return repo.get();
    }

    uint64_t getRevCount(const Hash & rev) override
    {
        std::unordered_set<git_oid> done;
        std::queue<Commit> todo;

        todo.push(peelObject<Commit>(*this, lookupObject(*this, hashToOID(rev)).get(), GIT_OBJECT_COMMIT));

        while (auto commit = pop(todo)) {
            if (!done.insert(*git_commit_id(commit->get())).second) continue;

            for (size_t n = 0; n < git_commit_parentcount(commit->get()); ++n) {
                git_commit * parent;
                if (git_commit_parent(&parent, commit->get(), n))
                    throw Error("getting parent of Git commit '%s': %s", *git_commit_id(commit->get()), git_error_last()->message);
                todo.push(Commit(parent));
            }
        }

        return done.size();
    }

    uint64_t getLastModified(const Hash & rev) override
    {
        auto commit = peelObject<Commit>(*this, lookupObject(*this, hashToOID(rev)).get(), GIT_OBJECT_COMMIT);

        return git_commit_time(commit.get());
    }

    bool isShallow() override
    {
        return git_repository_is_shallow(*this);
    }

    Hash resolveRef(std::string ref) override
    {
        // Handle revisions used as refs.
        {
            git_oid oid;
            if (git_oid_fromstr(&oid, ref.c_str()) == 0)
                return toHash(oid);
        }

        // Resolve short names like 'master'.
        Reference ref2;
        if (!git_reference_dwim(Setter(ref2), *this, ref.c_str()))
            ref = git_reference_name(ref2.get());

        // Resolve full references like 'refs/heads/master'.
        Reference ref3;
        if (git_reference_lookup(Setter(ref3), *this, ref.c_str()))
            throw Error("resolving Git reference '%s': %s", ref, git_error_last()->message);

        auto oid = git_reference_target(ref3.get());
        if (!oid)
            throw Error("cannot get OID for Git reference '%s'", git_reference_name(ref3.get()));

        return toHash(*oid);
    }

    WorkdirInfo getWorkdirInfo() override
    {
        WorkdirInfo info;

        /* Get the head revision, if any. */
        git_oid headRev;
        if (auto err = git_reference_name_to_id(&headRev, *this, "HEAD")) {
            if (err != GIT_ENOTFOUND)
                throw Error("resolving HEAD: %s", git_error_last()->message);
        } else
            info.headRev = toHash(headRev);

        /* Get all tracked files and determine whether the working
           directory is dirty. */
        std::function<int(const char * path, unsigned int statusFlags)> statusCallback = [&](const char * path, unsigned int statusFlags)
        {
            if (!(statusFlags & GIT_STATUS_INDEX_DELETED) &&
                !(statusFlags & GIT_STATUS_WT_DELETED))
                info.files.insert(CanonPath(path));
            if (statusFlags != GIT_STATUS_CURRENT)
                info.isDirty = true;
            return 0;
        };

        git_status_options options = GIT_STATUS_OPTIONS_INIT;
        options.flags |= GIT_STATUS_OPT_INCLUDE_UNMODIFIED;
        options.flags |= GIT_STATUS_OPT_EXCLUDE_SUBMODULES;
        if (git_status_foreach_ext(*this, &options, &statusCallbackTrampoline, &statusCallback))
            throw Error("getting working directory status: %s", git_error_last()->message);

        return info;
    }

    std::optional<std::string> getWorkdirRef() override
    {
        Reference ref;
        if (git_reference_lookup(Setter(ref), *this, "HEAD"))
            throw Error("looking up HEAD: %s", git_error_last()->message);

        if (auto target = git_reference_symbolic_target(ref.get()))
            return target;

        return std::nullopt;
    }

    bool hasObject(const Hash & oid_) override
    {
        auto oid = hashToOID(oid_);

        Object obj;
        if (auto errCode = git_object_lookup(Setter(obj), *this, &oid, GIT_OBJECT_ANY)) {
            if (errCode == GIT_ENOTFOUND) return false;
            auto err = git_error_last();
            throw Error("getting Git object '%s': %s", oid, err->message);
        }

        return true;
    }

    ref<InputAccessor> getAccessor(const Hash & rev) override;

    void fetch(
        const std::string & url,
        const std::string & refspec) override
    {
        /* FIXME: use libgit2. Unfortunately, it doesn't support
           ssh_config at the moment. */
        #if 0
        Remote remote;

        if (git_remote_create_anonymous(Setter(remote), *this, url.c_str()))
            throw Error("cannot create Git remote '%s': %s", url, git_error_last()->message);

        char * refspecs[] = {(char *) refspec.c_str()};
        git_strarray refspecs2 {
            .strings = refspecs,
            .count = 1
        };

        if (git_remote_fetch(remote.get(), &refspecs2, nullptr, nullptr))
            throw Error("fetching '%s' from '%s': %s", refspec, url, git_error_last()->message);
        #endif

        // FIXME: git stderr messes up our progress indicator, so
        // we're using --quiet for now. Should process its stderr.
        runProgram("git", true,
            { "-C", path.abs(),
              "--bare",
              "fetch",
              "--quiet",
              "--force",
              "--",
              url,
              refspec
            }, {}, true);
    }
};

ref<GitRepo> GitRepo::openRepo(const CanonPath & path, bool create, bool bare)
{
    return make_ref<GitRepoImpl>(path, create, bare);
}

struct GitInputAccessor : InputAccessor
{
    ref<GitRepoImpl> repo;
    Tree root;

    GitInputAccessor(ref<GitRepoImpl> repo_, const Hash & rev)
        : repo(repo_)
        , root(peelObject<Tree>(*repo, lookupObject(*repo, hashToOID(rev)).get(), GIT_OBJECT_TREE))
    {
    }

    std::string readBlob(const CanonPath & path, bool symlink)
    {
        auto blob = getBlob(path, symlink);

        auto data = std::string_view((const char *) git_blob_rawcontent(blob.get()), git_blob_rawsize(blob.get()));

        return std::string(data);
    }

    std::string readFile(const CanonPath & path) override
    {
        return readBlob(path, false);
    }

    bool pathExists(const CanonPath & path) override
    {
        return path.isRoot() ? true : (bool) lookup(path);
    }

    Stat lstat(const CanonPath & path) override
    {
        if (path.isRoot())
            return Stat { .type = tDirectory };

        auto entry = need(path);

        auto mode = git_tree_entry_filemode(entry);

        if (mode == GIT_FILEMODE_TREE)
            return Stat { .type = tDirectory };

        else if (mode == GIT_FILEMODE_BLOB)
            return Stat { .type = tRegular };

        else if (mode == GIT_FILEMODE_BLOB_EXECUTABLE)
            return Stat { .type = tRegular, .isExecutable = true };

        else if (mode == GIT_FILEMODE_LINK)
            return Stat { .type = tSymlink };

        else if (mode == GIT_FILEMODE_COMMIT)
            // Treat submodules as an empty directory.
            return Stat { .type = tDirectory };

        else
            throw Error("file '%s' has an unsupported Git file type");
    }

    DirEntries readDirectory(const CanonPath & path) override
    {
        return std::visit(overloaded {
            [&](Tree tree) {
                DirEntries res;

                auto count = git_tree_entrycount(tree.get());

                for (size_t n = 0; n < count; ++n) {
                    auto entry = git_tree_entry_byindex(tree.get(), n);
                    // FIXME: add to cache
                    res.emplace(std::string(git_tree_entry_name(entry)), DirEntry{});
                }

                return res;
            },
            [&](Submodule) {
                return DirEntries();
            }
        }, getTree(path));
    }

    std::string readLink(const CanonPath & path) override
    {
        return readBlob(path, true);
    }

    std::map<CanonPath, TreeEntry> lookupCache;

    /* Recursively look up 'path' relative to the root. */
    git_tree_entry * lookup(const CanonPath & path)
    {
        if (path.isRoot()) return nullptr;

        auto i = lookupCache.find(path);
        if (i == lookupCache.end()) {
            TreeEntry entry;
            if (auto err = git_tree_entry_bypath(Setter(entry), root.get(), std::string(path.rel()).c_str())) {
                if (err != GIT_ENOTFOUND)
                    throw Error("looking up '%s': %s", showPath(path), git_error_last()->message);
            }

            i = lookupCache.emplace(path, std::move(entry)).first;
        }

        return &*i->second;
    }

    git_tree_entry * need(const CanonPath & path)
    {
        auto entry = lookup(path);
        if (!entry)
            throw Error("'%s' does not exist", showPath(path));
        return entry;
    }

    struct Submodule { };

    std::variant<Tree, Submodule> getTree(const CanonPath & path)
    {
        if (path.isRoot()) {
            Tree tree;
            if (git_tree_dup(Setter(tree), root.get()))
                throw Error("duplicating directory '%s': %s", showPath(path), git_error_last()->message);
            return tree;
        }

        auto entry = need(path);

        if (git_tree_entry_type(entry) == GIT_OBJECT_COMMIT)
            return Submodule();

        if (git_tree_entry_type(entry) != GIT_OBJECT_TREE)
            throw Error("'%s' is not a directory", showPath(path));

        Tree tree;
        if (git_tree_entry_to_object((git_object * *) (git_tree * *) Setter(tree), *repo, entry))
            throw Error("looking up directory '%s': %s", showPath(path), git_error_last()->message);

        return tree;
    }

    Blob getBlob(const CanonPath & path, bool expectSymlink)
    {
        auto notExpected = [&]()
        {
            throw Error(
                expectSymlink
                ? "'%s' is not a symlink"
                : "'%s' is not a regular file",
                showPath(path));
        };

        if (path.isRoot()) notExpected();

        auto entry = need(path);

        if (git_tree_entry_type(entry) != GIT_OBJECT_BLOB)
            notExpected();

        auto mode = git_tree_entry_filemode(entry);
        if (expectSymlink) {
            if (mode != GIT_FILEMODE_LINK)
                notExpected();
        } else {
            if (mode != GIT_FILEMODE_BLOB && mode != GIT_FILEMODE_BLOB_EXECUTABLE)
                notExpected();
        }

        Blob blob;
        if (git_tree_entry_to_object((git_object * *) (git_blob * *) Setter(blob), *repo, entry))
            throw Error("looking up file '%s': %s", showPath(path), git_error_last()->message);

        return blob;
    }
};

ref<InputAccessor> GitRepoImpl::getAccessor(const Hash & rev)
{
    return make_ref<GitInputAccessor>(ref<GitRepoImpl>(shared_from_this()), rev);
}

}