import os

from git.compat import defenc
from git.objects import Object, Commit
from git.util import (
    join_path,
    join_path_native,
    to_native_path_linux,
    assure_directory_exists,
    hex_to_bin,
    LockedFD
)
from gitdb.exc import (
    BadObject,
    BadName
)

import os.path as osp

from .log import RefLog


__all__ = ["SymbolicReference"]


def _git_dir(repo, path):
    """ Find the git dir that's appropriate for the path"""
    name = "%s" % (path,)
    if name in ['HEAD', 'ORIG_HEAD', 'FETCH_HEAD', 'index', 'logs']:
        return repo.git_dir
    return repo.common_dir


class SymbolicReference(object):

    """Represents a special case of a reference such that this reference is symbolic.
    It does not point to a specific commit, but to another Head, which itself
    specifies a commit.

    A typical example for a symbolic reference is HEAD."""
    __slots__ = ("repo", "path")
    _resolve_ref_on_create = False
    _points_to_commits_only = True
    _common_path_default = ""
    _remote_common_path_default = "refs/remotes"
    _id_attribute_ = "name"

    def __init__(self, repo, path, check_path=None):
        self.repo = repo
        self.path = path

    def __str__(self):
        return self.path

    def __repr__(self):
        return '<git.%s "%s">' % (self.__class__.__name__, self.path)

    def __eq__(self, other):
        if hasattr(other, 'path'):
            return self.path == other.path
        return False

    def __ne__(self, other):
        return not (self == other)

    def __hash__(self):
        return hash(self.path)

    @property
    def name(self):
        """
        :return:
            In case of symbolic references, the shortest assumable name
            is the path itself."""
        return self.path

    @property
    def abspath(self):
        return join_path_native(_git_dir(self.repo, self.path), self.path)

    @classmethod
    def _get_packed_refs_path(cls, repo):
        return osp.join(repo.common_dir, 'packed-refs')

    @classmethod
    def _iter_packed_refs(cls, repo):
        """Returns an iterator yielding pairs of sha1/path pairs (as bytes) for the corresponding refs.
        :note: The packed refs file will be kept open as long as we iterate"""
        try:
            with open(cls._get_packed_refs_path(repo), 'rt', encoding='UTF-8') as fp:
                for line in fp:
                    line = line.strip()
                    if not line:
                        continue
                    if line.startswith('#'):
                        # "# pack-refs with: peeled fully-peeled sorted"
                        # the git source code shows "peeled",
                        # "fully-peeled" and "sorted" as the keywords
                        # that can go on this line, as per comments in git file
                        # refs/packed-backend.c
                        # I looked at master on 2017-10-11,
                        # commit 111ef79afe, after tag v2.15.0-rc1
                        # from repo https://github.com/git/git.git
                        if line.startswith('# pack-refs with:') and 'peeled' not in line:
                            raise TypeError("PackingType of packed-Refs not understood: %r" % line)
                        # END abort if we do not understand the packing scheme
                        continue
                    # END parse comment

                    # skip dereferenced tag object entries - previous line was actual
                    # tag reference for it
                    if line[0] == '^':
                        continue

                    yield tuple(line.split(' ', 1))
                # END for each line
        except (OSError, IOError):
            return
        # END no packed-refs file handling
        # NOTE: Had try-finally block around here to close the fp,
        # but some python version wouldn't allow yields within that.
        # I believe files are closing themselves on destruction, so it is
        # alright.

    @classmethod
    def dereference_recursive(cls, repo, ref_path):
        """
        :return: hexsha stored in the reference at the given ref_path, recursively dereferencing all
            intermediate references as required
        :param repo: the repository containing the reference at ref_path"""
        while True:
            hexsha, ref_path = cls._get_ref_info(repo, ref_path)
            if hexsha is not None:
                return hexsha
        # END recursive dereferencing

    @classmethod
    def _get_ref_info_helper(cls, repo, ref_path):
        """Return: (str(sha), str(target_ref_path)) if available, the sha the file at
        rela_path points to, or None. target_ref_path is the reference we
        point to, or None"""
        tokens = None
        repodir = _git_dir(repo, ref_path)
        try:
            with open(osp.join(repodir, ref_path), 'rt', encoding='UTF-8') as fp:
                value = fp.read().rstrip()
            # Don't only split on spaces, but on whitespace, which allows to parse lines like
            # 60b64ef992065e2600bfef6187a97f92398a9144                branch 'master' of git-server:/path/to/repo
            tokens = value.split()
            assert(len(tokens) != 0)
        except (OSError, IOError):
            # Probably we are just packed, find our entry in the packed refs file
            # NOTE: We are not a symbolic ref if we are in a packed file, as these
            # are excluded explicitly
            for sha, path in cls._iter_packed_refs(repo):
                if path != ref_path:
                    continue
                # sha will be used
                tokens = sha, path
                break
            # END for each packed ref
        # END handle packed refs
        if tokens is None:
            raise ValueError("Reference at %r does not exist" % ref_path)

        # is it a reference ?
        if tokens[0] == 'ref:':
            return (None, tokens[1])

        # its a commit
        if repo.re_hexsha_only.match(tokens[0]):
            return (tokens[0], None)

        raise ValueError("Failed to parse reference information from %r" % ref_path)

    @classmethod
    def _get_ref_info(cls, repo, ref_path):
        """Return: (str(sha), str(target_ref_path)) if available, the sha the file at
        rela_path points to, or None. target_ref_path is the reference we
        point to, or None"""
        return cls._get_ref_info_helper(repo, ref_path)

    def _get_object(self):
        """
        :return:
            The object our ref currently refers to. Refs can be cached, they will
            always point to the actual object as it gets re-created on each query"""
        # have to be dynamic here as we may be a tag which can point to anything
        # Our path will be resolved to the hexsha which will be used accordingly
        return Object.new_from_sha(self.repo, hex_to_bin(self.dereference_recursive(self.repo, self.path)))

    def _get_commit(self):
        """
        :return:
            Commit object we point to, works for detached and non-detached
            SymbolicReferences. The symbolic reference will be dereferenced recursively."""
        obj = self._get_object()
        if obj.type == 'tag':
            obj = obj.object
        # END dereference tag

        if obj.type != Commit.type:
            raise TypeError("Symbolic Reference pointed to object %r, commit was required" % obj)
        # END handle type
        return obj

    def set_commit(self, commit, logmsg=None):
        """As set_object, but restricts the type of object to be a Commit

        :raise ValueError: If commit is not a Commit object or doesn't point to
            a commit
        :return: self"""
        # check the type - assume the best if it is a base-string
        invalid_type = False
        if isinstance(commit, Object):
            invalid_type = commit.type != Commit.type
        elif isinstance(commit, SymbolicReference):
            invalid_type = commit.object.type != Commit.type
        else:
            try:
                invalid_type = self.repo.rev_parse(commit).type != Commit.type
            except (BadObject, BadName) as e:
                raise ValueError("Invalid object: %s" % commit) from e
            # END handle exception
        # END verify type

        if invalid_type:
            raise ValueError("Need commit, got %r" % commit)
        # END handle raise

        # we leave strings to the rev-parse method below
        self.set_object(commit, logmsg)

        return self

    def set_object(self, object, logmsg=None):  # @ReservedAssignment
        """Set the object we point to, possibly dereference our symbolic reference first.
        If the reference does not exist, it will be created

        :param object: a refspec, a SymbolicReference or an Object instance. SymbolicReferences
            will be dereferenced beforehand to obtain the object they point to
        :param logmsg: If not None, the message will be used in the reflog entry to be
            written. Otherwise the reflog is not altered
        :note: plain SymbolicReferences may not actually point to objects by convention
        :return: self"""
        if isinstance(object, SymbolicReference):
            object = object.object  # @ReservedAssignment
        # END resolve references

        is_detached = True
        try:
            is_detached = self.is_detached
        except ValueError:
            pass
        # END handle non-existing ones

        if is_detached:
            return self.set_reference(object, logmsg)

        # set the commit on our reference
        return self._get_reference().set_object(object, logmsg)

    commit = property(_get_commit, set_commit, doc="Query or set commits directly")
    object = property(_get_object, set_object, doc="Return the object our ref currently refers to")

    def _get_reference(self):
        """:return: Reference Object we point to
        :raise TypeError: If this symbolic reference is detached, hence it doesn't point
            to a reference, but to a commit"""
        sha, target_ref_path = self._get_ref_info(self.repo, self.path)
        if target_ref_path is None:
            raise TypeError("%s is a detached symbolic reference as it points to %r" % (self, sha))
        return self.from_path(self.repo, target_ref_path)

    def set_reference(self, ref, logmsg=None):
        """Set ourselves to the given ref. It will stay a symbol if the ref is a Reference.
        Otherwise an Object, given as Object instance or refspec, is assumed and if valid,
        will be set which effectively detaches the refererence if it was a purely
        symbolic one.

        :param ref: SymbolicReference instance, Object instance or refspec string
            Only if the ref is a SymbolicRef instance, we will point to it. Everything
            else is dereferenced to obtain the actual object.
        :param logmsg: If set to a string, the message will be used in the reflog.
            Otherwise, a reflog entry is not written for the changed reference.
            The previous commit of the entry will be the commit we point to now.

            See also: log_append()

        :return: self
        :note: This symbolic reference will not be dereferenced. For that, see
            ``set_object(...)``"""
        write_value = None
        obj = None
        if isinstance(ref, SymbolicReference):
            write_value = "ref: %s" % ref.path
        elif isinstance(ref, Object):
            obj = ref
            write_value = ref.hexsha
        elif isinstance(ref, str):
            try:
                obj = self.repo.rev_parse(ref + "^{}")    # optionally deref tags
                write_value = obj.hexsha
            except (BadObject, BadName) as e:
                raise ValueError("Could not extract object from %s" % ref) from e
            # END end try string
        else:
            raise ValueError("Unrecognized Value: %r" % ref)
        # END try commit attribute

        # typecheck
        if obj is not None and self._points_to_commits_only and obj.type != Commit.type:
            raise TypeError("Require commit, got %r" % obj)
        # END verify type

        oldbinsha = None
        if logmsg is not None:
            try:
                oldbinsha = self.commit.binsha
            except ValueError:
                oldbinsha = Commit.NULL_BIN_SHA
            # END handle non-existing
        # END retrieve old hexsha

        fpath = self.abspath
        assure_directory_exists(fpath, is_file=True)

        lfd = LockedFD(fpath)
        fd = lfd.open(write=True, stream=True)
        ok = True
        try:
            fd.write(write_value.encode('ascii') + b'\n')
            lfd.commit()
            ok = True
        finally:
            if not ok:
                lfd.rollback()
        # Adjust the reflog
        if logmsg is not None:
            self.log_append(oldbinsha, logmsg)

        return self

    # aliased reference
    reference = property(_get_reference, set_reference, doc="Returns the Reference we point to")
    ref = reference

    def is_valid(self):
        """
        :return:
            True if the reference is valid, hence it can be read and points to
            a valid object or reference."""
        try:
            self.object
        except (OSError, ValueError):
            return False
        else:
            return True

    @property
    def is_detached(self):
        """
        :return:
            True if we are a detached reference, hence we point to a specific commit
            instead to another reference"""
        try:
            self.ref
            return False
        except TypeError:
            return True

    def log(self):
        """
        :return: RefLog for this reference. Its last entry reflects the latest change
            applied to this reference

        .. note:: As the log is parsed every time, its recommended to cache it for use
            instead of calling this method repeatedly. It should be considered read-only."""
        return RefLog.from_file(RefLog.path(self))

    def log_append(self, oldbinsha, message, newbinsha=None):
        """Append a logentry to the logfile of this ref

        :param oldbinsha: binary sha this ref used to point to
        :param message: A message describing the change
        :param newbinsha: The sha the ref points to now. If None, our current commit sha
            will be used
        :return: added RefLogEntry instance"""
        # NOTE: we use the committer of the currently active commit - this should be
        # correct to allow overriding the committer on a per-commit level.
        # See https://github.com/gitpython-developers/GitPython/pull/146
        try:
            committer_or_reader = self.commit.committer
        except ValueError:
            committer_or_reader = self.repo.config_reader()
        # end handle newly cloned repositories
        return RefLog.append_entry(committer_or_reader, RefLog.path(self), oldbinsha,
                                   (newbinsha is None and self.commit.binsha) or newbinsha,
                                   message)

    def log_entry(self, index):
        """:return: RefLogEntry at the given index
        :param index: python list compatible positive or negative index

        .. note:: This method must read part of the reflog during execution, hence
            it should be used sparringly, or only if you need just one index.
            In that case, it will be faster than the ``log()`` method"""
        return RefLog.entry_at(RefLog.path(self), index)

    @classmethod
    def to_full_path(cls, path):
        """
        :return: string with a full repository-relative path which can be used to initialize
            a Reference instance, for instance by using ``Reference.from_path``"""
        if isinstance(path, SymbolicReference):
            path = path.path
        full_ref_path = path
        if not cls._common_path_default:
            return full_ref_path
        if not path.startswith(cls._common_path_default + "/"):
            full_ref_path = '%s/%s' % (cls._common_path_default, path)
        return full_ref_path

    @classmethod
    def delete(cls, repo, path):
        """Delete the reference at the given path

        :param repo:
            Repository to delete the reference from

        :param path:
            Short or full path pointing to the reference, i.e. refs/myreference
            or just "myreference", hence 'refs/' is implied.
            Alternatively the symbolic reference to be deleted"""
        full_ref_path = cls.to_full_path(path)
        abs_path = osp.join(repo.common_dir, full_ref_path)
        if osp.exists(abs_path):
            os.remove(abs_path)
        else:
            # check packed refs
            pack_file_path = cls._get_packed_refs_path(repo)
            try:
                with open(pack_file_path, 'rb') as reader:
                    new_lines = []
                    made_change = False
                    dropped_last_line = False
                    for line in reader:
                        line = line.decode(defenc)
                        _, _, line_ref = line.partition(' ')
                        line_ref = line_ref.strip()
                        # keep line if it is a comment or if the ref to delete is not
                        # in the line
                        # If we deleted the last line and this one is a tag-reference object,
                        # we drop it as well
                        if (line.startswith('#') or full_ref_path != line_ref) and \
                                (not dropped_last_line or dropped_last_line and not line.startswith('^')):
                            new_lines.append(line)
                            dropped_last_line = False
                            continue
                        # END skip comments and lines without our path

                        # drop this line
                        made_change = True
                        dropped_last_line = True

                # write the new lines
                if made_change:
                    # write-binary is required, otherwise windows will
                    # open the file in text mode and change LF to CRLF !
                    with open(pack_file_path, 'wb') as fd:
                        fd.writelines(line.encode(defenc) for line in new_lines)

            except (OSError, IOError):
                pass  # it didn't exist at all

        # delete the reflog
        reflog_path = RefLog.path(cls(repo, full_ref_path))
        if osp.isfile(reflog_path):
            os.remove(reflog_path)
        # END remove reflog

    @classmethod
    def _create(cls, repo, path, resolve, reference, force, logmsg=None):
        """internal method used to create a new symbolic reference.
        If resolve is False, the reference will be taken as is, creating
        a proper symbolic reference. Otherwise it will be resolved to the
        corresponding object and a detached symbolic reference will be created
        instead"""
        git_dir = _git_dir(repo, path)
        full_ref_path = cls.to_full_path(path)
        abs_ref_path = osp.join(git_dir, full_ref_path)

        # figure out target data
        target = reference
        if resolve:
            target = repo.rev_parse(str(reference))

        if not force and osp.isfile(abs_ref_path):
            target_data = str(target)
            if isinstance(target, SymbolicReference):
                target_data = target.path
            if not resolve:
                target_data = "ref: " + target_data
            with open(abs_ref_path, 'rb') as fd:
                existing_data = fd.read().decode(defenc).strip()
            if existing_data != target_data:
                raise OSError("Reference at %r does already exist, pointing to %r, requested was %r" %
                              (full_ref_path, existing_data, target_data))
        # END no force handling

        ref = cls(repo, full_ref_path)
        ref.set_reference(target, logmsg)
        return ref

    @classmethod
    def create(cls, repo, path, reference='HEAD', force=False, logmsg=None, **kwargs):
        """Create a new symbolic reference, hence a reference pointing to another reference.

        :param repo:
            Repository to create the reference in

        :param path:
            full path at which the new symbolic reference is supposed to be
            created at, i.e. "NEW_HEAD" or "symrefs/my_new_symref"

        :param reference:
            The reference to which the new symbolic reference should point to.
            If it is a commit'ish, the symbolic ref will be detached.

        :param force:
            if True, force creation even if a symbolic reference with that name already exists.
            Raise OSError otherwise

        :param logmsg:
            If not None, the message to append to the reflog. Otherwise no reflog
            entry is written.

        :return: Newly created symbolic Reference

        :raise OSError:
            If a (Symbolic)Reference with the same name but different contents
            already exists.

        :note: This does not alter the current HEAD, index or Working Tree"""
        return cls._create(repo, path, cls._resolve_ref_on_create, reference, force, logmsg)

    def rename(self, new_path, force=False):
        """Rename self to a new path

        :param new_path:
            Either a simple name or a full path, i.e. new_name or features/new_name.
            The prefix refs/ is implied for references and will be set as needed.
            In case this is a symbolic ref, there is no implied prefix

        :param force:
            If True, the rename will succeed even if a head with the target name
            already exists. It will be overwritten in that case

        :return: self
        :raise OSError: In case a file at path but a different contents already exists """
        new_path = self.to_full_path(new_path)
        if self.path == new_path:
            return self

        new_abs_path = osp.join(_git_dir(self.repo, new_path), new_path)
        cur_abs_path = osp.join(_git_dir(self.repo, self.path), self.path)
        if osp.isfile(new_abs_path):
            if not force:
                # if they point to the same file, its not an error
                with open(new_abs_path, 'rb') as fd1:
                    f1 = fd1.read().strip()
                with open(cur_abs_path, 'rb') as fd2:
                    f2 = fd2.read().strip()
                if f1 != f2:
                    raise OSError("File at path %r already exists" % new_abs_path)
                # else: we could remove ourselves and use the otherone, but
                # but clarity we just continue as usual
            # END not force handling
            os.remove(new_abs_path)
        # END handle existing target file

        dname = osp.dirname(new_abs_path)
        if not osp.isdir(dname):
            os.makedirs(dname)
        # END create directory

        os.rename(cur_abs_path, new_abs_path)
        self.path = new_path

        return self

    @classmethod
    def _iter_items(cls, repo, common_path=None):
        if common_path is None:
            common_path = cls._common_path_default
        rela_paths = set()

        # walk loose refs
        # Currently we do not follow links
        for root, dirs, files in os.walk(join_path_native(repo.common_dir, common_path)):
            if 'refs' not in root.split(os.sep):  # skip non-refs subfolders
                refs_id = [d for d in dirs if d == 'refs']
                if refs_id:
                    dirs[0:] = ['refs']
            # END prune non-refs folders

            for f in files:
                if f == 'packed-refs':
                    continue
                abs_path = to_native_path_linux(join_path(root, f))
                rela_paths.add(abs_path.replace(to_native_path_linux(repo.common_dir) + '/', ""))
            # END for each file in root directory
        # END for each directory to walk

        # read packed refs
        for _sha, rela_path in cls._iter_packed_refs(repo):
            if rela_path.startswith(common_path):
                rela_paths.add(rela_path)
            # END relative path matches common path
        # END packed refs reading

        # return paths in sorted order
        for path in sorted(rela_paths):
            try:
                yield cls.from_path(repo, path)
            except ValueError:
                continue
        # END for each sorted relative refpath

    @classmethod
    def iter_items(cls, repo, common_path=None):
        """Find all refs in the repository

        :param repo: is the Repo

        :param common_path:
            Optional keyword argument to the path which is to be shared by all
            returned Ref objects.
            Defaults to class specific portion if None assuring that only
            refs suitable for the actual class are returned.

        :return:
            git.SymbolicReference[], each of them is guaranteed to be a symbolic
            ref which is not detached and pointing to a valid ref

            List is lexicographically sorted
            The returned objects represent actual subclasses, such as Head or TagReference"""
        return (r for r in cls._iter_items(repo, common_path) if r.__class__ == SymbolicReference or not r.is_detached)

    @classmethod
    def from_path(cls, repo, path):
        """
        :param path: full .git-directory-relative path name to the Reference to instantiate
        :note: use to_full_path() if you only have a partial path of a known Reference Type
        :return:
            Instance of type Reference, Head, or Tag
            depending on the given path"""
        if not path:
            raise ValueError("Cannot create Reference from %r" % path)

        # Names like HEAD are inserted after the refs module is imported - we have an import dependency
        # cycle and don't want to import these names in-function
        from . import HEAD, Head, RemoteReference, TagReference, Reference
        for ref_type in (HEAD, Head, RemoteReference, TagReference, Reference, SymbolicReference):
            try:
                instance = ref_type(repo, path)
                if instance.__class__ == SymbolicReference and instance.is_detached:
                    raise ValueError("SymbolRef was detached, we drop it")
                return instance
            except ValueError:
                pass
            # END exception handling
        # END for each type to try
        raise ValueError("Could not find reference type suitable to handle path %r" % path)

    def is_remote(self):
        """:return: True if this symbolic reference points to a remote branch"""
        return self.path.startswith(self._remote_common_path_default + "/")
