import os
from git.objects import Object, Commit
from git.util import (
                    join_path, 
                    join_path_native, 
                    to_native_path_linux,
                    assure_directory_exists
                    )

from gitdb.exc import BadObject
from gitdb.util import (
                            join, 
                            dirname,
                            isdir,
                            exists,
                            isfile,
                            rename,
                            hex_to_bin,
                            LockedFD
                        )

from log import RefLog

__all__ = ["SymbolicReference"]

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):
        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(self.repo.git_dir, self.path)
        
    @classmethod
    def _get_packed_refs_path(cls, repo):
        return join(repo.git_dir, 'packed-refs')
        
    @classmethod
    def _iter_packed_refs(cls, repo):
        """Returns an iterator yielding pairs of sha1/path pairs for the corresponding refs.
        :note: The packed refs file will be kept open as long as we iterate"""
        try:
            fp = open(cls._get_packed_refs_path(repo), 'rb')
            for line in fp:
                line = line.strip()
                if not line:
                    continue
                if line.startswith('#'):
                    if line.startswith('# pack-refs with:') and not line.endswith('peeled'):
                        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):
            raise StopIteration
        # END no packed-refs file handling 
        # NOTE: Had try-finally block around here to close the fp, 
        # but some python version woudn'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(cls, repo, ref_path):
        """Return: (sha, 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
        try:
            fp = open(join(repo.git_dir, ref_path), 'r')
            value = fp.read().rstrip()
            fp.close()
            tokens = value.split(" ")
        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 explictly
            for sha, path in cls._iter_packed_refs(repo):
                if path != ref_path: continue
                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)
    
    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:
                raise ValueError("Invalid object: %s" % commit)
            #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):
        """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
        #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. Everthiny
            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, basestring):
            try:
                obj = self.repo.rev_parse(ref+"^{}")    # optionally deref tags
                write_value = obj.hexsha
            except BadObject:
                raise ValueError("Could not extract object from %s" % ref)
            # 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)
        fd.write(write_value)
        lfd.commit()
        
        # Adjust the reflog
        if logmsg is not None:
            self.log_append(oldbinsha, logmsg)
        #END handle reflog
        
        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"""
        return RefLog.append_entry(self.repo.config_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 = join(repo.git_dir, full_ref_path)
        if exists(abs_path):
            os.remove(abs_path)
        else:
            # check packed refs
            pack_file_path = cls._get_packed_refs_path(repo)
            try:
                reader = open(pack_file_path, 'rb')
            except (OSError,IOError):
                pass # it didnt exist at all
            else:
                new_lines = list()
                made_change = False
                dropped_last_line = False
                for line in reader:
                    # 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 not in line ) 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
                # END for each line in packed refs
                reader.close()
                
                # 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 !
                    open(pack_file_path, 'wb').writelines(new_lines)
                # END write out file
            # END open exception handling
        # END handle deletion
        
        # delete the reflog
        reflog_path = RefLog.path(cls(repo, full_ref_path))
        if os.path.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"""
        full_ref_path = cls.to_full_path(path)
        abs_ref_path = join(repo.git_dir, full_ref_path)
        
        # figure out target data
        target = reference
        if resolve:
            target = repo.rev_parse(str(reference))
            
        if not force and isfile(abs_ref_path):
            target_data = str(target)
            if isinstance(target, SymbolicReference):
                target_data = target.path
            if not resolve:
                target_data = "ref: " + target_data
            existing_data = open(abs_ref_path, 'rb').read().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):
        """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 = join(self.repo.git_dir, new_path)
        cur_abs_path = join(self.repo.git_dir, self.path)
        if isfile(new_abs_path):
            if not force:
                # if they point to the same file, its not an error
                if open(new_abs_path,'rb').read().strip() != open(cur_abs_path,'rb').read().strip():
                    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 = dirname(new_abs_path)
        if not isdir(dname):
            os.makedirs(dname)
        # END create directory
        
        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.git_dir, common_path)):
            if 'refs/' not in root: # 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:
                abs_path = to_native_path_linux(join_path(root, f))
                rela_paths.add(abs_path.replace(to_native_path_linux(repo.git_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 lexigraphically 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)
        
        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)
