#
#  Copyright (C) 2018 Bloomberg LP
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public
#  License as published by the Free Software Foundation; either
#  version 2 of the License, or (at your option) any later version.
#
#  This library is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
#  Lesser General Public License for more details.
#
#  You should have received a copy of the GNU Lesser General Public
#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
#  Authors:
#        Jim MacArthur <jim.macarthur@codethink.co.uk>

"""
CasBasedDirectory
=========

Implementation of the Directory class which backs onto a Merkle-tree based content
addressable storage system.

See also: :ref:`sandboxing`.
"""

import os

from .._protos.build.bazel.remote.execution.v2 import remote_execution_pb2
from .directory import Directory, VirtualDirectoryError, _FileType
from ._filebaseddirectory import FileBasedDirectory
from ..utils import FileListResult, _magic_timestamp


class IndexEntry():
    """ Directory entry used in CasBasedDirectory.index """
    def __init__(self, name, entrytype, *, digest=None, target=None, is_executable=False,
                 buildstream_object=None, modified=False):
        self.name = name
        self.type = entrytype
        self.digest = digest
        self.target = target
        self.is_executable = is_executable
        self.buildstream_object = buildstream_object
        self.modified = modified

    def get_directory(self, parent):
        if not self.buildstream_object:
            self.buildstream_object = CasBasedDirectory(parent.cas_cache, digest=self.digest,
                                                        parent=parent, filename=self.name)
            self.digest = None

        return self.buildstream_object


class ResolutionException(VirtualDirectoryError):
    """ Superclass of all exceptions that can be raised by
    CasBasedDirectory._resolve. Should not be used outside this module. """


class InfiniteSymlinkException(ResolutionException):
    """ Raised when an infinite symlink loop is found. """


class AbsoluteSymlinkException(ResolutionException):
    """Raised if we try to follow an absolute symlink (i.e. one whose
    target starts with the path separator) and we have disallowed
    following such symlinks.
    """


class UnexpectedFileException(ResolutionException):
    """Raised if we were found a file where a directory or symlink was
    expected, for example we try to resolve a symlink pointing to
    /a/b/c but /a/b is a file.
    """
    def __init__(self, message=""):
        """Allow constructor with no arguments, since this can be raised in
        places where there isn't sufficient information to write the
        message.
        """
        super().__init__(message)


# CasBasedDirectory intentionally doesn't call its superclass constuctor,
# which is meant to be unimplemented.
# pylint: disable=super-init-not-called

class CasBasedDirectory(Directory):
    """
    CAS-based directories can have two names; one is a 'common name' which has no effect
    on functionality, and the 'filename'. If a CasBasedDirectory has a parent, then 'filename'
    must be the name of an entry in the parent directory's index which points to this object.
    This is used to inform a parent directory that it must update the given hash for this
    object when this object changes.

    Typically a top-level CasBasedDirectory will have a common_name and no filename, and
    subdirectories wil have a filename and no common_name. common_name can used to identify
    CasBasedDirectory objects in a log file, since they have no unique position in a file
    system.
    """

    # Two constants which define the separators used by the remote execution API.
    _pb2_path_sep = "/"
    _pb2_absolute_path_prefix = "/"

    def __init__(self, cas_cache, *, digest=None, parent=None, common_name="untitled", filename=None):
        self.filename = filename
        self.common_name = common_name
        self.cas_cache = cas_cache
        self.__digest = digest
        self.index = {}
        self.parent = parent
        if digest:
            self._populate_index(digest)

    def _populate_index(self, digest):
        pb2_directory = remote_execution_pb2.Directory()
        with open(self.cas_cache.objpath(digest), 'rb') as f:
            pb2_directory.ParseFromString(f.read())

        for entry in pb2_directory.directories:
            self.index[entry.name] = IndexEntry(entry.name, _FileType.DIRECTORY,
                                                digest=entry.digest)
        for entry in pb2_directory.files:
            self.index[entry.name] = IndexEntry(entry.name, _FileType.REGULAR_FILE,
                                                digest=entry.digest,
                                                is_executable=entry.is_executable)
        for entry in pb2_directory.symlinks:
            self.index[entry.name] = IndexEntry(entry.name, _FileType.SYMLINK,
                                                target=entry.target)

    def _find_self_in_parent(self):
        assert self.parent is not None
        parent = self.parent
        for (k, v) in parent.index.items():
            if v.buildstream_object == self:
                return k
        return None

    def _add_directory(self, name):
        assert name not in self.index

        newdir = CasBasedDirectory(self.cas_cache, parent=self, filename=name)

        self.index[name] = IndexEntry(name, _FileType.DIRECTORY, buildstream_object=newdir)

        self.__invalidate_digest()

        return newdir

    def _add_file(self, basename, filename, modified=False):
        entry = IndexEntry(filename, _FileType.REGULAR_FILE,
                           modified=modified or filename in self.index)
        entry.digest = self.cas_cache.add_object(path=os.path.join(basename, filename))
        entry.is_executable = os.access(os.path.join(basename, filename), os.X_OK)
        self.index[filename] = entry

        self.__invalidate_digest()

    def _copy_link_from_filesystem(self, basename, filename):
        self._add_new_link_direct(filename, os.readlink(os.path.join(basename, filename)))

    def _add_new_link_direct(self, name, target):
        self.index[name] = IndexEntry(name, _FileType.SYMLINK, target=target, modified=name in self.index)

        self.__invalidate_digest()

    def delete_entry(self, name):
        if name in self.index:
            del self.index[name]

        self.__invalidate_digest()

    def descend(self, subdirectory_spec, create=False):
        """Descend one or more levels of directory hierarchy and return a new
        Directory object for that directory.

        Arguments:
        * subdirectory_spec (list of strings): A list of strings which are all directory
          names.
        * create (boolean): If this is true, the directories will be created if
          they don't already exist.

        Note: At the moment, creating a directory by descending does
        not update this object in the CAS cache. However, performing
        an import_files() into a subdirectory of any depth obtained by
        descending from this object *will* cause this directory to be
        updated and stored.

        """

        # It's very common to send a directory name instead of a list and this causes
        # bizarre errors, so check for it here
        if not isinstance(subdirectory_spec, list):
            subdirectory_spec = [subdirectory_spec]

        # Because of the way split works, it's common to get a list which begins with
        # an empty string. Detect these and remove them.
        while subdirectory_spec and subdirectory_spec[0] == "":
            subdirectory_spec.pop(0)

        # Descending into [] returns the same directory.
        if not subdirectory_spec:
            return self

        if subdirectory_spec[0] in self.index:
            entry = self.index[subdirectory_spec[0]]
            if entry.type == _FileType.DIRECTORY:
                subdir = entry.get_directory(self)
                return subdir.descend(subdirectory_spec[1:], create)
            else:
                error = "Cannot descend into {}, which is a '{}' in the directory {}"
                raise VirtualDirectoryError(error.format(subdirectory_spec[0],
                                                         self.index[subdirectory_spec[0]].type,
                                                         self))
        else:
            if create:
                newdir = self._add_directory(subdirectory_spec[0])
                return newdir.descend(subdirectory_spec[1:], create)
            else:
                error = "'{}' not found in {}"
                raise VirtualDirectoryError(error.format(subdirectory_spec[0], str(self)))
        return None

    def _check_replacement(self, name, path_prefix, fileListResult):
        """ Checks whether 'name' exists, and if so, whether we can overwrite it.
        If we can, add the name to 'overwritten_files' and delete the existing entry.
        Returns 'True' if the import should go ahead.
        fileListResult.overwritten and fileListResult.ignore are updated depending
        on the result. """
        existing_entry = self.index.get(name)
        relative_pathname = os.path.join(path_prefix, name)
        if existing_entry is None:
            return True
        elif existing_entry.type == _FileType.DIRECTORY:
            # If 'name' maps to a DirectoryNode, then there must be an entry in index
            # pointing to another Directory.
            subdir = existing_entry.get_directory(self)
            if subdir.is_empty():
                self.delete_entry(name)
                fileListResult.overwritten.append(relative_pathname)
                return True
            else:
                # We can't overwrite a non-empty directory, so we just ignore it.
                fileListResult.ignored.append(relative_pathname)
                return False
        else:
            self.delete_entry(name)
            fileListResult.overwritten.append(relative_pathname)
            return True

    def _import_files_from_directory(self, source_directory, filter_callback, *, path_prefix="", result):
        """ Import files from a traditional directory. """

        for direntry in sorted(os.scandir(source_directory), key=lambda e: e.name):
            # The destination filename, relative to the root where the import started
            relative_pathname = os.path.join(path_prefix, direntry.name)

            is_dir = direntry.is_dir(follow_symlinks=False)

            if is_dir:
                src_subdir = os.path.join(source_directory, direntry.name)

                try:
                    create_subdir = direntry.name not in self.index
                    dest_subdir = self.descend(direntry.name, create=create_subdir)
                except VirtualDirectoryError:
                    filetype = self.index[direntry.name].type
                    raise VirtualDirectoryError('Destination is a {}, not a directory: /{}'
                                                .format(filetype, relative_pathname))

                dest_subdir._import_files_from_directory(src_subdir, filter_callback,
                                                         path_prefix=relative_pathname, result=result)

            if filter_callback and not filter_callback(relative_pathname):
                if is_dir and create_subdir and dest_subdir.is_empty():
                    # Complete subdirectory has been filtered out, remove it
                    self.delete_entry(direntry.name)

                # Entry filtered out, move to next
                continue

            if direntry.is_file(follow_symlinks=False):
                if self._check_replacement(direntry.name, path_prefix, result):
                    self._add_file(source_directory, direntry.name, modified=relative_pathname in result.overwritten)
                    result.files_written.append(relative_pathname)
            elif direntry.is_symlink():
                if self._check_replacement(direntry.name, path_prefix, result):
                    self._copy_link_from_filesystem(source_directory, direntry.name)
                    result.files_written.append(relative_pathname)

    def _partial_import_cas_into_cas(self, source_directory, filter_callback, *, path_prefix="", result):
        """ Import files from a CAS-based directory. """

        for name, entry in sorted(source_directory.index.items()):
            # The destination filename, relative to the root where the import started
            relative_pathname = os.path.join(path_prefix, name)

            is_dir = entry.type == _FileType.DIRECTORY

            if is_dir:
                src_subdir = source_directory.descend(name)

                try:
                    create_subdir = name not in self.index
                    dest_subdir = self.descend(name, create=create_subdir)
                except VirtualDirectoryError:
                    filetype = self.index[name].type
                    raise VirtualDirectoryError('Destination is a {}, not a directory: /{}'
                                                .format(filetype, relative_pathname))

                dest_subdir._partial_import_cas_into_cas(src_subdir, filter_callback,
                                                         path_prefix=relative_pathname, result=result)

            if filter_callback and not filter_callback(relative_pathname):
                if is_dir and create_subdir and dest_subdir.is_empty():
                    # Complete subdirectory has been filtered out, remove it
                    self.delete_entry(name)

                # Entry filtered out, move to next
                continue

            if not is_dir:
                if self._check_replacement(name, path_prefix, result):
                    if entry.type == _FileType.REGULAR_FILE:
                        self.index[name] = IndexEntry(name, _FileType.REGULAR_FILE,
                                                      digest=entry.digest,
                                                      is_executable=entry.is_executable,
                                                      modified=True)
                        self.__invalidate_digest()
                    else:
                        assert entry.type == _FileType.SYMLINK
                        self._add_new_link_direct(name=name, target=entry.target)
                    result.files_written.append(relative_pathname)

    def import_files(self, external_pathspec, *,
                     filter_callback=None,
                     report_written=True, update_mtime=False,
                     can_link=False):
        """ See superclass Directory for arguments """

        result = FileListResult()

        if isinstance(external_pathspec, FileBasedDirectory):
            source_directory = external_pathspec._get_underlying_directory()
            self._import_files_from_directory(source_directory, filter_callback, result=result)
        elif isinstance(external_pathspec, str):
            source_directory = external_pathspec
            self._import_files_from_directory(source_directory, filter_callback, result=result)
        else:
            assert isinstance(external_pathspec, CasBasedDirectory)
            self._partial_import_cas_into_cas(external_pathspec, filter_callback, result=result)

        # TODO: No notice is taken of report_written, update_mtime or can_link.
        # Current behaviour is to fully populate the report, which is inefficient,
        # but still correct.

        return result

    def set_deterministic_mtime(self):
        """ Sets a static modification time for all regular files in this directory.
        Since we don't store any modification time, we don't need to do anything.
        """

    def set_deterministic_user(self):
        """ Sets all files in this directory to the current user's euid/egid.
        We also don't store user data, so this can be ignored.
        """

    def export_files(self, to_directory, *, can_link=False, can_destroy=False):
        """Copies everything from this into to_directory, which must be the name
        of a traditional filesystem directory.

        Arguments:

        to_directory (string): a path outside this directory object
        where the contents will be copied to.

        can_link (bool): Whether we can create hard links in to_directory
        instead of copying.

        can_destroy (bool): Whether we can destroy elements in this
        directory to export them (e.g. by renaming them as the
        target).

        """

        self.cas_cache.checkout(to_directory, self._get_digest(), can_link=can_link)

    def export_to_tar(self, tarfile, destination_dir, mtime=_magic_timestamp):
        raise NotImplementedError()

    def mark_changed(self):
        """ It should not be possible to externally modify a CAS-based
        directory at the moment."""
        raise NotImplementedError()

    def is_empty(self):
        """ Return true if this directory has no files, subdirectories or links in it.
        """
        return len(self.index) == 0

    def _mark_directory_unmodified(self):
        # Marks all entries in this directory and all child directories as unmodified.
        for i in self.index.values():
            i.modified = False
            if i.type == _FileType.DIRECTORY and i.buildstream_object:
                i.buildstream_object._mark_directory_unmodified()

    def _mark_entry_unmodified(self, name):
        # Marks an entry as unmodified. If the entry is a directory, it will
        # recursively mark all its tree as unmodified.
        self.index[name].modified = False
        if self.index[name].buildstream_object:
            self.index[name].buildstream_object._mark_directory_unmodified()

    def mark_unmodified(self):
        """ Marks all files in this directory (recursively) as unmodified.
        If we have a parent, we mark our own entry as unmodified in that parent's
        index.
        """
        if self.parent:
            self.parent._mark_entry_unmodified(self._find_self_in_parent())
        else:
            self._mark_directory_unmodified()

    def _lightweight_resolve_to_index(self, path):
        """A lightweight function for transforming paths into IndexEntry
        objects. This does not follow symlinks.

        path: The string to resolve. This should be a series of path
        components separated by the protocol buffer path separator
        _pb2_path_sep.

        Returns: the IndexEntry found, or None if any of the path components were not present.

        """
        directory = self
        path_components = path.split(CasBasedDirectory._pb2_path_sep)
        for component in path_components[:-1]:
            if component not in directory.index:
                return None
            if directory.index[component].type == _FileType.DIRECTORY:
                directory = directory.index[component].get_directory(self)
            else:
                return None
        return directory.index.get(path_components[-1], None)

    def list_modified_paths(self):
        """Provide a list of relative paths which have been modified since the
        last call to mark_unmodified.

        Return value: List(str) - list of modified paths
        """

        for p in self.list_relative_paths():
            i = self._lightweight_resolve_to_index(p)
            if i and i.modified:
                yield p

    def list_relative_paths(self, relpath=""):
        """Provide a list of all relative paths.

        Return value: List(str) - list of all paths
        """

        file_list = list(filter(lambda i: i[1].type != _FileType.DIRECTORY,
                                self.index.items()))
        directory_list = filter(lambda i: i[1].type == _FileType.DIRECTORY,
                                self.index.items())

        if relpath != "":
            yield relpath

        for (k, v) in sorted(file_list):
            yield os.path.join(relpath, k)

        for (k, v) in sorted(directory_list):
            subdir = v.get_directory(self)
            yield from subdir.list_relative_paths(relpath=os.path.join(relpath, k))

    def get_size(self):
        digest = self._get_digest()
        total = digest.size_bytes
        for i in self.index.values():
            if i.type == _FileType.DIRECTORY:
                subdir = i.get_directory(self)
                total += subdir.get_size()
            elif i.type == _FileType.REGULAR_FILE:
                src_name = self.cas_cache.objpath(i.digest)
                filesize = os.stat(src_name).st_size
                total += filesize
            # Symlink nodes are encoded as part of the directory serialization.
        return total

    def _get_identifier(self):
        path = ""
        if self.parent:
            path = self.parent._get_identifier()
        if self.filename:
            path += "/" + self.filename
        else:
            path += "/" + self.common_name
        return path

    def __str__(self):
        return "[CAS:{}]".format(self._get_identifier())

    def _get_underlying_directory(self):
        """ There is no underlying directory for a CAS-backed directory, so
        throw an exception. """
        raise VirtualDirectoryError("_get_underlying_directory was called on a CAS-backed directory," +
                                    " which has no underlying directory.")

    # _get_digest():
    #
    # Return the Digest for this directory.
    #
    # Returns:
    #   (Digest): The Digest protobuf object for the Directory protobuf
    #
    def _get_digest(self):
        if not self.__digest:
            # Create updated Directory proto
            pb2_directory = remote_execution_pb2.Directory()

            for name, entry in sorted(self.index.items()):
                if entry.type == _FileType.DIRECTORY:
                    dirnode = pb2_directory.directories.add()
                    dirnode.name = name

                    # Update digests for subdirectories in DirectoryNodes.
                    # No need to call entry.get_directory().
                    # If it hasn't been instantiated, digest must be up-to-date.
                    subdir = entry.buildstream_object
                    if subdir:
                        dirnode.digest.CopyFrom(subdir._get_digest())
                    else:
                        dirnode.digest.CopyFrom(entry.digest)
                elif entry.type == _FileType.REGULAR_FILE:
                    filenode = pb2_directory.files.add()
                    filenode.name = name
                    filenode.digest.CopyFrom(entry.digest)
                    filenode.is_executable = entry.is_executable
                elif entry.type == _FileType.SYMLINK:
                    symlinknode = pb2_directory.symlinks.add()
                    symlinknode.name = name
                    symlinknode.target = entry.target

            self.__digest = self.cas_cache.add_object(buffer=pb2_directory.SerializeToString())

        return self.__digest

    def _objpath(self, path):
        subdir = self.descend(path[:-1])
        entry = subdir.index[path[-1]]
        return self.cas_cache.objpath(entry.digest)

    def _exists(self, path):
        try:
            subdir = self.descend(path[:-1])
            return path[-1] in subdir.index
        except VirtualDirectoryError:
            return False

    def __invalidate_digest(self):
        if self.__digest:
            self.__digest = None
            if self.parent:
                self.parent.__invalidate_digest()