# This file is part of Radicale Server - Calendar Server
# Copyright © 2014 Jean-Marc Martins
# Copyright © 2012-2016 Guillaume Ayoub
#
# This library is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Radicale.  If not, see <http://www.gnu.org/licenses/>.

"""
Storage backends.

This module loads the storage backend, according to the storage configuration.

Default storage uses one folder per collection and one file per collection
entry.

"""

import json
import os
import posixpath
import shutil
import stat
import threading
import time
from contextlib import contextmanager
from hashlib import md5
from importlib import import_module
from itertools import groupby
from random import getrandbits

from atomicwrites import AtomicWriter
import vobject

if os.name == "nt":
    import ctypes
    import ctypes.wintypes
    import msvcrt

    LOCKFILE_EXCLUSIVE_LOCK = 2
    if ctypes.sizeof(ctypes.c_void_p) == 4:
        ULONG_PTR = ctypes.c_uint32
    else:
        ULONG_PTR = ctypes.c_uint64

    class Overlapped(ctypes.Structure):
        _fields_ = [("internal", ULONG_PTR),
                    ("internal_high", ULONG_PTR),
                    ("offset", ctypes.wintypes.DWORD),
                    ("offset_high", ctypes.wintypes.DWORD),
                    ("h_event", ctypes.wintypes.HANDLE)]

    lock_file_ex = ctypes.windll.kernel32.LockFileEx
    lock_file_ex.argtypes = [ctypes.wintypes.HANDLE,
                             ctypes.wintypes.DWORD,
                             ctypes.wintypes.DWORD,
                             ctypes.wintypes.DWORD,
                             ctypes.wintypes.DWORD,
                             ctypes.POINTER(Overlapped)]
    lock_file_ex.restype = ctypes.wintypes.BOOL
    unlock_file_ex = ctypes.windll.kernel32.UnlockFileEx
    unlock_file_ex.argtypes = [ctypes.wintypes.HANDLE,
                               ctypes.wintypes.DWORD,
                               ctypes.wintypes.DWORD,
                               ctypes.wintypes.DWORD,
                               ctypes.POINTER(Overlapped)]
    unlock_file_ex.restype = ctypes.wintypes.BOOL
elif os.name == "posix":
    import fcntl


def load(configuration, logger):
    """Load the storage manager chosen in configuration."""
    storage_type = configuration.get("storage", "type")
    if storage_type == "multifilesystem":
        collection_class = Collection
    else:
        collection_class = import_module(storage_type).Collection

    class CollectionCopy(collection_class):
        """Collection copy, avoids overriding the original class attributes."""
    CollectionCopy.configuration = configuration
    CollectionCopy.logger = logger
    return CollectionCopy


MIMETYPES = {"VADDRESSBOOK": "text/vcard", "VCALENDAR": "text/calendar"}


def get_etag(text):
    """Etag from collection or item."""
    etag = md5()
    etag.update(text.encode("utf-8"))
    return '"%s"' % etag.hexdigest()


def sanitize_path(path):
    """Make path absolute with leading slash to prevent access to other data.

    Preserve a potential trailing slash.

    """
    trailing_slash = "/" if path.endswith("/") else ""
    path = posixpath.normpath(path)
    new_path = "/"
    for part in path.split("/"):
        if not part or part in (".", ".."):
            continue
        new_path = posixpath.join(new_path, part)
    trailing_slash = "" if new_path.endswith("/") else trailing_slash
    return new_path + trailing_slash


def is_safe_filesystem_path_component(path):
    """Check if path is a single component of a filesystem path.

    Check that the path is safe to join too.

    """
    return (
        path and not os.path.splitdrive(path)[0] and
        not os.path.split(path)[0] and path not in (os.curdir, os.pardir) and
        not path.startswith(".") and not path.endswith("~"))


def path_to_filesystem(root, *paths):
    """Convert path to a local filesystem path relative to base_folder.

    `root` must be a secure filesystem path, it will be prepend to the path.

    Conversion of `paths` is done in a secure manner, or raises ``ValueError``.

    """
    paths = [sanitize_path(path).strip("/") for path in paths]
    safe_path = root
    for path in paths:
        if not path:
            continue
        for part in path.split("/"):
            if not is_safe_filesystem_path_component(part):
                raise ValueError(
                    "Can't tranlate name safely to filesystem: %s" % part)
            safe_path = os.path.join(safe_path, part)
    return safe_path


class _EncodedAtomicWriter(AtomicWriter):
    def __init__(self, path, encoding, mode="w", overwrite=True):
        self._encoding = encoding
        return super().__init__(path, mode, overwrite=True)

    def get_fileobject(self, **kwargs):
        return super().get_fileobject(encoding=self._encoding, **kwargs)


class Item:
    def __init__(self, collection, item, href, last_modified=None):
        self.collection = collection
        self.item = item
        self.href = href
        self.last_modified = last_modified

    def __getattr__(self, attr):
        return getattr(self.item, attr)

    @property
    def etag(self):
        return get_etag(self.serialize())


class BaseCollection:

    # Overriden on copy by the "load" function
    configuration = None
    logger = None

    def __init__(self, path, principal=False):
        """Initialize the collection.

        ``path`` must be the normalized relative path of the collection, using
        the slash as the folder delimiter, with no leading nor trailing slash.

        """
        raise NotImplementedError

    @classmethod
    def discover(cls, path, depth="1"):
        """Discover a list of collections under the given ``path``.

        If ``depth`` is "0", only the actual object under ``path`` is
        returned.

        If ``depth`` is anything but "0", it is considered as "1" and direct
        children are included in the result. If ``include_container`` is
        ``True`` (the default), the containing object is included in the
        result.

        The ``path`` is relative.

        """
        raise NotImplementedError

    @property
    def etag(self):
        return get_etag(self.serialize())

    @classmethod
    def create_collection(cls, href, collection=None, tag=None):
        """Create a collection.

        ``collection`` is a list of vobject components.

        ``tag`` is the type of collection (VCALENDAR or VADDRESSBOOK). If
        ``tag`` is not given, it is guessed from the collection.

        """
        raise NotImplementedError

    def list(self):
        """List collection items."""
        raise NotImplementedError

    def get(self, href):
        """Fetch a single item."""
        raise NotImplementedError

    def get_multi(self, hrefs):
        """Fetch multiple items. Duplicate hrefs must be ignored.

        Functionally similar to ``get``, but might bring performance benefits
        on some storages when used cleverly.

        """
        for href in set(hrefs):
            yield self.get(href)

    def pre_filtered_list(self, filters):
        """List collection items with optional pre filtering.

        This could largely improve performance of reports depending on
        the filters and this implementation.
        This returns all event by default
        """
        return [self.get(href) for href, _ in self.list()]

    def has(self, href):
        """Check if an item exists by its href.

        Functionally similar to ``get``, but might bring performance benefits
        on some storages when used cleverly.

        """
        return self.get(href) is not None

    def upload(self, href, vobject_item):
        """Upload a new item."""
        raise NotImplementedError

    def update(self, href, vobject_item, etag=None):
        """Update an item.

        Functionally similar to ``delete`` plus ``upload``, but might bring
        performance benefits on some storages when used cleverly.

        """
        self.delete(href, etag)
        self.upload(href, vobject_item)

    def delete(self, href=None, etag=None):
        """Delete an item.

        When ``href`` is ``None``, delete the collection.

        """
        raise NotImplementedError

    def get_meta(self, key):
        """Get metadata value for collection."""
        raise NotImplementedError

    def set_meta(self, key, value):
        """Set metadata value for collection."""
        raise NotImplementedError

    @property
    def last_modified(self):
        """Get the HTTP-datetime of when the collection was modified."""
        raise NotImplementedError

    def serialize(self):
        """Get the unicode string representing the whole collection."""
        raise NotImplementedError

    @classmethod
    @contextmanager
    def acquire_lock(cls, mode):
        """Set a context manager to lock the whole storage.

        ``mode`` must either be "r" for shared access or "w" for exclusive
        access.

        """
        raise NotImplementedError


class Collection(BaseCollection):
    """Collection stored in several files per calendar."""

    def __init__(self, path, principal=False):
        folder = os.path.expanduser(
            self.configuration.get("storage", "filesystem_folder"))
        # path should already be sanitized
        self.path = sanitize_path(path).strip("/")
        self.storage_encoding = self.configuration.get("encoding", "stock")
        self._filesystem_path = path_to_filesystem(folder, self.path)
        split_path = self.path.split("/")
        if len(split_path) > 1:
            # URL with at least one folder
            self.owner = split_path[0]
        else:
            self.owner = None
        self.is_principal = principal

    @contextmanager
    def _atomic_write(self, path, mode="w"):
        with _EncodedAtomicWriter(
                path, self.storage_encoding, mode).open() as fd:
            yield fd

    @classmethod
    def discover(cls, path, depth="1"):
        # path == None means wrong URL
        if path is None:
            return

        # path should already be sanitized
        sane_path = sanitize_path(path).strip("/")
        attributes = sane_path.split("/")
        if not attributes:
            return

        # Try to guess if the path leads to a collection or an item
        folder = os.path.expanduser(
            cls.configuration.get("storage", "filesystem_folder"))
        if not os.path.isdir(path_to_filesystem(folder, sane_path)):
            # path is not a collection
            if os.path.isfile(path_to_filesystem(folder, sane_path)):
                # path is an item
                attributes.pop()
            elif os.path.isdir(path_to_filesystem(folder, *attributes[:-1])):
                # path parent is a collection
                attributes.pop()
            # TODO: else: return?

        path = "/".join(attributes)

        principal = len(attributes) <= 1
        collection = cls(path, principal)
        yield collection
        if depth != "0":
            # TODO: fix this
            items = list(collection.list())
            if items:
                for item in items:
                    yield collection.get(item[0])
            _, directories, _ = next(os.walk(collection._filesystem_path))
            for sub_path in directories:
                if not is_safe_filesystem_path_component(sub_path):
                    cls.logger.debug(
                        "Skipping collection: %s", sub_path)
                    continue
                full_path = os.path.join(collection._filesystem_path, sub_path)
                if os.path.exists(full_path):
                    yield cls(posixpath.join(path, sub_path))

    @classmethod
    def create_collection(cls, href, collection=None, tag=None):
        folder = os.path.expanduser(
            cls.configuration.get("storage", "filesystem_folder"))
        path = path_to_filesystem(folder, href)
        if not os.path.exists(path):
            os.makedirs(path)
        if not tag and collection:
            tag = collection[0].name
        self = cls(href)
        if tag == "VCALENDAR":
            self.set_meta("tag", "VCALENDAR")
            if collection:
                collection, = collection
                items = []
                for content in ("vevent", "vtodo", "vjournal"):
                    items.extend(getattr(collection, "%s_list" % content, []))

                def get_uid(item):
                    return hasattr(item, 'uid') and item.uid.value

                items_by_uid = groupby(
                    sorted(items, key=get_uid), get_uid)

                for uid, items in items_by_uid:
                    new_collection = vobject.iCalendar()
                    for item in items:
                        new_collection.add(item)
                    file_name = hex(getrandbits(32))[2:]
                    self.upload(file_name, new_collection)

        elif tag == "VCARD":
            self.set_meta("tag", "VADDRESSBOOK")
            if collection:
                for card in collection:
                    file_name = hex(getrandbits(32))[2:]
                    self.upload(file_name, card)
        return self

    def list(self):
        try:
            hrefs = os.listdir(self._filesystem_path)
        except IOError:
            return

        for href in hrefs:
            if not is_safe_filesystem_path_component(href):
                self.logger.debug(
                    "Skipping component: %s", href)
                continue
            path = os.path.join(self._filesystem_path, href)
            if not href.endswith(".props") and os.path.isfile(path):
                with open(path, encoding=self.storage_encoding) as fd:
                    yield href, get_etag(fd.read())

    def get(self, href):
        if not href:
            return None
        href = href.strip("{}").replace("/", "_")
        if not is_safe_filesystem_path_component(href):
            self.logger.debug(
                "Can't tranlate name safely to filesystem: %s", href)
            return None
        path = path_to_filesystem(self._filesystem_path, href)
        if not os.path.isfile(path):
            return None
        with open(path, encoding=self.storage_encoding) as fd:
            text = fd.read()
        last_modified = time.strftime(
            "%a, %d %b %Y %H:%M:%S GMT",
            time.gmtime(os.path.getmtime(path)))
        return Item(self, vobject.readOne(text), href, last_modified)

    def has(self, href):
        return self.get(href) is not None

    def upload(self, href, vobject_item):
        # TODO: use returned object in code
        if not is_safe_filesystem_path_component(href):
            raise ValueError(
                "Can't tranlate name safely to filesystem: %s" % href)
        path = path_to_filesystem(self._filesystem_path, href)
        if os.path.exists(path):
            raise ValueError("Component already exists: %s" % href)
        item = Item(self, vobject_item, href)
        with self._atomic_write(path) as fd:
            fd.write(item.serialize())
        return item

    def update(self, href, vobject_item, etag=None):
        # TODO: use etag in code and test it here
        # TODO: use returned object in code
        if not is_safe_filesystem_path_component(href):
            raise ValueError(
                "Can't tranlate name safely to filesystem: %s" % href)
        path = path_to_filesystem(self._filesystem_path, href)
        if not os.path.isfile(path):
            raise ValueError("Component doesn't exist: %s" % href)
        with open(path, encoding=self.storage_encoding) as fd:
            text = fd.read()
        if etag and etag != get_etag(text):
            raise ValueError(
                "ETag doesn't match: %s != %s" % (etag, get_etag(text)))
        item = Item(self, vobject_item, href)
        with self._atomic_write(path) as fd:
            fd.write(item.serialize())
        return item

    def delete(self, href=None, etag=None):
        # TODO: use etag in code and test it here
        # TODO: use returned object in code
        if href is None:
            # Delete the collection
            if os.path.isdir(self._filesystem_path):
                shutil.rmtree(self._filesystem_path)
            props_path = self._filesystem_path + ".props"
            if os.path.isfile(props_path):
                os.remove(props_path)
        else:
            # Delete an item
            if not is_safe_filesystem_path_component(href):
                raise ValueError(
                    "Can't tranlate name safely to filesystem: %s" % href)
            path = path_to_filesystem(self._filesystem_path, href)
            if not os.path.isfile(path):
                raise ValueError("Component doesn't exist: %s" % href)
            with open(path, encoding=self.storage_encoding) as fd:
                text = fd.read()
            if etag and etag != get_etag(text):
                raise ValueError(
                    "ETag doesn't match: %s != %s" % (etag, get_etag(text)))
            os.remove(path)

    def get_meta(self, key):
        props_path = self._filesystem_path + ".props"
        if os.path.exists(props_path):
            with open(props_path, encoding=self.storage_encoding) as prop:
                return json.load(prop).get(key)

    def set_meta(self, key, value):
        props_path = self._filesystem_path + ".props"
        properties = {}
        if os.path.exists(props_path):
            with open(props_path, encoding=self.storage_encoding) as prop:
                properties.update(json.load(prop))

        if value:
            properties[key] = value
        else:
            properties.pop(key, None)

        with self._atomic_write(props_path, "w+") as prop:
            json.dump(properties, prop)

    @property
    def last_modified(self):
        last = max([os.path.getmtime(self._filesystem_path)] + [
            os.path.getmtime(os.path.join(self._filesystem_path, filename))
            for filename in os.listdir(self._filesystem_path)] or [0])
        return time.strftime("%a, %d %b %Y %H:%M:%S GMT", time.gmtime(last))

    def serialize(self):
        if not os.path.exists(self._filesystem_path):
            return None
        items = []
        for href in os.listdir(self._filesystem_path):
            path = os.path.join(self._filesystem_path, href)
            if os.path.isfile(path) and not path.endswith(".props"):
                with open(path, encoding=self.storage_encoding) as fd:
                    items.append(vobject.readOne(fd.read()))
        if self.get_meta("tag") == "VCALENDAR":
            collection = vobject.iCalendar()
            for item in items:
                for content in ("vevent", "vtodo", "vjournal"):
                    if content in item.contents:
                        for item_part in getattr(item, "%s_list" % content):
                            collection.add(item_part)
                        break
            return collection.serialize()
        elif self.get_meta("tag") == "VADDRESSBOOK":
            return "".join([item.serialize() for item in items])
        return ""

    _lock = threading.Lock()
    _waiters = []
    _lock_file = None
    _lock_file_locked = False
    _readers = 0
    _writer = False

    @classmethod
    @contextmanager
    def acquire_lock(cls, mode):
        def condition():
            if mode == "r":
                return not cls._writer
            else:
                return not cls._writer and cls._readers == 0

        if mode not in ("r", "w"):
            raise ValueError("Invalid lock mode: %s" % mode)
        # Use a primitive lock which only works within one process as a
        # precondition for inter-process file-based locking
        with cls._lock:
            if cls._waiters or not condition():
                # use FIFO for access requests
                waiter = threading.Condition(lock=cls._lock)
                cls._waiters.append(waiter)
                while True:
                    waiter.wait()
                    if condition():
                        break
                cls._waiters.pop(0)
            if mode == "r":
                cls._readers += 1
                # notify additional potential readers
                if cls._waiters:
                    cls._waiters[0].notify()
            else:
                cls._writer = True
            if not cls._lock_file:
                folder = os.path.expanduser(
                    cls.configuration.get("storage", "filesystem_folder"))
                if not os.path.exists(folder):
                    os.makedirs(folder, exist_ok=True)
                lock_path = os.path.join(folder, ".Radicale.lock")
                cls._lock_file = open(lock_path, "w+")
                # set access rights to a necessary minimum to prevent locking
                # by arbitrary users
                try:
                    os.chmod(lock_path, stat.S_IWUSR | stat.S_IRUSR)
                except OSError:
                    cls.logger.debug("Failed to set permissions on lock file")
            if not cls._lock_file_locked:
                if os.name == "nt":
                    handle = msvcrt.get_osfhandle(cls._lock_file.fileno())
                    flags = LOCKFILE_EXCLUSIVE_LOCK if mode == "w" else 0
                    overlapped = Overlapped()
                    if not lock_file_ex(handle, flags, 0, 1, 0, overlapped):
                        cls.logger.debug("Locking not supported")
                elif os.name == "posix":
                    _cmd = fcntl.LOCK_EX if mode == "w" else fcntl.LOCK_SH
                    try:
                        fcntl.lockf(cls._lock_file.fileno(), _cmd)
                    except OSError:
                        cls.logger.debug("Locking not supported")
                cls._lock_file_locked = True
        try:
            yield
        finally:
            with cls._lock:
                if mode == "r":
                    cls._readers -= 1
                else:
                    cls._writer = False
                if cls._readers == 0:
                    if os.name == "nt":
                        handle = msvcrt.get_osfhandle(cls._lock_file.fileno())
                        overlapped = Overlapped()
                        if not unlock_file_ex(handle, 0, 1, 0, overlapped):
                            cls.logger.debug("Unlocking not supported")
                    elif os.name == "posix":
                        try:
                            fcntl.lockf(cls._lock_file.fileno(), fcntl.LOCK_UN)
                        except OSError:
                            cls.logger.debug("Unlocking not supported")
                    cls._lock_file_locked = False
                if cls._waiters:
                    cls._waiters[0].notify()