import contextlib
import errno
import importlib
import itertools
import json
import os
import queue
import sys

from atomicwrites import atomic_write

import click

import click_threading

from . import cli_logger
from .. import BUGTRACKER_HOME, DOCS_HOME, exceptions
from ..sync.exceptions import IdentConflict, PartialSync, StorageEmpty, \
    SyncConflict
from ..sync.status import SqliteStatus
from ..utils import expand_path, get_storage_init_args


STATUS_PERMISSIONS = 0o600
STATUS_DIR_PERMISSIONS = 0o700


class _StorageIndex:
    def __init__(self):
        self._storages = dict(
            caldav='vdirsyncer.storage.dav.CalDAVStorage',
            carddav='vdirsyncer.storage.dav.CardDAVStorage',
            filesystem='vdirsyncer.storage.filesystem.FilesystemStorage',
            http='vdirsyncer.storage.http.HttpStorage',
            singlefile='vdirsyncer.storage.singlefile.SingleFileStorage',
            google_calendar='vdirsyncer.storage.google.GoogleCalendarStorage',
            google_contacts='vdirsyncer.storage.google.GoogleContactsStorage',
            etesync_calendars='vdirsyncer.storage.etesync.EtesyncCalendars',
            etesync_contacts='vdirsyncer.storage.etesync.EtesyncContacts'
        )

    def __getitem__(self, name):
        item = self._storages[name]
        if not isinstance(item, str):
            return item

        modname, clsname = item.rsplit('.', 1)
        mod = importlib.import_module(modname)
        self._storages[name] = rv = getattr(mod, clsname)
        assert rv.storage_name == name
        return rv


storage_names = _StorageIndex()
del _StorageIndex


class JobFailed(RuntimeError):
    pass


def handle_cli_error(status_name=None, e=None):
    '''
    Print a useful error message for the current exception.

    This is supposed to catch all exceptions, and should never raise any
    exceptions itself.
    '''

    try:
        if e is not None:
            raise e
        else:
            raise
    except exceptions.UserError as e:
        cli_logger.critical(e)
    except StorageEmpty as e:
        cli_logger.error(
            '{status_name}: Storage "{name}" was completely emptied. If you '
            'want to delete ALL entries on BOTH sides, then use '
            '`vdirsyncer sync --force-delete {status_name}`. '
            'Otherwise delete the files for {status_name} in your status '
            'directory.'.format(
                name=e.empty_storage.instance_name,
                status_name=status_name
            )
        )
    except PartialSync as e:
        cli_logger.error(
            '{status_name}: Attempted change on {storage}, which is read-only'
            '. Set `partial_sync` in your pair section to `ignore` to ignore '
            'those changes, or `revert` to revert them on the other side.'
            .format(status_name=status_name, storage=e.storage)
        )
    except SyncConflict as e:
        cli_logger.error(
            '{status_name}: One item changed on both sides. Resolve this '
            'conflict manually, or by setting the `conflict_resolution` '
            'parameter in your config file.\n'
            'See also {docs}/config.html#pair-section\n'
            'Item ID: {e.ident}\n'
            'Item href on side A: {e.href_a}\n'
            'Item href on side B: {e.href_b}\n'
            .format(status_name=status_name, e=e, docs=DOCS_HOME)
        )
    except IdentConflict as e:
        cli_logger.error(
            '{status_name}: Storage "{storage.instance_name}" contains '
            'multiple items with the same UID or even content. Vdirsyncer '
            'will now abort the synchronization of this collection, because '
            'the fix for this is not clear; It could be the result of a badly '
            'behaving server. You can try running:\n\n'
            '    vdirsyncer repair {storage.instance_name}\n\n'
            'But make sure to have a backup of your data in some form. The '
            'offending hrefs are:\n\n{href_list}\n'
            .format(status_name=status_name,
                    storage=e.storage,
                    href_list='\n'.join(map(repr, e.hrefs)))
        )
    except (click.Abort, KeyboardInterrupt, JobFailed):
        pass
    except exceptions.PairNotFound as e:
        cli_logger.error(
            'Pair {pair_name} does not exist. Please check your '
            'configuration file and make sure you\'ve typed the pair name '
            'correctly'.format(pair_name=e.pair_name)
        )
    except exceptions.InvalidResponse as e:
        cli_logger.error(
            'The server returned something vdirsyncer doesn\'t understand. '
            'Error message: {!r}\n'
            'While this is most likely a serverside problem, the vdirsyncer '
            'devs are generally interested in such bugs. Please report it in '
            'the issue tracker at {}'
            .format(e, BUGTRACKER_HOME)
        )
    except exceptions.CollectionRequired:
        cli_logger.error(
            'One or more storages don\'t support `collections = null`. '
            'You probably want to set `collections = ["from a", "from b"]`.'
        )
    except Exception as e:
        tb = sys.exc_info()[2]
        import traceback
        tb = traceback.format_tb(tb)
        if status_name:
            msg = 'Unknown error occurred for {}'.format(status_name)
        else:
            msg = 'Unknown error occurred'

        msg += ': {}\nUse `-vdebug` to see the full traceback.'.format(e)

        cli_logger.error(msg)
        cli_logger.debug(''.join(tb))


def get_status_name(pair, collection):
    if collection is None:
        return pair
    return pair + '/' + collection


def get_status_path(base_path, pair, collection=None, data_type=None):
    assert data_type is not None
    status_name = get_status_name(pair, collection)
    path = expand_path(os.path.join(base_path, status_name))
    if os.path.isfile(path) and data_type == 'items':
        new_path = path + '.items'
        # XXX: Legacy migration
        cli_logger.warning('Migrating statuses: Renaming {} to {}'
                           .format(path, new_path))
        os.rename(path, new_path)

    path += '.' + data_type
    return path


def load_status(base_path, pair, collection=None, data_type=None):
    path = get_status_path(base_path, pair, collection, data_type)
    if not os.path.exists(path):
        return None
    assert_permissions(path, STATUS_PERMISSIONS)

    with open(path) as f:
        try:
            return dict(json.load(f))
        except ValueError:
            pass

    return {}


def prepare_status_path(path):
    dirname = os.path.dirname(path)

    try:
        os.makedirs(dirname, STATUS_DIR_PERMISSIONS)
    except OSError as e:
        if e.errno != errno.EEXIST:
            raise


@contextlib.contextmanager
def manage_sync_status(base_path, pair_name, collection_name):
    path = get_status_path(base_path, pair_name, collection_name, 'items')
    status = None
    legacy_status = None
    try:
        # XXX: Legacy migration
        with open(path, 'rb') as f:
            if f.read(1) == b'{':
                f.seek(0)
                # json.load doesn't work on binary files for Python 3.5
                legacy_status = dict(json.loads(f.read().decode('utf-8')))
    except (OSError, ValueError):
        pass

    if legacy_status is not None:
        cli_logger.warning('Migrating legacy status to sqlite')
        os.remove(path)
        status = SqliteStatus(path)
        status.load_legacy_status(legacy_status)
    else:
        prepare_status_path(path)
        status = SqliteStatus(path)

    yield status


def save_status(base_path, pair, collection=None, data_type=None, data=None):
    assert data_type is not None
    assert data is not None
    status_name = get_status_name(pair, collection)
    path = expand_path(os.path.join(base_path, status_name)) + '.' + data_type
    prepare_status_path(path)

    with atomic_write(path, mode='w', overwrite=True) as f:
        json.dump(data, f)

    os.chmod(path, STATUS_PERMISSIONS)


def storage_class_from_config(config):
    config = dict(config)
    storage_name = config.pop('type')
    try:
        cls = storage_names[storage_name]
    except KeyError:
        raise exceptions.UserError(
            'Unknown storage type: {}'.format(storage_name))
    return cls, config


def storage_instance_from_config(config, create=True):
    '''
    :param config: A configuration dictionary to pass as kwargs to the class
        corresponding to config['type']
    '''

    cls, new_config = storage_class_from_config(config)

    try:
        return cls(**new_config)
    except exceptions.CollectionNotFound as e:
        if create:
            config = handle_collection_not_found(
                config, config.get('collection', None), e=str(e))
            return storage_instance_from_config(config, create=False)
        else:
            raise
    except Exception:
        return handle_storage_init_error(cls, new_config)


def handle_storage_init_error(cls, config):
    e = sys.exc_info()[1]
    if not isinstance(e, TypeError) or '__init__' not in repr(e):
        raise

    all, required = get_storage_init_args(cls)
    given = set(config)
    missing = required - given
    invalid = given - all

    problems = []

    if missing:
        problems.append(
            '{} storage requires the parameters: {}'
            .format(cls.storage_name, ', '.join(missing)))

    if invalid:
        problems.append(
            '{} storage doesn\'t take the parameters: {}'
            .format(cls.storage_name, ', '.join(invalid)))

    if not problems:
        raise e

    raise exceptions.UserError(
        'Failed to initialize {}'.format(config['instance_name']),
        problems=problems
    )


class WorkerQueue:
    '''
    A simple worker-queue setup.

    Note that workers quit if queue is empty. That means you have to first put
    things into the queue before spawning the worker!
    '''
    def __init__(self, max_workers):
        self._queue = queue.Queue()
        self._workers = []
        self._max_workers = max_workers
        self._shutdown_handlers = []

        # According to http://stackoverflow.com/a/27062830, those are
        # threadsafe compared to increasing a simple integer variable.
        self.num_done_tasks = itertools.count()
        self.num_failed_tasks = itertools.count()

    def shutdown(self):
        while self._shutdown_handlers:
            try:
                self._shutdown_handlers.pop()()
            except Exception:
                pass

    def _worker(self):
        while True:
            try:
                func = self._queue.get(False)
            except queue.Empty:
                break

            try:
                func(wq=self)
            except Exception:
                handle_cli_error()
                next(self.num_failed_tasks)
            finally:
                self._queue.task_done()
                next(self.num_done_tasks)
                if not self._queue.unfinished_tasks:
                    self.shutdown()

    def spawn_worker(self):
        if self._max_workers and len(self._workers) >= self._max_workers:
            return

        t = click_threading.Thread(target=self._worker)
        t.start()
        self._workers.append(t)

    @contextlib.contextmanager
    def join(self):
        assert self._workers or not self._queue.unfinished_tasks
        ui_worker = click_threading.UiWorker()
        self._shutdown_handlers.append(ui_worker.shutdown)
        _echo = click.echo

        with ui_worker.patch_click():
            yield

            if not self._workers:
                # Ugly hack, needed because ui_worker is not running.
                click.echo = _echo
                cli_logger.critical('Nothing to do.')
                sys.exit(5)

            ui_worker.run()
            self._queue.join()
            for worker in self._workers:
                worker.join()

        tasks_failed = next(self.num_failed_tasks)
        tasks_done = next(self.num_done_tasks)

        if tasks_failed > 0:
            cli_logger.error('{} out of {} tasks failed.'
                             .format(tasks_failed, tasks_done))
            sys.exit(1)

    def put(self, f):
        return self._queue.put(f)


def assert_permissions(path, wanted):
    permissions = os.stat(path).st_mode & 0o777
    if permissions > wanted:
        cli_logger.warning('Correcting permissions of {} from {:o} to {:o}'
                           .format(path, permissions, wanted))
        os.chmod(path, wanted)


def handle_collection_not_found(config, collection, e=None):
    storage_name = config.get('instance_name', None)

    cli_logger.warning('{}No collection {} found for storage {}.'
                       .format('{}\n'.format(e) if e else '',
                               json.dumps(collection), storage_name))

    if click.confirm('Should vdirsyncer attempt to create it?'):
        storage_type = config['type']
        cls, config = storage_class_from_config(config)
        config['collection'] = collection
        try:
            args = cls.create_collection(**config)
            args['type'] = storage_type
            return args
        except NotImplementedError as e:
            cli_logger.error(e)

    raise exceptions.UserError(
        'Unable to find or create collection "{collection}" for '
        'storage "{storage}". Please create the collection '
        'yourself.'.format(collection=collection,
                           storage=storage_name))
