from notmuch import Database, NotmuchError, XapianError
import notmuch
import multiprocessing
import logging

from collections import deque

from message import Message
from alot.settings import settings
from thread import Thread

DB_ENC = 'utf-8'


class DatabaseError(Exception):
    pass


class DatabaseROError(DatabaseError):
    """cannot write to read-only database"""
    pass


class DatabaseLockedError(DatabaseError):
    """cannot write to locked index"""
    pass


class NonexistantObjectError(DatabaseError):
    """requested thread or message does not exist in the index"""
    pass


class FillPipeProcess(multiprocessing.Process):
    def __init__(self, it, pipe, fun=(lambda x: x)):
        multiprocessing.Process.__init__(self)
        self.it = it
        self.pipe = pipe[1]
        self.fun = fun

    def run(self):
        for a in self.it:
            self.pipe.send(self.fun(a))
        self.pipe.close()


class DBManager(object):
    """
    Keeps track of your index parameters, maintains a write-queue and
    lets you look up threads and messages directly to the persistent wrapper
    classes.
    """
    _sort_orders = {
        'oldest_first': notmuch.database.Query.SORT.OLDEST_FIRST,
        'newest_first': notmuch.database.Query.SORT.NEWEST_FIRST,
        'unsorted': notmuch.database.Query.SORT.UNSORTED,
        'message_id': notmuch.database.Query.SORT.MESSAGE_ID,
    }
    """constants representing sort orders"""

    def __init__(self, path=None, ro=False):
        """
        :param path: absolute path to the notmuch index
        :type path: str
        :param ro: open the index in read-only mode
        :type ro: bool
        """
        self.ro = ro
        self.path = path
        self.writequeue = deque([])
        self.processes = []

    def flush(self):
        """
        write out all queued write-commands in order, each one in a separate
        :meth:`atomic <notmuch.Database.begin_atomic>` transaction.

        If this fails the current action is rolled back, stays in the write
        queue and an exception is raised.
        You are responsible to retry flushing at a later time if you want to
        ensure that the cached changes are applied to the database.

        :exception: :exc:`DatabaseROError` if db is opened in read-only mode
        :exception: :exc:`DatabaseLockedError` if db is locked
        """
        if self.ro:
            raise DatabaseROError()
        if self.writequeue:
            # aquire a writeable db handler
            try:
                mode = Database.MODE.READ_WRITE
                db = Database(path=self.path, mode=mode)
            except NotmuchError:
                raise DatabaseLockedError()

            # read notmuch's config regarding imap flag synchronization
            sync = settings.get_notmuch_setting('maildir', 'synchronize_flags')

            # go through writequeue entries
            while self.writequeue:
                current_item = self.writequeue.popleft()
                logging.debug('write-out item: %s' % str(current_item))

                # watch out for notmuch errors to re-insert current_item
                # to the queue on errors
                try:
                    # the first two coordinants are cnmdname and post-callback
                    cmd, afterwards = current_item[:2]

                    # make this a transaction
                    db.begin_atomic()

                    if cmd == 'add':
                        path, tags = current_item[2:]
                        msg, status = db.add_message(path,
                                                     sync_maildir_flags=sync)
                        msg.freeze()
                        for tag in tags:
                            msg.add_tag(tag.encode(DB_ENC),
                                        sync_maildir_flags=sync)
                        msg.thaw()

                    elif cmd == 'remove':
                        path = current_item[2]
                        db.remove_message(path)

                    else:  # tag/set/untag
                        querystring, tags = current_item[2:]
                        query = db.create_query(querystring)
                        for msg in query.search_messages():
                            msg.freeze()
                            if cmd == 'tag':
                                for tag in tags:
                                    msg.add_tag(tag.encode(DB_ENC),
                                                sync_maildir_flags=sync)
                            if cmd == 'set':
                                msg.remove_all_tags()
                                for tag in tags:
                                    msg.add_tag(tag.encode(DB_ENC),
                                                sync_maildir_flags=sync)
                            elif cmd == 'untag':
                                for tag in tags:
                                    msg.remove_tag(tag.encode(DB_ENC),
                                                  sync_maildir_flags=sync)
                            msg.thaw()

                    # end transaction and reinsert queue item on error
                    if db.end_atomic() != notmuch.STATUS.SUCCESS:
                        raise DatabaseError('fail-status from end_atomic')

                    # call post-callback
                    if callable(afterwards):
                        afterwards()

                # re-insert item to the queue upon Xapian/NotmuchErrors
                except (XapianError, NotmuchError) as e:
                    self.writequeue.appendleft(current_item)
                    raise DatabaseError(unicode(e))

    def kill_search_processes(self):
        """
        terminate all search processes that originate from
        this managers :meth:`get_threads`.
        """
        for p in self.processes:
            p.terminate()
        self.processes = []

    def tag(self, querystring, tags, afterwards=None, remove_rest=False):
        """
        add tags to messages matching `querystring`.
        This appends a tag operation to the write queue and raises
        :exc:`DatabaseROError` if in read only mode.

        :param querystring: notmuch search string
        :type querystring: str
        :param tags: a list of tags to be added
        :type tags: list of str
        :param afterwards: callback that gets called after successful
                           application of this tagging operation
        :type afterwards: callable
        :param remove_rest: remove tags from matching messages before tagging
        :type remove_rest: bool
        :exception: :exc:`DatabaseROError`

        .. note::
            You need to call :meth:`DBManager.flush` to actually write out.
        """
        if self.ro:
            raise DatabaseROError()
        if remove_rest:
            self.writequeue.append(('set', afterwards, querystring, tags))
        else:
            self.writequeue.append(('tag', afterwards, querystring, tags))

    def untag(self, querystring, tags, afterwards=None):
        """
        removes tags from messages that match `querystring`.
        This appends an untag operation to the write queue and raises
        :exc:`DatabaseROError` if in read only mode.

        :param querystring: notmuch search string
        :type querystring: str
        :param tags: a list of tags to be added
        :type tags: list of str
        :param afterwards: callback that gets called after successful
                           application of this tagging operation
        :type afterwards: callable
        :exception: :exc:`DatabaseROError`

        .. note::
            You need to call :meth:`DBManager.flush` to actually write out.
        """
        if self.ro:
            raise DatabaseROError()
        self.writequeue.append(('untag', afterwards, querystring, tags))

    def count_messages(self, querystring):
        """returns number of messages that match `querystring`"""
        return self.query(querystring).count_messages()

    def search_thread_ids(self, querystring):
        """
        returns the ids of all threads that match the `querystring`
        This copies! all integer thread ids into an new list.

        :returns: list of str
        """

        return self.query_threaded(querystring)

    def _get_notmuch_thread(self, tid):
        """returns :class:`notmuch.database.Thread` with given id"""
        query = self.query('thread:' + tid)
        try:
            return query.search_threads().next()
        except StopIteration:
            errmsg = 'no thread with id %s exists!' % tid
            raise NonexistantObjectError(errmsg)

    def get_thread(self, tid):
        """returns :class:`Thread` with given thread id (str)"""
        return Thread(self, self._get_notmuch_thread(tid))

    def _get_notmuch_message(self, mid):
        """returns :class:`notmuch.database.Message` with given id"""
        mode = Database.MODE.READ_ONLY
        db = Database(path=self.path, mode=mode)
        try:
            return db.find_message(mid)
        except:
            errmsg = 'no message with id %s exists!' % mid
            raise NonexistantObjectError(errmsg)

    def get_message(self, mid):
        """returns :class:`Message` with given message id (str)"""
        return Message(self, self._get_notmuch_message(mid))

    def get_all_tags(self):
        """
        returns all tagsstrings used in the database
        :rtype: list of str
        """
        db = Database(path=self.path)
        return [t for t in db.get_all_tags()]

    def async(self, cbl, fun):
        """
        return a pair (pipe, process) so that the process writes
        `fun(a)` to the pipe for each element `a` in the iterable returned
        by the callable `cbl`.

        :param cbl: a function returning something iterable
        :type cbl: callable
        :param fun: an unary translation function
        :type fun: callable
        :rtype: (:class:`multiprocessing.Pipe`,
                :class:`multiprocessing.Process`)
        """
        pipe = multiprocessing.Pipe(False)
        receiver, sender = pipe
        process = FillPipeProcess(cbl(), pipe, fun)
        process.start()
        self.processes.append(process)
        # closing the sending end in this (receiving) process guarantees
        # that here the apropriate EOFError is raised upon .recv in the walker
        sender.close()
        return receiver, process

    def get_threads(self, querystring, sort='newest_first'):
        """
        asynchronously look up thread ids matching `querystring`.

        :param querystring: The query string to use for the lookup
        :type querystring: str.
        :param sort: Sort order. one of ['oldest_first', 'newest_first',
                     'message_id', 'unsorted']
        :type query: str
        :returns: a pipe together with the process that asynchronously
                  writes to it.
        :rtype: (:class:`multiprocessing.Pipe`,
                :class:`multiprocessing.Process`)
        """
        assert sort in self._sort_orders.keys()
        q = self.query(querystring)
        q.set_sort(self._sort_orders[sort])
        return self.async(q.search_threads, (lambda a: a.get_thread_id()))

    def query(self, querystring):
        """
        creates :class:`notmuch.Query` objects on demand

        :param querystring: The query string to use for the lookup
        :type query: str.
        :returns: :class:`notmuch.Query` -- the query object.
        """
        mode = Database.MODE.READ_ONLY
        db = Database(path=self.path, mode=mode)
        return db.create_query(querystring)

    def add_message(self, path, tags=[], afterwards=None):
        """
        Adds a file to the notmuch index.

        :param path: path to the file
        :type path: str
        :param tags: tagstrings to add
        :type tags: list of str
        :param afterwards: callback to trigger after adding
        :type afterwards: callable or None
        """
        if self.ro:
            raise DatabaseROError()
        self.writequeue.append(('add', afterwards, path, tags))

    def remove_message(self, message, afterwards=None):
        """
        Remove a message from the notmuch index

        :param message: message to remove
        :type message: :class:`Message`
        :param afterwards: callback to trigger after removing
        :type afterwards: callable or None
        """
        if self.ro:
            raise DatabaseROError()
        path = message.get_filename()
        self.writequeue.append(('remove', afterwards, path))