# standard imports
import uuid

# local imports
from chainsyncer.error import FilterDone


class SyncSession:

    def __init__(self, session_store):
        self.session_store = session_store
        self.filters = []
        self.started = self.session_store.started
        self.get = self.session_store.get
        self.next = self.session_store.next_item
        self.item = None


    def register(self, fltr):
        if self.started:
            raise RuntimeError('filters cannot be changed after syncer start')
        self.session_store.register(fltr)
        self.filters.append(fltr)

    
    def start(self, offset=0, target=-1):
        self.session_store.start(offset=offset, target=target)
        self.item = self.session_store.next_item()


    def filter(self, conn, block, tx):
        self.session_store.connect()
        for fltr in self.filters:
            try:
                self.item.advance()
            except FilterDone:
                break
            interrupt = fltr.filter(conn, block, tx)
            self.item.release(interrupt=interrupt)
        try:
            self.item.advance()
            raise BackendError('filter state inconsitent with filter list')
        except FilterDone:
            self.item.reset()
        self.session_store.disconnect()