import json
import time
from itertools import islice
from fatcat.worker_common import FatcatWorker
from pykafka.common import OffsetType


class FatcatChangelogWorker(FatcatWorker):
    """
    Periodically polls the fatcat API looking for new changelogs. When they are
    found, fetch them and push (as JSON) into a Kafka topic.
    """

    def __init__(self, api_host_url, kafka_hosts, produce_topic, poll_interval=10.0, offset=None):
        # TODO: should be offset=0
        super().__init__(kafka_hosts=kafka_hosts,
                         produce_topic=produce_topic,
                         api_host_url=api_host_url)
        self.poll_interval = poll_interval
        self.offset = offset    # the fatcat changelog offset, not the kafka offset

    def most_recent_message(self, topic):
        """
        Tries to fetch the most recent message from a given topic.
        This only makes sense for single partition topics, though could be
        extended with "last N" behavior.

        Following "Consuming the last N messages from a topic"
        from https://pykafka.readthedocs.io/en/latest/usage.html#consumer-patterns
        """
        consumer = topic.get_simple_consumer(
            auto_offset_reset=OffsetType.LATEST,
            reset_offset_on_start=True)
        offsets = [(p, op.last_offset_consumed - 1)
                    for p, op in consumer._partitions.items()]
        offsets = [(p, (o if o > -1 else -2)) for p, o in offsets]
        if -2 in [o for p, o in offsets]:
            return None
        else:
            consumer.reset_offsets(offsets)
            msg = islice(consumer, 1)
            if msg:
                return list(msg)[0].value
            else:
                return None

    def run(self):
        topic = self.kafka.topics[self.produce_topic]
        # On start, try to consume the most recent from the topic, and using
        # that as the starting offset. Note that this is a single-partition
        # topic
        if self.offset is None:
            print("Checking for most recent changelog offset...")
            msg = self.most_recent_message(topic)
            if msg:
                self.offset = json.loads(msg.decode('utf-8'))['index']
            else:
                self.offset = 1

        with topic.get_sync_producer() as producer:
            while True: 
                latest = int(self.api.get_changelog(limit=1)[0].index)
                if latest > self.offset:
                    print("Fetching changelogs from {} through {}".format(
                        self.offset+1, latest))
                for i in range(self.offset+1, latest+1):
                    cle = self.api.get_changelog_entry(i)
                    obj = self.api.api_client.sanitize_for_serialization(cle)
                    producer.produce(
                        message=json.dumps(obj).encode('utf-8'),
                        partition_key=None,
                        timestamp=None,
                        #XXX: timestamp=cle.timestamp,
                    )
                    self.offset = i
                print("Sleeping {} seconds...".format(self.poll_interval))
                time.sleep(self.poll_interval)


class FatcatEntityUpdatesWorker(FatcatWorker):
    """
    Consumes from the changelog topic and publishes expanded entities (fetched
    from API) to update topics.

    For now, only release updates are published.
    """

    def __init__(self, api_host_url, kafka_hosts, consume_topic, release_topic):
        super().__init__(kafka_hosts=kafka_hosts,
                         consume_topic=consume_topic,
                         api_host_url=api_host_url)
        self.release_topic = release_topic
        self.consumer_group = "entity-updates"

    def run(self):
        changelog_topic = self.kafka.topics[self.consume_topic]
        release_topic = self.kafka.topics[self.release_topic]

        consumer = changelog_topic.get_balanced_consumer(
            consumer_group=self.consumer_group,
            managed=True,
            auto_offset_reset=OffsetType.LATEST,
            reset_offset_on_start=False,
        )

        with release_topic.get_sync_producer() as producer:
            for msg in consumer:
                cle = json.loads(msg.value.decode('utf-8'))
                #print(cle)
                release_edits = cle['editgroup']['edits']['releases']
                for re in release_edits:
                    ident = re['ident']
                    release = self.api.get_release(ident, expand="files,container")
                    release_dict = self.api.api_client.sanitize_for_serialization(release)
                    producer.produce(
                        message=json.dumps(release_dict).encode('utf-8'),
                        partition_key=ident.encode('utf-8'),
                        timestamp=None,
                    )
                consumer.commit_offsets()