import time
from logging import getLogger

from defence360agent.internals.feature_flags import (
    MESSAGE_LOSS_OBSERVABILITY_FLAG,
    is_enabled,
)
from defence360agent.model.instance import db
from defence360agent.model.messages_to_send import MessageToSend

logger = getLogger(__name__)


class PersistentMessagesQueue:
    """
    The queue to store messages sent to the server if it is unavailable.
    - stores more recent data; if a limit is exceeded,
       older messages are deleted.
    - no duplicate messages are sent

    NOTE: it is worth remembering that when writing a large number of messages,
          the amount of memory used may increase by the size of the sqlite
          cache (this may not be immediately obvious).
          https://www.sqlite.org/pragma.html#pragma_cache_size
    """

    def __init__(self, buffer_limit=20, storage_limit=1000, model=None):
        self._buffer_limit = buffer_limit
        self._storage_limit = storage_limit
        self._buffer = []  # [(timestamp, message),...]
        self._model = model or MessageToSend
        self.dropped_total = 0
        self._evicted = 0

    def pop_evicted(self) -> int:
        """Evictions since the last call, then reset (delta for metrics)."""
        evicted, self._evicted = self._evicted, 0
        return evicted

    def push_buffer_to_storage(self) -> None:
        if self._buffer:
            with db.atomic():
                # buffer may contain older messages than db,
                # so remove oldest items after insert
                self._model.insert_many(self._buffer)
                need_to_remove = self.storage_size - self._storage_limit
                if need_to_remove > 0:
                    # keep only the most recent messages
                    removed = self._model.delete_old(need_to_remove)
                    # This is the last point at which the messages exist, so it
                    # is the only place their loss can be reported.
                    self.dropped_total += removed
                    if is_enabled(MESSAGE_LOSS_OBSERVABILITY_FLAG):
                        self._evicted += removed
                    logger.warning(
                        "Persistent message queue overflow: dropped %d oldest"
                        " message(s), storage_limit=%d, dropped_total=%d",
                        removed,
                        self._storage_limit,
                        self.dropped_total,
                    )
                self._buffer = []

    def pop_all(self) -> list:
        items = []
        with db.atomic():
            items += list(
                self._model.select(
                    self._model.timestamp, self._model.message
                ).tuples()
            )
            self._model.delete().execute()
        items += self._buffer
        self._buffer = []
        return sorted(items)  # older first

    def peek_stored(self) -> list:
        """Return stored rows as (id, timestamp, message) oldest-first
        without deleting (buffer is neither flushed nor included)."""
        return list(self._model.get_all_ordered().tuples())

    def drain_buffer(self) -> list:
        """Return and clear the in-memory buffer as (timestamp, message)."""
        items, self._buffer = self._buffer, []
        return items

    def delete(self, ids: list) -> None:
        if ids:
            with db.atomic():
                self._model.delete_in(ids)

    def update_message(self, message_id: int, message: bytes) -> None:
        with db.atomic():
            self._model.set_message(message_id, message)

    def empty(self) -> bool:
        return self.qsize() == 0

    def qsize(self) -> int:
        return self.storage_size + len(self._buffer)

    @property
    def buffer_size(self) -> int:
        return len(self._buffer)

    @property
    def storage_size(self) -> int:
        return self._model.select().count()

    def put(self, message: bytes, timestamp=None):
        if timestamp is None:
            timestamp = time.time()
        self._buffer.append((timestamp, message))
        if self.buffer_size >= self._buffer_limit:
            self.push_buffer_to_storage()

    def put_many(self, messages: list[tuple[float, bytes]]) -> None:
        self._buffer.extend(messages)
        if self.buffer_size >= self._buffer_limit:
            self.push_buffer_to_storage()