from __future__ import annotations

import operator
import sys
from collections import defaultdict
from collections.abc import AsyncIterator
from contextlib import AsyncExitStack
from datetime import datetime, timedelta, timezone
from logging import Logger
from typing import Any, Callable, ClassVar, Generic, Iterable, Mapping, TypeVar
from uuid import UUID

import attrs
import pymongo
from anyio import to_thread
from attrs.validators import instance_of
from bson import CodecOptions, UuidRepresentation
from bson.codec_options import TypeEncoder, TypeRegistry
from pymongo import ASCENDING, DeleteOne, MongoClient, UpdateOne
from pymongo.collection import Collection
from pymongo.cursor import Cursor
from pymongo.errors import ConnectionFailure, DuplicateKeyError

from .._enums import CoalescePolicy, ConflictPolicy, JobOutcome
from .._events import (
    DataStoreEvent,
    JobAcquired,
    JobAdded,
    JobReleased,
    ScheduleAdded,
    ScheduleRemoved,
    ScheduleUpdated,
    TaskAdded,
    TaskRemoved,
    TaskUpdated,
)
from .._exceptions import (
    ConflictingIdError,
    DeserializationError,
    SerializationError,
    TaskLookupError,
)
from .._structures import Job, JobResult, Schedule, Task
from ..abc import EventBroker
from .base import BaseExternalDataStore

if sys.version_info >= (3, 11):
    from typing import Self
else:
    from typing_extensions import Self

T = TypeVar("T", bound=Mapping[str, Any])


class CustomEncoder(TypeEncoder):
    def __init__(self, python_type: type, encoder: Callable):
        self._python_type = python_type
        self._encoder = encoder

    @property
    def python_type(self) -> type:
        return self._python_type

    def transform_python(self, value: Any) -> Any:
        return self._encoder(value)


def marshal_timestamp(timestamp: datetime | None, key: str) -> Mapping[str, Any]:
    if timestamp is None:
        return {key: None, key + "_utcoffset": None}

    return {
        key: timestamp.timestamp(),
        key + "_utcoffset": timestamp.utcoffset().total_seconds() // 60,
    }


def marshal_document(document: dict[str, Any]) -> None:
    if "id" in document:
        document["_id"] = document.pop("id")

    for key, value in list(document.items()):
        if isinstance(value, datetime):
            document.update(marshal_timestamp(document[key], key))


def unmarshal_timestamps(document: dict[str, Any]) -> None:
    for key in list(document):
        if key.endswith("_utcoffset") and (value := document.pop(key)) is not None:
            offset = timedelta(seconds=value * 60)
            tzinfo = timezone(offset)
            time_micro = document[key[:-10]]
            document[key[:-10]] = datetime.fromtimestamp(time_micro, tzinfo)


class AsyncCursor(Generic[T]):
    sentinel: ClassVar[object] = object()

    def __init__(self, cursor: Cursor[T]):
        self._cursor = cursor

    def __aiter__(self) -> AsyncIterator[T]:
        return self

    async def __aenter__(self) -> Self:
        return self

    async def __aexit__(self, exc_type, exc_val, exc_tb) -> None:
        await to_thread.run_sync(self._cursor.close)

    def _get_next(self) -> T:
        try:
            return next(self._cursor)
        except StopIteration:
            return self.sentinel

    async def __anext__(self) -> T:
        obj = await to_thread.run_sync(self._get_next)
        if obj is self.sentinel:
            raise StopAsyncIteration

        return obj

    @classmethod
    async def create(cls, func: Callable[..., Cursor[T]]) -> AsyncCursor[T]:
        cursor = await to_thread.run_sync(func)
        return AsyncCursor(cursor)


@attrs.define(eq=False)
class MongoDBDataStore(BaseExternalDataStore):
    """
    Uses a MongoDB server to store data.

    When started, this data store creates the appropriate indexes on the given database
    if they're not already present.

    Operations are retried (in accordance to ``retry_settings``) when an operation
    raises :exc:`pymongo.errors.ConnectionFailure`.

    :param client_or_uri: a PyMongo client or a MongoDB connection URI
    :param database: name of the database to use

    .. note:: The data store will not manage the life cycle of any client instance
        passed to it, so you need to close the client afterwards when you're done with
        it.

    .. note:: Datetimes are stored as integers along with their UTC offsets instead of
        BSON datetimes due to the BSON datetimes only being accurate to the millisecond
        while Python datetimes are accurate to the microsecond.
    """

    client_or_uri: MongoClient | str = attrs.field(
        validator=instance_of((MongoClient, str))
    )
    database: str = attrs.field(
        default="apscheduler", kw_only=True, validator=instance_of(str)
    )

    _client: MongoClient = attrs.field(init=False)
    _close_on_exit: bool = attrs.field(init=False, default=False)
    _task_attrs: ClassVar[list[str]] = [field.name for field in attrs.fields(Task)]
    _schedule_attrs: ClassVar[list[str]] = [
        field.name for field in attrs.fields(Schedule)
    ]
    _job_attrs: ClassVar[list[str]] = [field.name for field in attrs.fields(Job)]
    _tasks: Collection = attrs.field(init=False)
    _schedules: Collection = attrs.field(init=False)
    _jobs: Collection = attrs.field(init=False)
    _jobs_results: Collection = attrs.field(init=False)

    @property
    def _temporary_failure_exceptions(self) -> tuple[type[Exception], ...]:
        return (ConnectionFailure,)

    def __attrs_post_init__(self) -> None:
        if isinstance(self.client_or_uri, str):
            self._client = MongoClient(self.client_or_uri)
            self._close_on_exit = True
        else:
            self._client = self.client_or_uri

        type_registry = TypeRegistry(
            [
                CustomEncoder(timedelta, timedelta.total_seconds),
                CustomEncoder(ConflictPolicy, operator.attrgetter("name")),
                CustomEncoder(CoalescePolicy, operator.attrgetter("name")),
                CustomEncoder(JobOutcome, operator.attrgetter("name")),
            ]
        )
        codec_options = CodecOptions(
            type_registry=type_registry,
            uuid_representation=UuidRepresentation.STANDARD,
        )
        database = self._client.get_database(self.database, codec_options=codec_options)
        self._tasks = database["tasks"]
        self._schedules = database["schedules"]
        self._jobs = database["jobs"]
        self._jobs_results = database["job_results"]

    def _initialize(self) -> None:
        with self._client.start_session() as session:
            if self.start_from_scratch:
                self._tasks.delete_many({}, session=session)
                self._schedules.delete_many({}, session=session)
                self._jobs.delete_many({}, session=session)
                self._jobs_results.delete_many({}, session=session)

            self._schedules.create_index("next_fire_time", session=session)
            self._jobs.create_index("task_id", session=session)
            self._jobs.create_index("schedule_id", session=session)
            self._jobs.create_index("created_at", session=session)
            self._jobs_results.create_index("finished_at", session=session)
            self._jobs_results.create_index("expires_at", session=session)

    async def start(
        self, exit_stack: AsyncExitStack, event_broker: EventBroker, logger: Logger
    ) -> None:
        if self._close_on_exit:
            exit_stack.push_async_callback(to_thread.run_sync, self._client.close)

        await super().start(exit_stack, event_broker, logger)
        server_info = await to_thread.run_sync(self._client.server_info)
        if server_info["versionArray"] < [4, 0]:
            raise RuntimeError(
                f"MongoDB server must be at least v4.0; current version = "
                f"{server_info['version']}"
            )

        async for attempt in self._retry():
            with attempt:
                await to_thread.run_sync(self._initialize)

    async def add_task(self, task: Task) -> None:
        async for attempt in self._retry():
            with attempt:
                previous = await to_thread.run_sync(
                    lambda: self._tasks.find_one_and_update(
                        {"_id": task.id},
                        {
                            "$set": task.marshal(self.serializer),
                            "$setOnInsert": {"running_jobs": 0},
                        },
                        upsert=True,
                    )
                )

        if previous:
            await self._event_broker.publish(TaskUpdated(task_id=task.id))
        else:
            await self._event_broker.publish(TaskAdded(task_id=task.id))

    async def remove_task(self, task_id: str) -> None:
        async for attempt in self._retry():
            with attempt:
                if not await to_thread.run_sync(
                    self._tasks.find_one_and_delete, {"_id": task_id}
                ):
                    raise TaskLookupError(task_id)

        await self._event_broker.publish(TaskRemoved(task_id=task_id))

    async def get_task(self, task_id: str) -> Task:
        async for attempt in self._retry():
            with attempt:
                document = await to_thread.run_sync(
                    lambda: self._tasks.find_one(
                        {"_id": task_id}, projection=self._task_attrs
                    )
                )

        if not document:
            raise TaskLookupError(task_id)

        document["id"] = document.pop("_id")
        task = Task.unmarshal(self.serializer, document)
        return task

    async def get_tasks(self) -> list[Task]:
        async for attempt in self._retry():
            with attempt:
                tasks: list[Task] = []
                async with await AsyncCursor.create(
                    lambda: self._tasks.find(
                        projection=self._task_attrs, sort=[("_id", pymongo.ASCENDING)]
                    )
                ) as cursor:
                    async for document in cursor:
                        document["id"] = document.pop("_id")
                        tasks.append(Task.unmarshal(self.serializer, document))

        return tasks

    async def get_schedules(self, ids: set[str] | None = None) -> list[Schedule]:
        filters = {"_id": {"$in": list(ids)}} if ids is not None else {}
        async for attempt in self._retry():
            with attempt:
                schedules: list[Schedule] = []
                async with await AsyncCursor.create(
                    lambda: self._schedules.find(filters).sort("_id")
                ) as cursor:
                    async for document in cursor:
                        document["id"] = document.pop("_id")
                        unmarshal_timestamps(document)
                        try:
                            schedule = Schedule.unmarshal(self.serializer, document)
                        except DeserializationError:
                            self._logger.warning(
                                "Failed to deserialize schedule %r", document["_id"]
                            )
                            continue

                        schedules.append(schedule)

        return schedules

    async def add_schedule(
        self, schedule: Schedule, conflict_policy: ConflictPolicy
    ) -> None:
        event: DataStoreEvent
        document = schedule.marshal(self.serializer)
        marshal_document(document)
        try:
            async for attempt in self._retry():
                with attempt:
                    await to_thread.run_sync(self._schedules.insert_one, document)
        except DuplicateKeyError:
            if conflict_policy is ConflictPolicy.exception:
                raise ConflictingIdError(schedule.id) from None
            elif conflict_policy is ConflictPolicy.replace:
                async for attempt in self._retry():
                    with attempt:
                        await to_thread.run_sync(
                            self._schedules.replace_one,
                            {"_id": schedule.id},
                            document,
                            True,
                        )

                event = ScheduleUpdated(
                    schedule_id=schedule.id,
                    task_id=schedule.task_id,
                    next_fire_time=schedule.next_fire_time,
                )
                await self._event_broker.publish(event)
        else:
            event = ScheduleAdded(
                schedule_id=schedule.id,
                task_id=schedule.task_id,
                next_fire_time=schedule.next_fire_time,
            )
            await self._event_broker.publish(event)

    async def remove_schedules(self, ids: Iterable[str]) -> None:
        filters = {"_id": {"$in": list(ids)}} if ids is not None else {}
        async for attempt in self._retry():
            with attempt, self._client.start_session() as session:
                async with await AsyncCursor.create(
                    lambda: self._schedules.find(
                        filters, projection=["_id", "task_id"], session=session
                    )
                ) as cursor:
                    ids = [(doc["_id"], doc["task_id"]) async for doc in cursor]
                    if ids:
                        self._schedules.delete_many(filters, session=session)

        for schedule_id, task_id in ids:
            await self._event_broker.publish(
                ScheduleRemoved(
                    schedule_id=schedule_id, task_id=task_id, finished=False
                )
            )

    async def acquire_schedules(self, scheduler_id: str, limit: int) -> list[Schedule]:
        async for attempt in self._retry():
            with attempt, self._client.start_session() as session:
                schedules: list[Schedule] = []
                now = datetime.now(timezone.utc).timestamp()
                async with await AsyncCursor.create(
                    lambda: self._schedules.find(
                        {
                            "next_fire_time": {"$lte": now},
                            "$and": [
                                {
                                    "$or": [
                                        {"paused": {"$exists": False}},
                                        {"paused": False},
                                    ]
                                },
                                {
                                    "$or": [
                                        {"acquired_until": {"$exists": False}},
                                        {"acquired_until": {"$lt": now}},
                                    ]
                                },
                            ],
                        },
                        session=session,
                    )
                    .sort("next_fire_time")
                    .limit(limit)
                ) as cursor:
                    async for document in cursor:
                        document["id"] = document.pop("_id")
                        unmarshal_timestamps(document)
                        schedule = Schedule.unmarshal(self.serializer, document)
                        schedules.append(schedule)

                if schedules:
                    now = datetime.now(timezone.utc)
                    acquired_until = now + timedelta(seconds=self.lock_expiration_delay)
                    filters = {"_id": {"$in": [schedule.id for schedule in schedules]}}
                    update = {
                        "$set": {
                            "acquired_by": scheduler_id,
                            **marshal_timestamp(acquired_until, "acquired_until"),
                        }
                    }
                    self._schedules.update_many(filters, update, session=session)

        return schedules

    async def release_schedules(
        self, scheduler_id: str, schedules: list[Schedule]
    ) -> None:
        updated_schedules: list[tuple[str, datetime]] = []
        finished_schedule_ids: list[str] = []
        task_ids = {schedule.id: schedule.task_id for schedule in schedules}

        requests = []
        for schedule in schedules:
            filters = {"_id": schedule.id, "acquired_by": scheduler_id}
            try:
                serialized_trigger = self.serializer.serialize(schedule.trigger)
            except SerializationError:
                self._logger.exception(
                    "Error serializing schedule %r – removing from data store",
                    schedule.id,
                )
                requests.append(DeleteOne(filters))
                finished_schedule_ids.append(schedule.id)
                continue

            update = {
                "$unset": {
                    "acquired_by": True,
                    "acquired_until": True,
                    "acquired_until_utcoffset": True,
                },
                "$set": {
                    "trigger": serialized_trigger,
                    **marshal_timestamp(schedule.next_fire_time, "next_fire_time"),
                },
            }
            requests.append(UpdateOne(filters, update))
            updated_schedules.append((schedule.id, schedule.next_fire_time))

        if requests:
            async for attempt in self._retry():
                with attempt, self._client.start_session() as session:
                    await to_thread.run_sync(
                        lambda: self._schedules.bulk_write(
                            requests, ordered=False, session=session
                        )
                    )

        for schedule_id, next_fire_time in updated_schedules:
            event = ScheduleUpdated(
                schedule_id=schedule_id,
                task_id=task_ids[schedule_id],
                next_fire_time=next_fire_time,
            )
            await self._event_broker.publish(event)

        for schedule_id in finished_schedule_ids:
            await self._event_broker.publish(
                ScheduleRemoved(
                    schedule_id=schedule_id,
                    task_id=task_ids[schedule_id],
                    finished=True,
                )
            )

    async def get_next_schedule_run_time(self) -> datetime | None:
        async for attempt in self._retry():
            with attempt:
                document = await to_thread.run_sync(
                    lambda: self._schedules.find_one(
                        {"next_fire_time": {"$ne": None}},
                        projection=["next_fire_time", "next_fire_time_utcoffset"],
                        sort=[("next_fire_time", ASCENDING)],
                    )
                )

        if document:
            unmarshal_timestamps(document)
            return document["next_fire_time"]
        else:
            return None

    async def add_job(self, job: Job) -> None:
        document = job.marshal(self.serializer)
        marshal_document(document)
        async for attempt in self._retry():
            with attempt:
                await to_thread.run_sync(self._jobs.insert_one, document)

        event = JobAdded(
            job_id=job.id,
            task_id=job.task_id,
            schedule_id=job.schedule_id,
        )
        await self._event_broker.publish(event)

    async def get_jobs(self, ids: Iterable[UUID] | None = None) -> list[Job]:
        filters = {"_id": {"$in": list(ids)}} if ids is not None else {}
        async for attempt in self._retry():
            with attempt:
                jobs: list[Job] = []
                async with await AsyncCursor.create(
                    lambda: self._jobs.find(filters).sort("_id")
                ) as cursor:
                    async for document in cursor:
                        document["id"] = document.pop("_id")
                        unmarshal_timestamps(document)
                        try:
                            job = Job.unmarshal(self.serializer, document)
                        except DeserializationError:
                            self._logger.warning(
                                "Failed to deserialize job %r", document["id"]
                            )
                            continue

                        jobs.append(job)

        return jobs

    async def acquire_jobs(
        self, scheduler_id: str, limit: int | None = None
    ) -> list[Job]:
        async for attempt in self._retry():
            with attempt, self._client.start_session() as session:
                now = datetime.now(timezone.utc)
                async with await AsyncCursor.create(
                    lambda: self._jobs.find(
                        {
                            "$or": [
                                {"acquired_until": {"$exists": False}},
                                {"acquired_until": {"$lt": now.timestamp()}},
                            ]
                        },
                        sort=[("created_at", ASCENDING)],
                        limit=limit,
                        session=session,
                    )
                ) as cursor:
                    documents = [doc async for doc in cursor]

                # Retrieve the limits
                task_ids: set[str] = {document["task_id"] for document in documents}
                task_limits = await to_thread.run_sync(
                    lambda: self._tasks.find(
                        {
                            "_id": {"$in": list(task_ids)},
                            "max_running_jobs": {"$ne": None},
                        },
                        projection=["max_running_jobs", "running_jobs"],
                        session=session,
                    )
                )
                job_slots_left = {
                    doc["_id"]: doc["max_running_jobs"] - doc["running_jobs"]
                    for doc in task_limits
                }

                # Filter out jobs that don't have free slots
                acquired_jobs: list[Job] = []
                increments: dict[str, int] = defaultdict(lambda: 0)
                for document in documents:
                    document["id"] = document.pop("_id")
                    unmarshal_timestamps(document)
                    job = Job.unmarshal(self.serializer, document)

                    # Don't acquire the job if there are no free slots left
                    slots_left = job_slots_left.get(job.task_id)
                    if slots_left == 0:
                        continue
                    elif slots_left is not None:
                        job_slots_left[job.task_id] -= 1

                    acquired_jobs.append(job)
                    increments[job.task_id] += 1

                if acquired_jobs:
                    now = datetime.now(timezone.utc)
                    acquired_until = datetime.fromtimestamp(
                        now.timestamp() + self.lock_expiration_delay, timezone.utc
                    )
                    filters = {"_id": {"$in": [job.id for job in acquired_jobs]}}
                    update = {
                        "$set": {
                            "acquired_by": scheduler_id,
                            **marshal_timestamp(acquired_until, "acquired_until"),
                        }
                    }
                    await to_thread.run_sync(
                        lambda: self._jobs.update_many(filters, update, session=session)
                    )

                    # Increment the running job counters on each task
                    for task_id, increment in increments.items():
                        await to_thread.run_sync(
                            lambda: self._tasks.find_one_and_update(
                                {"_id": task_id},
                                {"$inc": {"running_jobs": increment}},
                                session=session,
                            )
                        )

        # Publish the appropriate events
        for job in acquired_jobs:
            await self._event_broker.publish(
                JobAcquired.from_job(job, scheduler_id=scheduler_id)
            )

        return acquired_jobs

    async def release_job(self, scheduler_id: str, job: Job, result: JobResult) -> None:
        async for attempt in self._retry():
            with attempt, self._client.start_session() as session:
                # Record the job result
                if result.expires_at > result.finished_at:
                    document = result.marshal(self.serializer)
                    document["_id"] = document.pop("job_id")
                    marshal_document(document)
                    self._jobs_results.insert_one(document, session=session)

                # Decrement the running jobs counter
                await to_thread.run_sync(
                    lambda: self._tasks.find_one_and_update(
                        {"_id": job.task_id},
                        {"$inc": {"running_jobs": -1}},
                        session=session,
                    )
                )

                # Delete the job
                await to_thread.run_sync(
                    lambda: self._jobs.delete_one(
                        {"_id": result.job_id}, session=session
                    )
                )

        # Notify other schedulers
        await self._event_broker.publish(
            JobReleased.from_result(job, result, scheduler_id)
        )

    async def get_job_result(self, job_id: UUID) -> JobResult | None:
        async for attempt in self._retry():
            with attempt:
                document = await to_thread.run_sync(
                    lambda: self._jobs_results.find_one_and_delete({"_id": job_id})
                )

        if document:
            document["job_id"] = document.pop("_id")
            unmarshal_timestamps(document)
            return JobResult.unmarshal(self.serializer, document)
        else:
            return None

    async def cleanup(self) -> None:
        # Clean up expired job results
        async for attempt in self._retry():
            with attempt, self._client.start_session() as session:
                # Purge expired job results
                now = datetime.now(timezone.utc).timestamp()

                await to_thread.run_sync(
                    lambda: self._jobs_results.delete_many(
                        {"expires_at": {"$lte": now}}, session=session
                    )
                )

                # Find finished schedules
                async with await AsyncCursor.create(
                    lambda: self._schedules.find(
                        {"next_fire_time": None},
                        projection=["_id", "task_id"],
                        session=session,
                    )
                ) as cursor:
                    if finished_schedules := {
                        item["_id"]: item["task_id"] async for item in cursor
                    }:
                        # Find distinct schedule IDs of jobs associated with these
                        # schedules
                        for schedule_id in await to_thread.run_sync(
                            lambda: self._jobs.distinct(
                                "schedule_id",
                                {"schedule_id": {"$in": list(finished_schedules)}},
                                session=session,
                            )
                        ):
                            finished_schedules.pop(schedule_id)

                # Delete finished schedules that not having any associated jobs
                if finished_schedules:
                    await to_thread.run_sync(
                        lambda: self._schedules.delete_many(
                            {"_id": {"$in": list(finished_schedules)}},
                            session=session,
                        )
                    )

                for schedule_id, task_id in finished_schedules.items():
                    await self._event_broker.publish(
                        ScheduleRemoved(
                            schedule_id=schedule_id,
                            task_id=task_id,
                            finished=True,
                        )
                    )
