"""
> Based on parallel_file_transfer.py from mautrix-telegram, with permission to distribute under the MIT license
> Copyright (C) 2019 Tulir Asokan - https://github.com/tulir/mautrix-telegram
"""
import asyncio
import hashlib
import inspect
import logging
import math
import os
from collections import defaultdict
from io import BufferedReader, BytesIO
from typing import (AsyncGenerator, Awaitable, BinaryIO, DefaultDict, List,
                    Optional, Tuple, Union)

from telethon import TelegramClient, helpers, utils
from telethon.crypto import AuthKey
from telethon.network import MTProtoSender
from telethon.tl.functions.auth import (ExportAuthorizationRequest,
                                        ImportAuthorizationRequest)
from telethon.tl.functions.upload import (GetFileRequest,
                                          SaveBigFilePartRequest,
                                          SaveFilePartRequest)
from telethon.tl.types import (Document, InputDocumentFileLocation, InputFile,
                               InputFileBig, InputFileLocation,
                               InputPeerPhotoFileLocation,
                               InputPhotoFileLocation, TypeInputFile)

log: logging.Logger = logging.getLogger("telethon")
logging.basicConfig(level=logging.WARNING)
TypeLocation = Union[Document, InputDocumentFileLocation, InputPeerPhotoFileLocation,
                     InputFileLocation, InputPhotoFileLocation]


def stream_file(file_to_stream: BinaryIO, chunk_size=1024):
    while data_read := file_to_stream.read(chunk_size):
        yield data_read


class DownloadSender:
    sender: MTProtoSender
    request: GetFileRequest
    remaining: int
    stride: int

    def __init__(self, sender: MTProtoSender, file: TypeLocation, offset: int, limit: int,
                 stride: int, count: int) -> None:
        self.sender = sender
        self.request = GetFileRequest(file, offset=offset, limit=limit)
        self.stride = stride
        self.remaining = count

    async def next(self) -> Optional[bytes]:
        if not self.remaining:
            return

        result = await self.sender.send(self.request)
        self.remaining -= 1
        self.request.offset += self.stride
        return result.bytes

    def disconnect(self) -> Awaitable[None]:
        return self.sender.disconnect()


class UploadSender:
    sender: MTProtoSender
    request: Union[SaveFilePartRequest, SaveBigFilePartRequest]
    part_count: int
    stride: int
    previous: Optional[asyncio.Task]
    loop: asyncio.AbstractEventLoop

    def __init__(self, sender: MTProtoSender, file_id: int, part_count: int, big: bool, index: int,
                 stride: int, loop: asyncio.AbstractEventLoop) -> None:
        self.sender = sender
        self.part_count = part_count

        if big:
            self.request = SaveBigFilePartRequest(file_id, index, part_count, b"")
        else:
            self.request = SaveFilePartRequest(file_id, index, b"")

        self.stride = stride
        self.previous = None
        self.loop = loop

    async def next(self, data: bytes) -> None:
        if self.previous:
            await self.previous

        self.previous = self.loop.create_task(self._next(data))

    async def _next(self, data: bytes) -> None:
        self.request.bytes = data
        log.debug(f"Sending file part {self.request.file_part}/{self.part_count} with {len(data)} bytes")
        await self.sender.send(self.request)
        self.request.file_part += self.stride

    async def disconnect(self) -> None:
        if self.previous:
            await self.previous

        return await self.sender.disconnect()


class ParallelTransferrer:
    client: TelegramClient
    loop: asyncio.AbstractEventLoop
    dc_id: int
    senders: Optional[List[Union[DownloadSender, UploadSender]]]
    auth_key: AuthKey
    upload_ticker: int

    def __init__(self, client: TelegramClient, dc_id: Optional[int] = None) -> None:
        self.client = client
        self.loop = self.client.loop
        self.dc_id = dc_id or self.client.session.dc_id
        self.auth_key = (None if dc_id and self.client.session.dc_id != dc_id
                         else self.client.session.auth_key)
        self.senders = None
        self.upload_ticker = 0

    async def _cleanup(self) -> None:
        await asyncio.gather(*[sender.disconnect() for sender in self.senders])
        self.senders = None

    @staticmethod
    def _get_connection_count(file_size: int, max_count: int = 20,
                              full_size: int = 100 * 1024 * 1024) -> int:
        if file_size > full_size:
            return max_count

        return math.ceil((file_size / full_size) * max_count)

    async def _init_download(self, connections: int, file: TypeLocation, part_count: int,
                             part_size: int) -> None:
        minimum, remainder = divmod(part_count, connections)

        def get_part_count() -> int:
            nonlocal remainder

            if remainder > 0:
                remainder -= 1
                return minimum + 1

            return minimum

        # The first cross-DC sender will export+import the authorization, so we always create it
        # before creating any other senders.
        self.senders = [
            await self._create_download_sender(file, 0, part_size, connections * part_size,
                                               get_part_count()),
            *await asyncio.gather(
                *[self._create_download_sender(file, i, part_size, connections * part_size,
                                               get_part_count())
                  for i in range(1, connections)])
        ]

    async def _create_download_sender(self, file: TypeLocation, index: int, part_size: int,
                                      stride: int,
                                      part_count: int) -> DownloadSender:
        return DownloadSender(await self._create_sender(), file, index * part_size, part_size,
                              stride, part_count)

    async def _init_upload(self, connections: int, file_id: int, part_count: int, big: bool
                           ) -> None:
        self.senders = [
            await self._create_upload_sender(file_id, part_count, big, 0, connections),
            *await asyncio.gather(
                *[self._create_upload_sender(file_id, part_count, big, i, connections)
                  for i in range(1, connections)])
        ]

    async def _create_upload_sender(self, file_id: int, part_count: int, big: bool, index: int, stride: int) -> UploadSender:
        return UploadSender(await self._create_sender(), file_id, part_count, big, index, stride, loop=self.loop)

    async def _create_sender(self) -> MTProtoSender:
        dc = await self.client._get_dc(self.dc_id)
        sender = MTProtoSender(self.auth_key, loggers=self.client._log)
        await sender.connect(self.client._connection(dc.ip_address, dc.port, dc.id, loggers=self.client._log, proxy=self.client._proxy))

        if not self.auth_key:
            log.debug(f"Exporting auth to DC {self.dc_id}")
            auth = await self.client(ExportAuthorizationRequest(self.dc_id))
            req = self.client._init_with(ImportAuthorizationRequest(
                id=auth.id, bytes=auth.bytes
            ))
            await sender.send(req)
            self.auth_key = sender.auth_key

        return sender

    async def init_upload(self, file_id: int, file_size: int, part_size_kb: Optional[float] = None,
                          connection_count: Optional[int] = None) -> Tuple[int, int, bool]:
        connection_count = connection_count or self._get_connection_count(file_size)
        log.debug(f"init_upload count is {connection_count}")
        part_size = (part_size_kb or utils.get_appropriated_part_size(file_size)) * 1024
        part_count = (file_size + part_size - 1) // part_size
        is_large = file_size > 10 * 1024 * 1024
        await self._init_upload(connection_count, file_id, part_count, is_large)
        return part_size, part_count, is_large

    async def upload(self, part: bytes) -> None:
        await self.senders[self.upload_ticker].next(part)
        self.upload_ticker = (self.upload_ticker + 1) % len(self.senders)

    async def finish_upload(self) -> None:
        await self._cleanup()

    async def download(self, file: TypeLocation, file_size: int,
                       part_size_kb: Optional[float] = None,
                       connection_count: Optional[int] = None) -> AsyncGenerator[bytes, None]:
        connection_count = connection_count or self._get_connection_count(file_size)
        log.debug(f"Download count is {connection_count}")
        part_size = (part_size_kb or utils.get_appropriated_part_size(file_size)) * 1024
        part_count = math.ceil(file_size / part_size)
        log.debug(f"Starting parallel download: {connection_count} {part_size} {part_count} {file!s}")
        await self._init_download(connection_count, file, part_count, part_size)

        part = 0

        while part < part_count:
            tasks = []

            for sender in self.senders:
                tasks.append(self.loop.create_task(sender.next()))

            for task in tasks:
                data = await task

                if not data:
                    break

                yield data
                part += 1
                log.debug(f"Part {part} downloaded")

        log.debug("Parallel download finished, cleaning up connections")
        await self._cleanup()


parallel_transfer_locks: DefaultDict[int, asyncio.Lock] = defaultdict(lambda: asyncio.Lock())


async def _internal_transfer_to_telegram(client: TelegramClient,
                                         response: Union[BinaryIO, BytesIO, BufferedReader],
                                         progress_callback: callable,
                                         name: str = None
                                         ) -> Tuple[TypeInputFile, int]:
    file_id = helpers.generate_random_long()

    if isinstance(response, BytesIO):
        file_size = len(response.getvalue())
    else:
        file_size = os.path.getsize(name or response.name)

    hash_md5 = hashlib.md5()
    uploader = ParallelTransferrer(client)
    part_size, part_count, is_large = await uploader.init_upload(file_id, file_size)
    buffer = bytearray()

    for data in stream_file(response):
        if progress_callback:
            r = progress_callback(response.tell(), file_size)

            if inspect.isawaitable(r):
                await r

        if not is_large:
            hash_md5.update(data)

        if len(buffer) == 0 and len(data) == part_size:
            await uploader.upload(data)
            continue

        new_len = len(buffer) + len(data)

        if new_len >= part_size:
            cutoff = part_size - len(buffer)
            buffer.extend(data[:cutoff])
            await uploader.upload(bytes(buffer))
            buffer.clear()
            buffer.extend(data[cutoff:])
        else:
            buffer.extend(data)

    if len(buffer) > 0:
        await uploader.upload(bytes(buffer))

    await uploader.finish_upload()

    if is_large:
        return InputFileBig(file_id, part_count, name or "upload"), file_size

    return InputFile(file_id, part_count, name or "upload", hash_md5.hexdigest()), file_size


async def download_file(client: TelegramClient, location: TypeLocation, out: BinaryIO, progress_callback: callable = None) -> BinaryIO:
    size = location.size
    dc_id, location = utils.get_input_location(location)
    # We lock the transfers because telegram has connection count limits
    downloader = ParallelTransferrer(client, dc_id)
    downloaded = downloader.download(location, size)

    async for x in downloaded:
        out.write(x)

        if progress_callback:
            r = progress_callback(out.tell(), size)

            if inspect.isawaitable(r):
                await r

    return out


async def upload_file(client: TelegramClient, file: Union[BinaryIO, BytesIO, str], progress_callback: callable = None) -> TypeInputFile:
    if isinstance(file, str):
        with open(file, mode="rb") as fh:
            res = (await _internal_transfer_to_telegram(client, fh, progress_callback, file))[0]
    elif isinstance(file, BytesIO):
        res = (await _internal_transfer_to_telegram(client, file, progress_callback, file.name))[0]
    else:
        res = (await _internal_transfer_to_telegram(client, file, progress_callback))[0]

    return res