﻿#-------------------------------------------------------------------------
# Copyright (c) Microsoft.  All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#--------------------------------------------------------------------------
import threading

from time import sleep
from .._error import _ERROR_NO_SINGLE_THREAD_CHUNKING

def _download_file_chunks(file_service, share_name, directory_name, file_name,
                          download_size, block_size, progress, start_range, end_range, 
                          stream, max_connections, max_retries, retry_wait, progress_callback,
                          validate_content, timeout):
    if max_connections <= 1:
        raise ValueError(_ERROR_NO_SINGLE_THREAD_CHUNKING.format('file'))

    downloader = _FileChunkDownloader(
        file_service,
        share_name,
        directory_name, 
        file_name,
        download_size,
        block_size,
        progress,
        start_range,
        end_range,
        stream,
        max_retries,
        retry_wait,
        progress_callback,
        validate_content,
        timeout
    )

    import concurrent.futures
    executor = concurrent.futures.ThreadPoolExecutor(max_connections)
    result = list(executor.map(downloader.process_chunk, downloader.get_chunk_offsets()))

class _FileChunkDownloader(object):
    def __init__(self, file_service, share_name, directory_name, file_name, 
                 download_size, chunk_size, progress, start_range, end_range, 
                 stream, max_retries, retry_wait, progress_callback, validate_content, 
                 timeout):
        self.file_service = file_service
        self.share_name = share_name
        self.directory_name = directory_name
        self.file_name = file_name
        self.chunk_size = chunk_size

        self.download_size = download_size
        self.start_index = start_range    
        self.file_end = end_range

        self.stream = stream
        self.stream_start = stream.tell()
        self.stream_lock = threading.Lock()
        self.progress_callback = progress_callback
        self.progress_total = progress
        self.progress_lock = threading.Lock()
        self.max_retries = max_retries
        self.retry_wait = retry_wait
        self.validate_content = validate_content
        self.timeout = timeout

    def get_chunk_offsets(self):
        index = self.start_index
        while index < self.file_end:
            yield index
            index += self.chunk_size

    def process_chunk(self, chunk_start):
        if chunk_start + self.chunk_size > self.file_end:
            chunk_end = self.file_end
        else:
            chunk_end = chunk_start + self.chunk_size

        chunk_data = self._download_chunk_with_retries(chunk_start, chunk_end).content
        length = chunk_end - chunk_start
        if length > 0:
            self._write_to_stream(chunk_data, chunk_start)
            self._update_progress(length)

    def _update_progress(self, length):
        if self.progress_callback is not None:
            with self.progress_lock:
                self.progress_total += length
                total = self.progress_total
                self.progress_callback(total, self.download_size)

    def _write_to_stream(self, chunk_data, chunk_start):
        with self.stream_lock:
            self.stream.seek(self.stream_start + (chunk_start - self.start_index))
            self.stream.write(chunk_data)

    def _download_chunk_with_retries(self, chunk_start, chunk_end):
        retries = self.max_retries
        while True:
            try:
                return self.file_service._get_file(
                    self.share_name,
                    self.directory_name,
                    self.file_name,
                    start_range=chunk_start,
                    end_range=chunk_end - 1,
                    validate_content=self.validate_content,
                    timeout=self.timeout
                )
            except Exception:
                if retries > 0:
                    retries -= 1
                    sleep(self.retry_wait)
                else:
                    raise