# wikiget - CLI tool for downloading files from Wikimedia sites
# Copyright (C) 2018-2023 Cody Logan and contributors
# SPDX-License-Identifier: GPL-3.0-or-later
#
# Wikiget is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Wikiget is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Wikiget. If not, see <https://www.gnu.org/licenses/>.

"""Prepare and process file downloads."""

from __future__ import annotations

import logging
from concurrent.futures import ThreadPoolExecutor
from typing import TYPE_CHECKING

from mwclient import APIError, InvalidResponse, LoginError, Site
from requests import ConnectionError, HTTPError
from tqdm import tqdm

import wikiget
from wikiget.client import connect_to_site, query_api
from wikiget.exceptions import ParseError
from wikiget.logging import FileLogAdapter
from wikiget.parse import get_dest, read_batch_file
from wikiget.validations import verify_hash

if TYPE_CHECKING:
    from argparse import Namespace

    from wikiget.file import File

logger = logging.getLogger(__name__)


def prep_download(dl: str, args: Namespace) -> File:
    """Prepare to download a file by parsing the filename or URL and CLI arguments.

    Args:
        dl (str): the file or URL to download
        args (argparse.Namespace): command-line arguments and their values

    Raises:
        FileExistsError: the destination file already exists on disk

    Returns:
        wikiget.file.File: a File object representing the file to download
    """
    file = get_dest(dl, args)

    # check if the destination file already exists; don't overwrite unless the user says
    if file.dest.is_file() and not args.force:
        msg = f"[{file.dest}] File already exists; skipping download (use -f to force)"
        raise FileExistsError(msg)

    return file


def process_download(args: Namespace) -> int:
    """Process the download target given in the CLI args as a single file or batch file.

    If the target is a batch file, process with batch_download and return the number of
    errors encountered, if any. If there were any errors, log the number and exit with
    code 1. If no errors, exit with code 0.

    If the target is a single file or URL, process with prep_download and log any
    exceptions that it raises. If there aren't any, download the file and return the
    exit code appropriately.

    Args:
        args (argparse.Namespace): command-line arguments and their values

    Returns:
        int: program exit code (1 if there were any problems or 0 otherwise)
    """
    exit_code = 0

    if args.batch:
        # batch download mode
        errors = batch_download(args)
        if errors:
            # return non-zero exit code if any problems were encountered, even if some
            # downloads completed successfully
            logger.warning(
                "%i problem%s encountered during batch processing",
                errors,
                "s"[: errors ^ 1],
            )
            exit_code = 1  # completed with errors
    else:
        # single download mode
        try:
            file = prep_download(args.FILE, args)
            site = connect_to_site(file.site, args)
            file.image = query_api(file.name, site)
        except ParseError as e:
            logger.error(e)
            exit_code = 1
        except FileExistsError as e:
            logger.warning(e)
            exit_code = 1
        except (ConnectionError, HTTPError, InvalidResponse, LoginError, APIError):
            exit_code = 1
        else:
            errors = download(file, args)
            if errors:
                exit_code = 1  # completed with errors
    return exit_code


def batch_download(args: Namespace) -> int:
    """Download files specified in a batch file.

    The batch file is parsed into a dictionary, and the dictionary's items are checked
    for validity before being downloaded using a ThreadPool for simultaneous downloads,
    if threading was specified on the command line.

    Args:
        args (argparse.Namespace): command-line arguments and their values

    Returns:
        int: number of errors encountered during processing
    """
    errors = 0

    # parse batch file
    try:
        dl_dict = read_batch_file(args.FILE)
    except OSError as e:
        logger.error("File could not be read: %s", str(e))
        return 1

    with ThreadPoolExecutor(max_workers=args.threads) as executor:
        futures = []
        sites: list[Site] = []
        for line_num, line in dl_dict.items():
            # keep track of batch file line numbers for debugging/logging purposes
            logger.info("Processing '%s' at line %i", line, line_num)
            try:
                file = prep_download(line, args)
                site = next(
                    filter(
                        lambda site: site.host == file.site,
                        sites,
                    ),
                    None,
                )
                # if there's already a Site object matching the desired host, reuse it
                # to reduce the number of API calls made per file
                if site:
                    logger.debug("Reusing the existing connection to %s", site.host)
                else:
                    logger.debug("Making a new connection to %s", file.site)
                    site = connect_to_site(file.site, args)
                    # cache the new Site for reuse
                    sites.append(site)
                file.image = query_api(file.name, site)
            except ParseError as e:
                logger.warning("%s (line %i)", str(e), line_num)
                errors += 1
                continue
            except FileExistsError as e:
                logger.warning(e)
                errors += 1
                continue
            except (ConnectionError, HTTPError, InvalidResponse, LoginError, APIError):
                logger.warning(
                    "Unable to download '%s' (line %i) due to an error",
                    line,
                    line_num,
                )
                errors += 1
                continue
            future = executor.submit(download, file, args)
            futures.append(future)
        # wait for downloads to finish
        for future in futures:
            errors += future.result()
    return errors


def download(f: File, args: Namespace) -> int:
    """Fetch file information and contents if the file exists and save it to disk.

    Args:
        f (wikiget.file.File): a File object representing the file to be downloaded
        args (argparse.Namespace): command-line arguments and their values

    Returns:
        :return: number of errors encountered during processing
        :rtype: int
    """
    file = f.image
    filename = f.name
    dest = f.dest
    site = file.site

    errors = 0

    # prepend the current filename to all log messages
    adapter = FileLogAdapter(logger, {"filename": filename})

    if file.imageinfo:
        # file exists either locally or at a common repository, like Wikimedia Commons
        file_url = file.imageinfo["url"]
        file_size = file.imageinfo["size"]
        file_sha1 = file.imageinfo["sha1"]

        filename_log = f"Downloading '{filename}' ({file_size} bytes) from {site.host}"
        if args.output:
            filename_log += f" to '{dest}'"
        adapter.info(filename_log)
        adapter.info(f"{file_url}")

        if args.dry_run:
            adapter.warning("Dry run; download skipped")
            return errors

        try:
            with tqdm(
                desc=str(dest),
                leave=args.verbose >= wikiget.STD_VERBOSE,
                total=file_size,
                unit="B",
                unit_scale=True,
                unit_divisor=wikiget.CHUNKSIZE,
            ) as progress_bar, dest.open("wb") as fd:
                # download the file using the existing Site session
                res = site.connection.get(file_url, stream=True)
                for chunk in res.iter_content(wikiget.CHUNKSIZE):
                    fd.write(chunk)
                    progress_bar.update(len(chunk))
        except OSError as e:
            adapter.error(f"File could not be written: {e}")
            errors += 1
            return errors

        # verify file integrity and log the details
        try:
            dl_sha1 = verify_hash(dest)
        except OSError as e:
            adapter.error(f"File downloaded but could not be verified: {e}")
            errors += 1
            return errors

        adapter.info(f"Remote file SHA1 is {file_sha1}")
        adapter.info(f"Local file SHA1 is {dl_sha1}")
        if dl_sha1 == file_sha1:
            adapter.info("Hashes match!")
            # at this point, we've successfully downloaded the file
            success_log = f"'{filename}' downloaded"
            if args.output:
                success_log += f" to '{dest}'"
            adapter.info(success_log)
        else:
            adapter.error("Hash mismatch! Downloaded file may be corrupt.")
            errors += 1

    else:
        # no file information returned
        adapter.warning("Target does not appear to be a valid file")
        errors += 1

    return errors