"""Base Scraper implementation."""

from base64 import b64encode
from os import remove, stat
from os.path import exists, join, getsize
import re
from typing import List, Callable
from urllib.request import urlretrieve, URLopener
import hashlib

from scrapthechan import __version__
from scrapthechan.fileinfo import FileInfo

__all__ = ["Scraper"]


class Scraper:
    """Base scraper implementation.
    
    Arguments:
        save_directory             -- a path to a directory where file will be
                                      saved;
        files                      -- a list of FileInfo objects;
        download_progress_callback -- a callback function that will be called
                                      for each file started downloading.
    """
    def __init__(self, save_directory: str, files: List[FileInfo],
        download_progress_callback: Callable[[int], None] = None) -> None:
        self._save_directory = save_directory
        self._files = files
        self._url_opener = URLopener()
        self._url_opener.version = f"ScrapTheChan/{__version__}"
        self._progress_callback = download_progress_callback

    def run(self):
        raise NotImplementedError

    def _same_filename(self, filename: str, path: str) -> str:
        """Check if there is a file with same name. If so then add incremental
        number enclosed in brackets to a name of a new one."""
        newname = filename
        while exists(join(path, newname)):
            has_extension = newname.rfind(".") != -1
            if has_extension:
                l, r = newname.rsplit(".", 1)
                lbracket = l.rfind("(")
                if lbracket == -1:
                    newname = f"{l}(1).{r}"
                else:
                    num = l[lbracket+1:-1]
                    if num.isnumeric():
                        newname = f"{l[:lbracket]}({int(num)+1}).{r}"
                    else:
                        newname = f"{l}(1).{r}"
            else:
                lbracket = l.rfind("(")
                if lbracket == -1:
                    newname = f"{newname}(1)"
                else:
                    num = newname[lbracket+1:-1]
                    if num.isnumeric():
                        newname = f"{newname[:lbracket]}({int(num)+1})"
        return newname

    def _hash_file(self, filename: str, hash_algo: str = "md5",
                   blocksize: int = 1048576) -> (str, str):
        """Compute hash of a file."""
        hash_func = hashlib.new(hash_algo)
        with open(filename, 'rb') as f:
            buf = f.read(blocksize)
            while len(buf) > 0:
                hash_func.update(buf)
                buf = f.read(blocksize)
        return hash_func.hexdigest(), hash_func.digest()

    def _is_file_ok(self, f: FileInfo, filepath: str) -> bool:
        """Check if a file exist and isn't broken."""
        if not exists(filepath):
            return False
        computed_size = getsize(filepath)
        is_size_match = f.size == computed_size \
                        or f.size == round(computed_size / 1024)
        hexdig, dig = self._hash_file(filepath, f.hash_algo)
        is_hash_match = f.hash_value == hexdig \
                        or f.hash_value == b64encode(dig).decode()
        return is_size_match and is_hash_match

    def _download_file(self, f: FileInfo):
        """Download a single file."""
        filepath = join(self._save_directory, f.name)
        if self._is_file_ok(f, filepath):
            return True
        elif exists(filepath):
            filepath = join(self._save_directory, \
                self._same_filename(f.name, self._save_directory))
        self._url_opener.retrieve(f.dlurl, filepath)