from dataclasses import dataclass
import datetime
import gzip
import json
import os
from pathlib import Path
import re
from typing import Callable, Mapping

import requests

HTTP_DATE = '%a, %d %b %Y %H:%M:%S GMT'
SLUGIFY = re.compile('\W+')

def slug(text: str) -> str:
    return SLUGIFY.sub('-', text.lower()).strip('-')

@dataclass()
class Repository:
    family: str
    repo: str
    index_url: str
    parse: Callable[[Path], Mapping[str, str]]

    def _full_name(self):
        return f'{self.family} {self.repo}'

    def _cache_dir(self) -> Path:
        return Path('data') / slug(self.family) / slug(self.repo)

    def _cache_file(self, name: str) -> Path:
        return self._cache_dir() / name

    def get_versions(self) -> Mapping[str, str]:
        self._cache_dir().mkdir(parents=True, exist_ok=True)
        downloaded_file = self._cache_file('downloaded')
        if downloaded_file.exists():
            mtime = downloaded_file.stat().st_mtime
        else:
            mtime = 0
        mtime = datetime.datetime.fromtimestamp(mtime, datetime.timezone.utc)
        mtime = mtime.strftime(HTTP_DATE)

        parsed_file = self._cache_file('parsed.json.gz')

        response = requests.get(self.index_url, headers={
            'If-Modified-Since': mtime,
        }, stream=True)
        if response.status_code != requests.codes.not_modified:
            response.raise_for_status()
            print('Re-downloading', self._full_name())
            set_mtime = response.headers.get('Last-Modified', '')
            with downloaded_file.open('wb') as f:
                for chunk in response.iter_content(chunk_size=256):
                    f.write(chunk)
            if len(set_mtime) > 0:
                set_mtime = datetime.datetime.strptime(set_mtime, HTTP_DATE)
                os.utime(downloaded_file, (datetime.datetime.now().timestamp(), set_mtime.timestamp()))

            parsed_data = self.parse(downloaded_file)
            with gzip.open(parsed_file, 'wt') as f:
                json.dump(parsed_data, f)
            return parsed_data
        else:
            with gzip.open(parsed_file, 'rt') as f:
                return json.load(f)