# standard imports
import re
import urllib.request
import os
import logging

logg = logging.getLogger(__name__)


re_x = r'^HTTP_(X_.+)$'
def add_x_headers(env, header_f):
    for x in env:
        m = re.match(re_x, x)
        if m != None:
            header_orig = m[1].replace('_', '-')
            header_f(header_orig, env[x])

    
class ReverseProxy:

    def __init__(self, base_url, ignore_proxy_headers=[]):
        self.base_url = base_url
        if not isinstance(ignore_proxy_headers, list):
            raise ValueError('ignore_proxy_headers parameter must be a list of header keys')
        self.ignore_proxy_headers = []
        for h in ignore_proxy_headers:
            self.ignore_proxy_headers.append(h.lower())


    def proxy_pass(self, env, headers=[]):
        url = os.path.join(self.base_url, env['REQUEST_URI'][1:])
        logg.debug('access ok -> {}'.format(url))
        req = urllib.request.Request(url, method=env['REQUEST_METHOD'])
        add_x_headers(env, req.add_header)
        req.add_header('Content-Type', env.get('CONTENT_TYPE', 'application/octet-stream'))
        req.data = env.get('wsgi.input')
        res = urllib.request.urlopen(req)

        logg.debug('headers before reverse proxy {}'.format(headers))

        header_keys = {}
        for i, pair in enumerate(headers):
            header_keys[pair[0].lower()] = i

        for h in res.getheaders():
            k = h[0].lower()
            if k in self.ignore_proxy_headers:
                continue
            try:
                i = header_keys[k]
                headers[i] = h
            except KeyError:
                headers.append(h)

        logg.debug('headers after reverse proxy {}'.format(headers))

        status = '{} {}'.format(res.status, res.reason)
        content = res.read()
        return (status, headers, content)