#!/usr/bin/env python
"""A web application that retrieves other websites for you.

To start serving the application on port 8088, type

  python webproxy.py

To start the server on some other interface/port, use

  python -m gevent.wsgi -p 8000 -i 0.0.0.0 webproxy.py

"""
from __future__ import print_function
from gevent import monkey; monkey.patch_all()
import sys
import re
import traceback

try:
    from cgi import escape
except ImportError:
    # Python 3.8 removed this API
    from html import escape

try:
    import urllib2
    from urlparse import urlparse
    from urllib import unquote
except ImportError:
    # pylint:disable=import-error,no-name-in-module
    from urllib import request as urllib2
    from urllib.parse import urlparse
    from urllib.parse import unquote

LISTEN = ('127.0.0.1', 8088)


def _as_bytes(s):
    if not isinstance(s, bytes): # Py3
        s = s.encode('utf-8')
    return s


def _as_str(s):
    if not isinstance(s, str): # Py3
        s = s.decode('latin-1')
    return s


def application(env, start_response):
    proxy_url = 'http://%s/' % env['HTTP_HOST']
    method = env['REQUEST_METHOD']
    path = env['PATH_INFO']
    if env['QUERY_STRING']:
        path += '?' + env['QUERY_STRING']
    path = path.lstrip('/')

    if (method, path) == ('GET', ''):
        start_response('200 OK', [('Content-Type', 'text/html')])
        return [FORM]

    if method == 'GET':
        return proxy(path, start_response, proxy_url)

    if (method, path) == ('POST', ''):
        key, value = env['wsgi.input'].read().strip().split(b'=')
        assert key == b'url', repr(key)
        value = _as_str(value)
        start_response('302 Found', [('Location', _as_str(join(proxy_url, unquote(value))))])
    elif method == 'POST':
        start_response('404 Not Found', [])
    else:
        start_response('501 Not Implemented', [])
    return []


def proxy(path, start_response, proxy_url):
    # pylint:disable=too-many-locals
    if '://' not in path:
        path = 'http://' + path

    try:
        try:
            response = urllib2.urlopen(path)
        except urllib2.HTTPError as ex:
            response = ex
        print('%s: %s %s' % (path, response.code, response.msg))
        # Beginning in Python 3.8, headers aren't guaranteed to arrive in
        # lowercase; we must do so ourself.
        headers = [(k, v) for (k, v) in response.headers.items() if k.lower() not in DROP_HEADERS]
        scheme, netloc, path, _params, _query, _fragment = urlparse(path)
        host = (scheme or 'http') + '://' + netloc
    except Exception as ex: # pylint:disable=broad-except
        sys.stderr.write('error while reading %s:\n' % path)
        traceback.print_exc()
        tb = traceback.format_exc()
        start_response('502 Bad Gateway', [('Content-Type', 'text/html')])
        # pylint:disable=deprecated-method
        error_str = escape(str(ex) or ex.__class__.__name__ or 'Error')
        error_str = '<h1>%s</h1><h2>%s</h2><pre>%s</pre>' % (error_str, escape(path), escape(tb))
        return [_as_bytes(error_str)]
    else:
        print("Returning", headers)
        start_response('%s %s' % (response.code, response.msg), headers)
        data = response.read()
        data = fix_links(data, proxy_url, host)
        return [data]


def join(url1, *rest):
    if not rest:
        return url1
    url2, rest = rest[0], rest[1:]
    url1 = _as_bytes(url1)
    url2 = _as_bytes(url2)
    if url1.endswith(b'/'):
        if url2.startswith(b'/'):
            return join(url1 + url2[1:], *rest)
        return join(url1 + url2, *rest)

    if url2.startswith(b'/'):
        return join(url1 + url2, *rest)

    return join(url1 + b'/' + url2, *rest)


def fix_links(data, proxy_url, host_url):
    """
    >>> fix_links("><img src=images/hp0.gif width=158", 'http://127.0.0.1:8088', 'www.google.com')
    '><img src="http://127.0.0.1:8088/www.google.com/images/hp0.gif" width=158'
    """
    def fix_link_cb(m):
        url = m.group('url')
        if b'://' in url:
            result = m.group('before') + b'"' + join(proxy_url, url) + b'"'
        else:
            result = m.group('before') + b'"' + join(proxy_url, host_url, url) + b'"'
        #print('replaced %r -> %r' % (m.group(0), result))
        return result
    data = _link_re_1.sub(fix_link_cb, data)
    data = _link_re_2.sub(fix_link_cb, data)
    return data

_link_re_1 = re.compile(br'''(?P<before>(href|src|action)\s*=\s*)(?P<quote>['"])(?P<url>[^#].*?)(?P=quote)''')
_link_re_2 = re.compile(br'''(?P<before>(href|src|action)\s*=\s*)(?P<url>[^'"#>][^ >]*)''')

# The lowercase names of headers that we will *NOT* forward.
DROP_HEADERS = {
    'transfer-encoding',
    'set-cookie'
}

FORM = b"""<html><head>
<title>Web Proxy - gevent example</title></head><body>
<table width=60% height=100% align=center>
<tr height=30%><td align=center valign=bottom>Type in URL you want to visit and press Enter</td></tr>
<tr><td align=center valign=top>
<form action=/ method=post>
<input size=80 name=url value="http://www.gevent.org"/>
</form>
</td></tr>
</table></body></table>
"""

if __name__ == '__main__':
    from gevent.pywsgi import WSGIServer
    print('Serving on %s...' % (LISTEN,))
    WSGIServer(LISTEN, application).serve_forever()