#!/usr/bin/env python
'''
check_link.py

Parses a url, and checks links in it for validity.
Normally, does not check links to the source URL's pages.
Normally, only reports problem links.

Usage:
    check_link.py [-i] [-v] [-b BASEURL] <url>...

Options:
    -b BASEURL --base= BASEURL  checking multiple pages on a site?
                                set the base, and supages to check
                                ('/' will check BASEURL)
    -i --internal               also check links internal to the site;
    -v --verbose                report all link outcomes, good and bad;
    -h --help                   Show this message and exit;

Examples:
    check_link.py -b https://mysite.io books blog   # check only 2 subpages
    check_link.py -b https://mysite.io / /blog      # check home page too
'''
import sys
import requests
from urllib.parse import urljoin, urlsplit, urlunsplit
from docopt import docopt
from colorama import init as colorama_init
from colorama import Fore
from bs4 import BeautifulSoup, SoupStrainer

# this is a modification of a gist;
#   it got me quickly started for now.
#  Original:
#  git@gist.github.com:2872d7f994d192188970408980267e6e.git


def check(address, netloc):
    global VERBOSE
    global FULL_GET
    global session
    msg = None  # the normal "ok" is no message

    # optimize which retrieve we use:
    retrieve = session.get if netloc in FULL_GET else session.head
    try:
        # NOTE: amazon denies requests from python scripts, so we use
        #    a session with an updated 'User-Agent' throughout ('session')
        #    amazon.com remembers if the session.get() was from a python agent,
        #    and then denies the session.get(), even if it updated
        #    its 'user-agent' with a 503 - Service Unavailable
        # OPTIMIZATION:
        #    we try a light-weight session.head() call first;
        #    if it fails for a domain w/ 405 (Method Not Allowed), then
        #    we retry with a full session.get(), and log the location so
        #    we always try the long way;
        resp = retrieve(address)
        if resp.status_code == 405:
            resp = session.get(address)
            FULL_GET.add(netloc)
    except Exception as e:
        return f'{Fore.YELLOW}{e} - {address}{Fore.RESET}'

    if resp.status_code in \
            [301, 308,
             400, 401, 402, 403, 404, 405, 408, 409, 410,
             501, 502, 503]:
        msg = f'{resp.status_code} - {resp.reason} => {address}'
        # TODO: scrub other permanent redirection codes to include in this:
        if resp.status_code == 301:
            newaddress = urljoin(address,
                                 resp.headers["Location"].split(";")[0])
            msg += f'\n{" "*19}NEW: => {newaddress}'
    elif VERBOSE:
        msg = f'{Fore.GREEN}{resp.status_code} - ' \
              f'{resp.reason} => {address}{Fore.RESET}'
    return msg


def pattern_adjust(link_address, rbase=None):
    '''
    returns  "adjusted" address and netloc;

    don't follow local addresses, unless
    option set to follow internal addresses
    '''
    global website
    global INTERNAL

    # if we're checking local, might as well
    #   check on-page, too - for typos
    if link_address[0] == '#' and not INTERNAL:  # local
        return (None, None)

    # create a local static var:
    #  - depends on global "website"
    # if 'rbase' not in pattern_adjust.__dict__ \
    #    pattern_adjust.rbase = urlsplit(website)

    r = urlsplit(link_address)
    # don't follow local:
    if not INTERNAL and \
       r.netloc == rbase.netloc:
        return (None, None)
    # NOTE:  I don't really understand
    #    what this is doing, so annotating:
    #  if relative URL (local)
    # TODO: I am getting convinced what this wants to do
    #   should be done w/ a simple urljoin()
    #   I'm also thinking this code branch isn't traversed;
    if r.scheme == '' and (r.netloc != '' or r.path != ''):
        # reconstitute - it won't be a full path
        d = urlunsplit(r)
        # This if seems exceedingly wonky
        if d.startswith('//'):
            # if it starts with '//', throw that away...
            # m = re.search('(?<=//)\S+', d)
            # d = m.group(0)
            # TODO:  if r.netloc is empty, then this
            #  could result in an incorrect URL:
            # => if address = foo.com/something - then ok
            # => if address relaive: ./static/something - then trouble
            return ("https://" + d[2:], r.netloc)
    elif r.scheme == '' and r.netloc == '':
        # is this what I want to do?
        #  would I rather do urljoin(urlunsplit(rbase), link_address)?
        return (urljoin(website, link_address), r.netloc) \
                if INTERNAL else (None, None)
    else:
        return (link_address, r.netloc)


def string_trunc(s, field_width=73, fill='.'):
    '''
    usage:
        s, f, w = string_trunc(longurl)
        print(f']{s:{f}<{w}}[')
    returns:
        a truncated (if needed) string,
        a fill char, and
        a matching field_width
    '''
    str_width = len(s)

    if str_width > field_width:
        # room for 3 fill chars
        return s[:field_width-3], fill, field_width
    else:
        # this doesn't work: need real values
        # return s, None, None
        # width of zero seems to not do width,
        #   but I need returned str_width to clear progress line;
        # fill could be anything (another "0", but...)
        return s, " ", str_width


def progress(msg):
    '''
    hack to print progress
    '''
    if 'w' not in progress.__dict__:
        progress.w = 0

    # clear previous progress line
    print(f'\r{" "*progress.w}', end='', file=sys.stderr)
    s, f, w = string_trunc(msg)
    print(f'\r{s:{f}<{w}}', end='', file=sys.stderr)
    progress.w = w


def extract_link(address):
    global link_status
    global session

    tags = {'a': 'href', 'img': 'src', 'script': 'src', 'link': 'href'}

    # the partitioned pieces of URL we're checking
    rbase = urlsplit(address)
    response = session.get(address)
    for key, value in tags.items():
        for link in BeautifulSoup(response.content, "html.parser",
                                  parse_only=SoupStrainer(key)):
            if link.has_attr(value):
                # I'm jonesin' for some progress indicators
                progress(link[value])
                p, netloc = pattern_adjust(link[value], rbase)
                if p and p not in link_status:
                    link_status[p] = check(p, netloc)
                    if link_status[p]:
                        # the '\r' is a hack to show stdout ok w/ progress msgs
                        print('\r', end='', file=sys.stderr)
                        print(link_status[p])


if __name__ == "__main__":
    arguments = docopt(__doc__)
    BASEURL = arguments['--base']
    INTERNAL = arguments['--internal']
    VERBOSE = arguments['--verbose']
    websites = arguments['<url>']  # "https://davericho.com/books/"

    colorama_init()
    # to facilitate checking each link only once
    link_status = {}
    # sites which don't accept 'head' requests (dynamic)
    #  populate with results of urlsplit().netloc
    FULL_GET = ('www.amazon.com',)
    # for places like amazon.com, which will deny python scripts:
    #  Now - use session throughout this script!
    session = requests.Session()
    session.headers.update({'User-Agent': 'test'})
    for website in websites:
        if BASEURL:
            website = urljoin(BASEURL, website)
        print(f'{Fore.CYAN}--- checking links on {website} ---{Fore.RESET}')
        result = extract_link(website)