import argparse
import csv
import glob
import multiprocessing
import os
import pandas as pd
import queue
import requests
import sys
import time

from html.parser import HTMLParser
from lxml import html
from multiprocessing import Queue

#VERBOSE = False
VERBOSE = True

# Useful for debugging concurrency issues.
def log(msg):
    if not VERBOSE:
        return
    print(multiprocessing.current_process().name, msg, sys.stderr)


def get_urls(csv_file):
    df = pd.read_csv(csv_file)
    urls = df['url']
    assert urls[0]
    return df


# Fetches html content for a given url, saving content onto out_filename if GET
# is successful (i.e., HTTP GET returns status code 200).
def download_html(url, out_filename):
    response = requests.get(url, timeout=1)
    http_status = response.status_code
    if (http_status != 200):
        print('ERROR: request failed with HTTP status code ', http_status)
        return

    os.makedirs(os.path.dirname(out_filename), exist_ok=True)
    with open(out_filename, 'wb') as f:
        f.write(response.content)
        print('HTML contents saved under %s' % out_filename)


# Scrapes list of <category,regex> entries from previously downloaded HTML
# content, and enqueues them for later processing.
def scrape_html(out_queue, category, html_filename):
    with open(html_filename, 'r', encoding='utf-8') as f:
        contents = f.read()
        tree = html.fromstring(contents)

        # Valid as of Oct 2019.
        scraped_regexes = tree.xpath('.//tr[@class="expression"]/*[2]')

        csv_rows = []
        for regex in scraped_regexes:
            csv_row = to_csv_row(category, regex)
            if csv_row:
                csv_rows.append(csv_row)

        # YOUR CODE GOES HERE.
        # Add rows to out queue.


# Cleans scraped regex for saving onto output csv file.
def to_csv_row(category, scraped_regex):
    row = {'category': category}

    try:
        regex_bytes = bytes(scraped_regex[0].text, encoding='utf-8')
        regex_text = str(regex_bytes, encoding='utf-8')
        unescaped_regex = HTMLParser().unescape(regex_text)

        # Data quality check: skip regexes that contain new lines.
        if "\n" in unescaped_regex:
            return None

        clean_regex = unescaped_regex.replace(" ", "")
        # More cleaning: remove optional double quotes surrouding regex.
        if clean_regex.startswith('"') and clean_regex.endswith('"'):
            clean_regex = clean_regex[1:-1]
        row['regex'] = clean_regex
    except Exception as e:
        # Escaping won't throw exceptions for the included html files.
        template = 'Exception while escaping regex: type: {0}, args:\n{1!r}'
        msg = template.format(type(e).__name__, e.args)
        print(msg)
        return None

    return row


# Each worker will scrape regexes from local HTML files in parallel.
def worker(task_queue, out_queue):
    try:
      # YOUR CODE GOES HERE.
      # Dequeue tuples of (category,html_filename) from the task queue,
      # and use these as input for scrape_html.
    except queue.Empty:
        log('Done scraping!')


def main_task(urls_df, output_file, n_workers, redownload_html):
    # YOUR CODE GOES HERE.
    # 1. Create two Queues, one for adding tuples of (category, html_filename)
    #    for processing, and another to store the scraped regexes.
    # 2. Enqueue tuples of (category, html_filename) onto the task queue you
    #    created.
    # 3. Create your workers using Process and start them up.

    # NOTE: You need not enable this flag. This is here just so that you see
    # how the HTML files included under downloaded_html/ were originally
    # downloaded.
    if (redownload_html):
        print('Deleting existing html data...')
        os.system('rm -rf downloaded_html/')

        # Group urls by category, use index within same category for saving html.
        for category, group in urls_df.groupby('category'):
            i = 0
            for _, row in group.iterrows():
                html_filename = 'downloaded_html/%s/%02d.html' % (category, i)
                i += 1

                # Save local copy of downloaded html content.
                print('downloading:\n%s\nsaving: %s' % (row['url'],
                                                        html_filename))
                download_html(row['url'], html_filename)

    # Enqueue all tuples of <category, html_filename> for workers to scrape.
    html_filenames = glob.glob(os.path.join('', 'downloaded_html/*/*.html'))
    for f in html_filenames:
        category = f.split('/')[1]
        # YOUR CODE GOES HERE
        # Enqueue tuples of (category, html filename) onto the task queue.

    # YOUR CODE GOES HERE
    # Start up the workers.

    csv_rows = []
    try:
        while True:
            # https://bugs.python.org/issue20147
            csv_rows += out_queue.get(block=True, timeout=5)
    except queue.Empty:
        log('Done!')

    with open(output_file, 'w', encoding='utf-8') as csvfile:
        writer = csv.DictWriter(
            csvfile,
            fieldnames=['category', 'regex'],
            quotechar='"',
            quoting=csv.QUOTE_ALL)
        writer.writeheader()
        writer.writerows(csv_rows)


if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        description='Scrapes regexes from http://regexlib.com.')
    parser.add_argument(
        '-i',
        '--input_csv',
        help='Relative path of input CSV file containing regex '
        'category and URLs to scrape.',
        required='True')
    parser.add_argument(
        '-o',
        '--output_csv',
        help='Relative path of output CSV file containing '
        'scraped regexes for each category.',
        required='True')
    parser.add_argument(
        '-n',
        '--num_workers',
        help='Number of workers to use.',
        type=int,
        choices=range(1, 64),
        required='True')
    parser.add_argument(
        '--redownload_html',
        help='Redownloads HTML data from regexlib.com',
        dest='redownload_html',
        action='store_true')
    parser.set_defaults(redownload_html=False)
    args = parser.parse_args()

    print('Scraping regexes...')

    urls_df = get_urls(args.input_csv)
    main_task(urls_df, args.output_csv, args.num_workers, args.redownload_html)

    print('Regexes saved at "%s".' % args.output_csv)