# coding=utf-8
 #!/usr/bin/env python

import time
from datetime import timedelta

try:
  from HTMLParser import HTMLParser
  from urlparse import urljoin, urldefrag
except ImportError:
  from html.parser import HTMLParser
  from urllib.parse import urljoin, urldefrag

from tornado import httpclient, gen, ioloop, queues

 # 設(shè)置要爬取的網(wǎng)址
base_url = 'http://www.baidu.com'
 # 設(shè)置worker數(shù)量
concurrency = 10
 # 此代碼會(huì)獲取base_url下的所有其他url
@gen.coroutine
def get_links_from_url(url):

  try:
    # 通過(guò)異步向url發(fā)起請(qǐng)求
    response = yield httpclient.AsyncHTTPClient().fetch(url)
    print('fetched %s' % url)
    # 響應(yīng)如果是字節(jié)類型 進(jìn)行解碼
    html = response.body if isinstance(response.body, str) \
      else response.body.decode(errors='ignore')
    # 構(gòu)建url列表
    urls = [urljoin(url, remove_fragment(new_url))
        for new_url in get_links(html)]
  except Exception as e:
    print('Exception: %s %s' % (e, url))
    # 報(bào)錯(cuò)返回空列表
    raise gen.Return([])
  # 返回url列表
  raise gen.Return(urls)


def remove_fragment(url):
  #去除錨點(diǎn)
  pure_url, frag = urldefrag(url)

  return pure_url


def get_links(html):
  #從html頁(yè)面里提取url
  class URLSeeker(HTMLParser):
    def __init__(self):
      HTMLParser.__init__(self)
      self.urls = []

    def handle_starttag(self, tag, attrs):
      href = dict(attrs).get('href')
      if href and tag == 'a':
        self.urls.append(href)

  url_seeker = URLSeeker()
  url_seeker.feed(html)
  return url_seeker.urls


@gen.coroutine
def main():
  # 創(chuàng)建隊(duì)列
  q = queues.Queue()
  # 記錄開始時(shí)間戳
  start = time.time()
  # 構(gòu)建兩個(gè)集合
  fetching, fetched = set(), set()

  @gen.coroutine
  def fetch_url():
    # 從隊(duì)列中取出數(shù)據(jù)
    current_url = yield q.get()
    try:
      # 如果取出的數(shù)據(jù)在隊(duì)列中已經(jīng)存在 返回
      if current_url in fetching:
        return

      print('fetching %s' % current_url)
      # 如果不存在添加到集合當(dāng)中
      fetching.add(current_url)
      # 從新放入的鏈接中繼續(xù)獲取鏈接
      urls = yield get_links_from_url(current_url)
      # 將已經(jīng)請(qǐng)求玩的url放入第二個(gè)集合
      fetched.add(current_url)

      for new_url in urls:
        # Only follow links beneath the base URL
        # 如果鏈接是以傳入的url開始則放入隊(duì)列
        if new_url.startswith(base_url):
          yield q.put(new_url)

    finally:
      # 隊(duì)列內(nèi)數(shù)據(jù)減一
      q.task_done()

  @gen.coroutine
  def worker():
    while True:
      # 保證程序持續(xù)運(yùn)行
      yield fetch_url()
  # 將第一個(gè)url放入隊(duì)列
  q.put(base_url)

  # Start workers, then wait for the work queue to be empty.
  for _ in range(concurrency):
    # 啟動(dòng)對(duì)應(yīng)數(shù)量的worker
    worker()
  # 等待隊(duì)列數(shù)據(jù)處理完成
  yield q.join(timeout=timedelta(seconds=300))
  # 如果兩個(gè)集合不相等拋出異常
  assert fetching == fetched
  # 打印執(zhí)行時(shí)間
  print('Done in %d seconds, fetched %s URLs.' % (
    time.time() - start, len(fetched)))


if __name__ == '__main__':
  io_loop = ioloop.IOLoop.current()
  io_loop.run_sync(main)