Python browser crawler (Selenium)

"""Module defines the main entry point for the Scrapely Actor.

Feel free to modify this file to suit your specific needs.

To build Scrapely Actors, utilize the Scrapely SDK toolkit, read more at the official documentation:
"""

from __future__ import annotations

import asyncio
from urllib.parse import urljoin

from scrapely import Actor, Request
from selenium import webdriver
from selenium.webdriver.chrome.options import Options as ChromeOptions
from selenium.webdriver.common.by import By

# To run this Actor locally, you need to have the Selenium Chromedriver installed.
# Follow the installation guide at:
# https://www.selenium.dev/documentation/webdriver/getting_started/install_drivers/
# When running on the Scrapely platform, the Chromedriver is already included
# in the Actor's Docker image.

# Limit the crawl to max requests. Increase it to crawl more links.
MAX_REQUESTS_PER_CRAWL = 10

# Matches Playwright's default navigation timeout, which the sibling templates rely on.
PAGE_LOAD_TIMEOUT_SECS = 30


async def main() -> None:
    """Define a main entry point for the Scrapely Actor.

    This coroutine is executed using `asyncio.run()`, so it must remain an asynchronous function for proper execution.
    Asynchronous execution is required for communication with Scrapely platform, and it also enhances performance in
    the field of web scraping significantly.
    """
    # Enter the context of the Actor.
    async with Actor:
        # Retrieve the Actor input, and use default values if not provided.
        actor_input = await Actor.get_input() or {}
        start_urls = actor_input.get('start_urls', [{'url': 'https://crawlee.dev'}])
        max_depth = actor_input.get('max_depth', 1)

        # Exit if no start URLs are provided.
        if not start_urls:
            Actor.log.info('No start URLs specified in Actor input, exiting...')
            await Actor.exit()

        # Open the default request queue for handling URLs to be processed.
        request_queue = await Actor.open_request_queue()

        # Enqueue the start URLs with an initial crawl depth of 0.
        for start_url in start_urls:
            url = start_url.get('url')
            Actor.log.info(f'Enqueuing {url} ...')
            new_request = Request.from_url(url, user_data={'depth': 0})
            await request_queue.add_request(new_request)

        # Launch a new Selenium Chrome WebDriver and configure it.
        Actor.log.info('Launching Chrome WebDriver...')
        chrome_options = ChromeOptions()

        if Actor.configuration.headless:
            chrome_options.add_argument('--headless')

        chrome_options.add_argument('--no-sandbox')
        chrome_options.add_argument('--disable-dev-shm-usage')
        driver = webdriver.Chrome(options=chrome_options)

        # Without this a page that never finishes loading blocks for 120s, the client timeout.
        driver.set_page_load_timeout(PAGE_LOAD_TIMEOUT_SECS)

        # Test WebDriver setup by navigating to an example page.
        driver.get('http://www.example.com')
        if driver.title != 'Example Domain':
            raise ValueError('Failed to open example page.')

        handled_requests = 0

        # Process the URLs from the request queue.
        while handled_requests < MAX_REQUESTS_PER_CRAWL and (request := await request_queue.fetch_next_request()):
            url = request.url

            if not isinstance(request.user_data['depth'], (str, int)):
                raise TypeError('Request.depth is an enexpected type.')

            depth = int(request.user_data['depth'])
            Actor.log.info(f'Scraping {url} (depth={depth}) ...')

            try:
                # Navigate to the URL using Selenium WebDriver. Use asyncio.to_thread
                # for non-blocking execution.
                await asyncio.to_thread(driver.get, url)

                # If the current depth is less than max_depth, find nested links
                # and enqueue them.
                if depth < max_depth:
                    for link in driver.find_elements(By.TAG_NAME, 'a'):
                        link_href = link.get_attribute('href')
                        link_url = urljoin(url, link_href)

                        if link_url.startswith(('http://', 'https://')):
                            Actor.log.info(f'Enqueuing {link_url} ...')
                            new_request = Request.from_url(
                                link_url,
                                user_data={'depth': depth + 1},
                            )
                            await request_queue.add_request(new_request)

                # Extract the desired data.
                data = {
                    'url': url,
                    'title': driver.title,
                }

                # Store the extracted data to the default dataset.
                await Actor.push_data(data)

            except Exception:
                Actor.log.exception(f'Cannot extract data from {url}.')

            finally:
                # Mark the request as handled to ensure it is not processed again.
                await request_queue.mark_request_as_handled(request)
                handled_requests += 1

        driver.quit()