"""Set User-Agent header per spider or use a default value from settings"""

from scrapy import signals


class UserAgentMiddleware:
    """This middleware allows spiders to override the user_agent"""

    def __init__(self, user_agent="Scrapy"):
        self.user_agent = user_agent

    @classmethod
    def from_crawler(cls, crawler):
        o = cls(crawler.settings["USER_AGENT"])
        crawler.signals.connect(o.spider_opened, signal=signals.spider_opened)
        return o

    def spider_opened(self, spider):
        self.user_agent = getattr(spider, "user_agent", self.user_agent)

    def process_request(self, request, spider):
        if self.user_agent:
            request.headers.setdefault(b"User-Agent", self.user_agent)
