from io import BytesIO
from typing import Any

from repub import rss
from scrapy.exporters import BaseItemExporter

from .exceptions import *
from .items import ChannelElementItem


class RssExporter(BaseItemExporter):
    def __init__(self, file: BytesIO, **kwargs: Any):
        super().__init__(**kwargs)
        if not self.encoding:
            self.encoding = "utf-8"
        self.file: BytesIO = file
        self.rss = rss.rss()
        self.channel = None
        self.item_buffer = []

    def start_exporting(self) -> None:
        pass

    def export_item(self, item: Any):
        if isinstance(item, ChannelElementItem):
            self.channel = item.el
            self.rss.append(item.el)
            self.flush_buffer()
            return

        if self.channel is None:
            self.item_buffer.append(item)
        else:
            self.export_rss_item(item)

    def flush_buffer(self):
        for item in self.item_buffer:
            self.export_rss_item(item)
        self.item_buffer = []

    def export_rss_item(self, item: Any):
        assert self.channel is not None
        self.channel.append(item.el)

    def finish_exporting(self) -> None:
        xml_bytes = rss.serialize(self.rss)
        self.file.write(xml_bytes)