import asyncio
import json

from anyio.to_thread import run_sync
from tornado import web

from ...base.handlers import APIHandler


LOCK = asyncio.Lock()


class NbconvertRootHandler(APIHandler):
    @web.authenticated
    async def get(self):
        try:
            from nbconvert.exporters import base
        except ImportError as e:
            raise web.HTTPError(500, "Could not import nbconvert: %s" % e) from e
        res = {}
        # Some exporters use the filesystem when instantiating, delegate that
        # to a thread so we don't block the event loop for it.
        exporters = await run_sync(base.get_export_names)
        for exporter_name in exporters:
            try:
                async with LOCK:
                    exporter_class = await run_sync(base.get_exporter, exporter_name)
            except ValueError:
                # I think the only way this will happen is if the entrypoint
                # is uninstalled while this method is running
                continue
            # XXX: According to the docs, it looks like this should be set to None
            # if the exporter shouldn't be exposed to the front-end and a friendly
            # name if it should. However, none of the built-in exports have it defined.
            # if not exporter_class.export_from_notebook:
            #    continue
            res[exporter_name] = {
                "output_mimetype": exporter_class.output_mimetype,
            }

        self.finish(json.dumps(res))


default_handlers = [
    (r"/api/nbconvert", NbconvertRootHandler),
]