import os
from typing import Any, Iterator

import orjson
from django.core.management.base import BaseCommand, CommandParser
from django.db.models import QuerySet

from zerver.lib.message import render_markdown
from zerver.models import Message


def queryset_iterator(queryset: QuerySet, chunksize: int = 5000) -> Iterator[Any]:
    queryset = queryset.order_by("id")
    while queryset.exists():
        for row in queryset[:chunksize]:
            msg_id = row.id
            yield row
        queryset = queryset.filter(id__gt=msg_id)


class Command(BaseCommand):
    help = """
    Render messages to a file.
    Usage: ./manage.py render_messages <destination> [--amount=10000]
    """

    def add_arguments(self, parser: CommandParser) -> None:
        parser.add_argument("destination", help="Destination file path")
        parser.add_argument("--amount", default=100000, help="Number of messages to render")
        parser.add_argument("--latest_id", default=0, help="Last message id to render")

    def handle(self, *args: Any, **options: Any) -> None:
        dest_dir = os.path.realpath(os.path.dirname(options["destination"]))
        amount = int(options["amount"])
        latest = int(options["latest_id"]) or Message.objects.latest("id").id
        self.stdout.write(f"Latest message id: {latest}")
        if not os.path.exists(dest_dir):
            os.makedirs(dest_dir)

        with open(options["destination"], "wb") as result:
            result.write(b"[")
            messages = Message.objects.filter(id__gt=latest - amount, id__lte=latest).order_by("id")
            for message in queryset_iterator(messages):
                content = message.content
                # In order to ensure that the output of this tool is
                # consistent across the time, even if messages are
                # edited, we always render the original content
                # version, extracting it from the edit history if
                # necessary.
                if message.edit_history:
                    history = orjson.loads(message.edit_history)
                    history = sorted(history, key=lambda i: i["timestamp"])
                    for entry in history:
                        if "prev_content" in entry:
                            content = entry["prev_content"]
                            break
                result.write(
                    orjson.dumps(
                        {
                            "id": message.id,
                            "content": render_markdown(message, content),
                        }
                    )
                )
                if message.id != latest:
                    result.write(b",")
            result.write(b"]")