from typing import Optional, Iterable

import streamlit as st
from streamlit import cursor
from streamlit.report_thread import get_report_ctx as get_script_run_ctx
#from streamlit.script_run_context import get_script_run_ctx
from streamlit.errors import NoSessionContext
from streamlit.proto import Block_pb2
from streamlit.proto import ForwardMsg_pb2

from streamlit.elements.form import FormData, current_form_id
from streamlit.delta_generator import DeltaGenerator


def _block(self, block_proto=Block_pb2.Block()) -> "DeltaGenerator":
    # Operate on the active DeltaGenerator, in case we're in a `with` block.
    dg = self._active_dg

    # Prevent nested columns & expanders by checking all parents.
    block_type = block_proto.WhichOneof("type")
    # Convert the generator to a list, so we can use it multiple times.
    parent_block_types = frozenset(dg._parent_block_types)
    # if block_type == "column" and block_type in parent_block_types:
    #    raise StreamlitAPIException("Columns may not be nested inside other columns.")
    # if block_type == "expandable" and block_type in parent_block_types:
    #    raise StreamlitAPIException(
    #        "Expanders may not be nested inside other expanders."
    #    )

    if dg._root_container is None or dg._cursor is None:
        return dg

    msg = ForwardMsg_pb2.ForwardMsg()
    msg.metadata.delta_path[:] = dg._cursor.delta_path
    msg.delta.add_block.CopyFrom(block_proto)

    # Normally we'd return a new DeltaGenerator that uses the locked cursor
    # below. But in this case we want to return a DeltaGenerator that uses
    # a brand new cursor for this new block we're creating.
    block_cursor = cursor.RunningCursor(
        root_container=dg._root_container,
        parent_path=dg._cursor.parent_path + (dg._cursor.index,),
    )
    block_dg = DeltaGenerator(
        root_container=dg._root_container,
        cursor=block_cursor,
        parent=dg,
        block_type=block_type,
    )
    # Blocks inherit their parent form ids.
    # NOTE: Container form ids aren't set in proto.
    block_dg._form_data = FormData(current_form_id(dg))

    # Must be called to increment this cursor's index.
    dg._cursor.get_locked_cursor(last_index=None)
    _enqueue_message(msg)

    return block_dg


def _enqueue_message(msg):
    """Enqueues a ForwardMsg proto to send to the app."""
    ctx = get_script_run_ctx()

    if ctx is None:
        raise NoSessionContext()

    ctx.enqueue(msg)


DeltaGenerator._block = _block