from inspect import isawaitable
from typing import (
    Any,
    AsyncIterable,
    AsyncIterator,
    Awaitable,
    Dict,
    Optional,
    Union,
    cast,
)

from ..error import GraphQLError, located_error
from ..execution.execute import (
    assert_valid_execution_arguments,
    execute,
    get_field_def,
    ExecutionContext,
    ExecutionResult,
)
from ..language import DocumentNode
from ..pyutils import Path, inspect
from ..type import GraphQLFieldResolver, GraphQLSchema
from ..utilities import get_operation_root_type
from .map_async_iterator import MapAsyncIterator

__all__ = ["subscribe", "create_source_event_stream"]


async def subscribe(
    schema: GraphQLSchema,
    document: DocumentNode,
    root_value: Any = None,
    context_value: Any = None,
    variable_values: Optional[Dict[str, Any]] = None,
    operation_name: Optional[str] = None,
    field_resolver: Optional[GraphQLFieldResolver] = None,
    subscribe_field_resolver: Optional[GraphQLFieldResolver] = None,
) -> Union[AsyncIterator[ExecutionResult], ExecutionResult]:
    """Create a GraphQL subscription.

    Implements the "Subscribe" algorithm described in the GraphQL spec.

    Returns a coroutine object which yields either an AsyncIterator (if successful) or
    an ExecutionResult (client error). The coroutine will raise an exception if a server
    error occurs.

    If the client-provided arguments to this function do not result in a compliant
    subscription, a GraphQL Response (ExecutionResult) with descriptive errors and no
    data will be returned.

    If the source stream could not be created due to faulty subscription resolver logic
    or underlying systems, the coroutine object will yield a single ExecutionResult
    containing ``errors`` and no ``data``.

    If the operation succeeded, the coroutine will yield an AsyncIterator, which yields
    a stream of ExecutionResults representing the response stream.
    """
    try:
        result_or_stream = await create_source_event_stream(
            schema,
            document,
            root_value,
            context_value,
            variable_values,
            operation_name,
            subscribe_field_resolver,
        )
    except GraphQLError as error:
        return ExecutionResult(data=None, errors=[error])
    if isinstance(result_or_stream, ExecutionResult):
        return result_or_stream

    async def map_source_to_response(payload: Any) -> ExecutionResult:
        """Map source to response.

        For each payload yielded from a subscription, map it over the normal GraphQL
        :func:`~graphql.execute` function, with ``payload`` as the ``root_value``.
        This implements the "MapSourceToResponseEvent" algorithm described in the
        GraphQL specification. The :func:`~graphql.execute` function provides the
        "ExecuteSubscriptionEvent" algorithm, as it is nearly identical to the
        "ExecuteQuery" algorithm, for which :func:`~graphql.execute` is also used.
        """
        result = execute(
            schema,
            document,
            payload,
            context_value,
            variable_values,
            operation_name,
            field_resolver,
        )
        return await result if isawaitable(result) else result  # type: ignore

    return MapAsyncIterator(result_or_stream, map_source_to_response)


async def create_source_event_stream(
    schema: GraphQLSchema,
    document: DocumentNode,
    root_value: Any = None,
    context_value: Any = None,
    variable_values: Optional[Dict[str, Any]] = None,
    operation_name: Optional[str] = None,
    field_resolver: Optional[GraphQLFieldResolver] = None,
) -> Union[AsyncIterable[Any], ExecutionResult]:
    """Create source even stream

    Implements the "CreateSourceEventStream" algorithm described in the GraphQL
    specification, resolving the subscription source event stream.

    Returns a coroutine that yields an AsyncIterable.

    If the client provided invalid arguments, the source stream could not be created,
    or the resolver did not return an AsyncIterable, this function will throw an error,
    which should be caught and handled by the caller.

    A Source Event Stream represents a sequence of events, each of which triggers a
    GraphQL execution for that event.

    This may be useful when hosting the stateful subscription service in a different
    process or machine than the stateless GraphQL execution engine, or otherwise
    separating these two steps. For more on this, see the "Supporting Subscriptions
    at Scale" information in the GraphQL spec.
    """
    # If arguments are missing or incorrectly typed, this is an internal developer
    # mistake which should throw an early error.
    assert_valid_execution_arguments(schema, document, variable_values)

    # If a valid context cannot be created due to incorrect arguments, this will throw
    # an error.
    context = ExecutionContext.build(
        schema,
        document,
        root_value,
        context_value,
        variable_values,
        operation_name,
        field_resolver,
    )

    # Return early errors if execution context failed.
    if isinstance(context, list):
        return ExecutionResult(data=None, errors=context)

    type_ = get_operation_root_type(schema, context.operation)
    fields = context.collect_fields(type_, context.operation.selection_set, {}, set())
    response_names = list(fields)
    response_name = response_names[0]
    field_nodes = fields[response_name]
    field_node = field_nodes[0]
    field_name = field_node.name.value
    field_def = get_field_def(schema, type_, field_name)

    if not field_def:
        raise GraphQLError(
            f"The subscription field '{field_name}' is not defined.", field_nodes
        )

    # Call the `subscribe()` resolver or the default resolver to produce an
    # AsyncIterable yielding raw payloads.
    resolve_fn = field_def.subscribe or context.field_resolver

    path = Path(None, response_name)

    info = context.build_resolve_info(field_def, field_nodes, type_, path)

    # `resolve_field_value_or_error` implements the "ResolveFieldEventStream" algorithm
    # from GraphQL specification. It differs from `resolve_field_value` due to
    # providing a different `resolve_fn`.
    result = context.resolve_field_value_or_error(
        field_def, field_nodes, resolve_fn, root_value, info
    )
    event_stream = await cast(Awaitable, result) if isawaitable(result) else result
    # If `event_stream` is an Error, rethrow a located error.
    if isinstance(event_stream, Exception):
        raise located_error(event_stream, field_nodes, path.as_list())

    # Assert field returned an event stream, otherwise yield an error.
    if isinstance(event_stream, AsyncIterable):
        return event_stream
    raise TypeError(
        "Subscription field must return AsyncIterable."
        f" Received: {inspect(event_stream)}."
    )
