use crate::context::QueryEnv;
use crate::parser::types::{Selection, TypeCondition};
use crate::{Context, ContextSelectionSet, Response, Result, Schema, SchemaEnv, Type};
use futures::{Future, Stream};
use std::pin::Pin;

/// Represents a GraphQL subscription object
#[async_trait::async_trait]
pub trait SubscriptionType: Type {
    /// This function returns true of type `EmptySubscription` only
    #[doc(hidden)]
    fn is_empty() -> bool {
        false
    }

    #[doc(hidden)]
    async fn create_field_stream(
        &self,
        ctx: &Context<'_>,
        schema_env: SchemaEnv,
        query_env: QueryEnv,
    ) -> Result<Pin<Box<dyn Stream<Item = Response> + Send>>>;
}

type BoxCreateStreamFuture<'a> = Pin<Box<dyn Future<Output = Result<()>> + Send + 'a>>;

pub(crate) fn create_subscription_stream<'a, Query, Mutation, Subscription>(
    schema: &'a Schema<Query, Mutation, Subscription>,
    environment: QueryEnv,
    ctx: &'a ContextSelectionSet<'_>,
    streams: &'a mut Vec<Pin<Box<dyn Stream<Item = Response> + Send>>>,
) -> BoxCreateStreamFuture<'a>
where
    Query: Send + Sync,
    Mutation: Send + Sync,
    Subscription: SubscriptionType + Send + Sync + 'static + Sized,
{
    Box::pin(async move {
        for selection in &ctx.item.node.items {
            if ctx.is_skip(selection.node.directives())? {
                continue;
            }
            match &selection.node {
                Selection::Field(field) => streams.push(
                    schema
                        .subscription
                        .create_field_stream(
                            &ctx.with_field(field),
                            schema.env.clone(),
                            environment.clone(),
                        )
                        .await?,
                ),
                Selection::FragmentSpread(fragment_spread) => {
                    if let Some(fragment) = ctx
                        .query_env
                        .document
                        .fragments
                        .get(&fragment_spread.node.fragment_name.node)
                    {
                        create_subscription_stream(
                            schema,
                            environment.clone(),
                            &ctx.with_selection_set(&fragment.node.selection_set),
                            streams,
                        )
                        .await?;
                    }
                }
                Selection::InlineFragment(inline_fragment) => {
                    if let Some(TypeCondition { on: name }) = inline_fragment
                        .node
                        .type_condition
                        .as_ref()
                        .map(|v| &v.node)
                    {
                        if name.node.as_str() == Subscription::type_name() {
                            create_subscription_stream(
                                schema,
                                environment.clone(),
                                &ctx.with_selection_set(&inline_fragment.node.selection_set),
                                streams,
                            )
                            .await?;
                        }
                    } else {
                        create_subscription_stream(
                            schema,
                            environment.clone(),
                            &ctx.with_selection_set(&inline_fragment.node.selection_set),
                            streams,
                        )
                        .await?;
                    }
                }
            }
        }
        Ok(())
    })
}

#[async_trait::async_trait]
impl<T: SubscriptionType + Send + Sync> SubscriptionType for &T {
    async fn create_field_stream(
        &self,
        ctx: &Context<'_>,
        schema_env: SchemaEnv,
        query_env: QueryEnv,
    ) -> Result<Pin<Box<dyn Stream<Item = Response> + Send>>> {
        T::create_field_stream(*self, ctx, schema_env, query_env).await
    }
}