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use crate::context::DeferList;
use crate::registry::Registry;
use crate::{ContextSelectionSet, OutputValueType, Positioned, QueryResponse, Result, Type};
use async_graphql_parser::query::Field;
use itertools::Itertools;
use std::borrow::Cow;
use std::sync::atomic::AtomicUsize;

/// Deferred type
///
/// Allows to defer the type of results returned, only takes effect when the @defer directive exists on the field.
pub struct Deferred<T: Type + Send + Sync + Clone + 'static>(T);

impl<T: Type + Send + Sync + Clone + 'static> From<T> for Deferred<T> {
    fn from(value: T) -> Self {
        Self(value)
    }
}

impl<T: Type + Send + Sync + Clone + 'static> Type for Deferred<T> {
    fn type_name() -> Cow<'static, str> {
        T::type_name()
    }

    fn create_type_info(registry: &mut Registry) -> String {
        T::create_type_info(registry)
    }
}

#[async_trait::async_trait]
impl<T: OutputValueType + Send + Sync + Clone + 'static> OutputValueType for Deferred<T> {
    async fn resolve(
        &self,
        ctx: &ContextSelectionSet<'_>,
        field: &Positioned<Field>,
    ) -> Result<serde_json::Value> {
        if let Some(defer_list) = ctx.defer_list {
            if ctx.is_defer(&field.directives) {
                let obj = self.0.clone();
                let schema_env = ctx.schema_env.clone();
                let query_env = ctx.query_env.clone();
                let mut field = field.clone();

                // remove @defer directive
                if let Some((idx, _)) = field
                    .node
                    .directives
                    .iter()
                    .find_position(|d| d.name.as_str() == "defer")
                {
                    field.node.directives.remove(idx);
                }

                let path_prefix = ctx
                    .path_node
                    .as_ref()
                    .map(|path| path.to_json())
                    .unwrap_or_default();

                defer_list.append(async move {
                    let inc_resolve_id = AtomicUsize::default();
                    let defer_list = DeferList {
                        path_prefix: path_prefix.clone(),
                        futures: Default::default(),
                    };
                    let ctx = query_env.create_context(
                        &schema_env,
                        None,
                        &field.selection_set,
                        &inc_resolve_id,
                        Some(&defer_list),
                    );
                    let data = obj.resolve(&ctx, &field).await?;

                    Ok((
                        QueryResponse {
                            path: Some(path_prefix),
                            data,
                            extensions: None,
                            cache_control: Default::default(),
                        },
                        defer_list,
                    ))
                });
                return Ok(serde_json::Value::Null);
            }
        }
        OutputValueType::resolve(&self.0, ctx, field).await
    }
}