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use crate::context::ResolveId;
use crate::extensions::{Extension, ResolveInfo};
use chrono::{DateTime, Utc};
use parking_lot::Mutex;
use serde::ser::SerializeMap;
use serde::{Serialize, Serializer};
use std::collections::BTreeMap;
use std::ops::Deref;

struct PendingResolve {
    path: serde_json::Value,
    field_name: String,
    parent_type: String,
    return_type: String,
    start_time: DateTime<Utc>,
}

struct ResolveStat {
    pending_resolve: PendingResolve,
    end_time: DateTime<Utc>,
    start_offset: i64,
}

impl Deref for ResolveStat {
    type Target = PendingResolve;

    fn deref(&self) -> &Self::Target {
        &self.pending_resolve
    }
}

impl Serialize for ResolveStat {
    fn serialize<S: Serializer>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error> {
        let mut map = serializer.serialize_map(None)?;
        map.serialize_entry("path", &self.path)?;
        map.serialize_entry("fieldName", &self.field_name)?;
        map.serialize_entry("parentType", &self.parent_type)?;
        map.serialize_entry("returnType", &self.return_type)?;
        map.serialize_entry("startOffset", &self.start_offset)?;
        map.serialize_entry(
            "duration",
            &(self.end_time - self.start_time).num_nanoseconds(),
        )?;
        map.end()
    }
}

struct Inner {
    start_time: DateTime<Utc>,
    end_time: DateTime<Utc>,
    pending_resolves: BTreeMap<usize, PendingResolve>,
    resolves: Vec<ResolveStat>,
}

impl Default for Inner {
    fn default() -> Self {
        Self {
            start_time: Utc::now(),
            end_time: Utc::now(),
            pending_resolves: Default::default(),
            resolves: Default::default(),
        }
    }
}

/// Apollo tracing extension for performance tracing
///
/// Apollo Tracing works by including data in the extensions field of the GraphQL response, which is reserved by the GraphQL spec for extra information that a server wants to return. That way, you have access to performance traces alongside the data returned by your query.
/// It’s already supported by `Apollo Engine`, and we’re excited to see what other kinds of integrations people can build on top of this format.
#[derive(Default)]
pub struct ApolloTracing {
    inner: Mutex<Inner>,
}

impl Extension for ApolloTracing {
    fn name(&self) -> Option<&'static str> {
        Some("tracing")
    }

    fn parse_start(&self, _query_source: &str) {
        self.inner.lock().start_time = Utc::now();
    }

    fn execution_end(&self) {
        self.inner.lock().end_time = Utc::now();
    }

    fn resolve_field_start(&self, info: &ResolveInfo<'_>) {
        let mut inner = self.inner.lock();
        inner.pending_resolves.insert(
            info.resolve_id.current,
            PendingResolve {
                path: info.path_node.to_json(),
                field_name: info.path_node.field_name().to_string(),
                parent_type: info.parent_type.to_string(),
                return_type: info.return_type.to_string(),
                start_time: Utc::now(),
            },
        );
    }

    fn resolve_field_end(&self, resolve_id: ResolveId) {
        let mut inner = self.inner.lock();
        if let Some(pending_resolve) = inner.pending_resolves.remove(&resolve_id.current) {
            let start_offset = (pending_resolve.start_time - inner.start_time)
                .num_nanoseconds()
                .unwrap();
            inner.resolves.push(ResolveStat {
                pending_resolve,
                start_offset,
                end_time: Utc::now(),
            });
        }
    }

    fn result(&self) -> Option<serde_json::Value> {
        let mut inner = self.inner.lock();
        inner
            .resolves
            .sort_by(|a, b| a.start_offset.cmp(&b.start_offset));
        Some(serde_json::json!({
            "version": 1,
            "startTime": inner.start_time.to_rfc3339(),
            "endTime": inner.end_time.to_rfc3339(),
            "duration": (inner.end_time - inner.start_time).num_nanoseconds(),
            "execution": {
                "resolvers": inner.resolves
            }
        }))
    }
}