// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements.  See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License.  You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

//! Metricer methods.

use super::meter::{MeterId, Transform};
use crate::reporter::{CollectItem, DynReport, Report};
use std::{
    collections::HashMap,
    future::Future,
    pin::Pin,
    sync::Arc,
    task::{Context, Poll},
    time::Duration,
};
use tokio::{
    select, spawn,
    sync::mpsc,
    task::{spawn_blocking, JoinError, JoinHandle},
    time::interval,
};

/// Metricer handles skywalking metrics operations, integrate with reporter, can
/// be register with multiple [Transform].
pub struct Metricer {
    service_name: String,
    instance_name: String,
    reporter: Box<DynReport>,
    meter_map: HashMap<MeterId, Arc<dyn Transform>>,
    report_interval: Duration,
}

impl Metricer {
    /// New with service info and reporter.
    pub fn new(
        service_name: impl Into<String>,
        instance_name: impl Into<String>,
        reporter: impl Report + Send + Sync + 'static,
    ) -> Self {
        Self {
            service_name: service_name.into(),
            instance_name: instance_name.into(),
            reporter: Box::new(reporter),
            meter_map: Default::default(),
            report_interval: Duration::from_secs(20),
        }
    }

    /// Get service name.
    pub fn service_name(&self) -> &str {
        &self.service_name
    }

    /// Get instance name.
    pub fn instance_name(&self) -> &str {
        &self.instance_name
    }

    /// Set report interval, default is 20s.
    pub fn set_report_interval(&mut self, report_interval: Duration) {
        self.report_interval = report_interval;
    }

    /// Register new [Transform], and return it with [Arc] wrap.
    pub fn register<T: Transform + 'static>(&mut self, transform: T) -> Arc<T> {
        let transform = Arc::new(transform);
        self.meter_map
            .insert(transform.meter_id(), transform.clone());
        transform
    }

    /// Boot the reporting with the report interval previous set, will be run in
    /// background.
    pub fn boot(self) -> Booting {
        let (shutdown_tx, mut shutdown_rx) = mpsc::channel(1);

        let handle = spawn(async move {
            let mut ticker = interval(self.report_interval);
            let metricer = Arc::new(self);
            loop {
                let metricer_ = metricer.clone();
                let _ = spawn_blocking(move || {
                    for trans in metricer_.meter_map.values() {
                        metricer_
                            .reporter
                            .report(CollectItem::Meter(Box::new(trans.transform(&metricer_))));
                    }
                })
                .await;

                select! {
                    _ = ticker.tick() => {}
                    _ = shutdown_rx.recv() => { return; }
                }
            }
        });
        Booting {
            handle,
            shutdown_tx,
        }
    }
}

/// handle of [Metricer::boot].
pub struct Booting {
    handle: JoinHandle<()>,
    shutdown_tx: mpsc::Sender<()>,
}

impl Booting {
    /// Shutdown the metrics reporting.
    pub async fn shutdown(self) -> crate::Result<()> {
        self.shutdown_tx.send(()).await.unwrap();
        Ok(self.await?)
    }
}

impl Future for Booting {
    type Output = Result<(), JoinError>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        Pin::new(&mut self.handle).poll(cx)
    }
}