use tide::{Request, Response, Result, Next};
use prometheus::{self, IntCounterVec, HistogramVec, TextEncoder, Encoder, register_int_counter_vec, register_histogram_vec};
use lazy_static::lazy_static;
use async_trait::async_trait;
use std::time::{Instant, Duration};

// Copied from https://docs.rs/prometheus/0.12.0/src/prometheus/histogram.rs.html#885-889
#[inline]
fn duration_to_seconds(d: Duration) -> f64 {
    let nanos = f64::from(d.subsec_nanos()) / 1e9;
    d.as_secs() as f64 + nanos
}

lazy_static! {
    static ref HTTP_CONNS_COUNTER: IntCounterVec = register_int_counter_vec!(
        "http_requests_total", "Number of processed HTTP requests",
        &["code", "method", "url"]
    ).unwrap();

    static ref HTTP_REQUEST_DURATION_HISTOGRAM: HistogramVec = register_histogram_vec!(
        "http_request_duration_seconds", "Duration of HTTP requests",
        &["code", "method", "url"]
    ).unwrap();
}

pub struct InstrumentationMiddleware {}


#[async_trait]
impl<S> tide::Middleware<S> for InstrumentationMiddleware
where
    S: Send + Sync + Clone + 'static,
{
    async fn handle(
        &self,
        req: Request<S>,
        next: Next<'_, S>,
    ) -> Result {
        let url = req.url().to_string();
        let method = req.method().to_string();
        // Execute the request
        let instant = Instant::now();
        let res = next.run(req).await;
        let elapsed = duration_to_seconds(instant.elapsed());
        // Get the code from the response
        let code = res.status().to_string();

        HTTP_CONNS_COUNTER.with_label_values(&[&code, &method, &url]).inc();
        HTTP_REQUEST_DURATION_HISTOGRAM.with_label_values(&[&code, &method, &url]).observe(elapsed);

        Ok(res)
    }
}

pub async fn gather<S>(_: Request<S>) -> Result
where
    S: Send + Sync + Clone
{
    let mut buffer: Vec<u8> = vec![];
    let encoder = TextEncoder::new();
    let metric_families = prometheus::gather();
    encoder.encode(&metric_families, &mut buffer).unwrap();

    Ok(Response::builder(200).body(buffer).build())
}