//! Send metrics to a Prometheus server.

use crate::attributes::{Attributes, Buffered, MetricId, OnFlush, Prefixed, WithAttributes};
use crate::input::InputKind;
use crate::input::{Input, InputMetric, InputScope};
use crate::label::Labels;
use crate::metrics;
use crate::name::MetricName;
use crate::{CachedInput, QueuedInput};
use crate::{Flush, MetricValue};

use std::sync::Arc;

#[cfg(not(feature = "parking_lot"))]
use std::sync::{RwLock, RwLockWriteGuard};

#[cfg(feature = "parking_lot")]
use parking_lot::{RwLock, RwLockWriteGuard};
use std::io;

/// Prometheus Input holds a socket to a Prometheus server.
/// The socket is shared between scopes opened from the Input.
#[derive(Clone, Debug)]
pub struct Prometheus {
    attributes: Attributes,
    push_url: String,
}

impl Input for Prometheus {
    type SCOPE = PrometheusScope;

    fn metrics(&self) -> Self::SCOPE {
        PrometheusScope {
            attributes: self.attributes.clone(),
            buffer: Arc::new(RwLock::new(String::new())),
            push_url: self.push_url.clone(),
        }
    }
}

impl Prometheus {
    /// Send metrics to a Prometheus "push gateway" at the URL provided.
    /// URL path must include group identifier labels `job`
    /// as shown in https://github.com/prometheus/pushgateway#command-line
    /// For example `http://pushgateway.example.org:9091/metrics/job/some_job`
    pub fn push_to(url: &str) -> io::Result<Prometheus> {
        debug!("Pushing to Prometheus {:?}", url);

        Ok(Prometheus {
            attributes: Attributes::default(),
            push_url: url.to_string(),
        })
    }
}

impl WithAttributes for Prometheus {
    fn get_attributes(&self) -> &Attributes {
        &self.attributes
    }
    fn mut_attributes(&mut self) -> &mut Attributes {
        &mut self.attributes
    }
}

impl Buffered for Prometheus {}

/// Prometheus Input
#[derive(Debug, Clone)]
pub struct PrometheusScope {
    attributes: Attributes,
    buffer: Arc<RwLock<String>>,
    push_url: String,
}

impl InputScope for PrometheusScope {
    /// Define a metric of the specified type.
    fn new_metric(&self, name: MetricName, kind: InputKind) -> InputMetric {
        let prefix = self.prefix_prepend(name.clone()).join("_");

        let scale = match kind {
            // timers are in µs, but we give Prometheus milliseconds
            InputKind::Timer => 1000,
            _ => 1,
        };

        let cloned = self.clone();
        let metric = PrometheusMetric { prefix, scale };

        let metric_id = MetricId::forge("prometheus", name);

        InputMetric::new(metric_id, move |value, labels| {
            cloned.print(&metric, value, labels);
        })
    }
}

impl Flush for PrometheusScope {
    fn flush(&self) -> io::Result<()> {
        self.notify_flush_listeners();
        let buf = write_lock!(self.buffer);
        self.flush_inner(buf)
    }
}

impl PrometheusScope {
    fn print(&self, metric: &PrometheusMetric, value: MetricValue, labels: Labels) {
        let scaled_value = value / metric.scale;
        let value_str = scaled_value.to_string();

        let mut strbuf = String::new();
        // prometheus format be like `http_requests_total{method="post",code="200"} 1027 1395066363000`
        strbuf.push_str(&metric.prefix);

        let labels_map = labels.into_map();
        if !labels_map.is_empty() {
            strbuf.push('{');
            let mut i = labels_map.into_iter();
            let mut next = i.next();
            while let Some((k, v)) = next {
                strbuf.push_str(&k);
                strbuf.push_str("=\"");
                strbuf.push_str(&v);
                next = i.next();
                if next.is_some() {
                    strbuf.push_str("\",");
                } else {
                    strbuf.push('"');
                }
            }
            strbuf.push_str("} ");
        } else {
            strbuf.push(' ');
        }
        strbuf.push_str(&value_str);
        strbuf.push('\n');

        let mut buffer = write_lock!(self.buffer);
        if strbuf.len() + buffer.len() > BUFFER_FLUSH_THRESHOLD {
            metrics::PROMETHEUS_OVERFLOW.mark();
            warn!(
                "Prometheus Buffer Size Exceeded: {}",
                BUFFER_FLUSH_THRESHOLD
            );
            let _ = self.flush_inner(buffer);
            buffer = write_lock!(self.buffer);
        }

        buffer.push_str(&strbuf);

        if !self.is_buffered() {
            if let Err(e) = self.flush_inner(buffer) {
                debug!("Could not send to statsd {}", e)
            }
        }
    }

    fn flush_inner(&self, mut buf: RwLockWriteGuard<String>) -> io::Result<()> {
        if buf.is_empty() {
            return Ok(());
        }

        match minreq::post(self.push_url.as_str())
            .with_body(buf.as_str())
            .send()
        {
            Ok(http_result) => {
                metrics::PROMETHEUS_SENT_BYTES.count(buf.len());
                trace!(
                    "Sent {} bytes to Prometheus (resp status code: {})",
                    buf.len(),
                    http_result.status_code
                );
                buf.clear();
                Ok(())
            }
            Err(e) => {
                metrics::PROMETHEUS_SEND_ERR.mark();
                debug!("Failed to send buffer to Prometheus: {}", e);
                Err(io::Error::new(io::ErrorKind::Other, e))
            }
        }
    }
}

impl WithAttributes for PrometheusScope {
    fn get_attributes(&self) -> &Attributes {
        &self.attributes
    }
    fn mut_attributes(&mut self) -> &mut Attributes {
        &mut self.attributes
    }
}

impl Buffered for PrometheusScope {}

impl QueuedInput for Prometheus {}
impl CachedInput for Prometheus {}

/// Its hard to see how a single scope could get more metrics than this.
// TODO make configurable?
const BUFFER_FLUSH_THRESHOLD: usize = 65_536;

/// Key of a Prometheus metric.
#[derive(Debug, Clone)]
pub struct PrometheusMetric {
    prefix: String,
    scale: isize,
}

/// Any remaining buffered data is flushed on Drop.
impl Drop for PrometheusScope {
    fn drop(&mut self) {
        if let Err(err) = self.flush() {
            warn!("Could not flush Prometheus metrics upon Drop: {}", err)
        }
    }
}