// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

//! Statistical functions and helpers.

use std::{
    iter::FromIterator,
    ops::{Add, Deref, Div, Sub},
    time::Instant,
};

#[macro_use]
extern crate log;
pub extern crate prometheus;

/// Implements a prometheus metrics collector
pub trait PrometheusMetrics {
    fn prometheus_metrics(&self, registry: &mut prometheus::Registry);
}

/// Adds a new prometheus counter with the specified value
pub fn prometheus_counter(reg: &mut prometheus::Registry, name: &str, help: &str, value: i64) {
    let c = prometheus::IntCounter::new(name, help).expect("name and help must be non-empty");
    c.inc_by(value);
    reg.register(Box::new(c))
        .expect("prometheus identifiers must be unique");
}

/// Adds a new prometheus gauge with the specified gauge
pub fn prometheus_gauge(reg: &mut prometheus::Registry, name: &str, help: &str, value: i64) {
    let g = prometheus::IntGauge::new(name, help).expect("name and help must be non-empty");
    g.set(value);
    reg.register(Box::new(g))
        .expect("prometheus identifiers must be are unique");
}

/// Adds a new prometheus counter with the time spent in running the specified function
pub fn prometheus_optime<F: Fn() -> T, T>(r: &mut prometheus::Registry, name: &str, f: &F) -> T {
    let start = Instant::now();
    let t = f();
    let elapsed = start.elapsed();
    prometheus_gauge(
        r,
        &format!("optime_{}", name),
        &format!("Time to perform {}", name),
        elapsed.as_millis() as i64,
    );
    t
}

/// Sorted corpus of data.
#[derive(Debug, Clone, PartialEq)]
pub struct Corpus<T>(Vec<T>);

impl<T: Ord> From<Vec<T>> for Corpus<T> {
    fn from(mut data: Vec<T>) -> Self {
        data.sort();
        Corpus(data)
    }
}

impl<T: Ord> FromIterator<T> for Corpus<T> {
    fn from_iter<I: IntoIterator<Item = T>>(iterable: I) -> Self {
        iterable.into_iter().collect::<Vec<_>>().into()
    }
}

impl<T> Deref for Corpus<T> {
    type Target = [T];

    fn deref(&self) -> &[T] {
        &self.0[..]
    }
}

impl<T: Ord> Corpus<T> {
    /// Get given percentile (approximated).
    pub fn percentile(&self, val: usize) -> Option<&T> {
        let len = self.0.len();
        let x = val * len / 100;
        let x = ::std::cmp::min(x, len);
        if x == 0 {
            return None;
        }

        self.0.get(x - 1)
    }

    /// Get the median element, if it exists.
    pub fn median(&self) -> Option<&T> {
        self.0.get(self.0.len() / 2)
    }

    /// Whether the corpus is empty.
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    /// Number of elements in the corpus.
    pub fn len(&self) -> usize {
        self.0.len()
    }
}

impl<T: Ord + Copy + ::std::fmt::Display> Corpus<T>
where
    T: Add<Output = T> + Sub<Output = T> + Div<Output = T> + From<usize>,
{
    /// Create a histogram of this corpus if it at least spans the buckets. Bounds are left closed.
    /// Excludes outliers.
    pub fn histogram(&self, bucket_number: usize) -> Option<Histogram<T>> {
        // TODO: get outliers properly.
        let upto = self.len() - self.len() / 40;
        Histogram::create(&self.0[..upto], bucket_number)
    }
}

/// Discretised histogram.
#[derive(Debug, PartialEq)]
pub struct Histogram<T> {
    /// Bounds of each bucket.
    pub bucket_bounds: Vec<T>,
    /// Count within each bucket.
    pub counts: Vec<usize>,
}

impl<T: Ord + Copy + ::std::fmt::Display> Histogram<T>
where
    T: Add<Output = T> + Sub<Output = T> + Div<Output = T> + From<usize>,
{
    // Histogram of a sorted corpus if it at least spans the buckets. Bounds are left closed.
    fn create(corpus: &[T], bucket_number: usize) -> Option<Histogram<T>> {
        if corpus.len() < 1 {
            return None;
        }
        let corpus_end = corpus
            .last()
            .expect("there is at least 1 element; qed")
            .clone();
        let corpus_start = corpus
            .first()
            .expect("there is at least 1 element; qed")
            .clone();
        trace!(target: "stats", "Computing histogram from {} to {} with {} buckets.", corpus_start, corpus_end, bucket_number);
        // Bucket needs to be at least 1 wide.
        let bucket_size = {
            // Round up to get the entire corpus included.
            let raw_bucket_size =
                (corpus_end - corpus_start + bucket_number.into()) / bucket_number.into();
            if raw_bucket_size == 0.into() {
                1.into()
            } else {
                raw_bucket_size
            }
        };
        let mut bucket_end = corpus_start + bucket_size;

        let mut bucket_bounds = vec![corpus_start; bucket_number + 1];
        let mut counts = vec![0; bucket_number];
        let mut corpus_i = 0;
        // Go through the corpus adding to buckets.
        for bucket in 0..bucket_number {
            while corpus.get(corpus_i).map_or(false, |v| v < &bucket_end) {
                // Initialized to size bucket_number above; iterates up to bucket_number; qed
                counts[bucket] += 1;
                corpus_i += 1;
            }
            // Initialized to size bucket_number + 1 above; iterates up to bucket_number; subscript is in range; qed
            bucket_bounds[bucket + 1] = bucket_end;
            bucket_end = bucket_end + bucket_size;
        }
        Some(Histogram {
            bucket_bounds: bucket_bounds,
            counts: counts,
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn check_corpus() {
        let corpus = Corpus::from(vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
        assert_eq!(corpus.percentile(0), None);
        assert_eq!(corpus.percentile(1), None);
        assert_eq!(corpus.percentile(101), Some(&10));
        assert_eq!(corpus.percentile(100), Some(&10));
        assert_eq!(corpus.percentile(50), Some(&5));
        assert_eq!(corpus.percentile(60), Some(&6));
        assert_eq!(corpus.median(), Some(&6));
    }

    #[test]
    fn check_histogram() {
        let hist = Histogram::create(
            &[
                643, 689, 1408, 2000, 2296, 2512, 4250, 4320, 4842, 4958, 5804, 6065, 6098, 6354,
                7002, 7145, 7845, 8589, 8593, 8895,
            ],
            5,
        )
        .unwrap();
        let correct_bounds: Vec<usize> = vec![643, 2294, 3945, 5596, 7247, 8898];
        assert_eq!(
            Histogram {
                bucket_bounds: correct_bounds,
                counts: vec![4, 2, 4, 6, 4]
            },
            hist
        );
    }

    #[test]
    fn smaller_data_range_than_bucket_range() {
        assert_eq!(
            Histogram::create(&[1, 2, 2], 3),
            Some(Histogram {
                bucket_bounds: vec![1, 2, 3, 4],
                counts: vec![1, 2, 0]
            })
        );
    }

    #[test]
    fn data_range_is_not_multiple_of_bucket_range() {
        assert_eq!(
            Histogram::create(&[1, 2, 5], 2),
            Some(Histogram {
                bucket_bounds: vec![1, 4, 7],
                counts: vec![2, 1]
            })
        );
    }

    #[test]
    fn data_range_is_multiple_of_bucket_range() {
        assert_eq!(
            Histogram::create(&[1, 2, 6], 2),
            Some(Histogram {
                bucket_bounds: vec![1, 4, 7],
                counts: vec![2, 1]
            })
        );
    }

    #[test]
    fn none_when_too_few_data() {
        assert!(Histogram::<usize>::create(&[], 1).is_none());
    }
}