package main

import (
	"sort"
	"sync"
	"time"
)

// latency collects request durations and reports percentiles. It is safe for
// concurrent recording.
type latency struct {
	mu      sync.Mutex
	samples []time.Duration
}

func (l *latency) record(d time.Duration) {
	l.mu.Lock()
	l.samples = append(l.samples, d)
	l.mu.Unlock()
}

func (l *latency) count() int {
	l.mu.Lock()
	defer l.mu.Unlock()
	return len(l.samples)
}

// percentiles returns p50/p90/p99 and the max. Returns zeros when empty.
func (l *latency) percentiles() (p50, p90, p99, max time.Duration) {
	l.mu.Lock()
	s := append([]time.Duration(nil), l.samples...)
	l.mu.Unlock()
	if len(s) == 0 {
		return 0, 0, 0, 0
	}
	sort.Slice(s, func(i, j int) bool { return s[i] < s[j] })
	at := func(q float64) time.Duration {
		idx := int(q * float64(len(s)-1))
		return s[idx]
	}
	return at(0.50), at(0.90), at(0.99), s[len(s)-1]
}