1// Copyright 2016 Google LLC
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//      http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15package stat
16
17import (
18	"bytes"
19	"encoding/csv"
20	"fmt"
21	"io"
22	"math"
23	"sort"
24	"strconv"
25	"text/tabwriter"
26	"time"
27)
28
29type byDuration []time.Duration
30
31func (data byDuration) Len() int           { return len(data) }
32func (data byDuration) Swap(i, j int)      { data[i], data[j] = data[j], data[i] }
33func (data byDuration) Less(i, j int) bool { return data[i] < data[j] }
34
35// quantile returns a value representing the kth of q quantiles.
36// May alter the order of data.
37func quantile(data []time.Duration, k, q int) (quantile time.Duration, ok bool) {
38	if len(data) < 1 {
39		return 0, false
40	}
41	if k > q {
42		return 0, false
43	}
44	if k < 0 || q < 1 {
45		return 0, false
46	}
47
48	sort.Sort(byDuration(data))
49
50	if k == 0 {
51		return data[0], true
52	}
53	if k == q {
54		return data[len(data)-1], true
55	}
56
57	bucketSize := float64(len(data)-1) / float64(q)
58	i := float64(k) * bucketSize
59
60	lower := int(math.Trunc(i))
61	var upper int
62	if i > float64(lower) && lower+1 < len(data) {
63		// If the quantile lies between two elements
64		upper = lower + 1
65	} else {
66		upper = lower
67	}
68	weightUpper := i - float64(lower)
69	weightLower := 1 - weightUpper
70	return time.Duration(weightLower*float64(data[lower]) + weightUpper*float64(data[upper])), true
71}
72
73type Aggregate struct {
74	Name               string
75	Count, Errors      int
76	Min, Median, Max   time.Duration
77	P75, P90, P95, P99 time.Duration // percentiles
78}
79
80// NewAggregate constructs an aggregate from latencies. Returns nil if latencies does not contain aggregateable data.
81func NewAggregate(name string, latencies []time.Duration, errorCount int) *Aggregate {
82	agg := Aggregate{Name: name, Count: len(latencies), Errors: errorCount}
83
84	if len(latencies) == 0 {
85		return nil
86	}
87	var ok bool
88	if agg.Min, ok = quantile(latencies, 0, 2); !ok {
89		return nil
90	}
91	if agg.Median, ok = quantile(latencies, 1, 2); !ok {
92		return nil
93	}
94	if agg.Max, ok = quantile(latencies, 2, 2); !ok {
95		return nil
96	}
97	if agg.P75, ok = quantile(latencies, 75, 100); !ok {
98		return nil
99	}
100	if agg.P90, ok = quantile(latencies, 90, 100); !ok {
101		return nil
102	}
103	if agg.P95, ok = quantile(latencies, 95, 100); !ok {
104		return nil
105	}
106	if agg.P99, ok = quantile(latencies, 99, 100); !ok {
107		return nil
108	}
109	return &agg
110}
111
112func (agg *Aggregate) String() string {
113	if agg == nil {
114		return "no data"
115	}
116	var buf bytes.Buffer
117	tw := tabwriter.NewWriter(&buf, 0, 0, 1, ' ', 0) // one-space padding
118	fmt.Fprintf(tw, "min:\t%v\nmedian:\t%v\nmax:\t%v\n95th percentile:\t%v\n99th percentile:\t%v\n",
119		agg.Min, agg.Median, agg.Max, agg.P95, agg.P99)
120	tw.Flush()
121	return buf.String()
122}
123
124// WriteCSV writes a csv file to the given Writer,
125// with a header row and one row per aggregate.
126func WriteCSV(aggs []*Aggregate, iow io.Writer) (err error) {
127	w := csv.NewWriter(iow)
128	defer func() {
129		w.Flush()
130		if err == nil {
131			err = w.Error()
132		}
133	}()
134	err = w.Write([]string{"name", "count", "errors", "min", "median", "max", "p75", "p90", "p95", "p99"})
135	if err != nil {
136		return err
137	}
138	for _, agg := range aggs {
139		err = w.Write([]string{
140			agg.Name, strconv.Itoa(agg.Count), strconv.Itoa(agg.Errors),
141			agg.Min.String(), agg.Median.String(), agg.Max.String(),
142			agg.P75.String(), agg.P90.String(), agg.P95.String(), agg.P99.String(),
143		})
144		if err != nil {
145			return err
146		}
147	}
148	return nil
149}
150