1// Copyright 2016 Google Inc.  All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package uuid
6
7import (
8	"encoding/binary"
9	"sync"
10	"time"
11)
12
13// A Time represents a time as the number of 100's of nanoseconds since 15 Oct
14// 1582.
15type Time int64
16
17const (
18	lillian    = 2299160          // Julian day of 15 Oct 1582
19	unix       = 2440587          // Julian day of 1 Jan 1970
20	epoch      = unix - lillian   // Days between epochs
21	g1582      = epoch * 86400    // seconds between epochs
22	g1582ns100 = g1582 * 10000000 // 100s of a nanoseconds between epochs
23)
24
25var (
26	timeMu   sync.Mutex
27	lasttime uint64 // last time we returned
28	clockSeq uint16 // clock sequence for this run
29
30	timeNow = time.Now // for testing
31)
32
33// UnixTime converts t the number of seconds and nanoseconds using the Unix
34// epoch of 1 Jan 1970.
35func (t Time) UnixTime() (sec, nsec int64) {
36	sec = int64(t - g1582ns100)
37	nsec = (sec % 10000000) * 100
38	sec /= 10000000
39	return sec, nsec
40}
41
42// GetTime returns the current Time (100s of nanoseconds since 15 Oct 1582) and
43// clock sequence as well as adjusting the clock sequence as needed.  An error
44// is returned if the current time cannot be determined.
45func GetTime() (Time, uint16, error) {
46	defer timeMu.Unlock()
47	timeMu.Lock()
48	return getTime()
49}
50
51func getTime() (Time, uint16, error) {
52	t := timeNow()
53
54	// If we don't have a clock sequence already, set one.
55	if clockSeq == 0 {
56		setClockSequence(-1)
57	}
58	now := uint64(t.UnixNano()/100) + g1582ns100
59
60	// If time has gone backwards with this clock sequence then we
61	// increment the clock sequence
62	if now <= lasttime {
63		clockSeq = ((clockSeq + 1) & 0x3fff) | 0x8000
64	}
65	lasttime = now
66	return Time(now), clockSeq, nil
67}
68
69// ClockSequence returns the current clock sequence, generating one if not
70// already set.  The clock sequence is only used for Version 1 UUIDs.
71//
72// The uuid package does not use global static storage for the clock sequence or
73// the last time a UUID was generated.  Unless SetClockSequence is used, a new
74// random clock sequence is generated the first time a clock sequence is
75// requested by ClockSequence, GetTime, or NewUUID.  (section 4.2.1.1)
76func ClockSequence() int {
77	defer timeMu.Unlock()
78	timeMu.Lock()
79	return clockSequence()
80}
81
82func clockSequence() int {
83	if clockSeq == 0 {
84		setClockSequence(-1)
85	}
86	return int(clockSeq & 0x3fff)
87}
88
89// SetClockSequence sets the clock sequence to the lower 14 bits of seq.  Setting to
90// -1 causes a new sequence to be generated.
91func SetClockSequence(seq int) {
92	defer timeMu.Unlock()
93	timeMu.Lock()
94	setClockSequence(seq)
95}
96
97func setClockSequence(seq int) {
98	if seq == -1 {
99		var b [2]byte
100		randomBits(b[:]) // clock sequence
101		seq = int(b[0])<<8 | int(b[1])
102	}
103	oldSeq := clockSeq
104	clockSeq = uint16(seq&0x3fff) | 0x8000 // Set our variant
105	if oldSeq != clockSeq {
106		lasttime = 0
107	}
108}
109
110// Time returns the time in 100s of nanoseconds since 15 Oct 1582 encoded in
111// uuid.  The time is only defined for version 1 and 2 UUIDs.
112func (uuid UUID) Time() Time {
113	time := int64(binary.BigEndian.Uint32(uuid[0:4]))
114	time |= int64(binary.BigEndian.Uint16(uuid[4:6])) << 32
115	time |= int64(binary.BigEndian.Uint16(uuid[6:8])&0xfff) << 48
116	return Time(time)
117}
118
119// ClockSequence returns the clock sequence encoded in uuid.
120// The clock sequence is only well defined for version 1 and 2 UUIDs.
121func (uuid UUID) ClockSequence() int {
122	return int(binary.BigEndian.Uint16(uuid[8:10])) & 0x3fff
123}
124