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// Copyright 2016 Google Inc.  All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package uuid
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import (
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	"encoding/binary"
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	"sync"
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	"time"
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)
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// A Time represents a time as the number of 100's of nanoseconds since 15 Oct
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// 1582.
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type Time int64
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const (
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	lillian    = 2299160          // Julian day of 15 Oct 1582
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	unix       = 2440587          // Julian day of 1 Jan 1970
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	epoch      = unix - lillian   // Days between epochs
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	g1582      = epoch * 86400    // seconds between epochs
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	g1582ns100 = g1582 * 10000000 // 100s of a nanoseconds between epochs
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)
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var (
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	timeMu   sync.Mutex
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	lasttime uint64 // last time we returned
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	clockSeq uint16 // clock sequence for this run
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	timeNow = time.Now // for testing
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)
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// UnixTime converts t the number of seconds and nanoseconds using the Unix
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// epoch of 1 Jan 1970.
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func (t Time) UnixTime() (sec, nsec int64) {
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	sec = int64(t - g1582ns100)
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	nsec = (sec % 10000000) * 100
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	sec /= 10000000
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	return sec, nsec
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}
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// GetTime returns the current Time (100s of nanoseconds since 15 Oct 1582) and
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// clock sequence as well as adjusting the clock sequence as needed.  An error
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// is returned if the current time cannot be determined.
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func GetTime() (Time, uint16, error) {
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	defer timeMu.Unlock()
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	timeMu.Lock()
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	return getTime()
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}
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func getTime() (Time, uint16, error) {
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	t := timeNow()
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	// If we don't have a clock sequence already, set one.
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	if clockSeq == 0 {
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		setClockSequence(-1)
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	}
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	now := uint64(t.UnixNano()/100) + g1582ns100
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	// If time has gone backwards with this clock sequence then we
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	// increment the clock sequence
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	if now <= lasttime {
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		clockSeq = ((clockSeq + 1) & 0x3fff) | 0x8000
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	}
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	lasttime = now
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	return Time(now), clockSeq, nil
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}
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// ClockSequence returns the current clock sequence, generating one if not
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// already set.  The clock sequence is only used for Version 1 UUIDs.
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//
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// The uuid package does not use global static storage for the clock sequence or
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// the last time a UUID was generated.  Unless SetClockSequence is used, a new
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// random clock sequence is generated the first time a clock sequence is
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// requested by ClockSequence, GetTime, or NewUUID.  (section 4.2.1.1)
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func ClockSequence() int {
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	defer timeMu.Unlock()
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	timeMu.Lock()
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	return clockSequence()
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}
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func clockSequence() int {
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	if clockSeq == 0 {
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		setClockSequence(-1)
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	}
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	return int(clockSeq & 0x3fff)
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}
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// SetClockSequence sets the clock sequence to the lower 14 bits of seq.  Setting to
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// -1 causes a new sequence to be generated.
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func SetClockSequence(seq int) {
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	defer timeMu.Unlock()
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	timeMu.Lock()
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	setClockSequence(seq)
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}
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func setClockSequence(seq int) {
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	if seq == -1 {
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		var b [2]byte
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		randomBits(b[:]) // clock sequence
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		seq = int(b[0])<<8 | int(b[1])
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	}
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	oldSeq := clockSeq
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	clockSeq = uint16(seq&0x3fff) | 0x8000 // Set our variant
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	if oldSeq != clockSeq {
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		lasttime = 0
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	}
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}
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// Time returns the time in 100s of nanoseconds since 15 Oct 1582 encoded in
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// uuid.  The time is only defined for version 1, 2, 6 and 7 UUIDs.
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func (uuid UUID) Time() Time {
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	var t Time
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	switch uuid.Version() {
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	case 6:
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		time := binary.BigEndian.Uint64(uuid[:8]) // Ignore uuid[6] version b0110
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		t = Time(time)
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	case 7:
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		time := binary.BigEndian.Uint64(uuid[:8])
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		t = Time((time>>16)*10000 + g1582ns100)
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	default: // forward compatible
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		time := int64(binary.BigEndian.Uint32(uuid[0:4]))
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		time |= int64(binary.BigEndian.Uint16(uuid[4:6])) << 32
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		time |= int64(binary.BigEndian.Uint16(uuid[6:8])&0xfff) << 48
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		t = Time(time)
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	}
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	return t
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}
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// ClockSequence returns the clock sequence encoded in uuid.
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// The clock sequence is only well defined for version 1 and 2 UUIDs.
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func (uuid UUID) ClockSequence() int {
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	return int(binary.BigEndian.Uint16(uuid[8:10])) & 0x3fff
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}
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