time_format.go

// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package lork

import (
	"errors"
	"time"
)

const (
	_                        = iota
	stdLongMonth             = iota + stdNeedDate  // "January"
	stdMonth                                       // "Jan"
	stdNumMonth                                    // "1"
	stdZeroMonth                                   // "01"
	stdLongWeekDay                                 // "Monday"
	stdWeekDay                                     // "Mon"
	stdDay                                         // "2"
	stdUnderDay                                    // "_2"
	stdZeroDay                                     // "02"
	stdUnderYearDay                                // "__2"
	stdZeroYearDay                                 // "002"
	stdHour                  = iota + stdNeedClock // "15"
	stdHour12                                      // "3"
	stdZeroHour12                                  // "03"
	stdMinute                                      // "4"
	stdZeroMinute                                  // "04"
	stdSecond                                      // "5"
	stdZeroSecond                                  // "05"
	stdLongYear              = iota + stdNeedDate  // "2006"
	stdYear                                        // "06"
	stdPM                    = iota + stdNeedClock // "PM"
	stdpm                                          // "pm"
	stdTZ                    = iota                // "MST"
	stdISO8601TZ                                   // "Z0700"  // prints Z for UTC
	stdISO8601SecondsTZ                            // "Z070000"
	stdISO8601ShortTZ                              // "Z07"
	stdISO8601ColonTZ                              // "Z07:00" // prints Z for UTC
	stdISO8601ColonSecondsTZ                       // "Z07:00:00"
	stdNumTZ                                       // "-0700"  // always numeric
	stdNumSecondsTz                                // "-070000"
	stdNumShortTZ                                  // "-07"    // always numeric
	stdNumColonTZ                                  // "-07:00" // always numeric
	stdNumColonSecondsTZ                           // "-07:00:00"
	stdFracSecond0                                 // ".0", ".00", ... , trailing zeros included
	stdFracSecond9                                 // ".9", ".99", ..., trailing zeros omitted

	stdNeedDate  = 1 << 8             // need month, day, year
	stdNeedClock = 2 << 8             // need hour, minute, second
	stdArgShift  = 16                 // extra argument in high bits, above low stdArgShift
	stdMask      = 1<<stdArgShift - 1 // mask out argument
)

const (
	// The unsigned zero year for internal calculations.
	// Must be 1 mod 400, and times before it will not compute correctly,
	// but otherwise can be changed at will.
	absoluteZeroYear = -292277022399
	// The year of the zero Time.
	// Assumed by the unixToInternal computation below.
	internalYear = 1
	// Offsets to convert between internal and absolute or Unix times.
	absoluteToInternal int64 = (absoluteZeroYear - internalYear) * 365.2425 * secondsPerDay
	internalToAbsolute       = -absoluteToInternal
	unixToInternal     int64 = (1969*365 + 1969/4 - 1969/100 + 1969/400) * secondsPerDay

	secondsPerMinute = 60
	secondsPerHour   = 60 * secondsPerMinute
	secondsPerDay    = 24 * secondsPerHour
	daysPer400Years  = 365*400 + 97
	daysPer100Years  = 365*100 + 24
	daysPer4Years    = 365*4 + 1
)

// std0x records the std values for "01", "02", ..., "06".
var std0x = [...]int{stdZeroMonth, stdZeroDay, stdZeroHour12, stdZeroMinute, stdZeroSecond, stdYear}

// some common errors
var (
	errBad   = errors.New("bad value for field")
	errParse = errors.New("failed to parse given timestamp")
)

// startsWithLowerCase reports whether the string has a lower-case letter at the beginning.
// Its purpose is to prevent matching strings like "Month" when looking for "Mon".
func startsWithLowerCase(str string) bool {
	if len(str) == 0 {
		return false
	}
	c := str[0]
	return 'a' <= c && c <= 'z'
}

// isDigit reports whether s[i] is in range and is a decimal digit.
func isDigit(s []byte, i int) bool {
	if len(s) <= i {
		return false
	}
	c := s[i]
	return '0' <= c && c <= '9'
}

// nextStdChunk finds the first occurrence of a std string in
// layout and returns the text before, the std string, and the text after.
func nextStdChunk(layout string) (prefix string, std int, suffix string) {
	for i := 0; i < len(layout); i++ {
		switch c := int(layout[i]); c {
		case 'J': // January, Jan
			if len(layout) >= i+3 && layout[i:i+3] == "Jan" {
				if len(layout) >= i+7 && layout[i:i+7] == "January" {
					return layout[0:i], stdLongMonth, layout[i+7:]
				}
				if !startsWithLowerCase(layout[i+3:]) {
					return layout[0:i], stdMonth, layout[i+3:]
				}
			}

		case 'M': // Monday, Mon, MST
			if len(layout) >= i+3 {
				if layout[i:i+3] == "Mon" {
					if len(layout) >= i+6 && layout[i:i+6] == "Monday" {
						return layout[0:i], stdLongWeekDay, layout[i+6:]
					}
					if !startsWithLowerCase(layout[i+3:]) {
						return layout[0:i], stdWeekDay, layout[i+3:]
					}
				}
				if layout[i:i+3] == "MST" {
					return layout[0:i], stdTZ, layout[i+3:]
				}
			}

		case '0': // 01, 02, 03, 04, 05, 06, 002
			if len(layout) >= i+2 && '1' <= layout[i+1] && layout[i+1] <= '6' {
				return layout[0:i], std0x[layout[i+1]-'1'], layout[i+2:]
			}
			if len(layout) >= i+3 && layout[i+1] == '0' && layout[i+2] == '2' {
				return layout[0:i], stdZeroYearDay, layout[i+3:]
			}

		case '1': // 15, 1
			if len(layout) >= i+2 && layout[i+1] == '5' {
				return layout[0:i], stdHour, layout[i+2:]
			}
			return layout[0:i], stdNumMonth, layout[i+1:]

		case '2': // 2006, 2
			if len(layout) >= i+4 && layout[i:i+4] == "2006" {
				return layout[0:i], stdLongYear, layout[i+4:]
			}
			return layout[0:i], stdDay, layout[i+1:]

		case '_': // _2, _2006, __2
			if len(layout) >= i+2 && layout[i+1] == '2' {
				//_2006 is really a literal _, followed by stdLongYear
				if len(layout) >= i+5 && layout[i+1:i+5] == "2006" {
					return layout[0 : i+1], stdLongYear, layout[i+5:]
				}
				return layout[0:i], stdUnderDay, layout[i+2:]
			}
			if len(layout) >= i+3 && layout[i+1] == '_' && layout[i+2] == '2' {
				return layout[0:i], stdUnderYearDay, layout[i+3:]
			}

		case '3':
			return layout[0:i], stdHour12, layout[i+1:]

		case '4':
			return layout[0:i], stdMinute, layout[i+1:]

		case '5':
			return layout[0:i], stdSecond, layout[i+1:]

		case 'P': // PM
			if len(layout) >= i+2 && layout[i+1] == 'M' {
				return layout[0:i], stdPM, layout[i+2:]
			}

		case 'p': // pm
			if len(layout) >= i+2 && layout[i+1] == 'm' {
				return layout[0:i], stdpm, layout[i+2:]
			}

		case '-': // -070000, -07:00:00, -0700, -07:00, -07
			if len(layout) >= i+7 && layout[i:i+7] == "-070000" {
				return layout[0:i], stdNumSecondsTz, layout[i+7:]
			}
			if len(layout) >= i+9 && layout[i:i+9] == "-07:00:00" {
				return layout[0:i], stdNumColonSecondsTZ, layout[i+9:]
			}
			if len(layout) >= i+5 && layout[i:i+5] == "-0700" {
				return layout[0:i], stdNumTZ, layout[i+5:]
			}
			if len(layout) >= i+6 && layout[i:i+6] == "-07:00" {
				return layout[0:i], stdNumColonTZ, layout[i+6:]
			}
			if len(layout) >= i+3 && layout[i:i+3] == "-07" {
				return layout[0:i], stdNumShortTZ, layout[i+3:]
			}

		case 'Z': // Z070000, Z07:00:00, Z0700, Z07:00,
			if len(layout) >= i+7 && layout[i:i+7] == "Z070000" {
				return layout[0:i], stdISO8601SecondsTZ, layout[i+7:]
			}
			if len(layout) >= i+9 && layout[i:i+9] == "Z07:00:00" {
				return layout[0:i], stdISO8601ColonSecondsTZ, layout[i+9:]
			}
			if len(layout) >= i+5 && layout[i:i+5] == "Z0700" {
				return layout[0:i], stdISO8601TZ, layout[i+5:]
			}
			if len(layout) >= i+6 && layout[i:i+6] == "Z07:00" {
				return layout[0:i], stdISO8601ColonTZ, layout[i+6:]
			}
			if len(layout) >= i+3 && layout[i:i+3] == "Z07" {
				return layout[0:i], stdISO8601ShortTZ, layout[i+3:]
			}

		case '.': // .000 or .999 - repeated digits for fractional seconds.
			if i+1 < len(layout) && (layout[i+1] == '0' || layout[i+1] == '9') {
				ch := layout[i+1]
				j := i + 1
				for j < len(layout) && layout[j] == ch {
					j++
				}
				// String of digits must end here - only fractional second is all digits.
				if !isDigit([]byte(layout), j) {
					std := stdFracSecond0
					if layout[i+1] == '9' {
						std = stdFracSecond9
					}
					std |= (j - (i + 1)) << stdArgShift
					return layout[0:i], std, layout[j:]
				}
			}
		}
	}
	return layout, 0, ""
}

// skip removes the given prefix from value,
// treating runs of space characters as equivalent.
func skip(value []byte, prefix string) ([]byte, error) {
	for len(prefix) > 0 {
		if prefix[0] == ' ' {
			if len(value) > 0 && value[0] != ' ' {
				return value, errBad
			}
			prefix = cutspace(prefix)
			value = cutsBytesSpace(value)
			continue
		}
		if len(value) == 0 || value[0] != prefix[0] {
			return value, errBad
		}
		prefix = prefix[1:]
		value = value[1:]
	}
	return value, nil
}

func cutspace(s string) string {
	for len(s) > 0 && s[0] == ' ' {
		s = s[1:]
	}
	return s
}

func cutsBytesSpace(b []byte) []byte {
	for len(b) > 0 && b[0] == ' ' {
		b = b[1:]
	}
	return b
}

// appendInt appends the decimal form of x to b and returns the result.
// If the decimal form (excluding sign) is shorter than width, the result is padded with leading 0's.
// Duplicates functionality in strconv, but avoids dependency.
func appendInt(b []byte, x int, width int) []byte {
	u := uint(x)
	if x < 0 {
		b = append(b, '-')
		u = uint(-x)
	}

	// Assemble decimal in reverse order.
	var buf [20]byte
	i := len(buf)
	for u >= 10 {
		i--
		q := u / 10
		buf[i] = byte('0' + u - q*10)
		u = q
	}
	i--
	buf[i] = byte('0' + u)

	// Add 0-padding.
	for w := len(buf) - i; w < width; w++ {
		b = append(b, '0')
	}

	return append(b, buf[i:]...)
}

// getnum parses s[0:1] or s[0:2] (fixed forces s[0:2])
// as a decimal integer and returns the integer and the
// remainder of the string.
func getnum(s []byte, fixed bool) (int, []byte, error) {
	if !isDigit(s, 0) {
		return 0, s, errBad
	}
	if !isDigit(s, 1) {
		if fixed {
			return 0, s, errBad
		}
		return int(s[0] - '0'), s[1:], nil
	}
	return int(s[0]-'0')*10 + int(s[1]-'0'), s[2:], nil
}

func parseNanoseconds(value []byte, nbytes int) (ns int, errString string, err error) {
	if value[0] != '.' {
		err = errBad
		return
	}
	if ns, err = atoi(value[1:nbytes]); err != nil {
		return
	}
	if ns < 0 || 1e9 <= ns {
		errString = "fractional second"
		return
	}
	// We need nanoseconds, which means scaling by the number
	// of missing digits in the format, maximum length 10. If it's
	// longer than 10, we won't scale.
	scaleDigits := 10 - nbytes
	for i := 0; i < scaleDigits; i++ {
		ns *= 10
	}
	return
}

// formatNano appends a fractional second, as nanoseconds, to b
// and returns the result.
func formatNano(b []byte, nanosec uint, n int, trim bool) []byte {
	u := nanosec
	var buf [9]byte
	for start := len(buf); start > 0; {
		start--
		buf[start] = byte(u%10 + '0')
		u /= 10
	}

	if n > 9 {
		n = 9
	}
	if trim {
		for n > 0 && buf[n-1] == '0' {
			n--
		}
		if n == 0 {
			return b
		}
	}
	b = append(b, '.')
	return append(b, buf[:n]...)
}

// absDate is like date but operates on an absolute time.
func absDate(abs uint64, full bool) (year int, month time.Month, day int, yday int) {
	// Split into time and day.
	d := abs / secondsPerDay

	// Account for 400-year cycles.
	n := d / daysPer400Years
	y := 400 * n
	d -= daysPer400Years * n

	// Cut off 100-year cycles.
	// The last cycle has one extra leap year, so on the last day
	// of that year, day / daysPer100Years will be 4 instead of 3.
	// Cut it back down to 3 by subtracting n>>2.
	n = d / daysPer100Years
	n -= n >> 2
	y += 100 * n
	d -= daysPer100Years * n

	// Cut off 4-year cycles.
	// The last cycle has a missing leap year, which does not
	// affect the computation.
	n = d / daysPer4Years
	y += 4 * n
	d -= daysPer4Years * n

	// Cut off years within a 4-year cycle.
	// The last year is a leap year, so on the last day of that year,
	// day / 365 will be 4 instead of 3. Cut it back down to 3
	// by subtracting n>>2.
	n = d / 365
	n -= n >> 2
	y += n
	d -= 365 * n

	year = int(int64(y) + absoluteZeroYear)
	yday = int(d)

	if !full {
		return
	}

	day = yday
	if isLeap(year) {
		// Leap year
		switch {
		case day > 31+29-1:
			// After leap day; pretend it wasn't there.
			day--
		case day == 31+29-1:
			// Leap day.
			month = time.February
			day = 29
			return
		}
	}

	// Estimate month on assumption that every month has 31 days.
	// The estimate may be too low by at most one month, so adjust.
	month = time.Month(day / 31)
	end := int(daysBefore[month+1])
	var begin int
	if day >= end {
		month++
		begin = end
	} else {
		begin = int(daysBefore[month])
	}

	month++ // because January is 1
	day = day - begin + 1
	return
}

// absClock is like clock but operates on an absolute time.
func absClock(abs uint64) (hour, min, sec int) {
	sec = int(abs % secondsPerDay)
	hour = sec / secondsPerHour
	sec -= hour * secondsPerHour
	min = sec / secondsPerMinute
	sec -= min * secondsPerMinute
	return
}

// daysBefore[m] counts the number of days in a non-leap year
// before month m begins. There is an entry for m=12, counting
// the number of days before January of next year (365).
var daysBefore = [...]int32{
	0,
	31,
	31 + 28,
	31 + 28 + 31,
	31 + 28 + 31 + 30,
	31 + 28 + 31 + 30 + 31,
	31 + 28 + 31 + 30 + 31 + 30,
	31 + 28 + 31 + 30 + 31 + 30 + 31,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31,
}

func isLeap(year int) bool {
	return year%4 == 0 && (year%100 != 0 || year%400 == 0)
}

// convertFormat parses the origin timestamp in 2006-01-02T15:04:05.000Z07:00 format,
// and convert to new layout. This will append the textual representation to b and
// returns the extended buffer.
func convertFormat(b, origin []byte, originLayout, newLayout string) ([]byte, error) {
	if len(origin) == 0 {
		return b, errBad
	}

	utcUnixNano, err := toUTCUnixNano(origin, originLayout)
	if err != nil {
		return b, err
	}

	return appendFormatUnix(b, utcUnixNano, newLayout)
}

func appendFormat(b []byte, t time.Time, layout string) ([]byte, error) {
	return appendFormatUnix(b, t.UnixNano(), layout)
}

func appendFormatUnix(b []byte, utcUnixNano int64, layout string) ([]byte, error) {
	var (
		year  = -1
		month time.Month
		day   int
		hour  = -1
		min   int
		sec   int
	)

	local := time.Now()
	zoneName, offset := local.Zone()

	localTime := utcUnixNano + int64(offset*1000000000)
	unixSec := localTime / 1000000000
	abs := uint64(unixSec + (unixToInternal + internalToAbsolute))
	nano := localTime % 1000000000

	// Each iteration generates one std value.
	for layout != "" {
		prefix, std, suffix := nextStdChunk(layout)
		if prefix != "" {
			b = append(b, prefix...)
		}
		if std == 0 {
			break
		}
		layout = suffix

		// Compute year, month, day if needed.
		if year < 0 && std&stdNeedDate != 0 {
			year, month, day, _ = absDate(abs, true)
		}

		// Compute hour, minute, second if needed.
		if hour < 0 && std&stdNeedClock != 0 {
			hour, min, sec = absClock(abs)
		}

		switch std & stdMask {
		case stdYear:
			y := year
			if y < 0 {
				y = -y
			}
			b = appendInt(b, y%100, 2)
		case stdLongYear:
			b = appendInt(b, year, 4)
		case stdMonth:
			b = append(b, month.String()[:3]...)
		case stdLongMonth:
			m := month.String()
			b = append(b, m...)
		case stdNumMonth:
			b = appendInt(b, int(month), 0)
		case stdZeroMonth:
			b = appendInt(b, int(month), 2)
		case stdWeekDay:
		case stdLongWeekDay:
		case stdDay:
			b = appendInt(b, day, 0)
		case stdUnderDay:
			if day < 10 {
				b = append(b, ' ')
			}
			b = appendInt(b, day, 0)
		case stdZeroDay:
			b = appendInt(b, day, 2)
		case stdUnderYearDay:
		case stdZeroYearDay:
		case stdHour:
			b = appendInt(b, hour, 2)
		case stdHour12:
			// Noon is 12PM, midnight is 12AM.
			hr := hour % 12
			if hr == 0 {
				hr = 12
			}
			b = appendInt(b, hr, 0)
		case stdZeroHour12:
			// Noon is 12PM, midnight is 12AM.
			hr := hour % 12
			if hr == 0 {
				hr = 12
			}
			b = appendInt(b, hr, 2)
		case stdMinute:
			b = appendInt(b, min, 0)
		case stdZeroMinute:
			b = appendInt(b, min, 2)
		case stdSecond:
			b = appendInt(b, sec, 0)
		case stdZeroSecond:
			b = appendInt(b, sec, 2)
		case stdPM:
			if hour >= 12 {
				b = append(b, "PM"...)
			} else {
				b = append(b, "AM"...)
			}
		case stdpm:
			if hour >= 12 {
				b = append(b, "pm"...)
			} else {
				b = append(b, "am"...)
			}
		case stdISO8601TZ, stdISO8601ColonTZ, stdISO8601SecondsTZ, stdISO8601ShortTZ, stdISO8601ColonSecondsTZ, stdNumTZ, stdNumColonTZ, stdNumSecondsTz, stdNumShortTZ, stdNumColonSecondsTZ:
			// Ugly special case. We cheat and take the "Z" variants
			// to mean "the time zone as formatted for ISO 8601".
			if offset == 0 && (std == stdISO8601TZ || std == stdISO8601ColonTZ || std == stdISO8601SecondsTZ || std == stdISO8601ShortTZ || std == stdISO8601ColonSecondsTZ) {
				b = append(b, 'Z')
				break
			}

			zone := offset / 60 // convert to minutes
			absoffset := offset
			if zone < 0 {
				b = append(b, '-')
				zone = -zone
				absoffset = -absoffset
			} else {
				b = append(b, '+')
			}
			b = appendInt(b, zone/60, 2)
			if std == stdISO8601ColonTZ || std == stdNumColonTZ || std == stdISO8601ColonSecondsTZ || std == stdNumColonSecondsTZ {
				b = append(b, ':')
			}
			if std != stdNumShortTZ && std != stdISO8601ShortTZ {
				b = appendInt(b, zone%60, 2)
			}

			// append seconds if appropriate
			if std == stdISO8601SecondsTZ || std == stdNumSecondsTz || std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
				if std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
					b = append(b, ':')
				}
				b = appendInt(b, absoffset%60, 2)
			}

		case stdTZ:
			if zoneName != "" {
				b = append(b, zoneName...)
				break
			}
			// No time zone known for this time, but we must print one.
			// Use the -0700 format.
			zone := offset / 60 // convert to minutes
			if zone < 0 {
				b = append(b, '-')
				zone = -zone
			} else {
				b = append(b, '+')
			}
			b = appendInt(b, zone/60, 2)
			b = appendInt(b, zone%60, 2)

		case stdFracSecond0, stdFracSecond9:
			b = formatNano(b, uint(nano), std>>stdArgShift, std&stdMask == stdFracSecond9)
		}
	}

	return b, nil
}

func toUTCUnixNano(value []byte, layout string) (int64, error) {
	var (
		year           int
		month          = -1
		day            = -1
		hour           int
		min            int
		sec            int
		nsec           int
		zoneOffset     = 0
		err            error
		rangeErrString = ""
	)

	for {
		prefix, std, suffix := nextStdChunk(layout)
		value, err = skip(value, prefix)
		if err != nil {
			return 0, nil
		}
		if std == 0 {
			if len(value) != 0 {
				return 0, errParse
			}
			break
		}
		layout = suffix

		switch std & stdMask {
		case stdLongYear:
			if len(value) < 4 || !isDigit(value, 0) {
				err = errBad
				break
			}
			var p []byte
			p, value = value[0:4], value[4:]
			year, err = atoi(p)

		case stdNumMonth, stdZeroMonth:
			month, value, err = getnum(value, std == stdZeroMonth)
			if err == nil && (month <= 0 || 12 < month) {
				rangeErrString = "month"
			}

		case stdZeroDay:
			if std == stdUnderDay && len(value) > 0 && value[0] == ' ' {
				value = value[1:]
			}
			day, value, err = getnum(value, std == stdZeroDay)

		case stdHour:
			hour, value, err = getnum(value, false)
			if hour < 0 || 24 <= hour {
				rangeErrString = "hour"
			}

		case stdZeroMinute:
			min, value, err = getnum(value, std == stdZeroMinute)
			if min < 0 || 60 <= min {
				rangeErrString = "minute"
			}

		case stdZeroSecond:
			sec, value, err = getnum(value, std == stdZeroSecond)
			if sec < 0 || 60 <= sec {
				rangeErrString = "second"
				break
			}
			// Special case: do we have a fractional second but no
			// fractional second in the format?
			if len(value) >= 2 && value[0] == '.' && isDigit(value, 1) {
				_, std, _ = nextStdChunk(layout)
				std &= stdMask
				if std == stdFracSecond0 || std == stdFracSecond9 {
					// Fractional second in the layout; proceed normally
					break
				}
				// No fractional second in the layout, but we have one in the input.
				n := 2
				for ; n < len(value) && isDigit(value, n); n++ {
				}
				nsec, rangeErrString, err = parseNanoseconds(value, n)
				value = value[n:]
			}

		case stdISO8601ColonTZ:
			if std == stdISO8601ColonTZ && len(value) >= 1 && value[0] == 'Z' {
				value = value[1:]
				break
			}

			if len(value) < 6 {
				err = errBad
				break
			}
			if value[3] != ':' {
				err = errBad
				break
			}
			var sign, hour, min, seconds []byte
			sign, hour, min, seconds, value = value[0:1], value[1:3], value[4:6],
				[]byte("00"), value[6:]

			var hr, mm, ss int
			hr, err = atoi(hour)
			if err == nil {
				mm, err = atoi(min)
			}
			if err == nil {
				ss, err = atoi(seconds)
			}
			// offset is in seconds
			zoneOffset = (hr*60+mm)*60 + ss
			switch sign[0] {
			case '+':
				zoneOffset = -zoneOffset
			case '-':
				zoneOffset = +zoneOffset
			default:
				err = errBad
			}

		case stdFracSecond0:
			// stdFracSecond0 requires the exact number of digits as specified in
			// the layout.
			ndigit := 1 + (std >> stdArgShift)
			if len(value) < ndigit {
				err = errBad
				break
			}
			nsec, rangeErrString, err = parseNanoseconds(value, ndigit)
			value = value[ndigit:]

		case stdFracSecond9:
			if len(value) < 2 || value[0] != '.' || value[1] < '0' || '9' < value[1] {
				// Fractional second omitted.
				break
			}
			// Take any number of digits, even more than asked for,
			// because it is what the stdSecond case would do.
			i := 0
			for i < 9 && i+1 < len(value) && '0' <= value[i+1] && value[i+1] <= '9' {
				i++
			}
			nsec, rangeErrString, err = parseNanoseconds(value, 1+i)
			value = value[1+i:]
		}

		if rangeErrString != "" {
			return 0, errors.New(rangeErrString + " out of range")
		}
		if err != nil {
			return 0, errParse
		}
	}

	t := time.Date(year, time.Month(month), day, hour, min, sec+zoneOffset, nsec, time.UTC)

	return t.UnixNano(), nil
}