// Package dateparse parses date-strings without knowing the format
// in advance, using a fast lex based approach to eliminate shotgun
// attempts.  It leans towards US style dates when there is a conflict.
package dateparse

import (
	"fmt"
	"strconv"
	"time"
	"unicode"
	"unicode/utf8"
)

// func init() {
// 	gou.SetupLogging("debug")
// 	gou.SetColorOutput()
// }

type dateState uint8
type timeState uint8

const (
	dateStart dateState = iota
	dateDigit
	dateDigitDash
	dateDigitDashDash
	dateDigitDashDashWs
	dateDigitDashDashT
	dateDigitDashDashAlpha
	dateDigitDot
	dateDigitDotDot
	dateDigitSlash
	dateDigitChineseYear
	dateDigitChineseYearWs
	dateDigitWs
	dateDigitWsMoYear
	dateDigitWsMolong
	dateAlpha
	dateAlphaWs
	dateAlphaWsDigit
	dateAlphaWsDigitComma
	dateAlphaWsDigitCommaWs
	dateAlphaWsDigitCommaWsYear
	dateAlphaWsAlpha
	dateAlphaWsAlphaYearmaybe
	dateWeekdayComma
	dateWeekdayAbbrevComma
	//dateWeekdayAbbrevCommaDash
)
const (
	// Time state
	timeIgnore timeState = iota
	timeStart
	timeWs
	timeWsAlpha
	timeWsAlphaWs
	timeWsAlphaZoneOffset
	timeWsAlphaZoneOffsetWs
	timeWsAlphaZoneOffsetWsYear
	timeWsAlphaZoneOffsetWsExtra
	timeWsAMPMMaybe
	timeWsAMPM
	timeWsOffset
	timeWsOffsetWs
	timeWsOffsetColonAlpha
	timeWsOffsetColon
	timeWsYear
	timeOffset
	timeOffsetColon
	timeAlpha
	timePeriod
	timePeriodOffset
	timePeriodOffsetColon
	timePeriodOffsetColonWs
	timePeriodWs
	timePeriodWsAlpha
	timePeriodWsOffset
	timePeriodWsOffsetWs
	timePeriodWsOffsetWsAlpha
	timePeriodWsOffsetColon
	timePeriodWsOffsetColonAlpha
	timeZ
	timeZDigit
)

var (
	shortDates = []string{"01/02/2006", "1/2/2006", "06/01/02", "01/02/06", "1/2/06"}
)

// ParseAny parse an unknown date format, detect the layout, parse.
// Normal parse.  Equivalent Timezone rules as time.Parse()
func ParseAny(datestr string) (time.Time, error) {
	return parseTime(datestr, nil)
}

// ParseIn with Location, equivalent to time.ParseInLocation() timezone/offset
// rules.  Using location arg, if timezone/offset info exists in the
// datestring, it uses the given location rules for any zone interpretation.
// That is, MST means one thing when using America/Denver and something else
// in other locations.
func ParseIn(datestr string, loc *time.Location) (time.Time, error) {
	return parseTime(datestr, loc)
}

// ParseLocal Given an unknown date format, detect the layout,
// using time.Local, parse.
//
// Set Location to time.Local.  Same as ParseIn Location but lazily uses
// the global time.Local variable for Location argument.
//
//     denverLoc, _ := time.LoadLocation("America/Denver")
//     time.Local = denverLoc
//
//     t, err := dateparse.ParseLocal("3/1/2014")
//
// Equivalent to:
//
//     t, err := dateparse.ParseIn("3/1/2014", denverLoc)
//
func ParseLocal(datestr string) (time.Time, error) {
	return parseTime(datestr, time.Local)
}

// MustParse  parse a date, and panic if it can't be parsed.  Used for testing.
// Not recommended for most use-cases.
func MustParse(datestr string) time.Time {
	t, err := parseTime(datestr, nil)
	if err != nil {
		panic(err.Error())
	}
	return t
}

func parse(layout, datestr string, loc *time.Location) (time.Time, error) {
	if loc == nil {
		return time.Parse(layout, datestr)
	}
	return time.ParseInLocation(layout, datestr, loc)
}

type parser struct {
	loc              *time.Location
	preferMonthFirst bool
	stateDate        dateState
	stateTime        timeState
	format           []byte
	datestr          string
	skip             int
	extra            int
	part1Len         int
	yeari            int
	yearlen          int
	moi              int
	molen            int
	dayi             int
	daylen           int
	houri            int
	hourlen          int
	mini             int
	minlen           int
	seci             int
	seclen           int
	msi              int
	mslen            int
	offseti          int
	offsetlen        int
	tzi              int
	tzlen            int
}

func newParser(dateStr string, loc *time.Location) *parser {
	p := parser{
		stateDate:        dateStart,
		stateTime:        timeIgnore,
		datestr:          dateStr,
		loc:              loc,
		preferMonthFirst: true,
	}
	p.format = []byte(dateStr)
	return &p
}
func (p *parser) set(start int, val string) {
	if start < 0 {
		return
	}
	if len(p.format) < start+len(val) {
		return
	}
	for i, r := range val {
		p.format[start+i] = byte(r)
	}
}
func (p *parser) setMonth() {
	if p.molen == 2 {
		p.set(p.moi, "01")
	} else if p.molen == 1 {
		p.set(p.moi, "1")
	}
}

func (p *parser) setDay() {
	if p.daylen == 2 {
		p.set(p.dayi, "02")
	} else if p.daylen == 1 {
		p.set(p.dayi, "2")
	}
}
func (p *parser) setYear() {
	if p.yearlen == 2 {
		p.set(p.yeari, "06")
	} else if p.yearlen == 4 {
		p.set(p.yeari, "2006")
	}
}
func (p *parser) coalesceDate(end int) {
	if p.yeari > 0 {
		if p.yearlen == 0 {
			p.yearlen = end - p.yeari
		}
		p.setYear()
	}
	if p.moi > 0 && p.molen == 0 {
		p.molen = end - p.moi
		p.setMonth()
	}
	if p.dayi > 0 && p.daylen == 0 {
		p.daylen = end - p.dayi
		p.setDay()
	}
}
func (p *parser) ts() string {
	return fmt.Sprintf("h:(%d:%d) m:(%d:%d) s:(%d:%d)", p.houri, p.hourlen, p.mini, p.minlen, p.seci, p.seclen)
}
func (p *parser) ds() string {
	return fmt.Sprintf("%s d:(%d:%d) m:(%d:%d) y:(%d:%d)", p.datestr, p.dayi, p.daylen, p.moi, p.molen, p.yeari, p.yearlen)
}
func (p *parser) coalesceTime(end int) {
	// 03:04:05
	// 15:04:05
	// 3:04:05
	// 3:4:5
	// 15:04:05.00
	if p.houri > 0 {
		if p.hourlen == 2 {
			p.set(p.houri, "15")
		} else if p.hourlen == 1 {
			p.set(p.houri, "3")
		}
	}
	if p.mini > 0 {
		if p.minlen == 0 {
			p.minlen = end - p.mini
		}
		if p.minlen == 2 {
			p.set(p.mini, "04")
		} else {
			p.set(p.mini, "4")
		}
	}
	if p.seci > 0 {
		if p.seclen == 0 {
			p.seclen = end - p.seci
		}
		if p.seclen == 2 {
			p.set(p.seci, "05")
		} else {
			p.set(p.seci, "5")
		}
	}

	if p.msi > 0 {
		for i := 0; i < p.mslen; i++ {
			p.format[p.msi+i] = '0'
		}
	}
}

func (p *parser) trimExtra() {
	if p.extra > 0 && len(p.format) > p.extra {
		p.format = p.format[0:p.extra]
		p.datestr = p.datestr[0:p.extra]
	}
}

func (p *parser) parse() (time.Time, error) {
	if p.skip > 0 && len(p.format) > p.skip {
		p.format = p.format[p.skip:]
		p.datestr = p.datestr[p.skip:]
	}
	//gou.Debugf("parse %q   AS   %s", p.datestr, string(p.format))
	if p.loc == nil {
		return time.Parse(string(p.format), p.datestr)
	}
	return time.ParseInLocation(string(p.format), p.datestr, p.loc)
}
func parseTime(datestr string, loc *time.Location) (time.Time, error) {

	p := newParser(datestr, loc)
	i := 0

	// General strategy is to read rune by rune through the date looking for
	// certain hints of what type of date we are dealing with.
	// Hopefully we only need to read about 5 or 6 bytes before
	// we figure it out and then attempt a parse
iterRunes:
	for ; i < len(datestr); i++ {
		//r := rune(datestr[i])
		r, bytesConsumed := utf8.DecodeRuneInString(datestr[i:])
		if bytesConsumed > 1 {
			i += (bytesConsumed - 1)
		}

		switch p.stateDate {
		case dateStart:
			if unicode.IsDigit(r) {
				p.stateDate = dateDigit
			} else if unicode.IsLetter(r) {
				p.stateDate = dateAlpha
			}
		case dateDigit:

			switch r {
			case '-', '\u2212':
				// 2006-01-02
				// 2006-01-02T15:04:05Z07:00
				// 13-Feb-03
				// 2013-Feb-03
				p.stateDate = dateDigitDash
				p.yeari = 0
				p.yearlen = i
				p.moi = i + 1
				if i == 4 {
					p.set(0, "2006")
				}
			case '/':
				// 03/31/2005
				// 2014/02/24
				p.stateDate = dateDigitSlash
				if i == 4 {
					p.yearlen = i
					p.moi = i + 1
					p.setYear()
				} else {
					if p.preferMonthFirst {
						if p.molen == 0 {
							p.molen = i
							p.setMonth()
							p.dayi = i + 1
						}
					}
				}

			case '.':
				// 3.31.2014
				p.moi = 0
				p.molen = i
				p.setMonth()
				p.dayi = i + 1
				p.stateDate = dateDigitDot
			case ' ':
				// 18 January 2018
				// 8 January 2018
				// 8 jan 2018
				// 02 Jan 2018 23:59
				// 02 Jan 2018 23:59:34
				// 12 Feb 2006, 19:17
				// 12 Feb 2006, 19:17:22
				p.stateDate = dateDigitWs
				p.dayi = 0
				p.daylen = i
			case '年':
				// Chinese Year
				p.stateDate = dateDigitChineseYear
			default:
				//if unicode.IsDigit(r) {
				continue
			}
			p.part1Len = i

		case dateDigitDash:
			// 2006-01
			// 2006-01-02
			// dateDigitDashDashT
			//  2006-01-02T15:04:05Z07:00
			//  2017-06-25T17:46:57.45706582-07:00
			//  2006-01-02T15:04:05.999999999Z07:00
			//  2006-01-02T15:04:05+0000
			// dateDigitDashDashWs
			//  2012-08-03 18:31:59.257000000
			//  2014-04-26 17:24:37.3186369
			//  2017-01-27 00:07:31.945167
			//  2016-03-14 00:00:00.000
			//  2014-05-11 08:20:13,787
			//  2017-07-19 03:21:51+00:00
			//  2013-04-01 22:43:22
			//  2014-04-26 05:24:37 PM
			// dateDigitDashDashAlpha
			//  2013-Feb-03
			//  13-Feb-03
			switch r {
			case '-':
				p.molen = i - p.moi
				p.dayi = i + 1
				p.stateDate = dateDigitDashDash
				p.setMonth()
			default:
				if unicode.IsDigit(r) {
					//continue
				} else if unicode.IsLetter(r) {
					p.stateDate = dateDigitDashDashAlpha
				}
			}
		case dateDigitDashDash:
			// 2006-01-02
			// dateDigitDashDashT
			//  2006-01-02T15:04:05Z07:00
			//  2017-06-25T17:46:57.45706582-07:00
			//  2006-01-02T15:04:05.999999999Z07:00
			//  2006-01-02T15:04:05+0000
			// dateDigitDashDashWs
			//  2012-08-03 18:31:59.257000000
			//  2014-04-26 17:24:37.3186369
			//  2017-01-27 00:07:31.945167
			//  2016-03-14 00:00:00.000
			//  2014-05-11 08:20:13,787
			//  2017-07-19 03:21:51+00:00
			//  2013-04-01 22:43:22
			//  2014-04-26 05:24:37 PM

			switch r {
			case ' ':
				p.daylen = i - p.dayi
				p.stateDate = dateDigitDashDashWs
				p.stateTime = timeStart
				p.setDay()
				break iterRunes
			case 'T':
				p.daylen = i - p.dayi
				p.stateDate = dateDigitDashDashT
				p.stateTime = timeStart
				p.setDay()
				break iterRunes
			}
		case dateDigitDashDashAlpha:
			// 2013-Feb-03
			// 13-Feb-03
			switch r {
			case '-':
				p.molen = i - p.moi
				p.set(p.moi, "Jan")
				p.dayi = i + 1
			}
		case dateDigitSlash:
			// 2014/07/10 06:55:38.156283
			// 03/19/2012 10:11:59
			// 04/2/2014 03:00:37
			// 3/1/2012 10:11:59
			// 4/8/2014 22:05
			// 3/1/2014
			// 10/13/2014
			// 01/02/2006
			// 1/2/06

			switch r {
			case ' ':
				p.stateTime = timeStart
				if p.yearlen == 0 {
					p.yearlen = i - p.yeari
					p.setYear()
				} else if p.daylen == 0 {
					p.daylen = i - p.dayi
					p.setDay()
				}
				break iterRunes
			case '/':
				if p.yearlen > 0 {
					// 2014/07/10 06:55:38.156283
					if p.molen == 0 {
						p.molen = i - p.moi
						p.setMonth()
						p.dayi = i + 1
					}
				} else if p.preferMonthFirst {
					if p.daylen == 0 {
						p.daylen = i - p.dayi
						p.setDay()
						p.yeari = i + 1
					}
				}

			default:
				// if unicode.IsDigit(r) || r == '/' {
				// 	continue
				// }
			}

		case dateDigitWs:
			// 18 January 2018
			// 8 January 2018
			// 8 jan 2018
			// 1 jan 18
			// 02 Jan 2018 23:59
			// 02 Jan 2018 23:59:34
			// 12 Feb 2006, 19:17
			// 12 Feb 2006, 19:17:22
			switch r {
			case ' ':
				p.yeari = i + 1
				//p.yearlen = 4
				p.dayi = 0
				p.daylen = p.part1Len
				p.setDay()
				p.stateTime = timeStart
				if i <= len("12 Feb") {
					p.moi = p.daylen + 1
					p.molen = 3
					p.set(p.moi, "Jan")
					p.stateDate = dateDigitWsMoYear
				} else {
					p.stateDate = dateDigitWsMolong
				}
			}

		case dateDigitWsMoYear:
			// 8 jan 2018
			// 02 Jan 2018 23:59
			// 02 Jan 2018 23:59:34
			// 12 Feb 2006, 19:17
			// 12 Feb 2006, 19:17:22
			switch r {
			case ',':
				p.yearlen = i - p.yeari
				p.setYear()
				i++
				break iterRunes
			case ' ':
				p.yearlen = i - p.yeari
				p.setYear()
				break iterRunes
			}
		case dateDigitWsMolong:
			// 18 January 2018
			// 8 January 2018

		case dateDigitChineseYear:
			// dateDigitChineseYear
			//   2014年04月08日
			//               weekday  %Y年%m月%e日 %A %I:%M %p
			// 2013年07月18日 星期四 10:27 上午
			if r == ' ' {
				p.stateDate = dateDigitChineseYearWs
				break
			}
		case dateDigitDot:
			// 3.31.2014
			if r == '.' {
				p.daylen = i - p.dayi
				p.yeari = i + 1
				p.setDay()
				p.stateDate = dateDigitDotDot
			}
		case dateDigitDotDot:
			// iterate all the way through
		case dateAlpha:
			// dateAlphaWS
			//  Mon Jan _2 15:04:05 2006
			//  Mon Jan _2 15:04:05 MST 2006
			//  Mon Jan 02 15:04:05 -0700 2006
			//  Mon Aug 10 15:44:11 UTC+0100 2015
			//  Fri Jul 03 2015 18:04:07 GMT+0100 (GMT Daylight Time)
			//  dateAlphaWSDigit
			//    May 8, 2009 5:57:51 PM
			//    oct 1, 1970
			//
			// dateWeekdayComma
			//   Monday, 02 Jan 2006 15:04:05 MST
			//   Monday, 02-Jan-06 15:04:05 MST
			//   Monday, 02 Jan 2006 15:04:05 -0700
			//   Monday, 02 Jan 2006 15:04:05 +0100
			// dateWeekdayAbbrevComma
			//   Mon, 02 Jan 2006 15:04:05 MST
			//   Mon, 02 Jan 2006 15:04:05 -0700
			//   Thu, 13 Jul 2017 08:58:40 +0100
			//   Tue, 11 Jul 2017 16:28:13 +0200 (CEST)
			//   Mon, 02-Jan-06 15:04:05 MST

			switch {
			case r == ' ':
				p.stateDate = dateAlphaWs
			case r == ',':
				// p.moi = 0
				// p.molen = i
				if i == 3 {
					p.stateDate = dateWeekdayAbbrevComma
					p.set(0, "Mon")
				} else {
					p.stateDate = dateWeekdayComma
					//p.set(0, "Monday")
					p.skip = i + 2
					i++
					// TODO:  lets just make this "skip" as we don't need
					// the mon, monday, they are all superfelous and not needed
					// just lay down the skip, no need to fill and then skip
				}

			}
		case dateWeekdayComma:
			// Monday, 02 Jan 2006 15:04:05 MST
			// Monday, 02 Jan 2006 15:04:05 -0700
			// Monday, 02 Jan 2006 15:04:05 +0100
			// Monday, 02-Jan-06 15:04:05 MST
			if p.dayi == 0 {
				p.dayi = i
			}
			switch r {
			case ' ', '-':
				if p.moi == 0 {
					p.moi = i + 1
					p.daylen = i - p.dayi
					p.setDay()
				} else if p.yeari == 0 {

					p.yeari = i + 1
					p.molen = i - p.moi
					p.set(p.moi, "Jan")
				} else {
					p.stateTime = timeStart
					break iterRunes
				}
			}
		case dateWeekdayAbbrevComma:
			// Mon, 02 Jan 2006 15:04:05 MST
			// Mon, 02 Jan 2006 15:04:05 -0700
			// Thu, 13 Jul 2017 08:58:40 +0100
			// Thu, 4 Jan 2018 17:53:36 +0000
			// Tue, 11 Jul 2017 16:28:13 +0200 (CEST)
			// Mon, 02-Jan-06 15:04:05 MST
			switch r {
			case ' ', '-':
				if p.dayi == 0 {
					p.dayi = i + 1
				} else if p.moi == 0 {
					p.daylen = i - p.dayi
					p.setDay()
					p.moi = i + 1
				} else if p.yeari == 0 {
					p.molen = i - p.moi
					p.set(p.moi, "Jan")
					p.yeari = i + 1
				} else {
					p.yearlen = i - p.yeari
					p.setYear()
					p.stateTime = timeStart
					break iterRunes
				}
			}

		case dateAlphaWs:
			// dateAlphaWsAlpha
			//   Mon Jan _2 15:04:05 2006
			//   Mon Jan _2 15:04:05 MST 2006
			//   Mon Jan 02 15:04:05 -0700 2006
			//   Fri Jul 03 2015 18:04:07 GMT+0100 (GMT Daylight Time)
			//   Mon Aug 10 15:44:11 UTC+0100 2015
			//  dateAlphaWsDigit
			//    May 8, 2009 5:57:51 PM
			//    oct 1, 1970
			//    oct 7, '70
			switch {
			case unicode.IsLetter(r):
				p.set(0, "Mon")
				p.stateDate = dateAlphaWsAlpha
				//p.moi = i
				p.set(i, "Jan")
			case unicode.IsDigit(r):
				p.set(0, "Jan")
				p.stateDate = dateAlphaWsDigit
				p.dayi = i
			}

		case dateAlphaWsDigit:
			// May 8, 2009 5:57:51 PM
			// oct 1, 1970
			// oct 7, '70
			//gou.Debugf("%d %s dateAlphaWsDigit  %s %s", i, string(r), p.ds(), p.ts())
			if r == ',' {
				p.daylen = i - p.dayi
				p.setDay()
				p.stateDate = dateAlphaWsDigitComma
			}
		case dateAlphaWsDigitComma:
			//       x
			// May 8, 2009 5:57:51 PM
			// oct 1, 1970
			// oct 7, '70
			if r == ' ' {
				p.stateDate = dateAlphaWsDigitCommaWs
				p.yeari = i + 1
			}
		case dateAlphaWsDigitCommaWs:
			//            x
			// May 8, 2009 5:57:51 PM
			// oct 1, 1970
			// oct 7, '70
			switch r {
			case '\'':
				p.yeari = i + 1
			case ' ':
				p.stateDate = dateAlphaWsDigitCommaWsYear
				p.yearlen = i - p.yeari
				p.setYear()
				p.stateTime = timeStart
				break iterRunes
			}

		case dateAlphaWsAlpha:
			// Mon Jan _2 15:04:05 2006
			// Mon Jan 02 15:04:05 -0700 2006
			// Mon Jan _2 15:04:05 MST 2006
			// Mon Aug 10 15:44:11 UTC+0100 2015
			// Fri Jul 03 2015 18:04:07 GMT+0100 (GMT Daylight Time)
			if r == ' ' {
				if p.dayi > 0 {

					p.daylen = i - p.dayi
					p.setDay()
					p.yeari = i + 1
					p.stateDate = dateAlphaWsAlphaYearmaybe
					p.stateTime = timeStart
				}
			} else if unicode.IsDigit(r) {
				if p.dayi == 0 {
					p.dayi = i
				}
			}
		case dateAlphaWsAlphaYearmaybe:
			//            x
			// Mon Jan _2 15:04:05 2006
			// Fri Jul 03 2015 18:04:07 GMT+0100 (GMT Daylight Time)
			if r == ':' {
				i = i - 3
				p.stateDate = dateAlphaWsAlpha
				p.yeari = 0
				break iterRunes
			} else if r == ' ' {
				// must be year format, not 15:04
				p.yearlen = i - p.yeari
				p.setYear()
				break iterRunes
			}

		default:
			break iterRunes
		}
	}
	p.coalesceDate(i)
	if p.stateTime == timeStart {
		// increment first one, since the i++ occurs at end of loop
		if i < len(p.datestr) {
			i++
		}
		// ensure we skip any whitespace prefix
		for ; i < len(datestr); i++ {
			r := rune(datestr[i])
			if r != ' ' {
				break
			}
		}

	iterTimeRunes:
		for ; i < len(datestr); i++ {
			r := rune(datestr[i])

			//gou.Debugf("%d %s iterTimeRunes  %s %s", i, string(r), p.ds(), p.ts())

			switch p.stateTime {
			case timeStart:
				// 22:43:22
				// 22:43
				// timeComma
				//   08:20:13,787
				// timeWs
				//   05:24:37 PM
				//   06:20:00 UTC
				//   00:12:00 +0000 UTC
				//   15:04:05 -0700
				//   15:04:05 -07:00
				//   15:04:05 2008
				// timeOffset
				//   03:21:51+00:00
				//   19:55:00+0100
				// timePeriod
				//   17:24:37.3186369
				//   00:07:31.945167
				//   18:31:59.257000000
				//   00:00:00.000
				//   timePeriodOffset
				//     19:55:00.799+0100
				//     timePeriodOffsetColon
				//       15:04:05.999-07:00
				//   timePeriodWs
				//     timePeriodWsOffset
				//       00:07:31.945167 +0000
				//       00:00:00.000 +0000
				//     timePeriodWsOffsetAlpha
				//       00:07:31.945167 +0000 UTC
				//       00:00:00.000 +0000 UTC
				//     timePeriodWsAlpha
				//       06:20:00.000 UTC
				if p.houri == 0 {
					p.houri = i
				}
				switch r {
				case ',':
					// hm, lets just swap out comma for period.  for some reason go
					// won't parse it.
					// 2014-05-11 08:20:13,787
					ds := []byte(p.datestr)
					ds[i] = '.'
					return parseTime(string(ds), loc)
				case '-', '+':
					//   03:21:51+00:00
					p.stateTime = timeOffset
					p.seclen = i - p.seci
					p.offseti = i
				case '.':
					p.stateTime = timePeriod
					p.seclen = i - p.seci
					p.msi = i + 1
				case 'Z':
					p.stateTime = timeZ
					if p.seci == 0 {
						p.minlen = i - p.mini
					} else {
						p.seclen = i - p.seci
					}
				case ' ':
					p.coalesceTime(i)
					p.stateTime = timeWs
				case ':':
					if p.mini == 0 {
						p.mini = i + 1
						p.hourlen = i - p.houri
					} else if p.seci == 0 {
						p.seci = i + 1
						p.minlen = i - p.mini
					}

				}
			case timeOffset:
				// 19:55:00+0100
				// timeOffsetColon
				//   15:04:05+07:00
				//   15:04:05-07:00
				if r == ':' {
					p.stateTime = timeOffsetColon
				}
			case timeWs:
				// timeWsAlpha
				//   06:20:00 UTC
				//   15:44:11 UTC+0100 2015
				//   18:04:07 GMT+0100 (GMT Daylight Time)
				//   17:57:51 MST 2009
				//   timeWsAMPMMaybe
				//     05:24:37 PM
				// timeWsOffset
				//   15:04:05 -0700
				//   00:12:00 +0000 UTC
				//   timeWsOffsetColon
				//     15:04:05 -07:00
				//     17:57:51 -0700 2009
				//     timeWsOffsetColonAlpha
				//       00:12:00 +00:00 UTC
				// timeWsYear
				//     00:12:00 2008
				// timeZ
				//   15:04:05.99Z
				switch r {
				case 'A', 'P':
					// Could be AM/PM or could be PST or similar
					p.tzi = i
					p.stateTime = timeWsAMPMMaybe
				case '+', '-':
					p.offseti = i
					p.stateTime = timeWsOffset
				default:
					if unicode.IsLetter(r) {
						// 06:20:00 UTC
						// 15:44:11 UTC+0100 2015
						// 17:57:51 MST 2009
						p.tzi = i
						p.stateTime = timeWsAlpha
						//break iterTimeRunes
					} else if unicode.IsDigit(r) {
						// 00:12:00 2008
						p.stateTime = timeWsYear
						p.yeari = i
					}
				}
			case timeWsAlpha:
				// 06:20:00 UTC
				// timeWsAlphaWs
				//   17:57:51 MST 2009
				// timeWsAlphaZoneOffset
				// timeWsAlphaZoneOffsetWs
				//   timeWsAlphaZoneOffsetWsExtra
				//     18:04:07 GMT+0100 (GMT Daylight Time)
				//   timeWsAlphaZoneOffsetWsYear
				//     15:44:11 UTC+0100 2015
				switch r {
				case '+', '-':
					p.tzlen = i - p.tzi
					if p.tzlen == 4 {
						p.set(p.tzi, " MST")
					} else if p.tzlen == 3 {
						p.set(p.tzi, "MST")
					}
					p.stateTime = timeWsAlphaZoneOffset
					p.offseti = i
				case ' ':
					// 17:57:51 MST 2009
					p.stateTime = timeWsAlphaWs
					p.yeari = i + 1
				}
			case timeWsAlphaWs:
				//   17:57:51 MST 2009

			case timeWsAlphaZoneOffset:
				// timeWsAlphaZoneOffset
				// timeWsAlphaZoneOffsetWs
				//   timeWsAlphaZoneOffsetWsExtra
				//     18:04:07 GMT+0100 (GMT Daylight Time)
				//   timeWsAlphaZoneOffsetWsYear
				//     15:44:11 UTC+0100 2015
				switch r {
				case ' ':
					p.set(p.offseti, "-0700")
					p.yeari = i + 1
					p.stateTime = timeWsAlphaZoneOffsetWs
				}
			case timeWsAlphaZoneOffsetWs:
				// timeWsAlphaZoneOffsetWs
				//   timeWsAlphaZoneOffsetWsExtra
				//     18:04:07 GMT+0100 (GMT Daylight Time)
				//   timeWsAlphaZoneOffsetWsYear
				//     15:44:11 UTC+0100 2015
				if unicode.IsDigit(r) {
					p.stateTime = timeWsAlphaZoneOffsetWsYear
				} else {
					p.extra = i - 1
					p.stateTime = timeWsAlphaZoneOffsetWsExtra
				}
			case timeWsAlphaZoneOffsetWsYear:
				// 15:44:11 UTC+0100 2015
				if unicode.IsDigit(r) {
					p.yearlen = i - p.yeari + 1
					if p.yearlen == 4 {
						p.setYear()
					}
				}
			case timeWsAMPMMaybe:
				// timeWsAMPMMaybe
				//   timeWsAMPM
				//     05:24:37 PM
				//   timeWsAlpha
				//     00:12:00 PST
				//     15:44:11 UTC+0100 2015
				if r == 'M' {
					//return parse("2006-01-02 03:04:05 PM", datestr, loc)
					p.stateTime = timeWsAMPM
					p.set(i-1, "PM")
					if p.hourlen == 2 {
						p.set(p.houri, "03")
					} else if p.hourlen == 1 {
						p.set(p.houri, "3")
					}
				} else {
					p.stateTime = timeWsAlpha
				}

			case timeWsOffset:
				// timeWsOffset
				//   15:04:05 -0700
				//   timeWsOffsetWs
				//     17:57:51 -0700 2009
				//     00:12:00 +0000 UTC
				//   timeWsOffsetColon
				//     15:04:05 -07:00
				//     timeWsOffsetColonAlpha
				//       00:12:00 +00:00 UTC
				switch r {
				case ':':
					p.stateTime = timeWsOffsetColon
				case ' ':
					p.set(p.offseti, "-0700")
					p.yeari = i + 1
					p.stateTime = timeWsOffsetWs
				}
			case timeWsOffsetWs:
				// 17:57:51 -0700 2009
				// 00:12:00 +0000 UTC
				if unicode.IsDigit(r) {
					p.yearlen = i - p.yeari + 1
					if p.yearlen == 4 {
						p.setYear()
					}
				} else if unicode.IsLetter(r) {
					if p.tzi == 0 {
						p.tzi = i
					}
				}
			case timeWsOffsetColon:
				// timeWsOffsetColon
				//   15:04:05 -07:00
				//   timeWsOffsetColonAlpha
				//     2015-02-18 00:12:00 +00:00 UTC
				if unicode.IsLetter(r) {
					// 2015-02-18 00:12:00 +00:00 UTC
					p.stateTime = timeWsOffsetColonAlpha
					break iterTimeRunes
				}

			case timePeriod:
				// 15:04:05.999999999+07:00
				// 15:04:05.999999999-07:00
				// 15:04:05.999999+07:00
				// 15:04:05.999999-07:00
				// 15:04:05.999+07:00
				// 15:04:05.999-07:00
				// timePeriod
				//   17:24:37.3186369
				//   00:07:31.945167
				//   18:31:59.257000000
				//   00:00:00.000
				//   timePeriodOffset
				//     19:55:00.799+0100
				//     timePeriodOffsetColon
				//       15:04:05.999-07:00
				//   timePeriodWs
				//     timePeriodWsOffset
				//       00:07:31.945167 +0000
				//       00:00:00.000 +0000
				//     timePeriodWsOffsetAlpha
				//       00:07:31.945167 +0000 UTC
				//       00:00:00.000 +0000 UTC
				//     timePeriodWsAlpha
				//       06:20:00.000 UTC
				switch r {
				case ' ':
					p.mslen = i - p.msi
					p.stateTime = timePeriodWs
				case '+', '-':
					// This really shouldn't happen
					p.mslen = i - p.msi
					p.offseti = i
					p.stateTime = timePeriodOffset
				default:
					if unicode.IsLetter(r) {
						// 06:20:00.000 UTC
						p.mslen = i - p.msi
						p.stateTime = timePeriodWsAlpha
					}
				}
			case timePeriodOffset:
				// timePeriodOffset
				//   19:55:00.799+0100
				//   timePeriodOffsetColon
				//     15:04:05.999-07:00
				//     13:31:51.999-07:00 MST
				if r == ':' {
					p.stateTime = timePeriodOffsetColon
				}
			case timePeriodOffsetColon:
				// timePeriodOffset
				//   timePeriodOffsetColon
				//     15:04:05.999-07:00
				//     13:31:51.999 -07:00 MST
				switch r {
				case ' ':
					p.set(p.offseti, "-07:00")
					p.stateTime = timePeriodOffsetColonWs
					p.tzi = i + 1
				}
			case timePeriodOffsetColonWs:
				// continue
			case timePeriodWs:
				// timePeriodWs
				//   timePeriodWsOffset
				//     00:07:31.945167 +0000
				//     00:00:00.000 +0000
				//   timePeriodWsOffsetAlpha
				//     00:07:31.945167 +0000 UTC
				//     00:00:00.000 +0000 UTC
				//   timePeriodWsOffsetColon
				//     13:31:51.999 -07:00 MST
				//   timePeriodWsAlpha
				//     06:20:00.000 UTC
				if p.offseti == 0 {
					p.offseti = i
				}
				switch r {
				case '+', '-':
					p.mslen = i - p.msi - 1
					p.stateTime = timePeriodWsOffset
				default:
					if unicode.IsLetter(r) {
						//     00:07:31.945167 +0000 UTC
						//     00:00:00.000 +0000 UTC
						p.stateTime = timePeriodWsOffsetWsAlpha
						break iterTimeRunes
					}
				}

			case timePeriodWsOffset:

				// timePeriodWs
				//   timePeriodWsOffset
				//     00:07:31.945167 +0000
				//     00:00:00.000 +0000
				//   timePeriodWsOffsetAlpha
				//     00:07:31.945167 +0000 UTC
				//     00:00:00.000 +0000 UTC
				//   timePeriodWsOffsetColon
				//     13:31:51.999 -07:00 MST
				//   timePeriodWsAlpha
				//     06:20:00.000 UTC
				switch r {
				case ':':
					p.stateTime = timePeriodWsOffsetColon
				case ' ':
					p.set(p.offseti, "-0700")
				default:
					if unicode.IsLetter(r) {
						// 00:07:31.945167 +0000 UTC
						// 00:00:00.000 +0000 UTC
						p.stateTime = timePeriodWsOffsetWsAlpha
						break iterTimeRunes
					}
				}

			case timePeriodWsOffsetColon:
				// 13:31:51.999 -07:00 MST
				switch r {
				case ' ':
					p.set(p.offseti, "-07:00")
				default:
					if unicode.IsLetter(r) {
						// 13:31:51.999 -07:00 MST
						p.tzi = i
						p.stateTime = timePeriodWsOffsetColonAlpha
					}
				}
			case timePeriodWsOffsetColonAlpha:
				// continue
			case timeZ:
				// timeZ
				//   15:04:05.99Z
				// With a time-zone at end after Z
				// 2006-01-02T15:04:05.999999999Z07:00
				// 2006-01-02T15:04:05Z07:00
				// RFC3339     = "2006-01-02T15:04:05Z07:00"
				// RFC3339Nano = "2006-01-02T15:04:05.999999999Z07:00"
				if unicode.IsDigit(r) {
					p.stateTime = timeZDigit
				}

			}
		}

		switch p.stateTime {
		case timeWsAlphaWs:
			p.yearlen = i - p.yeari
			p.setYear()
		case timeWsYear:
			p.yearlen = i - p.yeari
			p.setYear()
		case timeWsAlphaZoneOffsetWsExtra:
			p.trimExtra()
		case timePeriod:
			p.mslen = i - p.msi
		case timeOffset:
			// 19:55:00+0100
			p.set(p.offseti, "-0700")
		case timeWsOffset:
			p.set(p.offseti, "-0700")
		case timeWsOffsetWs:
			// 17:57:51 -0700 2009
			// 00:12:00 +0000 UTC
		case timeWsOffsetColon:
			// 17:57:51 -07:00
			p.set(p.offseti, "-07:00")
		case timeOffsetColon:
			// 15:04:05+07:00
			p.set(p.offseti, "-07:00")
		case timePeriodOffset:
			// 19:55:00.799+0100
			p.set(p.offseti, "-0700")
		case timePeriodOffsetColon:
			p.set(p.offseti, "-07:00")
		case timePeriodWsOffsetColonAlpha:
			p.tzlen = i - p.tzi
			switch p.tzlen {
			case 3:
				p.set(p.tzi, "MST")
			case 4:
				p.set(p.tzi, "MST ")
			}
		case timePeriodWsOffset:
			p.set(p.offseti, "-0700")
		}
		p.coalesceTime(i)
	}

	switch p.stateDate {
	case dateDigit:
		// unixy timestamps ish
		//  1499979655583057426  nanoseconds
		//  1499979795437000     micro-seconds
		//  1499979795437        milliseconds
		//  1384216367189
		//  1332151919           seconds
		//  20140601             yyyymmdd
		//  2014                 yyyy
		t := time.Time{}
		if len(datestr) > len("1499979795437000") {
			if nanoSecs, err := strconv.ParseInt(datestr, 10, 64); err == nil {
				t = time.Unix(0, nanoSecs)
			}
		} else if len(datestr) > len("1499979795437") {
			if microSecs, err := strconv.ParseInt(datestr, 10, 64); err == nil {
				t = time.Unix(0, microSecs*1000)
			}
		} else if len(datestr) > len("1332151919") {
			if miliSecs, err := strconv.ParseInt(datestr, 10, 64); err == nil {
				t = time.Unix(0, miliSecs*1000*1000)
			}
		} else if len(datestr) == len("20140601") {
			return parse("20060102", datestr, loc)
		} else if len(datestr) == len("2014") {
			return parse("2006", datestr, loc)
		}
		if t.IsZero() {
			if secs, err := strconv.ParseInt(datestr, 10, 64); err == nil {
				if secs < 0 {
					// Now, for unix-seconds we aren't going to guess a lot
					// nothing before unix-epoch
				} else {
					t = time.Unix(secs, 0)
				}
			}
		}
		if !t.IsZero() {
			if loc == nil {
				return t, nil
			}
			return t.In(loc), nil
		}

	case dateDigitDash:
		// 2006-01
		return p.parse()

	case dateDigitDashDash:
		// 2006-01-02
		// 2006-1-02
		// 2006-1-2
		// 2006-01-2
		return p.parse()

	case dateDigitDashDashAlpha:
		// 2013-Feb-03
		// 2013-Feb-3
		p.daylen = i - p.dayi
		p.setDay()
		return p.parse()

	case dateDigitDashDashWs: // starts digit then dash 02-  then whitespace   1 << 2  << 5 + 3
		// 2013-04-01 22:43:22
		// 2013-04-01 22:43
		return p.parse()

	case dateDigitDashDashT:
		return p.parse()

	case dateDigitDotDot:
		// 03.31.1981
		// 3.2.1981
		// 3.2.81
		p.setYear()
		p.yearlen = i - p.yeari
		return p.parse()

	case dateDigitWsMoYear:
		// 2 Jan 2018
		// 2 Jan 18
		// 2 Jan 2018 23:59
		// 02 Jan 2018 23:59
		// 02 Jan 2018 23:59:45
		// 12 Feb 2006, 19:17
		// 12 Feb 2006, 19:17:22
		return p.parse()

	case dateDigitWsMolong:
		// 18 January 2018
		// 8 January 2018
		if p.daylen == 2 {
			return parse("02 January 2006", datestr, loc)
		}
		return parse("2 January 2006", datestr, loc)

	case dateAlphaWsDigitCommaWs:
		// oct 1, 1970
		p.yearlen = i - p.yeari
		p.setYear()
		return p.parse()

	case dateAlphaWsDigitCommaWsYear:
		// May 8, 2009 5:57:51 PM
		return p.parse()

	case dateAlphaWsAlpha:
		return p.parse()

	case dateAlphaWsAlphaYearmaybe:
		return p.parse()

	case dateDigitSlash:
		// 3/1/2014
		// 10/13/2014
		// 01/02/2006
		// 2014/10/13
		return p.parse()

	case dateDigitChineseYear:
		// dateDigitChineseYear
		//   2014年04月08日
		return parse("2006年01月02日", datestr, loc)

	case dateDigitChineseYearWs:
		return parse("2006年01月02日 15:04:05", datestr, loc)

	case dateWeekdayComma:
		// Monday, 02 Jan 2006 15:04:05 -0700
		// Monday, 02 Jan 2006 15:04:05 +0100
		// Monday, 02-Jan-06 15:04:05 MST
		return p.parse()

	case dateWeekdayAbbrevComma:
		// Mon, 02-Jan-06 15:04:05 MST
		// Mon, 02 Jan 2006 15:04:05 MST
		return p.parse()

	}

	return time.Time{}, fmt.Errorf("Could not find date format for %s", datestr)
}