package sneklog

import "strings"

const (
	Layout   = "%m/%d %I:%M:%S%p '%y %z"
	ANSIC    = "%a %b %e %H:%M:%S %Y"
	UnixDate = "%a %b %e %H:%M:%S %Z %Y"
	RubyDate = "%a %b %d %H:%M:%S %z %Y"

	RFC822      = "%d %b %y %H:%M %Z"
	RFC822Z     = "%d %b %y %H:%M %z"
	RFC850      = "%A, %d-%b-%y %H:%M:%S %Z"
	RFC1123     = "%a, %d %b %Y %H:%M:%S %Z"
	RFC1123Z    = "%a, %d %b %Y %H:%M:%S %z"
	RFC3339     = "%Y-%m-%dT%H:%M:%S%:z"
	RFC3339Nano = "%Y-%m-%dT%H:%M:%S%#N%:z"
	Kitchen     = "%-I:%M%p"

	Stamp      = "%b %e %H:%M:%S"
	StampMilli = "%b %e %H:%M:%S.%L"
	StampMicro = "%b %e %H:%M:%S.%f"
	StampNano  = "%b %e %H:%M:%S.%N"
	DateTime   = "%Y-%m-%d %H:%M:%S"
	DateOnly   = "%Y-%m-%d"
	TimeOnly   = "%H:%M:%S"
)

type rule struct {
	strf     string
	goLayout string
}

var strftimeToGoRules = []rule{
	// Long/special tokens first.
	{"%::z", "Z07:00:00"},
	{"%:::z", "Z07"},
	{"%:z", "Z07:00"},

	{"%#N", ".999999999"},
	{"%#f", ".999999"},
	{"%#L", ".999"},

	{"%-m", "1"},
	{"%#m", "1"},
	{"%-d", "2"},
	{"%#d", "2"},
	{"%-H", "15"},
	{"%#H", "15"},
	{"%-I", "3"},
	{"%#I", "3"},
	{"%-M", "4"},
	{"%#M", "4"},
	{"%-S", "5"},
	{"%#S", "5"},

	{"%%", "%"},

	{"%Y", "2006"},
	{"%y", "06"},

	{"%B", "January"},
	{"%b", "Jan"},
	{"%h", "Jan"},
	{"%m", "01"},

	{"%d", "02"},
	{"%e", "_2"},

	{"%A", "Monday"},
	{"%a", "Mon"},

	{"%H", "15"},
	{"%I", "03"},
	{"%M", "04"},
	{"%S", "05"},

	{"%p", "PM"},

	{"%z", "-0700"},
	{"%Z", "MST"},

	{"%N", "000000000"},
	{"%f", "000000"},
	{"%L", "000"},

	{"%F", "2006-01-02"},
	{"%T", "15:04:05"},
	{"%R", "15:04"},
	{"%D", "01/02/06"},
	{"%r", "03:04:05 PM"},
}

// StrftimeToGo converts a strftime-like layout into a Go time layout.
func StrftimeToGo(format string) string {
	var out strings.Builder

	for i := 0; i < len(format); {
		if format[i] != '%' {
			out.WriteByte(format[i])
			i++
			continue
		}

		matched := false
		for _, r := range strftimeToGoRules {
			if strings.HasPrefix(format[i:], r.strf) {
				out.WriteString(r.goLayout)
				i += len(r.strf)
				matched = true
				break
			}
		}

		if !matched {
			// Можно заменить на ошибку, если хочешь strict mode.
			out.WriteByte(format[i])
			i++
		}
	}

	return out.String()
}

// GoToStrftime converts a Go time layout into an approximate strftime-like layout.
func GoToStrftime(format string) string {
	format = strings.ReplaceAll(format, "2006", "%Y")
	format = strings.ReplaceAll(format, "06", "%y")

	format = strings.ReplaceAll(format, "15", "%H")
	format = strings.ReplaceAll(format, "03", "%I")
	format = strings.ReplaceAll(format, "3", "%-I")
	format = strings.ReplaceAll(format, "3", "%#I")

	format = strings.ReplaceAll(format, "January", "%B")
	format = strings.ReplaceAll(format, "Jan", "%b")
	format = strings.ReplaceAll(format, "01", "%m")
	format = strings.ReplaceAll(format, "1", "%-m")

	format = strings.ReplaceAll(format, "02", "%d")
	format = strings.ReplaceAll(format, "_2", "%e")
	format = strings.ReplaceAll(format, "2", "%-d")

	format = strings.ReplaceAll(format, "Monday", "%A")
	format = strings.ReplaceAll(format, "Mon", "%a")

	format = strings.ReplaceAll(format, "04", "%M")
	format = strings.ReplaceAll(format, "05", "%S")
	format = strings.ReplaceAll(format, ".999999999", "%#N")
	format = strings.ReplaceAll(format, "000000000", "%N")
	format = strings.ReplaceAll(format, ".999999", "%#f")
	format = strings.ReplaceAll(format, "000000", "%f")
	format = strings.ReplaceAll(format, ".999", "%#L")
	format = strings.ReplaceAll(format, "000", "%L")
	format = strings.ReplaceAll(format, "PM", "%p")

	format = strings.ReplaceAll(format, "-0700", "%z")
	format = strings.ReplaceAll(format, "MST", "%Z")
	format = strings.ReplaceAll(format, "Z07:00", "%:z")
	format = strings.ReplaceAll(format, "Z07:00:00", "%::z")
	format = strings.ReplaceAll(format, "Z07", "%:::z")
	return format
}