package datetime

import (
	"fmt"
	"strings"
	"time"
)

func abs[N ~int | ~int64](e N) N {
	if e < 0 {
		return -e
	}
	return e
}

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

func daysInMonth(year int, month time.Month) int {
	switch month {
	case time.February:
		if isYearBissextil(year) {
			return 29
		}
		return 28
	case time.April, time.June, time.September, time.November:
		return 30
	default:
		return 31
	}
}

func internetHour(t time.Time) int {
	t, _ = ToTimezone(t, "CET").Ok()
	h, m, s := t.Clock()
	n := t.Nanosecond()
	d := time.Duration(n)*Nanosecond + time.Duration(s)*Second + time.Duration(m)*Minute + time.Duration(h)*Hour
	i := d * 1000 / Day
	return int(i)
}

func gmtDiff(t time.Time) time.Duration {
	d0 := t.Day()
	h0, m0, _ := t.Clock()
	g, _ := ToTimezone(t, "GMT").Ok()
	d1 := g.Day()
	h1, m1, _ := t.Clock()

	return time.Duration(d0-d1)*Day + time.Duration(h0-h1)*Hour + time.Duration(m0-m1)*Minute
}

// Jour
func format_j(t time.Time) string { return fmt.Sprintf("%d", t.Day()) }
func format_d(t time.Time) string { return fmt.Sprintf("%02d", t.Day()) }
func format_N(t time.Time) string { return fmt.Sprintf("%d", t.Weekday()+1) }
func format_w(t time.Time) string { return fmt.Sprintf("%d", t.Weekday()) }
func format_D(t time.Time) string { return shortDays[t.Weekday()] }
func format_l(t time.Time) string { return longDays[t.Weekday()] }
func format_z(t time.Time) string { return fmt.Sprintf("%d", t.YearDay()) }

// Semaine
func format_W(t time.Time) string {
	_, w := t.ISOWeek()
	return fmt.Sprintf("%d", w)
}

// Mois
func format_n(t time.Time) string { return fmt.Sprintf("%d", t.Month()+1) }
func format_m(t time.Time) string { return fmt.Sprintf("%02d", t.Month()+1) }
func format_M(t time.Time) string { return shortMonths[t.Month()] }
func format_F(t time.Time) string { return longMonths[t.Month()] }
func format_t(t time.Time) string { return fmt.Sprintf("%d", daysInMonth(t.Year(), t.Month())) }

// Année
func format_y(t time.Time) string { return fmt.Sprintf("%02d", t.Year()%100) }
func format_Y(t time.Time) string { return fmt.Sprintf("%d", t.Year()) }
func format_L(t time.Time) string {
	if isYearBissextil(t.Year()) {
		return "1"
	}
	return "0"
}

// Heure
func format_a(t time.Time) string {
	if t.Hour() < 12 {
		return "am"
	}
	return "pm"
}
func format_A(t time.Time) string {
	if t.Hour() < 12 {
		return "AM"
	}
	return "PM"
}
func format_B(t time.Time) string { return fmt.Sprintf("%03d", internetHour(t)) }
func format_g(t time.Time) string {
	h := t.Hour() % 12
	if h == 0 {
		h = 12
	}
	return fmt.Sprintf("%d", h)
}
func format_G(t time.Time) string { return fmt.Sprintf("%d", t.Hour()) }
func format_h(t time.Time) string {
	h := t.Hour() % 12
	if h == 0 {
		h = 12
	}
	return fmt.Sprintf("%02d", h)
}
func format_H(t time.Time) string { return fmt.Sprintf("%02d", t.Hour()) }
func format_i(t time.Time) string { return fmt.Sprintf("%02d", t.Minute()) }
func format_s(t time.Time) string { return fmt.Sprintf("%02d", t.Second()) }
func format_v(t time.Time) string { return fmt.Sprintf("%03d", t.Nanosecond()/1000000) }
func format_u(t time.Time) string { return fmt.Sprintf("%06d", t.Nanosecond()/1000) }

// Fuseau horaire
func format_T(t time.Time) string {
	name := t.Location().String()
	if !strings.Contains(name, "/") {
		return name
	}
	diff := gmtDiff(t)
	h, m := diff/Hour, (diff%Hour)/Minute
	s := "+"
	if h < 0 {
		s = "-"
	}
	if m == 0 {
		return fmt.Sprintf("%s%02d", s, abs(h))
	}
	return fmt.Sprintf("%s%02d:%02d", s, abs(h), abs(m))
}
func format_e(t time.Time) string { return fmt.Sprintf("%s", t.Location()) }
func format_I(t time.Time) string {
	if t.IsDST() {
		return "1"
	}
	return "0"
}
func format_O(t time.Time) string {
	diff := gmtDiff(t)
	h, m := diff/Hour, (diff%Hour)/Minute
	s := "+"
	if h < 0 {
		s = "-"
	}
	return fmt.Sprintf("%s%02d%02d", s, abs(h), abs(m))
}
func format_P(t time.Time) string {
	diff := gmtDiff(t)
	h, m := diff/Hour, (diff%Hour)/Minute
	s := "+"
	if h < 0 {
		s = "-"
	}
	return fmt.Sprintf("%s%02d:%02d", s, abs(h), abs(m))
}
func format_p(t time.Time) string {
	diff := gmtDiff(t)
	if diff == 0 {
		return "Z"
	}
	return format_P(t)
}
func format_Z(t time.Time) string {
	diff := gmtDiff(t)
	return fmt.Sprintf("%d", diff/Second)
}

// Date et heure complète
func format_c(t time.Time) string {
	// Équivalent à "Y-m-d\TH:i:sP"
	return fmt.Sprintf("%s-%s-%sT%s:%s:%s%s", format_Y(t), format_m(t), format_d(t), format_H(t), format_i(t), format_s(t), format_P(t))
}
func format_r(t time.Time) string {
	// Équivalent à "D, j M Y H:i:sO"
	return fmt.Sprintf("%s, %s %s %s %s:%s:%s%s", format_D(t), format_j(t), format_M(t), format_Y(t), format_H(t), format_i(t), format_s(t), format_P(t))
}
func format_U(t time.Time) string { return fmt.Sprintf("%d", t.Unix()) }

// Format retourne la représentation de la date dans le format indiqué.
// Pour connaître toutes les options possibles pour le format, veullez consulter
// https://www.php.net/manual/fr/datetime.format.php
// (ou le fichier const.go).
func Format(t time.Time, format string) string {
	var buffer strings.Builder

	runes := []rune(format)
	for i := 0; i < len(runes); i++ {
		if f, ok := formatters[runes[i]]; ok {
			buffer.WriteString(f(t))
		} else {
			switch runes[i] {
			case '\\': // raw output, no parse
				buffer.WriteRune(runes[i+1])
				i++
			default:
				buffer.WriteRune(runes[i])
			}
		}
	}

	return buffer.String()
}