package datetime

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

func gmtDiff(t time.Time) (hour, minute int) {
	g := toTZ(t, "GMT")
	d0, h0, m0 := t.Day(), t.Hour(), t.Minute()
	d1, h1, m1 := g.Day(), g.Hour(), g.Minute()

	m := (d0-d1)*MinutePerDay + (h0-h1)*MinutePerHour + (m0 - m1)
	return m / MinutePerHour, m % MillisecondPerHour
}

// 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", monthLen(t.Year(), uint(t.Month())+1)) }

// 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 bissextil(t.Year()) {
		return "1"
	}
	return "0"
}

// Heure
func format_a(t time.Time) string { return amPmLow[t.Hour() < 12] }
func format_A(t time.Time) string { return amPmUp[t.Hour() < 12] }
func format_B(t time.Time) string {
	h, m, s := t.Clock()
	n := t.Nanosecond() / NanosecondPerMillisecond

	return fmt.Sprintf("%03d", sit(uint(h), uint(m), uint(s), uint(n)))
}
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()/NanosecondPerMillisecond)
}
func format_u(t time.Time) string {
	return fmt.Sprintf("%06d", t.Nanosecond()/NanosecondPerMicrosecond)
}

// Fuseau horaire
func format_T(t time.Time) string {
	name := t.Location().String()
	if !strings.Contains(name, "/") {
		return name
	}
	h, m := gmtDiff(t)
	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 {
	h, m := gmtDiff(t)
	s := "+"
	if h < 0 {
		s = "-"
	}

	return fmt.Sprintf("%s%02d%02d", s, abs(h), abs(m))
}
func format_P(t time.Time) string {
	h, m := gmtDiff(t)
	s := "+"
	if h < 0 {
		s = "-"
	}

	return fmt.Sprintf("%s%02d:%02d", s, abs(h), abs(m))
}
func format_p(t time.Time) string {
	h, m := gmtDiff(t)
	diff := h*MinutePerHour + m
	if diff == 0 {
		return "Z"
	}

	return format_P(t)
}
func format_Z(t time.Time) string {
	h, m := gmtDiff(t)
	diff := h*SecondPerHour + m*SecondPerMinute

	return fmt.Sprintf("%d", diff)
}

// 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()) }

func formatT(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()
}