package notifications

import (
	"fmt"
	"strings"
)

// Vars are the placeholder values rendered into a template string.
// The fields here must match the {{…}} markers in templates below.
type Vars struct {
	Title       string
	Date        string // YYYY-MM-DD
	DatePretty  string // e.g. "Donnerstag, 15. Oktober"
	ClassName   string // empty = whole school
	TeacherName string
}

// Render picks the right template based on event type, audience, lead-day
// bucket and language, then substitutes the {{var}} placeholders.
//
// lead is grouped into three buckets:
//   0    → "today"
//   1    → "tomorrow"
//   >=2  → "in X days" with X = lead value
//
// Falls back through (lang → de) and (event_type → "andere") so we never
// fail to render even with custom rule combos.
func Render(eventType, audience string, lead int, lang string, v Vars) (subject, body string) {
	bucket := bucketFor(lead)
	lc := strings.ToLower(lang)
	if _, ok := templates[lc]; !ok {
		lc = "de"
	}
	t := lookup(lc, eventType, audience, bucket)
	subject = substitute(t.Subject, lead, v)
	body = substitute(t.Body, lead, v)
	return subject, body
}

func bucketFor(lead int) string {
	switch {
	case lead <= 0:
		return "today"
	case lead == 1:
		return "tomorrow"
	default:
		return "days"
	}
}

// lookup walks the templates map applying the (lang → de) and
// (event_type → andere) fallbacks. The bucket is guaranteed to exist for
// every audience because we always define today/tomorrow/days in the de
// baseline.
func lookup(lang, eventType, audience, bucket string) tmpl {
	byEvent, ok := templates[lang][eventType]
	if !ok {
		byEvent = templates[lang]["andere"]
	}
	byAudience, ok := byEvent[audience]
	if !ok {
		byAudience = byEvent["parents"]
	}
	t, ok := byAudience[bucket]
	if !ok {
		t = byAudience["days"]
	}
	return t
}

func substitute(s string, lead int, v Vars) string {
	classSuffix := ""
	if v.ClassName != "" {
		classSuffix = " (" + v.ClassName + ")"
	}
	repl := strings.NewReplacer(
		"{{title}}", v.Title,
		"{{date}}", v.Date,
		"{{date_pretty}}", v.DatePretty,
		"{{class_name}}", v.ClassName,
		"{{class_suffix}}", classSuffix,
		"{{teacher_name}}", v.TeacherName,
		"{{lead}}", fmt.Sprintf("%d", lead),
	)
	return repl.Replace(s)
}

type tmpl struct {
	Subject string
	Body    string
}

// templates[lang][eventType][audience][bucket] → tmpl
//
// Only the eight parent languages we ship subject-i18n.ts for are covered.
// Custom event_types fall back to the "andere" branch. Custom languages
// fall back to "de". This keeps the file under 500 LOC; if more locales
// are needed, split into one file per language.
var templates = map[string]map[string]map[string]map[string]tmpl{
	"de": deTemplates(),
	"en": enTemplates(),
	"tr": trTemplates(),
	"ar": arTemplates(),
	"uk": ukTemplates(),
	"ru": ruTemplates(),
	"pl": plTemplates(),
	"fr": frTemplates(),
}

func deTemplates() map[string]map[string]map[string]tmpl {
	// All event types share the same template family; we only vary by audience
	// and bucket. Specialise where wording really differs (e.g. fortbildung
	// is school-free, schulfeier invites attendance).
	parentToday := tmpl{
		Subject: "Heute: {{title}}{{class_suffix}}",
		Body:    "Liebe Eltern, heute findet {{title}} statt{{class_suffix}}. Datum: {{date_pretty}}.",
	}
	parentTomorrow := tmpl{
		Subject: "Morgen: {{title}}{{class_suffix}}",
		Body:    "Liebe Eltern, morgen ({{date_pretty}}) findet {{title}} statt{{class_suffix}}.",
	}
	parentDays := tmpl{
		Subject: "In {{lead}} Tagen: {{title}}{{class_suffix}}",
		Body:    "Liebe Eltern, in {{lead}} Tagen ({{date_pretty}}) findet {{title}} statt{{class_suffix}}.",
	}
	studentToday := tmpl{
		Subject: "Heute: {{title}}",
		Body:    "Heute ist {{title}}{{class_suffix}}.",
	}
	studentTomorrow := tmpl{
		Subject: "Morgen: {{title}}",
		Body:    "Morgen ({{date_pretty}}) ist {{title}}{{class_suffix}}.",
	}
	studentDays := tmpl{
		Subject: "In {{lead}} Tagen: {{title}}",
		Body:    "In {{lead}} Tagen ({{date_pretty}}) ist {{title}}{{class_suffix}}.",
	}
	bucket := func(today, tomorrow, days tmpl) map[string]tmpl {
		return map[string]tmpl{"today": today, "tomorrow": tomorrow, "days": days}
	}
	universal := map[string]map[string]tmpl{
		"parents":  bucket(parentToday, parentTomorrow, parentDays),
		"students": bucket(studentToday, studentTomorrow, studentDays),
	}
	return map[string]map[string]map[string]tmpl{
		"fortbildung":  universal,
		"schulfeier":   universal,
		"klassenfahrt": universal,
		"projekttag":   universal,
		"eltern_info":  universal,
		"andere":       universal,
	}
}

// The non-DE templates use the same structure; only the strings change.
// Defined in a single helper that takes the translation map and reuses the
// DE family glue.

func makeFamily(
	pT, pTm, pD, sT, sTm, sD tmpl,
) map[string]map[string]map[string]tmpl {
	bucket := func(today, tomorrow, days tmpl) map[string]tmpl {
		return map[string]tmpl{"today": today, "tomorrow": tomorrow, "days": days}
	}
	universal := map[string]map[string]tmpl{
		"parents":  bucket(pT, pTm, pD),
		"students": bucket(sT, sTm, sD),
	}
	return map[string]map[string]map[string]tmpl{
		"fortbildung":  universal,
		"schulfeier":   universal,
		"klassenfahrt": universal,
		"projekttag":   universal,
		"eltern_info":  universal,
		"andere":       universal,
	}
}

func enTemplates() map[string]map[string]map[string]tmpl {
	return makeFamily(
		tmpl{"Today: {{title}}{{class_suffix}}", "Dear parents, today {{title}} takes place{{class_suffix}}. Date: {{date_pretty}}."},
		tmpl{"Tomorrow: {{title}}{{class_suffix}}", "Dear parents, tomorrow ({{date_pretty}}) {{title}} takes place{{class_suffix}}."},
		tmpl{"In {{lead}} days: {{title}}{{class_suffix}}", "Dear parents, in {{lead}} days ({{date_pretty}}) {{title}} takes place{{class_suffix}}."},
		tmpl{"Today: {{title}}", "Today is {{title}}{{class_suffix}}."},
		tmpl{"Tomorrow: {{title}}", "Tomorrow ({{date_pretty}}) is {{title}}{{class_suffix}}."},
		tmpl{"In {{lead}} days: {{title}}", "In {{lead}} days ({{date_pretty}}) is {{title}}{{class_suffix}}."},
	)
}

func trTemplates() map[string]map[string]map[string]tmpl {
	return makeFamily(
		tmpl{"Bugün: {{title}}{{class_suffix}}", "Sayın veliler, bugün {{title}} gerçekleşiyor{{class_suffix}}. Tarih: {{date_pretty}}."},
		tmpl{"Yarın: {{title}}{{class_suffix}}", "Sayın veliler, yarın ({{date_pretty}}) {{title}} gerçekleşiyor{{class_suffix}}."},
		tmpl{"{{lead}} gün sonra: {{title}}{{class_suffix}}", "Sayın veliler, {{lead}} gün sonra ({{date_pretty}}) {{title}} gerçekleşiyor{{class_suffix}}."},
		tmpl{"Bugün: {{title}}", "Bugün {{title}}{{class_suffix}}."},
		tmpl{"Yarın: {{title}}", "Yarın ({{date_pretty}}) {{title}}{{class_suffix}}."},
		tmpl{"{{lead}} gün sonra: {{title}}", "{{lead}} gün sonra ({{date_pretty}}) {{title}}{{class_suffix}}."},
	)
}

func arTemplates() map[string]map[string]map[string]tmpl {
	return makeFamily(
		tmpl{"اليوم: {{title}}{{class_suffix}}", "أعزائي أولياء الأمور، اليوم يقام {{title}}{{class_suffix}}. التاريخ: {{date_pretty}}."},
		tmpl{"غدًا: {{title}}{{class_suffix}}", "أعزائي أولياء الأمور، غدًا ({{date_pretty}}) يقام {{title}}{{class_suffix}}."},
		tmpl{"بعد {{lead}} أيام: {{title}}{{class_suffix}}", "أعزائي أولياء الأمور، بعد {{lead}} أيام ({{date_pretty}}) يقام {{title}}{{class_suffix}}."},
		tmpl{"اليوم: {{title}}", "اليوم {{title}}{{class_suffix}}."},
		tmpl{"غدًا: {{title}}", "غدًا ({{date_pretty}}) {{title}}{{class_suffix}}."},
		tmpl{"بعد {{lead}} أيام: {{title}}", "بعد {{lead}} أيام ({{date_pretty}}) {{title}}{{class_suffix}}."},
	)
}

func ukTemplates() map[string]map[string]map[string]tmpl {
	return makeFamily(
		tmpl{"Сьогодні: {{title}}{{class_suffix}}", "Шановні батьки, сьогодні відбудеться {{title}}{{class_suffix}}. Дата: {{date_pretty}}."},
		tmpl{"Завтра: {{title}}{{class_suffix}}", "Шановні батьки, завтра ({{date_pretty}}) відбудеться {{title}}{{class_suffix}}."},
		tmpl{"Через {{lead}} днів: {{title}}{{class_suffix}}", "Шановні батьки, через {{lead}} днів ({{date_pretty}}) відбудеться {{title}}{{class_suffix}}."},
		tmpl{"Сьогодні: {{title}}", "Сьогодні {{title}}{{class_suffix}}."},
		tmpl{"Завтра: {{title}}", "Завтра ({{date_pretty}}) {{title}}{{class_suffix}}."},
		tmpl{"Через {{lead}} днів: {{title}}", "Через {{lead}} днів ({{date_pretty}}) {{title}}{{class_suffix}}."},
	)
}

func ruTemplates() map[string]map[string]map[string]tmpl {
	return makeFamily(
		tmpl{"Сегодня: {{title}}{{class_suffix}}", "Уважаемые родители, сегодня состоится {{title}}{{class_suffix}}. Дата: {{date_pretty}}."},
		tmpl{"Завтра: {{title}}{{class_suffix}}", "Уважаемые родители, завтра ({{date_pretty}}) состоится {{title}}{{class_suffix}}."},
		tmpl{"Через {{lead}} дней: {{title}}{{class_suffix}}", "Уважаемые родители, через {{lead}} дней ({{date_pretty}}) состоится {{title}}{{class_suffix}}."},
		tmpl{"Сегодня: {{title}}", "Сегодня {{title}}{{class_suffix}}."},
		tmpl{"Завтра: {{title}}", "Завтра ({{date_pretty}}) {{title}}{{class_suffix}}."},
		tmpl{"Через {{lead}} дней: {{title}}", "Через {{lead}} дней ({{date_pretty}}) {{title}}{{class_suffix}}."},
	)
}

func plTemplates() map[string]map[string]map[string]tmpl {
	return makeFamily(
		tmpl{"Dzisiaj: {{title}}{{class_suffix}}", "Drodzy rodzice, dzisiaj odbywa się {{title}}{{class_suffix}}. Data: {{date_pretty}}."},
		tmpl{"Jutro: {{title}}{{class_suffix}}", "Drodzy rodzice, jutro ({{date_pretty}}) odbywa się {{title}}{{class_suffix}}."},
		tmpl{"Za {{lead}} dni: {{title}}{{class_suffix}}", "Drodzy rodzice, za {{lead}} dni ({{date_pretty}}) odbywa się {{title}}{{class_suffix}}."},
		tmpl{"Dzisiaj: {{title}}", "Dzisiaj {{title}}{{class_suffix}}."},
		tmpl{"Jutro: {{title}}", "Jutro ({{date_pretty}}) {{title}}{{class_suffix}}."},
		tmpl{"Za {{lead}} dni: {{title}}", "Za {{lead}} dni ({{date_pretty}}) {{title}}{{class_suffix}}."},
	)
}

func frTemplates() map[string]map[string]map[string]tmpl {
	return makeFamily(
		tmpl{"Aujourd'hui : {{title}}{{class_suffix}}", "Chers parents, aujourd'hui a lieu {{title}}{{class_suffix}}. Date : {{date_pretty}}."},
		tmpl{"Demain : {{title}}{{class_suffix}}", "Chers parents, demain ({{date_pretty}}) a lieu {{title}}{{class_suffix}}."},
		tmpl{"Dans {{lead}} jours : {{title}}{{class_suffix}}", "Chers parents, dans {{lead}} jours ({{date_pretty}}) a lieu {{title}}{{class_suffix}}."},
		tmpl{"Aujourd'hui : {{title}}", "Aujourd'hui c'est {{title}}{{class_suffix}}."},
		tmpl{"Demain : {{title}}", "Demain ({{date_pretty}}) c'est {{title}}{{class_suffix}}."},
		tmpl{"Dans {{lead}} jours : {{title}}", "Dans {{lead}} jours ({{date_pretty}}) c'est {{title}}{{class_suffix}}."},
	)
}