package telegram

import (
	"fmt"
	"strings"
	"time"

	"git.vakhrushev.me/av/remembos/internal/memos"
	"git.vakhrushev.me/av/remembos/internal/search"
)

const (
	maxMessageLen = 4096
	maxCaptionLen = 1024
)

// formatMemory returns (mainText, captionText) formatted as HTML for Telegram.
// mainText is for sendMessage (up to 4096 chars), captionText for photo captions (up to 1024 chars).
func formatMemory(mem *search.Memory, publicURL string) (mainText, captionText string) {
	var b strings.Builder

	// Header: date and "ago" text
	b.WriteString(fmt.Sprintf("<b>%s</b>", formatDate(mem.Date)))
	if ago := agoText(mem.Date); ago != "" {
		b.WriteString(fmt.Sprintf(" <i>(%s)</i>", ago))
	}
	b.WriteString("\n\n")

	// Content
	b.WriteString(escapeHTML(mem.Memo.Content))

	// Tags
	if len(mem.Memo.Tags) > 0 {
		b.WriteString("\n\n")
		tags := make([]string, len(mem.Memo.Tags))
		for i, t := range mem.Memo.Tags {
			tags[i] = "#" + t
		}
		b.WriteString(strings.Join(tags, " "))
	}

	// Link to original
	memoURL := fmt.Sprintf("%s/%s", publicURL, mem.Memo.Name)
	b.WriteString("\n\n<a href=\"" + memoURL + "\">Оригинал</a>")

	full := b.String()
	mainText = truncateHTML(full, maxMessageLen)
	captionText = truncateHTML(full, maxCaptionLen)
	return mainText, captionText
}

// imageAttachments returns image attachments from the memo.
func imageAttachments(memo *memos.Memo) []memos.Attachment {
	var images []memos.Attachment
	for _, att := range memo.Attachments {
		if att.IsImage() {
			images = append(images, att)
		}
	}
	return images
}

// truncateHTML truncates text to maxLen, cutting at a word/line boundary and adding "...".
func truncateHTML(text string, maxLen int) string {
	if len(text) <= maxLen {
		return text
	}

	// Reserve space for "..."
	cut := maxLen - 3

	// Find last newline or space before cut point
	idx := strings.LastIndexAny(text[:cut], "\n ")
	if idx <= 0 {
		idx = cut
	}

	return text[:idx] + "..."
}

// escapeHTML escapes special HTML characters for Telegram HTML parse mode.
func escapeHTML(s string) string {
	s = strings.ReplaceAll(s, "&", "&amp;")
	s = strings.ReplaceAll(s, "<", "&lt;")
	s = strings.ReplaceAll(s, ">", "&gt;")
	return s
}

var months = [...]string{
	1: "января", 2: "февраля", 3: "марта",
	4: "апреля", 5: "мая", 6: "июня",
	7: "июля", 8: "августа", 9: "сентября",
	10: "октября", 11: "ноября", 12: "декабря",
}

func formatDate(t time.Time) string {
	return fmt.Sprintf("%d %s %d", t.Day(), months[t.Month()], t.Year())
}

func agoText(t time.Time) string {
	now := time.Now()
	years := now.Year() - t.Year()
	monthsDiff := int(now.Month()) - int(t.Month())
	if monthsDiff < 0 {
		years--
		monthsDiff += 12
	}

	if years > 0 {
		return fmt.Sprintf("%s назад", pluralYears(years))
	}
	if monthsDiff > 0 {
		return fmt.Sprintf("%s назад", pluralMonths(monthsDiff))
	}
	return ""
}

func pluralYears(n int) string {
	mod10 := n % 10
	mod100 := n % 100
	switch {
	case mod100 >= 11 && mod100 <= 14:
		return fmt.Sprintf("%d лет", n)
	case mod10 == 1:
		return fmt.Sprintf("%d год", n)
	case mod10 >= 2 && mod10 <= 4:
		return fmt.Sprintf("%d года", n)
	default:
		return fmt.Sprintf("%d лет", n)
	}
}

func pluralMonths(n int) string {
	mod10 := n % 10
	mod100 := n % 100
	switch {
	case mod100 >= 11 && mod100 <= 14:
		return fmt.Sprintf("%d месяцев", n)
	case mod10 == 1:
		return fmt.Sprintf("%d месяц", n)
	case mod10 >= 2 && mod10 <= 4:
		return fmt.Sprintf("%d месяца", n)
	default:
		return fmt.Sprintf("%d месяцев", n)
	}
}