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 the full message text formatted as HTML for Telegram.
// The text is NOT truncated — the caller is responsible for splitting if needed.
func formatMemory(mem *search.Memory, publicURL string) 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))

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

	return b.String()
}

// mediaAttachments splits memo attachments into images, videos, and audios.
func mediaAttachments(memo *memos.Memo) (images, videos, audios []memos.Attachment) {
	for _, att := range memo.Attachments {
		switch {
		case att.IsImage():
			images = append(images, att)
		case att.IsVideo():
			videos = append(videos, att)
		case att.IsAudio():
			audios = append(audios, att)
		}
	}
	return
}

// splitText splits text into chunks of at most maxLen bytes,
// breaking at paragraph (\n\n), line (\n), or word boundaries.
func splitText(text string, maxLen int) []string {
	if len(text) <= maxLen {
		return []string{text}
	}

	var parts []string
	remaining := text

	for len(remaining) > maxLen {
		chunk := remaining[:maxLen]

		// Try to break at a paragraph boundary
		idx := strings.LastIndex(chunk, "\n\n")
		if idx <= 0 {
			// Try a line boundary
			idx = strings.LastIndex(chunk, "\n")
		}
		if idx <= 0 {
			// Try a word boundary
			idx = strings.LastIndexByte(chunk, ' ')
		}
		if idx <= 0 {
			// Hard cut as last resort
			idx = maxLen
		}

		parts = append(parts, remaining[:idx])
		remaining = strings.TrimLeft(remaining[idx:], "\n ")
	}

	if remaining != "" {
		parts = append(parts, remaining)
	}

	return parts
}

// 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)
	}
}