package shared

import (
	"strings"
	"unicode/utf8"

	"github.com/mymmrac/telego"
	tu "github.com/mymmrac/telego/telegoutil"
)

var escaper = strings.NewReplacer("&", "&amp;", "<", "&lt;", ">", "&gt;")

func Button(text, data string) telego.InlineKeyboardButton {
	return tu.InlineKeyboardButton(text).WithCallbackData(data)
}

func Escape(text string) string {
	return escaper.Replace(text)
}

func Truncate(text string, max int) string {
	if utf8.RuneCountInString(text) <= max {
		return text
	}
	runes := []rune(text)
	return string(runes[:max-1]) + "…"
}

// TelegramMessageLimit is Telegram's maximum text length in characters.
const TelegramMessageLimit = 4096

// FitMessage truncates rendered HTML to the Telegram message limit without
// cutting an entity or leaving a tag open.
func FitMessage(text string) string {
	runes := []rune(text)
	if len(runes) <= TelegramMessageLimit {
		return text
	}

	limit := TelegramMessageLimit - 1 // reserve the ellipsis
	cut := safeCut(runes, limit)
	for cut > 0 {
		closers := closingTags(runes[:cut])
		if cut+utf8.RuneCountInString(closers) <= limit {
			return string(runes[:cut]) + closers + "…"
		}
		cut = safeCut(runes, cut-1)
	}
	return "…"
}

// safeCut returns the largest index up to limit that is not inside an HTML tag
// or entity.
func safeCut(runes []rune, limit int) int {
	if limit > len(runes) {
		limit = len(runes)
	}
	inTag := false
	entityStart := -1
	for i := 0; i < limit; i++ {
		char := runes[i]
		switch {
		case inTag:
			if char == '>' {
				inTag = false
			}
		case entityStart >= 0:
			if char == ';' {
				entityStart = -1
			}
		case char == '<':
			inTag = true
		case char == '&':
			entityStart = i
		}
	}
	if inTag {
		for i := limit - 1; i >= 0; i-- {
			if runes[i] == '<' {
				return i
			}
		}
		return 0
	}
	if entityStart >= 0 {
		return entityStart
	}
	return limit
}

// closingTags returns the closing tags needed for any HTML left open by prefix.
func closingTags(prefix []rune) string {
	var open []string
	for i := 0; i < len(prefix); i++ {
		if prefix[i] != '<' {
			continue
		}
		end := i + 1
		for end < len(prefix) && prefix[end] != '>' {
			end++
		}
		if end >= len(prefix) {
			break
		}
		raw := strings.TrimSpace(string(prefix[i+1 : end]))
		i = end
		if raw == "" {
			continue
		}
		if strings.HasPrefix(raw, "/") {
			name := strings.TrimSpace(raw[1:])
			if len(open) > 0 && open[len(open)-1] == name {
				open = open[:len(open)-1]
			}
			continue
		}
		name := raw
		if space := strings.IndexAny(name, " \t\n"); space >= 0 {
			name = name[:space]
		}
		if strings.HasSuffix(name, "/") || name == "br" {
			continue
		}
		open = append(open, name)
	}

	var closers strings.Builder
	for i := len(open) - 1; i >= 0; i-- {
		closers.WriteString("</")
		closers.WriteString(open[i])
		closers.WriteByte('>')
	}
	return closers.String()
}