package shorturl

import (
	"regexp"
	"strings"
)

// botSubstrings catches the named social-platform link previewers explicitly,
// so we don't over-count human clicks from OG scraping.
var botSubstrings = []string{
	"facebookexternalhit",
	"facebot",
	"twitterbot",
	"linkedinbot",
	"slackbot",
	"telegrambot",
	"discordbot",
	"pinterest",
	"whatsapp",
	"applebot",
	"googlebot",
	"bingbot",
	"yahoo! slurp",
	"duckduckbot",
	"baiduspider",
	"yandex",
	"redditbot",
	"embedly",
	"vkshare",
	"viber",
	"signal",
	"skypeuripreview",
}

var botFallbackRe = regexp.MustCompile(`(?i)\b(bot|crawler|spider|preview|fetch)\b`)

// IsBot returns true if the user-agent looks like an OG scraper / search
// crawler / link previewer, rather than a real human browser. False positives
// here only affect analytics aggregation (the is_bot flag); they never change
// redirect behavior.
func IsBot(userAgent string) bool {
	if userAgent == "" {
		return true // missing UA is almost always a bot or curl
	}
	ua := strings.ToLower(userAgent)
	for _, needle := range botSubstrings {
		if strings.Contains(ua, needle) {
			return true
		}
	}
	return botFallbackRe.MatchString(ua)
}