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path: root/internal/flood/flood.go
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package flood

import (
	"math"
	"sort"
	"strings"
	"unicode/utf8"
)

const (
	runes = 6
	words = 6
	black = "\u24B6\u262D\u272F\u262E\u2721\u5350\u534D\u2719\u0FD5\u0FD6\u16CB\uA5A6\u0FD7\u0FD8"
)

type Kicker interface {
	Kick(nick string, message ...string)
}

type Check struct {
	k Kicker
}

func New(k Kicker) *Check {
	return &Check{k: k}
}

func (c Check) Check(text, nick string) {
	if isFlood(text) {
		c.k.Kick(nick)
	}
}

func entropy(s string) (e float64) {
	n := make(map[rune]float64)
	for _, r := range s {
		n[r] += 1 / float64(len(s))
	}
	for _, v := range n {
		e -= v * math.Log2(v)
	}
	return e
}

func isFlood(s string) bool {
	if strings.ContainsAny(s, black) {
		return true
	}
	if utf8.RuneCountInString(s) <= runes {
		return false
	}
	if v := strings.Fields(s); len(v) >= words {
		return commonWord(v) >= len(v)/2
	}
	return entropy(s) <= 1
}

func commonWord(v []string) int {
	m := make(map[string]int)
	for _, w := range v {
		m[w]++
	}
	l := make([]int, len(m))
	for _, n := range m {
		l = append(l, n)
	}
	sort.Sort(sort.Reverse(sort.IntSlice(l)))
	return l[0]
}