MyClub/internal/services/spam.go

package services

import (
	"regexp"
	"strings"
)

// Simple heuristics to evaluate spammy text. Returns score 0..1 and triggered rules.
func EvaluateSpamScore(s string) (float64, []string) {
	var rules []string
	content := strings.TrimSpace(s)
	if content == "" {
		return 1.0, []string{"empty"}
	}
	// Too short
	if len([]rune(content)) < 6 {
		rules = append(rules, "too_short")
	}
	// Excessive repeated characters like 'aaaaaa' or '!!!!'
	if hasExcessiveRepetition(content, 5) {
		rules = append(rules, "repeated_chars")
	}
	// Low vowel ratio suggests gibberish in Czech/English latin text
	letters := regexp.MustCompile(`[A-Za-zÁáÉéĚěÍíÓóÚúŮůÝýŽžŠšČčŘřŤťŇňĎď]`).FindAllString(content, -1)
	if len(letters) >= 8 {
		vowels := regexp.MustCompile(`[AaEeIiOoUuYyÁáÉéĚěÍíÓóÚúŮůÝý]`).FindAllString(content, -1)
		ratio := float64(len(vowels)) / float64(len(letters))
		if ratio < 0.18 { // very low vowel ratio
			rules = append(rules, "low_vowel_ratio")
		}
	}
	// Too many links
	linkCount := len(regexp.MustCompile(`https?://`).FindAllStringIndex(content, -1))
	if linkCount >= 3 {
		rules = append(rules, "too_many_links")
	}
	// All-caps shouting
	if content == strings.ToUpper(content) && len(content) >= 8 {
		rules = append(rules, "all_caps")
	}
	// Compute score by rules weight
	weights := map[string]float64{
		"empty":           1.0,
		"too_short":       0.4,
		"repeated_chars":  0.3,
		"low_vowel_ratio": 0.3,
		"too_many_links":  0.5,
		"all_caps":        0.2,
	}
	score := 0.0
	for _, r := range rules { score += weights[r] }
	if score > 1.0 { score = 1.0 }
	return score, rules
}

// hasExcessiveRepetition checks if s contains a run of the same character of length >= minRun
// Limited to ASCII letters and the punctuation characters ! ? . to mirror the previous intent.
func hasExcessiveRepetition(s string, minRun int) bool {
	if minRun < 2 { minRun = 2 }
	run := 1
	var prev rune
	first := true
	for _, r := range s {
		if first {
			prev = r
			first = false
			continue
		}
		if r == prev && (isAsciiLetter(r) || r == '!' || r == '?' || r == '.') {
			run++
			if run >= minRun {
				return true
			}
		} else {
			prev = r
			run = 1
		}
	}
	return false
}

func isAsciiLetter(r rune) bool {
	return (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z')
}