package event

import (
	"regexp"
	"strings"
)

// mentionRegex matches @username patterns
// Supports alphanumeric characters, underscores, and hyphens
var mentionRegex = regexp.MustCompile(`@([a-zA-Z0-9_-]+)`)

// ExtractMentions extracts all @mentioned usernames from text
func ExtractMentions(text string) []string {
	if text == "" {
		return nil
	}

	matches := mentionRegex.FindAllStringSubmatch(text, -1)
	if len(matches) == 0 {
		return nil
	}

	// Deduplicate mentions
	seen := make(map[string]bool)
	var usernames []string

	for _, match := range matches {
		if len(match) < 2 {
			continue
		}
		username := strings.ToLower(match[1])

		// Skip common false positives
		if isCommonFalsePositive(username) {
			continue
		}

		if !seen[username] {
			seen[username] = true
			usernames = append(usernames, username)
		}
	}

	return usernames
}

// ReplaceMentionsWithSlackIDs replaces @username with <@SLACK_ID> format
func ReplaceMentionsWithSlackIDs(text string, usernameToSlackID map[string]string) string {
	if text == "" || len(usernameToSlackID) == 0 {
		return text
	}

	result := mentionRegex.ReplaceAllStringFunc(text, func(match string) string {
		username := strings.ToLower(strings.TrimPrefix(match, "@"))
		if slackID, ok := usernameToSlackID[username]; ok {
			return "<@" + slackID + ">"
		}
		return match // Keep original if no mapping found
	})

	return result
}

// isCommonFalsePositive checks if a mention is likely not a real username
func isCommonFalsePositive(username string) bool {
	// Common patterns that look like mentions but aren't
	falsePositives := map[string]bool{
		"param":      true,
		"returns":    true,
		"throws":     true,
		"deprecated": true,
		"see":        true,
		"link":       true,
		"code":       true,
		"example":    true,
		"todo":       true,
		"fixme":      true,
		"note":       true,
		"warning":    true,
		"author":     true,
		"version":    true,
		"since":      true,
	}

	return falsePositives[username]
}