// Package main — discovered channels (#688).
//
// When a decoded channel message text mentions a previously-unknown hashtag
// channel (e.g. "Hey, I created new channel called #mesh, please join"), we
// auto-register that hashtag so future traffic can be displayed. This file
// owns the parsing helper plus the integration glue exposed via GetChannels.
package main

import "regexp"

// hashtagRE matches MeshCore-style hashtag channel mentions inside free text.
// A valid channel name starts with '#', followed by one or more letters,
// digits, underscore, or dash. Trailing punctuation (.,!?:;) is excluded by
// the character class.
var hashtagRE = regexp.MustCompile(`#[A-Za-z0-9_\-]+`)

// extractHashtagsFromText scans a decoded message text and returns the unique
// hashtag channel mentions found, in first-seen order. The leading '#' is
// preserved so callers can match against canonical channel names directly.
//
// Examples:
//   extractHashtagsFromText("hi #mesh and #fun")       => []string{"#mesh", "#fun"}
//   extractHashtagsFromText("nothing here")             => nil
//   extractHashtagsFromText("dup #x and #x again")      => []string{"#x"}
//
func extractHashtagsFromText(text string) []string {
	if text == "" {
		return nil
	}
	matches := hashtagRE.FindAllString(text, -1)
	if len(matches) == 0 {
		return nil
	}
	seen := make(map[string]struct{}, len(matches))
	out := make([]string, 0, len(matches))
	for _, m := range matches {
		if len(m) < 2 { // bare '#' guard (regex requires 1+ chars but be defensive)
			continue
		}
		if _, ok := seen[m]; ok {
			continue
		}
		seen[m] = struct{}{}
		out = append(out, m)
	}
	if len(out) == 0 {
		return nil
	}
	return out
}