package main

import (
	"strings"
	"unicode"
)

// Trailing dotted suffixes that EPG providers commonly append to channel ids
// (e.g. "Italia 1.it"). Conservative allow-list to avoid eating real id chars.
var idSuffixes = []string{".it", ".uk", ".de", ".com", ".us", ".fr", ".es", ".tv"}

// Trailing video-quality markers commonly appended by either the playlist or
// the EPG (e.g. open-epg uses "Italia 1 HD.it" while the playlist may say
// "Italia 1"). Stripped symmetrically from both sides. Order matters: longer
// markers first so " full hd" wins over a partial " hd" match.
var qualitySuffixes = []string{" full hd", " uhd", " fhd", " hd", " 4k", " sd"}

// normalizeChannelID returns a stable lookup key for a channel identifier,
// collapsing cosmetic divergences across sources:
//
//	"Italia 1" / "Italia 1.it" / "Italia 1 HD.it" / "italia1" → "italia1"
func normalizeChannelID(id string) string {
	s := strings.ToLower(strings.TrimSpace(id))

	for _, suf := range idSuffixes {
		if strings.HasSuffix(s, suf) {
			s = s[:len(s)-len(suf)]
			break
		}
	}

	// Strip trailing quality markers, possibly stacked ("Italia 1 Full HD HD").
	for {
		matched := false
		for _, suf := range qualitySuffixes {
			if strings.HasSuffix(s, suf) {
				s = s[:len(s)-len(suf)]
				matched = true
				break
			}
		}
		if !matched {
			break
		}
	}

	var b strings.Builder
	b.Grow(len(s))
	for _, r := range s {
		if unicode.IsLetter(r) || unicode.IsDigit(r) {
			b.WriteRune(r)
		}
	}
	return b.String()
}

// buildIDMap turns a list of playlist tvg-ids into a normalized→canonical
// lookup. The canonical form is the playlist's exact tvg-id string; the EPG
// merger uses it to rewrite incoming channel/programme references.
func buildIDMap(tvgIDs []string) map[string]string {
	m := make(map[string]string, len(tvgIDs))
	for _, id := range tvgIDs {
		key := normalizeChannelID(id)
		if key == "" {
			continue
		}
		if _, exists := m[key]; !exists {
			m[key] = id
		}
	}
	return m
}