package m3u

import (
	"bufio"
	"crypto/sha256"
	"fmt"
	"os"
	"strings"

	"tuner/models"
)

// ParseFile reads and parses an M3U/M3U8 playlist file into a slice of Channels.
func ParseFile(path string) ([]models.Channel, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("open playlist: %w", err)
	}
	defer f.Close()

	var channels []models.Channel
	scanner := bufio.NewScanner(f)

	var extinf string
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())

		if strings.HasPrefix(line, "#EXTINF:") {
			extinf = line
			continue
		}

		// Skip comments and blank lines
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}

		// If we have a pending EXTINF, this line is the URL
		if extinf != "" {
			ch := parseExtinf(extinf, line)
			channels = append(channels, ch)
			extinf = ""
		}
	}

	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("read playlist: %w", err)
	}

	return channels, nil
}

// parseExtinf extracts channel metadata from an #EXTINF line and pairs it with a stream URL.
func parseExtinf(extinf string, streamURL string) models.Channel {
	ch := models.Channel{
		StreamURL: streamURL,
	}

	// Extract attributes from the EXTINF line
	ch.Name = extractDisplayName(extinf)
	ch.Group = extractAttribute(extinf, "group-title")
	ch.LogoURL = extractAttribute(extinf, "tvg-logo")

	tvgName := extractAttribute(extinf, "tvg-name")
	if tvgName != "" && ch.Name == "" {
		ch.Name = tvgName
	}

	// Generate stable ID from name + URL
	ch.ID = generateID(ch.Name, ch.StreamURL)

	return ch
}

// extractAttribute extracts a named attribute value from an EXTINF line.
// Example: `#EXTINF:-1 tvg-name="CNN" group-title="News",CNN HD`
func extractAttribute(line string, attr string) string {
	key := attr + `="`
	idx := strings.Index(line, key)
	if idx == -1 {
		return ""
	}
	start := idx + len(key)
	end := strings.Index(line[start:], `"`)
	if end == -1 {
		return ""
	}
	return line[start : start+end]
}

// extractDisplayName extracts the display name (the part after the last comma in the EXTINF line).
func extractDisplayName(line string) string {
	// The display name is after the last comma
	idx := strings.LastIndex(line, ",")
	if idx == -1 {
		return ""
	}
	return strings.TrimSpace(line[idx+1:])
}

// generateID creates a stable ID for a channel based on its name and stream URL.
func generateID(name, url string) string {
	h := sha256.Sum256([]byte(name + "|" + url))
	return fmt.Sprintf("%x", h[:8])
}

// FilterChannels returns channels matching the given search term and/or group.
func FilterChannels(channels []models.Channel, search string, group string) []models.Channel {
	if search == "" && group == "" {
		return channels
	}

	searchLower := strings.ToLower(search)
	var result []models.Channel

	for _, ch := range channels {
		if group != "" && !strings.EqualFold(ch.Group, group) {
			continue
		}
		if search != "" && !strings.Contains(strings.ToLower(ch.Name), searchLower) {
			continue
		}
		result = append(result, ch)
	}

	return result
}

// GetGroups returns a deduplicated, sorted list of group names from the channel list.
func GetGroups(channels []models.Channel) []string {
	seen := make(map[string]bool)
	var groups []string

	for _, ch := range channels {
		if ch.Group != "" && !seen[ch.Group] {
			seen[ch.Group] = true
			groups = append(groups, ch.Group)
		}
	}

	return groups
}