import Foundation

/// M3U 播放列表解析器（支持 IPTV EXTINF 格式）
enum M3UParser {
    
    struct Channel {
        var name: String
        var url: String
        var group: String?
        var logoURL: String?
        var type: String  // "stream" or "url"
    }
    
    /// 从字符串内容解析 M3U
    static func parse(_ content: String) -> [Channel] {
        let lines = content.components(separatedBy: .newlines)
        var channels: [Channel] = []
        var pendingName: String?
        var pendingGroup: String?
        var pendingLogo: String?
        
        for rawLine in lines {
            let line = rawLine.trimmingCharacters(in: .whitespacesAndNewlines)
            guard !line.isEmpty else { continue }
            
            // 跳过 M3U 头部
            if line.hasPrefix("#EXTM3U") { continue }
            
            // 跳过其他注释（非 EXTINF）
            if line.hasPrefix("#") && !line.hasPrefix("#EXTINF") { continue }
            
            if line.hasPrefix("#EXTINF") {
                // 解析 #EXTINF:-1 tvg-name="..." group-title="..." tvg-logo="...",Channel Name
                let info = String(line.dropFirst("#EXTINF".count))
                
                // 提取逗号后的频道名
                if let commaIdx = info.lastIndex(of: ",") {
                    let afterComma = String(info[info.index(after: commaIdx)...])
                    pendingName = afterComma.trimmingCharacters(in: .whitespaces)
                }
                
                // 提取属性
                let attrs = parseAttributes(info)
                
                if let tvgName = attrs["tvg-name"], (pendingName ?? "").isEmpty {
                    pendingName = tvgName
                }
                pendingGroup = attrs["group-title"]
                pendingLogo = attrs["tvg-logo"]
                
            } else if !line.hasPrefix("#") {
                // URL 行
                let url = line
                let name = (pendingName ?? "").isEmpty
                    ? (URL(string: url)?.host ?? url)
                    : pendingName!
                
                let isStream = url.contains(".m3u8") || url.contains(".m3u")
                    || url.contains("://") && !url.hasSuffix(".mp4")
                
                channels.append(Channel(
                    name: name,
                    url: url,
                    group: pendingGroup,
                    logoURL: pendingLogo,
                    type: isStream ? "stream" : "url"
                ))
                
                pendingName = nil
                pendingGroup = nil
                pendingLogo = nil
            }
        }
        
        return channels
    }
    
    /// 从 URL 异步下载并解析 M3U
    static func fetchAndParse(url: URL) async throws -> [Channel] {
        let (data, _) = try await URLSession.shared.data(from: url)
        guard let content = String(data: data, encoding: .utf8) else {
            throw M3UError.invalidEncoding
        }
        return parse(content)
    }
    
    // MARK: - 私有
    
    private static func parseAttributes(_ line: String) -> [String: String] {
        var attrs: [String: String] = [:]
        // 匹配 key="value"
        let pattern = #"([a-zA-Z\-]+)="([^"]*)""#
        guard let regex = try? NSRegularExpression(pattern: pattern) else { return attrs }
        let matches = regex.matches(in: line, range: NSRange(line.startIndex..., in: line))
        for m in matches {
            guard m.numberOfRanges == 3,
                  let keyRange = Range(m.range(at: 1), in: line),
                  let valRange = Range(m.range(at: 2), in: line) else { continue }
            attrs[String(line[keyRange])] = String(line[valRange])
        }
        return attrs
    }
    
    enum M3UError: Error, LocalizedError {
        case invalidEncoding
        case invalidURL
        case emptyResult
        
        var errorDescription: String? {
            switch self {
            case .invalidEncoding: return "无法解码M3U文件（需要UTF-8编码）"
            case .invalidURL: return "无效的URL"
            case .emptyResult: return "M3U文件中未找到频道"
            }
        }
    }
}