StreamRecorder/Sources/StreamRecorderKit/HLSVariantResolver.swift

import Foundation

/// HLS 变体解析器
public struct HLSVariantResolver {
    
    public struct Variant {
        public let bandwidth: Int
        public let resolution: String
        public let path: String
        public let fullURL: URL
        
        public var width: Int? {
            let parts = resolution.components(separatedBy: "x")
            return parts.count == 2 ? Int(parts[0]) : nil
        }
        
        public var height: Int? {
            let parts = resolution.components(separatedBy: "x")
            return parts.count == 2 ? Int(parts[1]) : nil
        }
    }
    
    /// 解析 master playlist，返回最佳变体 URL
    /// - Parameters:
    ///   - url: master playlist URL
    ///   - maxWidth: 最大宽度限制（默认 1280）
    /// - Returns: 最佳变体 URL，如果不是 master playlist 则返回 nil
    public static func resolve(url: URL, maxWidth: Int = 1280) -> URL? {
        guard url.absoluteString.contains(".m3u8"),
              let data = try? Data(contentsOf: url),
              let content = String(data: data, encoding: .utf8),
              content.contains("EXT-X-STREAM-INF") else {
            return nil
        }
        
        let variants = parseVariants(from: content, baseURL: url)
        guard !variants.isEmpty else { return nil }
        
        // 选择最佳变体（带宽最高且宽度 <= maxWidth）
        let sorted = variants.sorted { $0.bandwidth > $1.bandwidth }
        let chosen = sorted.first { variant in
            guard let w = variant.width else { return true }
            return w <= maxWidth
        } ?? sorted[0]
        
        return chosen.fullURL
    }
    
    private static func parseVariants(from content: String, baseURL: URL) -> [Variant] {
        var variants: [Variant] = []
        let lines = content.components(separatedBy: "\n")
        
        var i = 0
        while i < lines.count - 1 {
            let line = lines[i]
            if line.hasPrefix("#EXT-X-STREAM-INF:") {
                var bandwidth = 0
                var resolution = ""
                
                let attrs = line.replacingOccurrences(of: "#EXT-X-STREAM-INF:", with: "")
                for attr in attrs.components(separatedBy: ",") {
                    let trimmed = attr.trimmingCharacters(in: .whitespaces)
                    if trimmed.hasPrefix("BANDWIDTH=") {
                        bandwidth = Int(trimmed.replacingOccurrences(of: "BANDWIDTH=", with: "")) ?? 0
                    } else if trimmed.hasPrefix("RESOLUTION=") {
                        resolution = trimmed.replacingOccurrences(of: "RESOLUTION=", with: "")
                    }
                }
                
                let nextLine = lines[i + 1].trimmingCharacters(in: .whitespacesAndNewlines)
                if !nextLine.isEmpty && !nextLine.hasPrefix("#") {
                    let variantURL = baseURL.deletingLastPathComponent().appendingPathComponent(nextLine)
                    variants.append(Variant(
                        bandwidth: bandwidth,
                        resolution: resolution,
                        path: nextLine,
                        fullURL: variantURL
                    ))
                }
            }
            i += 1
        }
        
        return variants
    }
}