import Foundation
import AVFoundation

// MARK: - SMB 流式加载器
/// 将 smb:// URL 包装为 miniplayer-smb:// 自定义协议，
/// AVPlayer 请求数据时逐块从 SMB 读取，无需复制整个文件。

final class SMBStreamingLoader: NSObject, AVAssetResourceLoaderDelegate {
    
    private var smbURL: URL
    private var fileHandle: FileHandle?
    private var contentLength: Int64 = 0
    private var contentType: String = "video/mp4"
    private let readChunkSize = 256 * 1024 // 256KB chunks
    
    init(smbURL: URL) {
        self.smbURL = smbURL
        super.init()
        
        // 根据扩展名推断 content type
        let ext = smbURL.pathExtension.lowercased()
        switch ext {
        case "mp4", "m4v": contentType = "video/mp4"
        case "mov": contentType = "video/quicktime"
        case "mkv": contentType = "video/x-matroska"
        case "avi": contentType = "video/x-msvideo"
        case "webm": contentType = "video/webm"
        case "ts": contentType = "video/mp2t"
        case "m3u8": contentType = "application/vnd.apple.mpegurl"
        case "mp3", "mpeg": contentType = "audio/mpeg"
        case "wav": contentType = "audio/wav"
        case "m4a": contentType = "audio/mp4"
        case "aac": contentType = "audio/aac"
        default: contentType = "video/mp4"
        }
    }
    
    deinit {
        try? fileHandle?.close()
    }
    
    // 创建包装后的本地 URL
    func wrappedURL() -> URL {
        // 用自定义 scheme，path 部分编码原始 smb URL
        let encoded = smbURL.absoluteString.data(using: .utf8)!.base64EncodedString()
            .replacingOccurrences(of: "+", with: "-")
            .replacingOccurrences(of: "/", with: "_")
            .replacingOccurrences(of: "=", with: "")
        return URL(string: "miniplayer-smb://stream/\(encoded)")!
    }
    
    // 从 wrapped URL 解码原始 smb URL
    static func decodeSMBURL(from wrapped: URL) -> URL? {
        guard wrapped.scheme == "miniplayer-smb" else { return nil }
        var encoded = wrapped.path.replacingOccurrences(of: "/stream/", with: "")
        // 还原 base64 填充
        encoded = encoded
            .replacingOccurrences(of: "-", with: "+")
            .replacingOccurrences(of: "_", with: "/")
        let padding = (4 - encoded.count % 4) % 4
        encoded += String(repeating: "=", count: padding)
        guard let data = Data(base64Encoded: encoded),
              let str = String(data: data, encoding: .utf8),
              let url = URL(string: str) else { return nil }
        return url
    }
    
    // MARK: - AVAssetResourceLoaderDelegate
    
    func resourceLoader(_ resourceLoader: AVAssetResourceLoader,
                        shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool {
        
        // 延迟打开 FileHandle，避免阻塞
        if fileHandle == nil {
            do {
                fileHandle = try FileHandle(forReadingFrom: smbURL)
                contentLength = Int64(try fileHandle!.seekToEnd())
                fileHandle!.seek(toFileOffset: 0)
            } catch {
                loadingRequest.finishLoading(with: error)
                return true
            }
        }
        
        // 处理 content information request
        if let infoRequest = loadingRequest.contentInformationRequest {
            infoRequest.contentType = contentType
            infoRequest.contentLength = contentLength
            infoRequest.isByteRangeAccessSupported = true
        }
        
        // 处理 data request
        if let dataRequest = loadingRequest.dataRequest {
            let offset = dataRequest.currentOffset > 0
                ? dataRequest.currentOffset
                : (dataRequest.requestedOffset > 0 ? dataRequest.requestedOffset : 0)
            let length = dataRequest.requestedLength > 0
                ? dataRequest.requestedLength
                : readChunkSize
            
            do {
                try fileHandle?.seek(toOffset: UInt64(offset))
                let data = fileHandle?.readData(ofLength: length) ?? Data()
                
                if !data.isEmpty {
                    dataRequest.respond(with: data)
                    loadingRequest.finishLoading()
                } else {
                    // 读到末尾
                    loadingRequest.finishLoading()
                }
            } catch {
                loadingRequest.finishLoading(with: error)
            }
        } else {
            // 没有 data request 只有 info request（预检）
            loadingRequest.finishLoading()
        }
        
        return true
    }
    
    func resourceLoader(_ resourceLoader: AVAssetResourceLoader,
                        didCancel loadingRequest: AVAssetResourceLoadingRequest) {
        // 取消请求，无需额外处理
    }
}