VideoLoader.swift

//
//  VideoLoader.swift
//  Aerial
//
//  Created by John Coates on 10/29/15.
//  Copyright © 2015 John Coates. All rights reserved.
//

import Foundation
import AVFoundation

protocol VideoLoaderDelegate: NSObjectProtocol {
    func videoLoader(_ videoLoader: VideoLoader, receivedResponse response: URLResponse)
    func videoLoader(_ videoLoader: VideoLoader, receivedData data: Data, forRange range: NSRange)
}

final class VideoLoader: NSObject, NSURLConnectionDataDelegate {
    var connection: NSURLConnection?
    var response: HTTPURLResponse?
    weak var delegate: VideoLoaderDelegate?
    var loadingRequest: AVAssetResourceLoadingRequest

    // range params
    var loadedRange: NSRange
    var requestedRange: NSRange
    var loadRange: Bool

    let queue = DispatchQueue.main

    init(url: URL, loadingRequest: AVAssetResourceLoadingRequest, delegate: VideoLoaderDelegate) {
        //debugLog("videoloader init")
        self.delegate = delegate
        self.loadingRequest = loadingRequest

        let request = NSMutableURLRequest(url: url)
        request.cachePolicy = NSURLRequest.CachePolicy.reloadIgnoringLocalCacheData

        loadRange = false
        loadedRange = NSRange(location: 0, length: 0)
        requestedRange = NSRange(location: 0, length: 0)

        if let dataRequest = loadingRequest.dataRequest {
            if dataRequest.requestedOffset > 0 {
                loadRange = true
                let startOffset = Int(dataRequest.requestedOffset)
                let requestedBytes = Int(dataRequest.requestedLength)
                loadedRange = NSRange(location: startOffset, length: 0)
                requestedRange = NSRange(location: startOffset, length: requestedBytes)

                // set Range: bytes=startOffset-endOffset
                let requestRange = "bytes=\(requestedRange.location)-\(requestedRange.location+requestedRange.length)"
                request.setValue(requestRange, forHTTPHeaderField: "Range")
            }
        }
        //debugLog("loadedRange \(loadedRange)")
        //debugLog("requestedRange \(requestedRange)")
        super.init()

        connection = NSURLConnection(request: request as URLRequest, delegate: self, startImmediately: false)

        guard let connection = connection else {
            errorLog("Couldn't instantiate connection.")
            return
        }

        connection.setDelegateQueue(OperationQueue.main)
        loadedRange = NSRange(location: requestedRange.location, length: 0)

        connection.start()
        //debugLog("Starting request: \(request)")
    }

    deinit {
        connection?.cancel()
    }

    // MARK: - NSURLConnection Delegate

    func connection(_ connection: NSURLConnection, didReceive response: URLResponse) {

        if loadRange {
            if let startOffset = startOffsetFromResponse(response) {
                loadedRange.location = startOffset
            }
        }

        self.response = response as? HTTPURLResponse

        queue.async { () -> Void in
            self.delegate?.videoLoader(self, receivedResponse: response)
            self.fillInContentInformation(self.loadingRequest)
        }
    }

    func connection(_ connection: NSURLConnection, didReceive data: Data) {

        queue.async { () -> Void in
            self.fillInContentInformation(self.loadingRequest)

            guard let dataRequest = self.loadingRequest.dataRequest else {
                errorLog("Data request missing for \(self.loadingRequest)")
                return
            }
            //debugLog("drl \(dataRequest.requestedLength) dro \(dataRequest.requestedOffset)")
            //debugLog("\(dataRequest)")

            /*if (data.count > 100000) {
                debugLog("NOTGOOD")
                dataLog(data)
            }*/
            let requestedRange = self.requestedRange
            let loadedRange = self.loadedRange
            let loadedLocation = loadedRange.location + loadedRange.length

            let dataRange = NSRange(location: loadedRange.location + loadedRange.length,
                                    length: data.count)
            //debugLog("\(dataRange)")

            self.delegate?.videoLoader(self, receivedData: data, forRange: dataRange)

            // check if we've already been sending content, or we're at right byte offset
            if loadedLocation >= requestedRange.location {
                //debugLog("case1")
                let requestedEndOffset = Int(dataRequest.requestedOffset + Int64(dataRequest.requestedLength))

                let pendingDataEndOffset = loadedLocation + data.count
                //debugLog("r \(requestedEndOffset) p \(pendingDataEndOffset)")

                if pendingDataEndOffset > requestedEndOffset {
                    let truncateDataLength = pendingDataEndOffset - requestedEndOffset
                    let truncatedData = data.subdata(in: 0..<data.count - truncateDataLength)
                    dataRequest.respond(with: truncatedData)
                    self.loadingRequest.finishLoading()
                    self.connection?.cancel()
                } else {
                    //debugLog("rr")
                    dataRequest.respond(with: data)
                }
                //debugLog("Responding with data")
            }
                // check if we're at a point now where we can send content
            else if loadedLocation + data.count >= requestedRange.location {
                //debugLog("case2")
                // calculate how far along we need to be into the data before it's part of what
                // was requested
                let inset = requestedRange.location - loadedRange.location

                if inset > 0 {
                    let start = inset
                    let length = data.count - inset
                    let end = start + length
                    let responseData = data.subdata(in: inset..<end)
                    dataRequest.respond(with: responseData)

                    if dataRequest.currentOffset >= dataRequest.requestedOffset + Int64(dataRequest.requestedLength) {
                        self.loadingRequest.finishLoading()
                        self.connection?.cancel()
                    }
                } else if inset < 1 {
                    errorLog("Inset is invalid value: \(inset)")
                }

            }

            //debugLog("Received data with length: \(data.count)")

            self.loadedRange.length += data.count

        }
    }

    func connectionDidFinishLoading(_ connection: NSURLConnection) {

        queue.async { () -> Void in
            debugLog("connectionDidFinishLoading")
            self.loadingRequest.finishLoading()
        }
    }

    func fillInContentInformation(_ loadingRequest: AVAssetResourceLoadingRequest) {

        guard let contentInformationRequest = loadingRequest.contentInformationRequest else {
            return
        }

        guard let response = self.response else {
            debugLog("No response")
            return
        }

        guard let mimeType = response.mimeType else {
            debugLog("no mimeType for \(response)")
            return
        }

        guard let uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassMIMEType, mimeType as CFString, nil) else {
            debugLog("couldn't create prefered identifier for tag \(mimeType)")
            return
        }

        debugLog("Processsing contentInformationRequest")

        let contentType: String = uti.takeRetainedValue() as String

        contentInformationRequest.isByteRangeAccessSupported = true
        contentInformationRequest.contentType = contentType
        contentInformationRequest.contentLength = response.expectedContentLength

        debugLog("expected content length: \(response.expectedContentLength) type:\(contentType)")
    }

    // MARK: - Range

    func startOffsetFromResponse(_ response: URLResponse) -> Int? {

        // get range response
        var regex: NSRegularExpression!
        do {
            // Check to see if the server returned a valid byte-range
            regex = try NSRegularExpression(pattern: "bytes (\\d+)-\\d+/\\d+",
                                            options: NSRegularExpression.Options.caseInsensitive)
        } catch let error as NSError {
            errorLog("Error formatting regex: \(error)")
            return nil
        }

        let httpResponse = response as! HTTPURLResponse

        guard let contentRange = httpResponse.allHeaderFields["Content-Range"] as? NSString else {
            errorLog("Weird, no byte response: \(response)")
            return nil
        }

        guard let match = regex.firstMatch(in: contentRange as String,
                                           options: NSRegularExpression.MatchingOptions.anchored,
                                           range: NSRange(location: 0, length: contentRange.length)) else {
            errorLog("Weird, couldn't make a regex match for byte offset: \(contentRange)")
            return nil
        }
        let offsetMatchRange = match.range(at: 1)
        let offsetString = contentRange.substring(with: offsetMatchRange) as NSString

        let offset = offsetString.longLongValue

        //debugLog("content range: \(contentRange), start offset: \(offset)")

        return Int(offset)
    }

}