Alamofire/Source/Download.swift

//
//  Download.swift
//
//  Copyright (c) 2014-2016 Alamofire Software Foundation (http://alamofire.org/)
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import Foundation

extension Manager {
    private enum Downloadable {
        case request(Foundation.URLRequest)
        case resumeData(Data)
    }

    private func download(_ downloadable: Downloadable, destination: Request.DownloadFileDestination) -> Request {
        var downloadTask: URLSessionDownloadTask!

        switch downloadable {
        case .request(let request):
            queue.sync {
                downloadTask = self.session.downloadTask(with: request)
            }
        case .resumeData(let resumeData):
            queue.sync {
                downloadTask = self.session.downloadTask(withResumeData: resumeData)
            }
        }

        let request = Request(session: session, task: downloadTask)

        if let downloadDelegate = request.delegate as? Request.DownloadTaskDelegate {
            downloadDelegate.downloadTaskDidFinishDownloadingToURL = { session, downloadTask, URL in
                return destination(URL, downloadTask.response as! HTTPURLResponse)
            }
        }

        delegate[request.delegate.task] = request.delegate

        if startRequestsImmediately {
            request.resume()
        }

        return request
    }

    // MARK: Request

    /**
        Creates a download request for the specified method, URL string, parameters, parameter encoding, headers
        and destination.

        If `startRequestsImmediately` is `true`, the request will have `resume()` called before being returned.

        - parameter method:      The HTTP method.
        - parameter URLString:   The URL string.
        - parameter parameters:  The parameters. `nil` by default.
        - parameter encoding:    The parameter encoding. `.URL` by default.
        - parameter headers:     The HTTP headers. `nil` by default.
        - parameter destination: The closure used to determine the destination of the downloaded file.

        - returns: The created download request.
    */
    public func download(
        _ method: Method,
        _ URLString: URLStringConvertible,
        parameters: [String: AnyObject]? = nil,
        encoding: ParameterEncoding = .url,
        headers: [String: String]? = nil,
        destination: Request.DownloadFileDestination)
        -> Request
    {
        let mutableURLRequest = URLRequest(method, URLString, headers: headers)
        let encodedURLRequest = encoding.encode(mutableURLRequest, parameters: parameters).0

        return download(encodedURLRequest, destination: destination)
    }

    /**
        Creates a request for downloading from the specified URL request.

        If `startRequestsImmediately` is `true`, the request will have `resume()` called before being returned.

        - parameter urlRequest:  The URL request
        - parameter destination: The closure used to determine the destination of the downloaded file.

        - returns: The created download request.
    */
    public func download(_ urlRequest: URLRequestConvertible, destination: Request.DownloadFileDestination) -> Request {
        return download(.request(urlRequest.urlRequest), destination: destination)
    }

    // MARK: Resume Data

    /**
        Creates a request for downloading from the resume data produced from a previous request cancellation.

        If `startRequestsImmediately` is `true`, the request will have `resume()` called before being returned.

        - parameter resumeData:  The resume data. This is an opaque data blob produced by `NSURLSessionDownloadTask`
                                 when a task is cancelled. See `NSURLSession -downloadTaskWithResumeData:` for
                                 additional information.
        - parameter destination: The closure used to determine the destination of the downloaded file.

        - returns: The created download request.
    */
    public func download(_ resumeData: Data, destination: Request.DownloadFileDestination) -> Request {
        return download(.resumeData(resumeData), destination: destination)
    }
}

// MARK: -

extension Request {
    /**
        A closure executed once a request has successfully completed in order to determine where to move the temporary
        file written to during the download process. The closure takes two arguments: the temporary file URL and the URL
        response, and returns a single argument: the file URL where the temporary file should be moved.
    */
    public typealias DownloadFileDestination = (URL, HTTPURLResponse) -> URL

    /**
        Creates a download file destination closure which uses the default file manager to move the temporary file to a
        file URL in the first available directory with the specified search path directory and search path domain mask.

        - parameter directory: The search path directory. `.DocumentDirectory` by default.
        - parameter domain:    The search path domain mask. `.UserDomainMask` by default.

        - returns: A download file destination closure.
    */
    public class func suggestedDownloadDestination(
        directory: FileManager.SearchPathDirectory = .documentDirectory,
        domain: FileManager.SearchPathDomainMask = .userDomainMask)
        -> DownloadFileDestination
    {
        return { temporaryURL, response -> URL in
            let directoryURLs = FileManager.default.urlsForDirectory(directory, inDomains: domain)

            if !directoryURLs.isEmpty {
                return try! directoryURLs[0].appendingPathComponent(response.suggestedFilename!)
            }

            return temporaryURL
        }
    }

    /// The resume data of the underlying download task if available after a failure.
    public var resumeData: Data? {
        var data: Data?

        if let delegate = delegate as? DownloadTaskDelegate {
            data = delegate.resumeData
        }

        return data
    }

    // MARK: - DownloadTaskDelegate

    class DownloadTaskDelegate: TaskDelegate, URLSessionDownloadDelegate {
        var downloadTask: URLSessionDownloadTask? { return task as? URLSessionDownloadTask }
        var downloadProgress: ((Int64, Int64, Int64) -> Void)?

        var resumeData: Data?
        override var data: Data? { return resumeData }

        // MARK: - NSURLSessionDownloadDelegate

        // MARK: Override Closures

        var downloadTaskDidFinishDownloadingToURL: ((Foundation.URLSession, URLSessionDownloadTask, URL) -> URL)?
        var downloadTaskDidWriteData: ((Foundation.URLSession, URLSessionDownloadTask, Int64, Int64, Int64) -> Void)?
        var downloadTaskDidResumeAtOffset: ((Foundation.URLSession, URLSessionDownloadTask, Int64, Int64) -> Void)?

        // MARK: Delegate Methods

        func urlSession(
            _ session: URLSession,
            downloadTask: URLSessionDownloadTask,
            didFinishDownloadingTo location: URL)
        {
            if let downloadTaskDidFinishDownloadingToURL = downloadTaskDidFinishDownloadingToURL {
                do {
                    let destination = downloadTaskDidFinishDownloadingToURL(session, downloadTask, location)
                    try FileManager.default.moveItem(at: location, to: destination)
                } catch {
                    self.error = error as NSError
                }
            }
        }

        func urlSession(
            _ session: URLSession,
            downloadTask: URLSessionDownloadTask,
            didWriteData bytesWritten: Int64,
            totalBytesWritten: Int64,
            totalBytesExpectedToWrite: Int64)
        {
            if initialResponseTime == nil { initialResponseTime = CFAbsoluteTimeGetCurrent() }

            if let downloadTaskDidWriteData = downloadTaskDidWriteData {
                downloadTaskDidWriteData(
                    session,
                    downloadTask,
                    bytesWritten,
                    totalBytesWritten,
                    totalBytesExpectedToWrite
                )
            } else {
                progress.totalUnitCount = totalBytesExpectedToWrite
                progress.completedUnitCount = totalBytesWritten

                downloadProgress?(bytesWritten, totalBytesWritten, totalBytesExpectedToWrite)
            }
        }

        func urlSession(
            _ session: URLSession,
            downloadTask: URLSessionDownloadTask,
            didResumeAtOffset fileOffset: Int64,
            expectedTotalBytes: Int64)
        {
            if let downloadTaskDidResumeAtOffset = downloadTaskDidResumeAtOffset {
                downloadTaskDidResumeAtOffset(session, downloadTask, fileOffset, expectedTotalBytes)
            } else {
                progress.totalUnitCount = expectedTotalBytes
                progress.completedUnitCount = fileOffset
            }
        }
    }
}