sakiweiblog-rewrite-objective-c-file-reader-to-swift-swift-file-handle.swift

class FileReader {
  
  // 1.
  private let fileHanlde: NSFileHandle
  private let lineDelimiter = "\n"
  private let chunkSize: Int = 16
  private let totalFileLen: UInt64
  private var currentOffset: UInt64 = 0
  
  // 2.
  init?(path: String) {
    guard let fh = NSFileHandle(forReadingAtPath: path) else { return nil }
    fileHanlde = fh
    fileHanlde.seekToEndOfFile()
    totalFileLen = fileHanlde.offsetInFile
  }
  
  // 3.
  deinit {
    fileHanlde.closeFile()
  }
  
  func readLine() -> String? {
    // 4.
    guard let newLineData = lineDelimiter.dataUsingEncoding(NSUTF8StringEncoding) where currentOffset < totalFileLen else { return nil }
    
    fileHanlde.seekToFileOffset(currentOffset)
    
    let currentData = NSMutableData()
    
    var shouldReadMore = true
    
    // 5.
    autoreleasepool {
      while (shouldReadMore) {
        if currentOffset >= totalFileLen {
          break;
        }
        
        var chunk = fileHanlde.readDataOfLength(chunkSize);
        let newLineRange = chunk.rangeOfData_dd(newLineData)
        if newLineRange.location != NSNotFound {
          // include the length so we can include the delimiter in the string
          chunk = chunk.subdataWithRange(NSMakeRange(0, newLineRange.location + newLineData.length))
          shouldReadMore = false
        }
        currentData.appendData(chunk)
        currentOffset += UInt64(chunk.length)
      }
    }
    return NSString(data: currentData, encoding: NSUTF8StringEncoding) as? String
  }
  
  func readTrimmedLine() -> String? {
    return self.readLine()?.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())
  }
  
  // 6.
  func enumerateLines(callback: (String) -> Bool) {
    var stop = false
    while !stop {
      if let l = self.readLine() {
        // if returns false from callback, the loop will exit
        stop = !callback(l)
      } else {
        break;
      }
    }
  }
}