FileReader.swift

import Foundation

private let DefaultChunkSize: Int    = 256
private let DefaultEndOfLine: String = "\n"

/// Class for reading file line by line.
///
/// Based on DDFileReader by Dave DeLong.
/// [How to read data from NSFileHandle line by line?](http://stackoverflow.com/a/3711079/666371)
public class FileReader {
  private let _filePath: String!
  
  private let _EOLData: NSData!
  private let _EOLDataSize: Int!
  private let _EOLCharacterSet: NSCharacterSet!
  
  private let _chunkSize: Int!
  
  private let _fileHandle: NSFileHandle!
  private let _totalFileLength: UInt64!
  
  private var _offset: UInt64 = 0
  
  public init?(filePath: String,
               chunkSize: Int = DefaultChunkSize,
               endOfLine: String = DefaultEndOfLine)
  {
    if let data = endOfLine.dataUsingEncoding(NSUTF8StringEncoding) {
      _EOLData = data
      _EOLDataSize = data.length
      _EOLCharacterSet = NSCharacterSet(charactersInString: endOfLine)
    } else {
      return nil
    }
    
    if let handle = NSFileHandle(forReadingAtPath: filePath) {
      _filePath = filePath
      _fileHandle = handle
      _totalFileLength = _fileHandle.seekToEndOfFile()
      _chunkSize = chunkSize
    } else {
      return nil
    }
  }
  
  /// Closes the file read.
  deinit {
    _fileHandle.closeFile()
  }
  
  
  /// Returns line including EOL.
  public func readLine() -> String? {
    if _offset >= _totalFileLength { return nil }
    
    _fileHandle.seekToFileOffset(_offset)
    
    let readData = NSMutableData()
    var foundEOL = false
    while !foundEOL {
      if _offset >= _totalFileLength { break }
      
      autoreleasepool {[unowned self] in
        var chunk = self._fileHandle.readDataOfLength(self._chunkSize)
        if let range = chunk.rangeOfData(self._EOLData) {
          foundEOL = true
          let n = range.location + self._EOLDataSize
          chunk = chunk.subdataWithRange(NSRange(location: 0, length: n))
        }
        readData.appendData(chunk)
        self._offset += UInt64(chunk.length)
      }
    }
    
    return NSString(data: readData, encoding: NSUTF8StringEncoding)
  }
  
  /// Returns line without EOL.
  public func readTrimmedLine() -> String? {
    return self.readLine()?.stringByTrimmingCharactersInSet(_EOLCharacterSet)
  }
  
  /// Enumerates lines with EOL, optionally stopping.
  public func enumerateLines(body: (String, inout Bool)->()) {
    var stop = false
    while !stop {
      if let line = self.readLine() {
        body(line, &stop)
      } else {
        break
      }
    }
  }
  
  /// Enumerates lines without EOL, optionally stopping.
  public func enumerateTrimmedLines(body: (String, inout Bool)->()) {
    var stop = false
    while !stop {
      if let line = self.readTrimmedLine() {
        body(line, &stop)
      } else {
        break
      }
    }
  }
  
  /// Enumerate all lines without EOL.
  public func enumerateTrimmedLines(body: (String)->()) {
    while let line = self.readTrimmedLine() { body(line) }
  }
  
  /// Enumerate all lines with EOL.
  public func enumerateLines(body: (String)->()) {
    while let line = self.readLine() { body(line) }
  }
 
  
  /// Reset offset to 0.
  public func resetOffset() {
    _offset = 0
  }
}


private extension NSData {
  func rangeOfData(dataToFind: NSData) -> NSRange? {
    let _bytes = UnsafePointer<Int8>(bytes)
    let _searchBytes = UnsafePointer<Int8>(dataToFind.bytes)
    let _searchLength = dataToFind.length
    
    var searchIndex = 0
    var range = NSRange(location: NSNotFound, length: _searchLength)
    for idx in 0..<length {
      if _bytes[idx] == _searchBytes[searchIndex] {
        if range.location == NSNotFound { range.location = idx }
        searchIndex++
        if searchIndex == _searchLength { return range }
      } else { // No match or Matching sequence broke.
        searchIndex = 0             // Return to the first search index
        range.location = NSNotFound // discarding previous found location.
      }
    }
    
    return (range.location != NSNotFound) ? range : nil
  }
}