import Foundation

class StreamReader {
    let encoding: NSStringEncoding
    let chunkSize: Int
    let fileHandle: NSFileHandle
    var buffer: NSMutableData
    let delimPattern : NSData
    var isAtEOF: Bool = false
    
    init?(_ handle: NSFileHandle, delimeter: String = "\n", encoding: NSStringEncoding = NSUTF8StringEncoding, chunkSize: Int = 4096)
    {
        self.fileHandle = handle
        self.chunkSize = chunkSize
        self.encoding = encoding
        self.buffer = NSMutableData(capacity: chunkSize)!
        self.delimPattern = delimeter.dataUsingEncoding(NSUTF8StringEncoding)!
    }
    
    
    deinit {
        fileHandle.closeFile()
    }
    
    func rewind() {
        fileHandle.seekToFileOffset(0)
        buffer = NSMutableData(capacity: chunkSize)!
        isAtEOF = false
    }
    
    func nextLine() -> String? {
        if isAtEOF { return nil }
        
        repeat {
            let range = buffer.rangeOfData(delimPattern, options: [], range: NSRange(location: 0,length: buffer.length))
            if range.location != NSNotFound {
                if range.location == 0 {
                    let remain = NSRange(location: range.length,
                        length: buffer.length - range.length )
                    buffer = buffer.subdataWithRange(remain).mutableCopy() as! NSMutableData
                    continue
                }
                let datarange = NSRange(location: 0, length: range.location)
                let lengthWithDelimiter = range.location + range.length
                let subData = buffer.subdataWithRange(datarange)
                let line = String(data: subData, encoding: encoding)
                let remain = NSRange(location: datarange.location + lengthWithDelimiter,
                    length: buffer.length - lengthWithDelimiter )
                buffer = buffer.subdataWithRange(remain).mutableCopy() as! NSMutableData
                return line
            } else {
                let tempData = fileHandle.readDataOfLength(chunkSize)
                if tempData.length == 0 {
                    isAtEOF = true
                    return (buffer.length > 0) ? String(data: buffer, encoding: encoding) : nil
                }
                buffer.appendData(tempData)
            }
        } while true
    }
}