Suggest.scala

import io.Source
import java.io.File

/**
 * Template for predictive text suggester
 */
object Suggest {
  type FreqMap= Map[String, Int];
  type FreqMaps = (FreqMap, FreqMap)
  /**
   * Please implement this method and any supporting methods/classes
   */
  def printSuggestions(f: File, seq: String): Unit = {

    log("Parsing file " + f.getAbsolutePath)
    val text=Source.fromFile(f)
    val (exact,prefix)=text.getLines.foldLeft((Map[String, Int](), Map[String, Int]()))( scanLine(_,_,seq) )
    text.close()
    log("Exact matches for " + seq + ": ")
    sortByFreq(exact).foreach( wf => println (wf._1) )
    log("Prefix matches for " + seq + ": ")
    sortByFreq(prefix).take(5).foreach( wf => println (wf._1) )
  }
  
  def sortByFreq(m:FreqMap)= m.toList.sortWith( _._2 > _._2 )

  def lineToNumeric(line:String)= line.split("[^A-Za-z]").map( _.toLowerCase)
  def scanLine( mp:FreqMaps, line:String, seq:String)= lineToNumeric(line).foldLeft(mp)(predictWord(_,_,seq))

  def predictWord (mp:FreqMaps, word:String, seq:String)= {
    val (exact,prefix)=mp
    val numword=toNumeric(word)
    if (numword.startsWith(seq)){
      if (numword.length() == seq.length())
        (incrementCount(word,exact),prefix)
      else
        (exact,incrementCount(word,prefix))
    } else {
      //do nothing
      mp
    }
  }

  def incrementCount(word:String, map:FreqMap)= {
    val count=map.getOrElse(word,1)
    map+(word->(count+1))
  }
  /**
   * Utility method to convert a word (e.g. "cat") to its numeric
   * representation (e.g. 228). In must be lowercase. A runtime
   * exception is thrown in case non alphabet characters are provided.
   */
  def toNumeric(word: String): String = word.map( convert )

  val KEYPAD_MAP = Map(
    ("abc"-> '2'),
    ("def"-> '3'),
    ("ghi"-> '4'),
    ("jkl"-> '5'),
    ("mno"-> '6'),
    ("pqrs"->'7'),
    ("tuv"-> '8'),
    ("wxyz"->'9')
  )
  
  def convert(c:Char)= KEYPAD_MAP.find(_._1 contains c).getOrElse(throw new RuntimeException("Can't convert char: " + c) )._2

  def main(args: Array[String]): Unit = {
    if (args.length != 2) {
      log("Usage: java Suggest filename seq")
      System.exit(1)
    }
    val f: File = new File(args(0))
    if (!f.exists || !f.isFile) {
      log(args(0) + " is not a valid file")
      System.exit(2)
    }
    val seq: String = args(1)
    printSuggestions(f, seq)
  }

  private def log(s: String): Unit = {
    System.out.println(s)
  }


}