/*
需求：為檔案建立倒排索引
step1：
    |--為所有的檔案建立索引號 FileID_Number
      |--首先查詢到所有的檔案目錄 file.list[]
      |--將所有的檔案寫到一個檔案索引檔案中 fileIndex.txt
step2:
    |--根據檔案的路徑將檔案載入到程式中，並將其中的單詞分詞統計
      |--統計每個單詞在各個檔案中出現的頻率，並將統計資訊寫到結果檔案wordIndex.txt中

*/

import java.io.*;
import java.util.*;

class InvertedEngine
{
    public static void
 
 main(String[] args) throws IOException
    {   
        String filePath = "documents";
        String docIndex = "docIndex.txt";
        String wordIndex = "wordIndex.txt";
        getFileIndex(filePath , docIndex);
        getWordsFrequency(docIndex,wordIndex);
        System.out.println("Work Done!"
 
);
    }

    public static void getFileIndex(String filePath , String docIndex)
    {
        //通過傳入的filePath找到檔案所在，並將該檔案下所有檔案資訊寫到docIndex.txt中
        File file = new File(filePath);
        File[] fileList = file.listFiles();     
        BufferedWriter bufw = null;
        try 
        {   //將所有filePath下的檔案路徑寫到docIndex檔案中
 

            bufw = new BufferedWriter(new FileWriter(docIndex));
            for(int x = 0 ; x <fileList.length ; x++ )
            {
                String docPath = fileList[x].getAbsolutePath();         
                bufw.write("DocID_" + x + "\t" + docPath);
                bufw.newLine();bufw.flush();//重新整理寫入
            }
        }
        catch (IOException e)
        {
            System.out.println("開啟檔案失敗" + e);
        }
        finally
        {
            try
            {
                if(bufw != null)
                    bufw.close();
            }
            catch (IOException ex)
            {
                System.out.println("關閉檔案失敗" + ex);
            }
        }
    }
    public static void getWordsFrequency(String docIndex , String wordIndex) throws IOException
    { //通過docIndex檔案中的內容找到每個檔案，並將檔案中的內容做單詞統計
       TreeMap<String,TreeMap<String,Integer>>  tmp = new TreeMap<String,TreeMap<String,Integer>>();//統計map
       BufferedReader bufr = new BufferedReader(new FileReader(docIndex));//讀取docIndex.txt
       BufferedWriter bufw = new BufferedWriter(new FileWriter(wordIndex));//寫入到wordIndex.txt
       BufferedReader bufrDoc = null;
       String docIDandPath = null;
       while( (docIDandPath = bufr.readLine()) != null)
        {
              String[] docInfo = docIDandPath.split("\t");
              String docID = docInfo[0]; String docPath = docInfo[1];//獲取到docID和檔案的路徑
              bufrDoc = new BufferedReader(new FileReader(docPath));
              String  wordLine = null;   
              while( (wordLine = bufrDoc.readLine()) != null)
                {
                  String[] words = wordLine.split("\\W");
                  for(String wordOfDoc : words)
                      if(!wordOfDoc.equals(""))
                          wordDeal(wordOfDoc,docID,tmp);//將從docIndex讀取到對應檔案內容對做統計處理                            
                }
        } 
        //將處理後的結果寫入到wordIndex.txt檔案中        
        String wordFreInfo = null;
        Set<Map.Entry<String,TreeMap<String,Integer>>> entrySet = tmp.entrySet();
        Iterator<Map.Entry<String,TreeMap<String,Integer>>> it = entrySet.iterator();
        while(it.hasNext())
        {
            Map.Entry<String,TreeMap<String,Integer>> em = it.next();
            wordFreInfo = em.getKey() +"\t" + em.getValue();
            bufw.write(wordFreInfo);
            bufw.newLine();bufw.flush();
        }
        bufw.close();
        bufr.close();
        bufrDoc.close();
    }
    public static void wordDeal(String wordOfDoc,String docID,TreeMap<String,TreeMap<String,Integer>> tmp)
    {
        wordOfDoc = wordOfDoc.toLowerCase();
        if(!tmp.containsKey(wordOfDoc))
        {   
          //單詞在統計中是首次出現 
            TreeMap<String , Integer> tmpST = new TreeMap<String , Integer>();
            tmpST.put(docID,1);
            tmp.put(wordOfDoc,tmpST);
        }        
        else
        {//單詞在tmp中已近存在獲取該單詞在對應docID中出現次數，若是首次出現
         //count = null，則將（docID ,1)加入到tmpST中；若不是首次出現，則將count++後，再將資訊回寫到tmpST中。
         TreeMap<String ,Integer> tmpST = tmp.get(wordOfDoc);
         Integer count = tmpST.get(docID);
         count = ((count == null) ? 1 : count++);
         tmpST.put(docID,count);                
         tmp.put(wordOfDoc,tmpST);  //將最新結果回寫到tmp中   
        }
    }
}