// BSD License (http://www.galagosearch.org/license)

 package org.galagosearch.core.index;

 import java.io.BufferedInputStream;

 import java.io.DataInputStream;

 import java.io.FileInputStream;

 import java.io.IOException;

 import java.util.ArrayList;

 import org.galagosearch.tupleflow.Utility;

 /**

  * Reads a binary file of document names produced by DocumentNameWriter.

  * The names are loaded into RAM for quick access.

  *

  * @author trevor

  */

 public class DocumentNameReader {

     private static class NameSlot {

         public String prefix;

         public int offset;

         public int footerWidth;

         public int[] footers;

     }

     ArrayList<NameSlot> slots;

     int documentCount;

     /** Creates a new instance of DocumentNameReader */

     public DocumentNameReader(String filename) throws IOException {

         FileInputStream f = new FileInputStream(filename);

         DataInputStream input = new DataInputStream(new BufferedInputStream(f));

         slots = new ArrayList();

         read(input);

         input.close();

     }

     private String getInSlot(NameSlot slot, int footerIndex) {

         int footer = slot.footers[footerIndex-slot.offset];

         String prefix = slot.prefix;

         String documentName;

         if(slot.footerWidth == 0) {

             documentName = slot.prefix;

         } else {

             String format = "%s-%0" + slot.footerWidth + "d";

             documentName = String.format(format, prefix, footer);

         }

         return documentName;

     }

     public String get(int index) {

         assert index >= 0;

         assert index < documentCount;

         if(index >= documentCount) 

             return "unknown";

         if(index < 0)

             return "unknown";

         int big = slots.size()-1;

         int small = 0;

         while(big-small > 1) {

             int middle = small + (big-small)/2;

             if(slots.get(middle).offset >= index)

                 big = middle;

             else

                 small = middle;

         }

         NameSlot one = slots.get(small);

         NameSlot two = slots.get(big);

         String result = "";

         if (two.offset <= index)

             result = getInSlot(two, index);

         else

             result = getInSlot(one, index);

         return result;

     }

     public void read(DataInputStream input) throws IOException {

         int offset = 0;

         // open a file

         while(input.available() > 0) {

             // read the prefix

             int prefixLength = input.readInt();

             byte[] prefixData = new byte[prefixLength];

             input.read(prefixData);

             // read the footers

             int footerWidth = input.readInt();

             int footerCount = input.readInt();

             NameSlot slot = new NameSlot();

             slot.footerWidth = footerWidth;

             slot.offset = offset;

             slot.prefix = Utility.makeString(prefixData);

             slot.footers = new int[footerCount];

             for(int i=0; i<footerCount; i++) {

                 slot.footers[i] = input.readInt();

             }

             slots.add(slot);

             offset += slot.footers.length;

         }

         documentCount = offset;

     }

 }