/*

an simple example to show some RandomAccessFile methods
in action: generate a RandomAccessFile comprising random
doubles, then read them back in an sum up sequentially
and in random order, both twice ...

 */

import java.nio.*;
import java.nio.channels.*;
import java.util.*;
import java.io.IOException;
import java.io.RandomAccessFile;

public class RandomAccessFileTest {

  public static void main(String[] args) throws Exception {

    long before = System.currentTimeMillis();
    int numRows = Integer.parseInt(args[0]);
    int seed = Integer.parseInt(args[1]);
    int k = 1000;
    System.out.println("generating " + numRows + " rows with " + k + " doubles, seed = " + seed);

    RandomAccessFile file = new RandomAccessFile("doubles","rw");
    Random r = new Random(seed);

    double sum = 0.0;
    for(int i = 0; i < numRows; i++) {
      for(int j = 0; j < k; j++) {
	double x = r.nextDouble();
	sum += x;
	file.writeDouble(x);
      }
    }

    long after = System.currentTimeMillis();
    System.out.println("finished writing, sum = " + sum  + " time " + (after-before));
    file.close();

    readInOrder(numRows,k);
    readInRandomOrder(numRows,k,r);

    readInOrder(numRows,k);
    readInRandomOrder(numRows,k,r);

  }


  public static void readInOrder(int numRows, int k) throws Exception {

    long before = System.currentTimeMillis();
    RandomAccessFile file = new RandomAccessFile("doubles","r");

    double sum = 0.0;
    for(int i = 0; i < numRows; i++) {
      int base = i * k * 8;
      for(int j = 0; j < k; j++) {
	file.seek(base);
	double x = file.readDouble();
	sum += x;
	base += 8;
      }
    }

    long after = System.currentTimeMillis();
    System.out.println("finished reading, sum = " + sum  + " time " + (after-before));
    file.close();
  }



  public static void readInRandomOrder(int numRows, int k, Random r) throws Exception {

    List<Integer> rows = new ArrayList<Integer>(numRows);
    for(int i = 0; i < numRows; i++) {
      rows.add(i);
    }
    Collections.shuffle(rows,r);

    long before = System.currentTimeMillis();
    RandomAccessFile file = new RandomAccessFile("doubles","r");

    double sum = 0.0;
    for(Integer row: rows) {
      int base = row * k * 8;
      for(int j = 0; j < k; j++) {
	file.seek(base);
	double x = file.readDouble();
	sum += x;
	base += 8;
      }
    }

    long after = System.currentTimeMillis();
    System.out.println("finished randomR, sum = " + sum  + " time " + (after-before));
    file.close();
  }

}