/*
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 */
package javaapplication5;

import java.io.*;

/**
 * @author Daxo
 */
public class KopiujDane {

  public void copy(File source, File output, int linesToCopy) throws IOException {
    validateLineNumber(source, linesToCopy);
    validateFile(source);

    if (!output.exists()) {
      System.out.println("Plik nie istnieje. Tworzę nowy.");
      output.createNewFile();
    }

    //Try with resources - używając tego nie trzeba zadeklarowanych streamów zamykać czyli omijamy 'finaly'
    try(BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream(source)));
        FileOutputStream out = new FileOutputStream(output)) {

      for(int i = 0; i < linesToCopy; i++) {
        out.write((in.readLine() + "\n").getBytes());
      }

    }
  }

  private void validateFile(final File source) {
    if(!source.exists()) {
      throw new IllegalArgumentException("Plik " + source.getAbsolutePath() + " nie istnieje.");
    }
  }

  private void validateLineNumber(final File source, final int linesToCopy) throws IOException {
    if(linesToCopy > countLinesNumber(source)) {
      throw new IllegalArgumentException("Liczba linii do skopiowania jest większa niż " +
          "rzeczywista liczba linii w pliku");
    }
  }

  private int countLinesNumber(File file) throws IOException {
    int lines = 0;
    try(BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(file)))) {
      while (reader.readLine() != null) {
        lines++;
      }
    }
    return lines;
  }
}