/*
 * grep.java
 *
 * Implementation of the GREP command.
 */
package commands;

import java.io.*;

import kernel.*;

/**
 * Searches the files given by the input arguments for a specific pattern. If
 * there are no files requested or the argument "-" is used, the command finds
 * the pattern in the standard input.
 * 
 * @author Jan Horky
 */
public class grep extends AbstractProcess {
  /**
   * Realizes the GREP command.
   * 
   * @throws AppException
   *             Exception caused by an error in the virtual machines manager.
   */
  public void realization() throws AppException {
    BufferedReader in = (this.getIn() != null) ? new BufferedReader(
        new InputStreamReader(this.getIn())) : null;
    BufferedWriter out = new BufferedWriter(new OutputStreamWriter(this
        .getOut()));
    try {
      if (getArgs().size() == 0) {
        this.getErrOut().write(("grep: Too few arguments\n").getBytes());
        this.getErrOut().flush();
      } else {
        String pattern = getArgs().get(0);
        if (getArgs().size() == 1)
          processInput(in, out, pattern, true);
        else {
          for (int i = 1; i < getArgs().size(); i++)
            if (getArgs().get(i).equals("-")) {
              in = new BufferedReader(new InputStreamReader(((shell) this
                  .getParent()).getStdInPipe().getPipeIn()));
              processInput(in, out, pattern, true);
            } else {
              in = new BufferedReader(openFile(getArgs().get(i)));
              processInput(in, out, pattern, false);
              in.close();
            }
        }
      }
    } catch (FileNotFoundException fnfe) {
      try {
        this.getErrOut().write((fnfe.getMessage() + "\n").getBytes());
        this.getErrOut().flush();
      } catch (IOException e) {
        e.printStackTrace();
      }
      fnfe.printStackTrace();
    } catch (IOException ioe) {
      ioe.printStackTrace();
      throw new AppException("I/O operation error\n" + ioe.getMessage(), ioe);
    } catch (NullPointerException npe) {
      npe.printStackTrace();
      throw new AppException("Input or output wasn't defined\n"
          + npe.getMessage(), npe);
    } catch (Exception e) {
      e.printStackTrace();
      throw new AppException("Unexpected error\n" + e.getMessage(), e);
    }
  }

  private FileReader openFile(String fileName) throws FileNotFoundException {
    File file = new File(fileName);
    if (!file.isAbsolute())
      fileName = this.getCurrentPath() + System.getProperty("file.separator")
          + fileName;
    return new FileReader(fileName);
  }

  private void processInput(BufferedReader in, BufferedWriter out,
      String pattern, boolean stIn) throws IOException {
    String data;
    // If we are expecting the data from the standard input ...
    if (getIn() == null) {
      enableStdIn();
      in = new BufferedReader(new InputStreamReader(((shell) this.getParent())
          .getStdInPipe().getPipeIn()));

      // Read and process the input data until the CTRL+D
      while ((data = in.readLine()) != null) {
        if (data.indexOf(pattern) != -1) {
          out.write(data);
          out.newLine();
          out.flush();
        }
      }
    }
    // Otherwise we are reading from a file or pipe ...
    else
      while ((data = in.readLine()) != null)
        if (data.indexOf(pattern) != -1) {
          out.write(data);
          out.newLine();
          out.flush();
        }
  }

  /**
   * Provides full description of the command to be used in the MAN command.
   * 
   * @return Full description of the command including the syntax.
   */
  public String getHelp() {
    return "\n\nDescription:\nSearches the input streams for a specified substring and returns the corresponding lines.\n\nUsage:\n"
        + "grep [input1 [input2 [...]]]\n\n"
        + "input1, input2, ...\tFiles to be searched or '-' representing the standard input";
  }
}