import java.io.*;
import java.net.*;
import java.util.Scanner;

/** Fetches the HTML content of a web page (or HTTP header) as a String. */
public final class WebPageFetcher {

  /**
  * Demo harness.
  *
  * <ul>
  * <li>aArgs[0] : an HTTP URL
  * <li>aArgs[1] : (header | content)
  * </ul>
  */
  public static void main(String... aArgs) throws MalformedURLException {
    String url = aArgs[0];
    String option = aArgs[1];
    WebPageFetcher fetcher = new  WebPageFetcher(url);
    if ( HEADER.equalsIgnoreCase(option) ) {
      log( fetcher.getPageHeader() );
    }
    else if ( CONTENT.equalsIgnoreCase(option) ) {
      log( fetcher.getPageContent() );
    }
    else {
      log("Unknown option.");
    }
  }

  public WebPageFetcher( URL aURL ){
    if ( ! HTTP.equals(aURL.getProtocol())  ) {
      throw new IllegalArgumentException("URL is not for HTTP Protocol: " + aURL);
    }
    fURL = aURL;
  }

  public WebPageFetcher( String aUrlName ) throws MalformedURLException {
    this ( new URL(aUrlName) );
  }

  /** Fetch the HTML content of the page as simple text.   */
  public String getPageContent() {
    String result = null;
    URLConnection connection = null;
    try {
      connection =  fURL.openConnection();
      Scanner scanner = new Scanner(connection.getInputStream());
      scanner.useDelimiter(END_OF_INPUT);
      result = scanner.next();
    }
    catch ( IOException ex ) {
      log("Cannot open connection to " + fURL.toString());
    }
    return result;
  }

  /** Fetch HTML headers as simple text.  */
  public String getPageHeader(){
    StringBuilder result = new StringBuilder();

    URLConnection connection = null;
    try {
      connection = fURL.openConnection();
    }
    catch (IOException ex) {
      log("Cannot open connection to URL: " + fURL);
    }

    //not all headers come in key-value pairs - sometimes the key is
    //null or an empty String
    int headerIdx = 0;
    String headerKey = null;
    String headerValue = null;
    while ( (headerValue = connection.getHeaderField(headerIdx)) != null ) {
      headerKey = connection.getHeaderFieldKey(headerIdx);
      if ( headerKey != null && headerKey.length()>0 ) {
        result.append( headerKey );
        result.append(" : ");
      }
      result.append( headerValue );
      result.append(NEWLINE);
      headerIdx++;
    }
    return result.toString();
  }

  // PRIVATE //
  private URL fURL;
 
  private static final String HTTP = "http";
  private static final String HEADER = "header";
  private static final String CONTENT = "content";
  private static final String END_OF_INPUT = "\\Z";
  private static final String NEWLINE = System.getProperty("line.separator");

  private static void log(Object aObject){
    System.out.println(aObject);
  }
}