package eu.simuline.octave;
   
   import java.util.Collection;
   import java.util.HashSet;
   import java.util.Random;
   
   import java.util.regex.Pattern;
   
   import java.nio.charset.Charset;
  
  import eu.simuline.octave.type.OctaveCell;
  import eu.simuline.octave.type.OctaveString;
  
  /**
   * Small utility functions that can be used with JavaOctave.
   * 
   * Holder class for static functions.
   */
  public final class OctaveUtils {
  
      /**
       * A variable name not to be listed by {@link #listVars(OctaveEngine)}. 
       */
      private static final String NARGIN = "__nargin__";
  
      /**
       * A variable name not to be listed by {@link #listVars(OctaveEngine)}. 
       */
      private static final String ANS    = "ans";
  
      private static final Random RANDOM = new Random();
  
      private OctaveUtils() {
          throw new UnsupportedOperationException("Do not instantiate");
      }
  
  
      /**
       * Returns the charset UTF-8 used throughout. 
       */
      public static Charset getUTF8() {
  	return Charset.forName("UTF-8");
      }
  
      /**
       * @param octave
       * @return list of variables
       */
      @edu.umd.cs.findbugs.annotations.SuppressWarnings
      (value = "VA_FORMAT_STRING_USES_NEWLINE", 
       justification = "Format string evaluates in octave independent of os. ")
      public static Collection<String> listVars(final OctaveEngine octave) {
          final String varName = randomVarName();
  	String evalStr = // %1 is varName 
  	    "%1$s = cell(0, 1);\n" + 
  	    "if strncmp(OCTAVE_VERSION(), \"3.0.\", 4)\n" + 
  	    "  %1$s_1 = whos -v;\n" + // version 3.0
  	    "else\n" + 
  	    "  %1$s_1 = whos;\n" + // version 3.2 (and other)
  	    "endif\n" + 
  	    "for %1$s_2 = 1 : numel(%1$s_1)\n" + 
  	    "  %1$s{%1$s_2} = %1$s_1(%1$s_2).name;\n" + 
  	    "endfor\n" + 
  	    "clear %1$s_1 %1$s_2\n";
          octave.eval(String.format(evalStr, varName));
          final OctaveCell data = octave.get(OctaveCell.class, varName);
          octave.eval("clear " + varName);
          final Collection<String> collection = new HashSet<String>();
          final Pattern pattern = Pattern.compile("javaoctave_[0-9a-f]{12}_eval");
          for (int i = 1; i <= data.getSize(2); ++i) {
              final String name = data.get(OctaveString.class, 1, i).getString();
              if (varName.equals(name) || 
  		NARGIN .equals(name) || 
  		ANS    .equals(name) || 
  		pattern.matcher(name).matches()) {
                  continue;
              }
              collection.add(name);
          }
          return collection;
      }
  
      @SuppressWarnings("checkstyle:magicnumber")
      // 30 is some number, compromize between security and performance 
      private static synchronized int nextInt() {
          return RANDOM.nextInt(1 << 30);
      }
  
  
      /**
       * Returns a variable with value not accessible. 
       *
       * @return a <code>String</code> value
       */
      private static String randomVarName() {
          return String.format("_OctaveUtils_%d", nextInt());
      }
  
  }