package com.github.davidmoten.rx.internal.operators;
   
   import java.util.regex.Pattern;
   
   import com.github.davidmoten.rx.Functions;
   
   import rx.Observable.Transformer;
   import rx.Subscriber;
   import rx.functions.Func0;
  import rx.functions.Func2;
  import rx.functions.Func3;
  
  public final class TransformerStringSplit {
  
  	public static <T> Transformer<String, String> split(final String pattern, final Pattern compiledPattern) {
  		Func0<String> initialState = Functions.constant0(null);
  		Func3<String, String, Subscriber<String>, String> transition = new Func3<String, String, Subscriber<String>, String>() {
  
  			@Override
  			public String call(String leftOver, String s, Subscriber<String> observer) {
                  // prepend leftover to the string before splitting
  			    if (leftOver != null) {
  			        s = leftOver + s;
  			    }
  			    
  				String[] parts;
  				if (compiledPattern != null) {
  					parts = compiledPattern.split(s, -1);
  				} else {
  					parts = s.split(pattern, -1);
  				}
  
  				// can emit all parts except the last part because it hasn't
  				// been terminated by the pattern/end-of-stream yet
  				for (int i = 0; i < parts.length - 1; i++) {
  					if (observer.isUnsubscribed()) {
  						// won't be used so can return null
  						return null;
  					}
  					observer.onNext(parts[i]);
  				}
  
  				// we have to assign the last part as leftOver because we
  				// don't know if it has been terminated yet
  				return parts[parts.length - 1];
  			}
  		};
  
  		Func2<String, Subscriber<String>, Boolean> completion = new Func2<String, Subscriber<String>, Boolean>() {
  
  			@Override
  			public Boolean call(String leftOver, Subscriber<String> observer) {
  				if (leftOver != null && !observer.isUnsubscribed())
  					observer.onNext(leftOver);
  				// TODO is this check needed?
  				if (!observer.isUnsubscribed())
  					observer.onCompleted();
  				return true;
  			}
  		};
  		return com.github.davidmoten.rx.Transformers.stateMachine(initialState, transition, completion);
  	}
  
  }