/*
 * Copyright 2000-2017 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.jetbrains.python.toolbox;

import com.intellij.util.containers.ContainerUtil;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.util.Collections;
import java.util.Iterator;

/**
 * Iterable that splices other iterables and iterates over them sequentially.
 * User: dcheryasov
 * Date: Nov 20, 2009 8:01:23 AM
 */
public class ChainIterable<T> extends ChainedListBase<Iterable<T>> implements Iterable<T> {

  public ChainIterable(@Nullable Iterable<T> initial) {
    super(initial);
  }

  public ChainIterable() {
    super(null);
  }
  
  public ChainIterable(@NotNull T initial) {
    super(Collections.singleton(initial));
  }


  @Override
  public ChainIterable<T> add(@NotNull Iterable<T> another) {
    return (ChainIterable<T>)super.add(another);
  }

  /**
   * Apply wrapper to another and add the result. Convenience to avoid cluttering code with apply() calls.
   * @param wrapper
   * @param another
   * @return
   */
  public ChainIterable<T> addWith(FP.Lambda1<Iterable<T>, Iterable<T>> wrapper, Iterable<T> another) {
    return (ChainIterable<T>)super.add(wrapper.apply(another));
  }

  /**
   * Convenience: add an item wrapping it into a SingleIterable behind the scenes.
   */
  public ChainIterable<T> addItem(@NotNull T item) {
    return add(Collections.singleton(item));
  }

  /**
   * Convenience, works without ever touching an iterator.
   * @return true if the chain contains at least one iterable (but all iterables in the chain may happen to be empty).
   */
  public boolean isEmpty() {
    return (myPayload == null);
  }

  @Override
  public Iterator<T> iterator() {
    return new ChainIterator<>(this);
  }

  @Override
  public String toString() {
    return FP.fold(new FP.StringCollector<>(), this, new StringBuilder()).toString();
  }

  private static class ChainIterator<T> implements Iterator<T> {
  
    private ChainedListBase<Iterable<T>> myLink; // link of the chain we're currently at
    @NotNull private Iterator<T> myCurrent = ContainerUtil.emptyIterator();
  
    public ChainIterator(@Nullable ChainedListBase<Iterable<T>> initial) {
      myLink = initial;
    }
  
    // returns either null or a non-exhausted iterator.
    @NotNull
    private Iterator<T> getCurrent() {
      while (!myCurrent.hasNext() && myLink != null) { // fix myCurrent
        if (myLink.myPayload != null) {
          myCurrent = myLink.myPayload.iterator();
        }
        myLink= myLink.myNext;
      }
      return myCurrent;
    }
  
    @Override
    public boolean hasNext() {
      return getCurrent().hasNext();
    }
  
    @Override
    public T next() {
      return getCurrent().next();
    }
  
    @Override
    public void remove() {
      throw new UnsupportedOperationException("Cannot remove from ChainIterator");
    }
  }
}