content: /*
   * Copyright 2015, 2024 StreamEx contributors
   *
   * 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 one.util.streamex;
  
  import java.util.Spliterator;
  import java.util.function.*;
  
  import static one.util.streamex.Internals.*;
  
  /**
   * @author Tagir Valeev
   */
  /* package */abstract class PairSpliterator<T, S extends Spliterator<T>, R, SS extends PairSpliterator<T, S, R, SS>>
          extends CloneableSpliterator<R, SS> {
      static final int MODE_PAIRS = 0;
      static final int MODE_MAP_FIRST = 1;
      static final int MODE_MAP_LAST = 2;
      static final int MODE_MAP_FIRST_OR_ELSE = 3;
      static final int MODE_MAP_LAST_OR_ELSE = 4;
      
      static final Sink<?> EMPTY = new Sink<>(null);
      // Common lock for all the derived spliterators
      final Object lock = new Object();
      final int mode;
      S source;
      @SuppressWarnings("unchecked")
      Sink<T> left = (Sink<T>) EMPTY;
      @SuppressWarnings("unchecked")
      Sink<T> right = (Sink<T>) EMPTY;
  
      static final class Sink<T> {
          Sink<T> other;
          private T payload = none();
          private final Object lock;
  
          Sink(Object lock) {
              this.lock = lock;
          }
  
          boolean push(T payload, BiConsumer<T, T> fn, boolean isLeft) {
              if (lock == null)
                  return false;
              T otherPayload;
              synchronized (lock) {
                  Sink<T> that = other;
                  if (that == null)
                      return false;
                  otherPayload = that.payload;
                  if (otherPayload == NONE) {
                      this.payload = payload;
                      return false;
                  }
                  other = null;
                  that.clear();
              }
              if (isLeft)
                  fn.accept(payload, otherPayload);
              else
                  fn.accept(otherPayload, payload);
              return true;
          }
  
          boolean connect(Sink<T> right, BiConsumer<T, T> fn) {
              if (lock == null)
                  return false;
              T a, b;
              synchronized (lock) {
                  Sink<T> leftLeft = this.other;
                  Sink<T> rightRight = right.other;
                  if (leftLeft == null || rightRight == null) {
                      if (rightRight != null)
                          rightRight.clear();
                      if (leftLeft != null)
                          leftLeft.clear();
                      return false;
                  }
                  rightRight.other = leftLeft;
                  leftLeft.other = rightRight;
                  if (leftLeft.payload == NONE || rightRight.payload == NONE)
                      return false;
                  a = leftLeft.payload;
                  b = rightRight.payload;
                  leftLeft.clear();
                  rightRight.clear();
              }
              fn.accept(a, b);
              return true;
          }
  
          void clear() {
              other = null;
              payload = none();
          }
      }
  
      PairSpliterator(S source, int mode, T headTail) {
          this.source = source;
          this.mode = mode;
          if (mode != MODE_PAIRS) {
              Sink<T> sink = new Sink<>(this.lock);
              Sink<T> other = new Sink<>(this.lock);
              sink.other = other;
              other.other = sink;
              other.push(headTail, null, true);
              if (mode == MODE_MAP_FIRST || mode == MODE_MAP_FIRST_OR_ELSE)
                  this.left = sink;
              else
                  this.right = sink;
          }
      }
      
      @Override
      public long estimateSize() {
          long size = source.estimateSize();
          if (size == Long.MAX_VALUE || size == 0)
              return size;
          return size - 1;
      }
  
      @Override
      public int characteristics() {
          return source.characteristics()
              & ((left == EMPTY && right == EMPTY ? SIZED : 0) | CONCURRENT | IMMUTABLE | ORDERED);
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public SS trySplit() {
          S prefixSource = (S) source.trySplit();
          if (prefixSource == null)
              return null;
          SS clone = doClone();
          Sink<T> left = new Sink<>(lock);
          Sink<T> right = new Sink<>(lock);
          clone.source = prefixSource;
          clone.right = right.other = left;
          this.left = left.other = right;
          return clone;
      }
  
      void finish(BiConsumer<T, T> fn, T cur) {
          Sink<T> r = right, l = left;
          right = left = null;
          if (l != null) {
              l.connect(r, fn);
          } else if (r != null) {
              r.push(cur, fn, true);
          }
      }
  
      static class PSOfRef<T, R> extends PairSpliterator<T, Spliterator<T>, R, PSOfRef<T, R>> implements
              Consumer<T>, TailSpliterator<R> {
          private static final Object HEAD_TAIL = new Object();
  
          private final BiFunction<? super T, ? super T, ? extends R> mapper;
          private T cur;
  
          PSOfRef(BiFunction<? super T, ? super T, ? extends R> mapper, Spliterator<T> source) {
              super(source, MODE_PAIRS, null);
              this.mapper = mapper;
          }
  
          // Must be called only if T == R
          @SuppressWarnings("unchecked")
          PSOfRef(Function<? super T, ? extends R> mapper, Spliterator<T> source, boolean first) {
              super(source, first ? MODE_MAP_FIRST : MODE_MAP_LAST, (T) HEAD_TAIL);
              BiFunction<? super T, ? super T, ?> m = first ?
                      ((a, b) -> a == HEAD_TAIL ? mapper.apply(b) : (T) b) :
                      ((a, b) -> b == HEAD_TAIL ? mapper.apply(a) : (T) a);
              this.mapper = (BiFunction<? super T, ? super T, ? extends R>) m;
          }
  
          @SuppressWarnings("unchecked")
          PSOfRef(Function<? super T, ? extends R> boundMapper, Function<? super T, ? extends R> elseMapper, Spliterator<T> source, boolean first) {
              super(source, first ? MODE_MAP_FIRST_OR_ELSE : MODE_MAP_LAST_OR_ELSE, (T) HEAD_TAIL);
              this.mapper = first ? 
                  ((a, b) -> a == HEAD_TAIL ? boundMapper.apply(b) : elseMapper.apply(b)) :
                  ((a, b) -> b == HEAD_TAIL ? boundMapper.apply(a) : elseMapper.apply(a));
          }
  
          @Override
          public void accept(T t) {
              cur = t;
          }
  
          private BiConsumer<T, T> fn(Consumer<? super R> action) {
              return (a, b) -> action.accept(mapper.apply(a, b));
          }
  
          @Override
          public boolean tryAdvance(Consumer<? super R> action) {
              Sink<T> l = left, r = right;
              if (l != null) {
                  left = null;
                  if (!source.tryAdvance(this)) {
                      right = null;
                      return l.connect(r, fn(action));
                  }
                  if (l.push(cur, fn(action), false))
                      return true;
              }
              T prev = cur;
              if (!source.tryAdvance(this)) {
                  right = null;
                  return r != null && r.push(prev, fn(action), true);
              }
              action.accept(mapper.apply(prev, cur));
              return true;
          }
  
          @Override
          public void forEachRemaining(Consumer<? super R> action) {
              BiConsumer<T, T> fn = fn(action);
              source.forEachRemaining(next -> {
                  if (left != null) {
                      left.push(cur = next, fn, false);
                      left = null;
                  } else {
                      action.accept(mapper.apply(cur, cur = next));
                  }
              });
              finish(fn, cur);
          }
  
          @Override
          public Spliterator<R> tryAdvanceOrTail(Consumer<? super R> action) {
              if (mode != MODE_MAP_FIRST || right != EMPTY) {
                  return tryAdvance(action) ? this : null;
              }
              if (left != null) {
                  Sink<T> l = left;
                  left = null;
                  source = TailSpliterator.tryAdvanceWithTail(source, this);
                  if (source == null) {
                      right = null;
                      return null;
                  }
                  if (l.push(cur, fn(action), false))
                      return this;
              }
              @SuppressWarnings("unchecked")
              Spliterator<R> s = (Spliterator<R>) source;
              source = null;
              return s;
          }
          
          @Override
          public Spliterator<R> forEachOrTail(Consumer<? super R> action) {
              if (mode != MODE_MAP_FIRST || right != EMPTY) {
                  forEachRemaining(action);
                  return null;
              }
              while (true) {
                  Spliterator<R> tail = tryAdvanceOrTail(action);
                  if (tail != this)
                      return tail;
              }
          }
      }
  
      static final class PSOfInt extends PairSpliterator<Integer, Spliterator.OfInt, Integer, PSOfInt> implements
              Spliterator.OfInt, IntConsumer {
          private final IntBinaryOperator mapper;
          private final IntUnaryOperator unaryMapper;
          private int cur;
  
          PSOfInt(IntBinaryOperator mapper, IntUnaryOperator unaryMapper, Spliterator.OfInt source, int mode) {
              super(source, mode, null);
              this.mapper = mapper;
              this.unaryMapper = unaryMapper;
          }
          
          @Override
          public void accept(int t) {
              cur = t;
          }
  
          private BiConsumer<Integer, Integer> fn(IntConsumer action) {
              switch (mode) {
              case MODE_MAP_FIRST:
                  return (a, b) -> action.accept(a == null ? unaryMapper.applyAsInt(b) : b);
              case MODE_MAP_LAST:
                  return (a, b) -> action.accept(b == null ? unaryMapper.applyAsInt(a) : a);
              default:
                  return (a, b) -> action.accept(mapper.applyAsInt(a, b));
              }
          }
  
          @Override
          public boolean tryAdvance(IntConsumer action) {
              Sink<Integer> l = left, r = right;
              if (l != null) {
                  left = null;
                  if (!source.tryAdvance(this)) {
                      right = null;
                      return l.connect(r, fn(action));
                  }
                  if (l.push(cur, fn(action), false))
                      return true;
              }
              int prev = cur;
              if (!source.tryAdvance(this)) {
                  right = null;
                  return r != null && r.push(prev, fn(action), true);
              }
              action.accept(mapper.applyAsInt(prev, cur));
              return true;
          }
  
          @Override
          public void forEachRemaining(IntConsumer action) {
              BiConsumer<Integer, Integer> fn = fn(action);
              source.forEachRemaining((int next) -> {
                  if (left != null) {
                      left.push(cur = next, fn, false);
                      left = null;
                  } else {
                      action.accept(mapper.applyAsInt(cur, cur = next));
                  }
              });
              finish(fn, cur);
          }
      }
  
      static final class PSOfLong extends PairSpliterator<Long, Spliterator.OfLong, Long, PSOfLong> implements
              Spliterator.OfLong, LongConsumer {
          private final LongBinaryOperator mapper;
          private final LongUnaryOperator unaryMapper;
          private long cur;
  
          PSOfLong(LongBinaryOperator mapper, LongUnaryOperator unaryMapper, Spliterator.OfLong source, int mode) {
              super(source, mode, null);
              this.mapper = mapper;
              this.unaryMapper = unaryMapper;
          }
  
          @Override
          public void accept(long t) {
              cur = t;
          }
  
          private BiConsumer<Long, Long> fn(LongConsumer action) {
              switch (mode) {
              case MODE_MAP_FIRST:
                  return (a, b) -> action.accept(a == null ? unaryMapper.applyAsLong(b) : b);
              case MODE_MAP_LAST:
                  return (a, b) -> action.accept(b == null ? unaryMapper.applyAsLong(a) : a);
              default:
                  return (a, b) -> action.accept(mapper.applyAsLong(a, b));
              }
          }
  
          @Override
          public boolean tryAdvance(LongConsumer action) {
              Sink<Long> l = left, r = right;
              if (l != null) {
                  left = null;
                  if (!source.tryAdvance(this)) {
                      right = null;
                      return l.connect(r, fn(action));
                  }
                  if (l.push(cur, fn(action), false))
                      return true;
              }
              long prev = cur;
              if (!source.tryAdvance(this)) {
                  right = null;
                  return r != null && r.push(prev, fn(action), true);
              }
              action.accept(mapper.applyAsLong(prev, cur));
              return true;
          }
  
          @Override
          public void forEachRemaining(LongConsumer action) {
              BiConsumer<Long, Long> fn = fn(action);
              source.forEachRemaining((long next) -> {
                  if (left != null) {
                      left.push(cur = next, fn, false);
                      left = null;
                  } else {
                      action.accept(mapper.applyAsLong(cur, cur = next));
                  }
              });
              finish(fn, cur);
          }
      }
  
      static final class PSOfDouble extends PairSpliterator<Double, Spliterator.OfDouble, Double, PSOfDouble> implements
              Spliterator.OfDouble, DoubleConsumer {
          private final DoubleBinaryOperator mapper;
          private final DoubleUnaryOperator unaryMapper;
          private double cur;
  
          PSOfDouble(DoubleBinaryOperator mapper, DoubleUnaryOperator unaryMapper, Spliterator.OfDouble source, int mode) {
              super(source, mode, null);
              this.mapper = mapper;
              this.unaryMapper = unaryMapper;
          }
  
          @Override
          public void accept(double t) {
              cur = t;
          }
  
          private BiConsumer<Double, Double> fn(DoubleConsumer action) {
              switch (mode) {
              case MODE_MAP_FIRST:
                  return (a, b) -> action.accept(a == null ? unaryMapper.applyAsDouble(b) : b);
              case MODE_MAP_LAST:
                  return (a, b) -> action.accept(b == null ? unaryMapper.applyAsDouble(a) : a);
              default:
                  return (a, b) -> action.accept(mapper.applyAsDouble(a, b));
              }
          }
  
          @Override
          public boolean tryAdvance(DoubleConsumer action) {
              Sink<Double> l = left, r = right;
              if (l != null) {
                  left = null;
                  if (!source.tryAdvance(this)) {
                      right = null;
                      return l.connect(r, fn(action));
                  }
                  if (l.push(cur, fn(action), false))
                      return true;
              }
              double prev = cur;
              if (!source.tryAdvance(this)) {
                  right = null;
                  return r != null && r.push(prev, fn(action), true);
              }
              action.accept(mapper.applyAsDouble(prev, cur));
              return true;
          }
  
          @Override
          public void forEachRemaining(DoubleConsumer action) {
              BiConsumer<Double, Double> fn = fn(action);
              source.forEachRemaining((double next) -> {
                  if (left != null) {
                      left.push(cur = next, fn, false);
                      left = null;
                  } else {
                      action.accept(mapper.applyAsDouble(cur, cur = next));
                  }
              });
              finish(fn, cur);
          }
      }
  }
  