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// Burton Computer Corporation
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package org.javimmutable.collections.list;

import org.javimmutable.collections.JImmutableStack;
import org.javimmutable.collections.SplitableIterator;
import org.javimmutable.collections.common.StreamConstants;
import org.javimmutable.collections.iterators.IteratorHelper;
import org.javimmutable.collections.iterators.SequenceIterator;
import org.javimmutable.collections.serialization.JImmutableStackProxy;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

/**
 * Singly linked list implementation of JImmutableStack that stores and retrieves values
 * in the reverse order of the corresponding add() method calls.  If forward or random
 * access to stored values is required use JImmutableList instead, but this class may be
 * significantly faster when its limitations are acceptable.
 */
@Immutable
public class JImmutableLinkedStack
    implements JImmutableStack,
               Serializable
{
    @SuppressWarnings("unchecked")
    private static final JImmutableLinkedStack EMPTY = new JImmutableLinkedStack(null, null);
    private static final long serialVersionUID = -121805;

    private final V value;
    private final JImmutableLinkedStack next;

    private JImmutableLinkedStack(V value,
                                  JImmutableLinkedStack next)
    {
        this.value = value;
        this.next = next;
    }

    @SuppressWarnings("unchecked")
    public static  JImmutableStack of()
    {
        return EMPTY;
    }

    @SuppressWarnings("unchecked")
    public static  JImmutableStack of(T value)
    {
        return new JImmutableLinkedStack<>(value, EMPTY);
    }

    public static  JImmutableStack of(List values)
    {
        JImmutableStack list = of();
        for (T value : values) {
            list = list.insert(value);
        }
        return list;
    }

    @SafeVarargs
    public static  JImmutableStack of(T... values)
    {
        JImmutableStack list = of();
        for (T value : values) {
            list = list.insert(value);
        }
        return list;
    }

    public boolean isEmpty()
    {
        return next == null;
    }

    @Override
    public boolean isNonEmpty()
    {
        return next != null;
    }

    public V getHead()
    {
        if (next == null) {
            throw new UnsupportedOperationException();
        }
        return value;
    }

    @Nonnull
    @Override
    public JImmutableStack getTail()
    {
        if (next == null) {
            return this;
        } else {
            return next;
        }
    }

    @Nonnull
    @Override
    public JImmutableStack insert(@Nullable V value)
    {
        return new JImmutableLinkedStack<>(value, this);
    }

    @Nonnull
    @Override
    public JImmutableStack remove()
    {
        return getTail();
    }

    @Override
    public int getSpliteratorCharacteristics()
    {
        return StreamConstants.SPLITERATOR_ORDERED;
    }

    public List makeList()
    {
        final List answer = new ArrayList<>();
        JImmutableStack next = this;
        while (!next.isEmpty()) {
            answer.add(next.getHead());
            next = next.getTail();
        }
        return answer;
    }

    @Override
    public boolean equals(Object o)
    {
        return (o instanceof JImmutableStack) && IteratorHelper.iteratorEquals(iterator(), ((JImmutableStack)o).iterator());
    }

    @Override
    public int hashCode()
    {
        return IteratorHelper.iteratorHashCode(iterator());
    }

    @Override
    public String toString()
    {
        return IteratorHelper.iteratorToString(iterator());
    }

    @Nonnull
    @Override
    public JImmutableStack getInsertableSelf()
    {
        return this;
    }

    @Nonnull
    @Override
    public SplitableIterator iterator()
    {
        return SequenceIterator.iterator(this);
    }

    @Override
    public void checkInvariants()
    {
        if ((next == null) && !(this == EMPTY)) {
            throw new IllegalStateException();
        }
    }

    private Object writeReplace()
    {
        return new JImmutableStackProxy(this);
    }
}