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

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.JImmutableStack;
import org.javimmutable.collections.SplitableIterator;
import org.javimmutable.collections.common.StreamConstants;
import org.javimmutable.collections.cursors.Cursors;
import org.javimmutable.collections.cursors.SequenceCursor;
import org.javimmutable.collections.cursors.SingleValueCursor;
import org.javimmutable.collections.cursors.StandardCursor;
import org.javimmutable.collections.iterators.EmptyIterator;
import org.javimmutable.collections.iterators.SequenceIterator;
import org.javimmutable.collections.iterators.SingleValueIterator;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;
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 JImmutableArrayList or JImmutableTreeList
 * instead, but this class is significantly faster when its limitations are acceptable.
 */
@Immutable
public abstract class JImmutableLinkedStack
{
    private static final EmptySequence EMPTY = new EmptySequence();

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

    public static  JImmutableStack of(T value)
    {
        return new Single<>(value);
    }

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

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

    private static abstract class Base
        implements JImmutableStack
    {
        @Nonnull
        public abstract JImmutableStack insert(@Nullable V value);

        @Nonnull
        public abstract JImmutableStack getTail();

        @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) && Cursors.areEqual(cursor(), ((JImmutableStack)o).cursor());
        }

        @Override
        public int hashCode()
        {
            return Cursors.computeHashCode(cursor());
        }

        @Override
        public String toString()
        {
            return Cursors.makeString(cursor());
        }
    }

    private static class EmptySequence
        extends Base
    {
        public boolean isEmpty()
        {
            return true;
        }

        public V getHead()
        {
            throw new UnsupportedOperationException();
        }

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

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

        @Nonnull
        public Cursor cursor()
        {
            return StandardCursor.of();
        }

        @Nonnull
        @Override
        public SplitableIterator iterator()
        {
            return EmptyIterator.of();
        }

        @Override
        public void checkInvariants()
        {
            //no invariants
        }
    }

    private static class Single
        extends Base
    {
        private final V value;

        private Single(V value)
        {
            this.value = value;
        }

        public boolean isEmpty()
        {
            return false;
        }

        public V getHead()
        {
            return value;
        }

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

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

        @Nonnull
        public Cursor cursor()
        {
            return SingleValueCursor.of(value);
        }

        @Nonnull
        @Override
        public SplitableIterator iterator()
        {
            return SingleValueIterator.of(value);
        }

        @Override
        public void checkInvariants()
        {
            //no invariants
        }
    }

    private static class Chain
        extends Base
    {
        private final V value;
        private final JImmutableStack next;

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

        public boolean isEmpty()
        {
            return false;
        }

        public V getHead()
        {
            return value;
        }

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

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

        @Override
        @Nonnull
        public Cursor cursor()
        {
            return SequenceCursor.of(this);
        }

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

        @Override
        public void checkInvariants()
        {
            //no invariants
        }
    }
}