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/*******************************************************************************
 *
 * Copyright (c) 2004-2009 Oracle Corporation.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * 
 *    Kohsuke Kawaguchi
 *
 *
 *******************************************************************************/ 

package hudson.util;

import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.ListIterator;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Set;
import java.util.HashSet;

/**
 * Varios {@link Iterator} implementations.
 *
 * @author Kohsuke Kawaguchi
 * @see AdaptedIterator
 */
public class Iterators {

    /**
     * Returns the empty iterator.
     */
    public static  Iterator empty() {
        return Collections.emptyList().iterator();
    }

    /**
     * Produces {A,B,C,D,E,F} from {{A,B},{C},{},{D,E,F}}.
     */
    public static abstract class FlattenIterator implements Iterator {

        private final Iterator core;
        private Iterator cur;

        protected FlattenIterator(Iterator core) {
            this.core = core;
            cur = Collections.emptyList().iterator();
        }

        protected FlattenIterator(Iterable core) {
            this(core.iterator());
        }

        protected abstract Iterator expand(T t);

        public boolean hasNext() {
            while (!cur.hasNext()) {
                if (!core.hasNext()) {
                    return false;
                }
                cur = expand(core.next());
            }
            return true;
        }

        public U next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            return cur.next();
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    /**
     * Creates a filtered view of another iterator.
     *
     * @since 1.150
     */
    public static abstract class FilterIterator implements Iterator {

        private final Iterator core;
        private T next;
        private boolean fetched;

        protected FilterIterator(Iterator core) {
            this.core = core;
        }

        protected FilterIterator(Iterable core) {
            this(core.iterator());
        }

        private void fetch() {
            while (!fetched && core.hasNext()) {
                T n = core.next();
                if (filter(n)) {
                    next = n;
                    fetched = true;
                }
            }
        }

        /**
         * Filter out items in the original collection.
         *
         * @return true to leave this item and return this item from this
         * iterator. false to hide this item.
         */
        protected abstract boolean filter(T t);

        public boolean hasNext() {
            fetch();
            return fetched;
        }

        public T next() {
            fetch();
            if (!fetched) {
                throw new NoSuchElementException();
            }
            fetched = false;
            return next;
        }

        public void remove() {
            core.remove();
        }
    }

    /**
     * Remove duplicates from another iterator.
     */
    public static final class DuplicateFilterIterator extends FilterIterator {

        private final Set seen = new HashSet();

        public DuplicateFilterIterator(Iterator core) {
            super(core);
        }

        public DuplicateFilterIterator(Iterable core) {
            super(core);
        }

        protected boolean filter(T t) {
            return seen.add(t);
        }
    }

    /**
     * Returns the {@link Iterable} that lists items in the reverse order.
     *
     * @since 1.150
     */
    public static  Iterable reverse(final List lst) {
        return new Iterable() {
            public Iterator iterator() {
                final ListIterator itr = lst.listIterator(lst.size());
                return new Iterator() {
                    public boolean hasNext() {
                        return itr.hasPrevious();
                    }

                    public T next() {
                        return itr.previous();
                    }

                    public void remove() {
                        itr.remove();
                    }
                };
            }
        };
    }

    /**
     * Returns a list that represents [start,end).
     *
     * For example sequence(1,5,1)={1,2,3,4}, and sequence(7,1,-2)={7.5,3}
     *
     * @since 1.150
     */
    public static List sequence(final int start, int end, final int step) {

        final int size = (end - start) / step;
        if (size < 0) {
            throw new IllegalArgumentException("List size is negative");
        }

        return new AbstractList() {
            public Integer get(int index) {
                if (index < 0 || index >= size) {
                    throw new IndexOutOfBoundsException();
                }
                return start + index * step;
            }

            public int size() {
                return size;
            }
        };
    }

    public static List sequence(int start, int end) {
        return sequence(start, end, 1);
    }

    /**
     * The short cut for {@code reverse(sequence(start,end,step))}.
     *
     * @since 1.150
     */
    public static List reverseSequence(int start, int end, int step) {
        return sequence(end - 1, start - 1, -step);
    }

    public static List reverseSequence(int start, int end) {
        return reverseSequence(start, end, 1);
    }

    /**
     * Casts {@link Iterator} by taking advantage of its covariant-ness.
     */
    @SuppressWarnings({"unchecked" })
    public static  Iterator cast(Iterator itr) {
        return (Iterator) itr;
    }

    /**
     * Casts {@link Iterable} by taking advantage of its covariant-ness.
     */
    @SuppressWarnings({"unchecked" })
    public static  Iterable cast(Iterable itr) {
        return (Iterable) itr;
    }

    /**
     * Returns an {@link Iterator} that only returns items of the given subtype.
     */
    @SuppressWarnings({"unchecked" })
    public static  Iterator subType(Iterator itr, final Class type) {
        return (Iterator) new FilterIterator(itr) {
            protected boolean filter(U u) {
                return type.isInstance(u);
            }
        };
    }

    /**
     * Creates a read-only mutator that disallows {@link Iterator#remove()}.
     */
    public static  Iterator readOnly(final Iterator itr) {
        return new Iterator() {
            public boolean hasNext() {
                return itr.hasNext();
            }

            public T next() {
                return itr.next();
            }

            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    /**
     * Wraps another iterator and throws away nulls.
     */
    public static  Iterator removeNull(final Iterator itr) {
        return new FilterIterator(itr) {
            @Override
            protected boolean filter(T t) {
                return t != null;
            }
        };
    }

    /**
     * Returns an {@link Iterable} that iterates over all the given
     * {@link Iterable}s.
     *
     *  That is, this creates {A,B,C,D} from {A,B},{C,D}.
     */
    public static  Iterable sequence(final Iterable... iterables) {
        return new Iterable() {
            public Iterator iterator() {
                return new FlattenIterator>(Arrays.asList(iterables)) {
                    protected Iterator expand(Iterable iterable) {
                        return cast(iterable).iterator();
                    }
                };
            }
        };
    }
}