/*
 * Copyright 2008 Google Inc.
 *
 * 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.google.gwt.gen2.table.client;

import com.google.gwt.gen2.table.client.TableModelHelper.*;

import java.util.*;

/**
 * A {@link MutableTableModel} used when the data source can be accessed
 * synchronously.
 */
public abstract class ClientTableModel extends MutableTableModel<List<Object>> {
    /**
     * Convenience class to support custom iterators.
     */
    private abstract static class StubIterator<E> implements Iterator<E> {
        int index;
        E next;
        boolean done = false;

        protected abstract E computeNext();

        public boolean hasNext() {
            if ( done ) {
                return false;
            }
            if ( next == null ) {
                next = computeNext();
                if ( next == null ) {
                    done = true;
                    return false;
                }
            }
            return true;
        }

        public E next() {
            if ( !hasNext() ) {
                throw new NoSuchElementException();
            } else {
                E accum = next;
                next = null;
                return accum;
            }
        }

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

    private class ColumnIterator extends StubIterator<Object> {
        private int row = 0;

        @Override
        public Object computeNext() {
            return getCell( row, index++ );
        }
    }

    /**
     * An iterator over the rows of of client data.
     */
    private class RowIterator extends StubIterator<List<Object>> {
        private int max;

        public RowIterator( Request request ) {
            index = request.getStartRow();
            if ( request.getNumRows() == -1 ) {
                max = Integer.MAX_VALUE;
            } else {
                max = request.getNumRows() + index;
            }
        }

        @Override
        protected List<Object> computeNext() {
            // Reset column iterator rather than creating new one.
            final ColumnIterator colIt = new ColumnIterator();
            colIt.index = 0;
            colIt.row = index++;
            colIt.done = false;
            colIt.next = null;

            // Now check for next.
            if ( colIt.hasNext() && colIt.row < max ) {
                List<Object> next = new ArrayList<Object>();
                while ( colIt.hasNext() ) {
                    next.add( colIt.next() );
                }
                return next;
            } else {
                return null;
            }
        }
    }

    /**
     * Get the value for a given cell. Return null if no more values are
     * available.
     *
     * @param rowNum the row index
     * @param colNum the column index
     *
     * @return the value at the given row and column
     */
    public abstract Object getCell( int rowNum, int colNum );

    @Override
    public void requestRows( Request request, Callback<List<Object>> callback ) {
        final RowIterator rowIter = new RowIterator( request );
        Response<List<Object>> response = new Response<List<Object>>() {
            @Override
            public Iterator<List<Object>> getRowValues() {
                return rowIter;
            }
        };
        callback.onRowsReady( request, response );
    }
}