/*
 * 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.event.shared.*;
import com.google.gwt.gen2.table.client.TableModelHelper.*;
import com.google.gwt.gen2.table.event.client.*;

/**
 * A class to retrieve row data to be used in a table.
 *
 * @param <RowType> the data type of the row values
 */
public abstract class TableModel<RowType> implements HasRowCountChangeHandlers {
    /**
     * Callback for {@link TableModel}. Every {@link Request} should be associated
     * with a {@link TableModel.Callback} that should be called after a
     * {@link Response} is generated.
     *
     * @param <RowType> the data type of the row values
     */
    public static interface Callback<RowType> {
        /**
         * Called when an error occurs and the rows cannot be loaded.
         *
         * @param caught the exception that was thrown
         */
        void onFailure( Throwable caught );

        /**
         * Consume the data created by {@link TableModel} in response to a Request.
         *
         * @param request  the request
         * @param response the response
         */
        void onRowsReady( Request request, Response<RowType> response );
    }

    /**
     * Use the ALL_ROWS value in place of the numRows variable when requesting all
     * rows.
     */
    public static final int ALL_ROWS = -1;

    /**
     * Indicates that the number of rows is unknown, and therefore unbounded.
     */
    public static final int UNKNOWN_ROW_COUNT = -1;

    /**
     * The manager of events.
     */
    private HandlerManager handlers = new HandlerManager( this );

    /**
     * The total number of rows available in the model.
     */
    private int rowCount = UNKNOWN_ROW_COUNT;

    public HandlerRegistration addRowCountChangeHandler( RowCountChangeHandler handler ) {
        return addHandler( RowCountChangeEvent.TYPE, handler );
    }

    /**
     * Return the total number of rows. If the number is not known, return
     * {@link #UNKNOWN_ROW_COUNT}.
     *
     * @return the total number of rows, or {@link #UNKNOWN_ROW_COUNT}
     */
    public int getRowCount() {
        return rowCount;
    }

    /**
     * Generate a {@link Response} based on a specific {@link Request}. The
     * response is passed into the {@link Callback}.
     *
     * @param request  the {@link Request} for row data
     * @param callback the {@link Callback} to use for the {@link Response}
     */
    public abstract void requestRows( Request request, Callback<RowType> callback );

    /**
     * Set the total number of rows.
     *
     * @param rowCount the row count
     */
    public void setRowCount( int rowCount ) {
        if ( this.rowCount != rowCount ) {
            int oldRowCount = this.rowCount;
            this.rowCount = rowCount;
            fireEvent( new RowCountChangeEvent( oldRowCount, rowCount ) );
        }
    }

    /**
     * Adds this handler to the widget.
     *
     * @param key     the event key
     * @param handler the handler
     */
    protected <HandlerType extends EventHandler> HandlerRegistration addHandler( AbstractEvent.Type<?, HandlerType> key, final HandlerType handler ) {
        return handlers.addHandler( key, handler );
    }

    /**
     * Fires an event.
     *
     * @param event the event
     */
    protected void fireEvent( AbstractEvent event ) {
        handlers.fireEvent( event );
    }

    /**
     * Returns this widget's {@link HandlerManager} used for event management.
     */
    protected final HandlerManager getHandlerManager() {
        return handlers;
    }

    /**
     * Is the event handled by one or more handlers?
     */
    protected final boolean isEventHandled( AbstractEvent.Type key ) {
        return handlers.isEventHandled( key );
    }

    /**
     * Removes the given handler from the specified event key. Normally,
     * applications should call {@link HandlerRegistration#removeHandler()}
     * instead. This method is provided primary to support the deprecated
     * listeners api.
     *
     * @param key     the event key
     * @param handler the handler
     */
    protected <T extends EventHandler> void removeHandler( AbstractEvent.Type<?, T> key, final T handler ) {
        handlers.removeHandler( key, handler );
    }
}