/**
 *
 * Copyright
 * 2009-2015 Jayway Products AB
 * 2016-2017 Föreningen Sambruk
 *
 * Licensed under AGPL, Version 3.0 (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.gnu.org/licenses/agpl.txt
 *
 * 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 se.streamsource.streamflow.web.management;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.qi4j.api.util.ListMap;

/**
 * TODO
 */
public class UpdateRules
{
    // to-version -> List of from-versions
    ListMap<String, String> versionChanges = new ListMap<String, String>();

    // key=fromversion->toversion value=list of rules for that transition
    ListMap<String, UpdateRule> rules = new ListMap<String, UpdateRule>();

    public void addRule( UpdateRule updateRule)
    {
        versionChanges.add( updateRule.toVersion(), updateRule.fromVersion() );
        rules.add( updateRule.fromVersion() + "->" + updateRule.toVersion(), updateRule );
    }

    public Iterable<UpdateRule> getRules( String fromVersion, String toVersion )
    {
        try
        {
            String ruleToVersion = findHighestToVersion( toVersion );

            return getMigrationRules( fromVersion, ruleToVersion );
        }
        catch( IllegalArgumentException e )
        {
            return null;
        }
    }

    private List<UpdateRule> getMigrationRules( String fromVersion, String toVersion )
    {
        List<String> list = versionChanges.get( toVersion );

        if( list == null )
        {
            return null; // No possible rules for this transition
        }

        for( String possibleFromVersion : list )
        {
            if( fromVersion.equals( possibleFromVersion ) )
            {
                // We found the end of the version transitions - return rules, but filter on entity type
                return new ArrayList<UpdateRule>( getRulesForTransition( fromVersion, toVersion ) );
            }
            else
            {
                List<UpdateRule> migrationRules = getMigrationRules( fromVersion, possibleFromVersion );
                if( migrationRules == null )
                {
                    continue; // Wrong transition - try another one
                }

                // Add entity-filtered rules from this part of the version transition
                migrationRules.addAll( getRulesForTransition( possibleFromVersion, toVersion ) );
                return migrationRules;
            }
        }
        return null;
    }

    /**
     * Find highest version below the given to-version for which there are rules registered.
     *
     * @param toVersion The ending toVersion in the search.
     *
     * @return The highest version below the given version for which there are rules registered.
     */
    private String findHighestToVersion( String toVersion )
    {
        if( versionChanges.get( toVersion ) == null )
        {
            List<String> toVersions = new ArrayList<String>( versionChanges.keySet() );
            Collections.sort(toVersions, Collections.reverseOrder());
            for( String version : toVersions )
            {
                if( version.compareTo( toVersion ) <= 0 )
                {
                    // Found version to change to
                    return version;
                }
            }
            throw new IllegalArgumentException( "No version found in rules that matches the given to-version:" + toVersion );
        }
        else
        {
            return toVersion;
        }
    }

    private List<UpdateRule> getRulesForTransition( String fromVersion, String toVersion )
    {
        return rules.get( fromVersion + "->" + toVersion );
    }
}