package de.saring.exerciseviewer.parser;

import de.saring.exerciseviewer.core.EVException;

import java.util.ArrayList;
import java.util.List;
import java.util.ServiceLoader;

/**
 * This factory will always returns the proper ExerciseParser implementation
 * for the specified filename. This factory uses the singleton pattern.
 * <p/>
 * New parsers can be added just by implementing the ExerciseParser interfaces
 * and registering them in the META-INF/service directory. New parsers must not
 * be part of the SportsTracker-Jar, the parser-Jar just needs to be added to
 * the application classpath.
 * <p/>
 * The parsers can also be implemented as Groovy scripts, but these needs to be
 * compiled to class-Files too. It would also be possible to run the Groovy
 * parsers without compile using the GroovyClassLoader, but the disadvantages
 * are slower performance and no syntax check via the compiler.
 *
 * @author Stefan Saring
 * @version 2.0
 */
public class ExerciseParserFactory {

    /**
     * The singleton instance.
     */
    private static ExerciseParserFactory instance;

    /**
     * The ServiceLoader instance for all ExerciseParser implementations.
     */
    private final ServiceLoader<ExerciseParser> exerciseParserLoader;

    /**
     * Creates a new instance of ExerciseParserFactory and loads all
     * ExerciseParser implementations available in the classpath.
     */
    private ExerciseParserFactory() {
        exerciseParserLoader = ServiceLoader.load(ExerciseParser.class);
    }

    /**
     * Returns the instance of the appropriate exercise parser for the specified
     * exercise filename. The proper parser will be assigned by using the
     * filename suffix.
     *
     * @param filename name of the exercise file to parse
     * @return instance of the appropriate exercise parser
     * @throws EVException when no proper parser has been found
     */
    public static ExerciseParser getParser(String filename) throws EVException {
        createInstance();

        // return the parser implementation which matches the filename suffix
        for (ExerciseParser parser : instance.exerciseParserLoader) {
            for (String suffix : parser.getInfo().getSuffixes()) {
                if (filename.endsWith("." + suffix)) {
                    return parser;
                }
            }
        }

        throw new EVException("No parser has been found for filename '" + filename + "' ...");
    }

    /**
     * Returns the list of all ExerciseParserInfo objects for all available parser
     * implementations (useful e.g. for File Open dialogs for list of suffixes).
     *
     * @return list of ExerciseParserInfo objects for all parser implementations
     */
    public static List<ExerciseParserInfo> getExerciseParserInfos() {
        createInstance();

        List<ExerciseParserInfo> lInfos = new ArrayList<>();
        for (ExerciseParser parser : instance.exerciseParserLoader) {
            lInfos.add(parser.getInfo());
        }
        return lInfos;
    }

    /**
     * Creates the singleton instance of the factory when not done yet.
     */
    private static synchronized void createInstance() {
        if (instance == null) {
            instance = new ExerciseParserFactory();
        }
    }
}