package pt.ist.fenixframework.backend;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import pt.ist.fenixframework.Config;
import pt.ist.fenixframework.ConfigError;
import pt.ist.fenixframework.atomic.ContextFactory;
import pt.ist.fenixframework.dml.CodeGenerator;

/**
 * This class represents a feature that all DML code generators must implement: All {@link
 * pt.ist.fenixframework.dml.CodeGenerator} implementations should generate a class named {@link
 * pt.ist.fenixframework.backend.CurrentBackEndId} (see {@link
 * pt.ist.fenixframework.dml.CodeGenerator#generateBackEndId}) that implements this abstract class
 * and provides information about the current backend that is being used to manage the domain model.
 * This is also part of the support required for configuration by convention.
 *
 * @see pt.ist.fenixframework.FenixFramework
 */
public abstract class BackEndId {
    private static final Logger logger = LoggerFactory.getLogger(BackEndId.class);

    /**
     * This map holds generic parameters that each module may wish to add.  It does not support
     * <code>null</code> values.
     */
    private final Map<String, String> params = new ConcurrentHashMap<String, String>();

    /**
     *  Adds a parameter to the map of parameters.  The typical usage of this method is during the
     *  initialization of this class, to store parameters, e.g., a module may register that is
     *  active by setting a key with a given value.
     */
    protected final String setParam(String key, String value) {
        return this.params.put(key, value);
    }

    /**
     * Search for a parameter value given its key.
     * param key The parameter to lookup.
     * @return null if the corresponding key does not exist.
     */
    public final String getParam(String key) {
        return this.params.get(key);
    }

    /**
     * Get the (unique) name of this {@link BackEnd}.  The String returned by this method should
     * contain only valid characters in a filename (because it can be used for configuration by
     * convention (see {@link pt.ist.fenixframework.FenixFramework}).
     *
     * @see pt.ist.fenixframework.FenixFramework
     */
    public abstract String getBackEndName();

    /**
     * Get the Class instance that represents the default configuration class to use for this
     * backend.  This class is used to instantite a {@link Config} instance is none is explicitly
     * indicated.
     */
    public abstract Class<? extends Config> getDefaultConfigClass();

    /**
     * Get the Class instance for the factory that creates {@link
     * pt.ist.fenixframework.atomic.AtomicContext}s.  These contexts are backend-specific (thus the
     * backend provides the factory), because they control the logic required to execute a {@link
     * java.util.concurrent.Callable} within a transactional context.
     */
    public abstract Class<? extends ContextFactory> getAtomicContextFactoryClass();
    
    /**
     *  Lookup via reflection the {@link pt.ist.fenixframework.backend.CurrentBackEndId} class and
     *  return an instance of it.
     *
     * @throws ConfigError if the expected class does not exit, or it does not extend the BackEndId
     * class
     */
    public static final BackEndId getBackEndId() throws ConfigError {
        Exception ex = null;
        try {
            Class<CurrentBackEndId> currentBackEndIdClass =
                (Class<CurrentBackEndId>)Class.forName(CurrentBackEndId.class.getName());
            BackEndId beId = (BackEndId)currentBackEndIdClass.newInstance();
            return beId;
        } catch (ClassNotFoundException e) {
            ex = e;
        } catch (InstantiationException e) {
            ex = e;
        } catch (IllegalAccessException e) {
            ex = e;
        }

        String message = "Missing required BackEndId: " + CodeGenerator.BACKEND_PACKAGE
            + "." + CodeGenerator.CURRENT_BACKEND_ID_CLASS;
        logger.error(message);
        throw new ConfigError(message);
    }
}