/* $Id: PluginCreateRule.java,v 1.19 2004/05/10 06:44:13 skitching Exp $
 *
 * Copyright 2003-2004 The Apache Software Foundation.
 * 
 * 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 org.apache.commons.digester.plugins;

import java.util.Iterator;
import java.util.ListIterator;
import java.util.List;
import java.io.File;

import org.apache.commons.digester.Digester;
import org.apache.commons.digester.Rule;
import org.apache.commons.digester.Rules;
import org.apache.commons.logging.Log;

/**
 * Allows the original rules for parsing the configuration file to define
 * points at which plugins are allowed, by configuring a PluginCreateRule
 * with the appropriate pattern.
 *
 * @since 1.6
 */
public class PluginCreateRule extends Rule implements InitializableRule {

    // see setPluginClassAttribute
    private String pluginClassAttrNs = null;
    private String pluginClassAttr = null;
    
    // see setPluginIdAttribute
    private String pluginIdAttrNs = null;
    private String pluginIdAttr = null;
    
    /**
     * In order to invoke the addRules method on the plugin class correctly,
     * we need to know the pattern which this rule is matched by.
     */
    private String pattern;

    /** A base class that any plugin must derive from. */
    private Class baseClass = null;

    /**
     * Info about optional default plugin to be used if no plugin-id is
     * specified in the input data. This can simplify the syntax where one
     * particular plugin is usually used.
     */
    private Declaration defaultPlugin;

    /**
     * Currently, none of the Rules methods allow exceptions to be thrown.
     * Therefore if this class cannot initialise itself properly, it cannot
     * cause the digester to stop. Instead, we cache the exception and throw
     * it the first time the begin() method is called.
     */
    private PluginConfigurationException initException;

    //-------------------- constructors -------------------------------------

    /**
     * Create a plugin rule where the user <i>must</i> specify a plugin-class
     * or plugin-id.
     * 
     * @param baseClass is the class which any specified plugin <i>must</i> be
     * descended from.
     */
    public PluginCreateRule(Class baseClass) {
        this.baseClass = baseClass;
    }

    /**
     * Create a plugin rule where the user <i>may</i> specify a plugin.
     * If the user doesn't specify a plugin, then the default class specified 
     * in this constructor is used.
     * 
     * @param baseClass is the class which any specified plugin <i>must</i> be
     * descended from.
     * @param dfltPluginClass is the class which will be used if the user
     * doesn't specify any plugin-class or plugin-id. This class will have
     * custom rules installed for it just like a declared plugin.
     */
    public PluginCreateRule(Class baseClass, Class dfltPluginClass) {
        this.baseClass = baseClass;
        if (dfltPluginClass != null) {
            defaultPlugin = new Declaration(dfltPluginClass);
        }
    }

    /**
     * Create a plugin rule where the user <i>may</i> specify a plugin.
     * If the user doesn't specify a plugin, then the default class specified 
     * in this constructor is used.
     * 
     * @param baseClass is the class which any specified plugin <i>must</i> be
     * descended from.
     * @param dfltPluginClass is the class which will be used if the user
     * doesn't specify any plugin-class or plugin-id. This class will have
     * custom rules installed for it just like a declared plugin.
     * @param dfltPluginRuleLoader is a RuleLoader instance which knows how
     * to load the custom rules associated with this default plugin.
     */
    public PluginCreateRule(Class baseClass, Class dfltPluginClass,
                    RuleLoader dfltPluginRuleLoader) {

        this.baseClass = baseClass;
        if (dfltPluginClass != null) {
            defaultPlugin = 
                new Declaration(dfltPluginClass, dfltPluginRuleLoader);
        }
    }

    //------------------- properties ---------------------------------------
    
    /**
     * Sets the xml attribute which the input xml uses to indicate to a 
     * PluginCreateRule which class should be instantiated.
     * <p>
     * See {@link PluginRules#setPluginClassAttribute} for more info.
     */
    public void setPluginClassAttribute(String namespaceUri, String attrName) {
        pluginClassAttrNs = namespaceUri;
        pluginClassAttr = attrName;
    }

    /**
     * Sets the xml attribute which the input xml uses to indicate to a 
     * PluginCreateRule which plugin declaration is being referenced.
     * <p>
     * See {@link PluginRules#setPluginIdAttribute} for more info.
     */
    public void setPluginIdAttribute(String namespaceUri, String attrName) {
        pluginIdAttrNs = namespaceUri;
        pluginIdAttr = attrName;
    }

    //------------------- methods --------------------------------------------

    /**
     * Invoked after this rule has been added to the set of digester rules,
     * associated with the specified pattern. Check all configuration data is
     * valid and remember the pattern for later.
     * 
     * @param matchPattern is the digester match pattern that is associated 
     * with this rule instance, eg "root/widget".
     * @exception PluginConfigurationException
     */
    public void postRegisterInit(String matchPattern)
                                 throws PluginConfigurationException {
        Log log = LogUtils.getLogger(digester);
        boolean debug = log.isDebugEnabled();
        if (debug) {
            log.debug("PluginCreateRule.postRegisterInit" + 
                      ": rule registered for pattern [" + matchPattern + "]");
        }

        if (digester == null) {
            // We require setDigester to be called before this method.
            // Note that this means that PluginCreateRule cannot be added
            // to a Rules object which has not yet been added to a
            // Digester object.
            initException = new PluginConfigurationException(
                 "Invalid invocation of postRegisterInit" + 
                 ": digester not set.");
            throw initException;
        }

        if (pattern != null) {
            // We have been called twice, ie a single instance has been
            // associated with multiple patterns.
            //
            // Generally, Digester Rule instances can be associated with 
            // multiple patterns. However for plugins, this creates some 
            // complications. Some day this may be supported; however for 
            // now we just reject this situation.
            initException = new PluginConfigurationException(
               "A single PluginCreateRule instance has been mapped to" + 
                 " multiple patterns; this is not supported.");
            throw initException;
        }

        if (matchPattern.indexOf('*') != -1) {
            // having wildcards in patterns is extremely difficult to
            // deal with. For now, we refuse to allow this.
            //
            // TODO: check for any chars not valid in xml element name
            // rather than just *.
            //
            // Reasons include:
            // (a) handling recursive plugins, and
            // (b) determining whether one pattern is "below" another,
            //     as done by PluginRules. Without wildcards, "below"
            //     just means startsWith, which is easy to check.
            initException = new PluginConfigurationException(
                 "A PluginCreateRule instance has been mapped to" + 
                 " pattern [" + matchPattern + "]." + 
                 " This pattern includes a wildcard character." + 
                 " This is not supported by the plugin architecture.");
            throw initException;
        }

        if (baseClass == null) {
            baseClass = Object.class;
        }
        
        PluginRules rules = (PluginRules) digester.getRules();
        PluginManager pm = rules.getPluginManager();

        // check default class is valid
        if (defaultPlugin != null) {
            if (!baseClass.isAssignableFrom(defaultPlugin.getPluginClass())) {
                initException = new PluginConfigurationException(
                     "Default class [" + 
                     defaultPlugin.getPluginClass().getName() + 
                     "] does not inherit from [" + 
                     baseClass.getName() + "].");
                throw initException;
            }

            try {
                defaultPlugin.init(digester, pm);
                
            } catch(PluginException pwe) {
            
                throw new PluginConfigurationException(
                    pwe.getMessage(), pwe.getCause());
            }
        }

        // remember the pattern for later
        pattern = matchPattern;
        
        if (pluginClassAttr ==  null) {
            // the user hasn't set explicit xml attr names on this rule,
            // so fetch the default values
            pluginClassAttrNs = rules.getPluginClassAttrNs();
            pluginClassAttr = rules.getPluginClassAttr();
            
            if (debug) {
                log.debug(
                    "init: pluginClassAttr set to per-digester values ["
                    + "ns=" + pluginClassAttrNs 
                    + ", name=" + pluginClassAttr + "]");
            }
        } else {
            if (debug) {
                log.debug(
                    "init: pluginClassAttr set to rule-specific values ["
                    + "ns=" + pluginClassAttrNs 
                    + ", name=" + pluginClassAttr + "]");
            }
        }
        
        if (pluginIdAttr ==  null) {
            // the user hasn't set explicit xml attr names on this rule,
            // so fetch the default values
            pluginIdAttrNs = rules.getPluginIdAttrNs();
            pluginIdAttr = rules.getPluginIdAttr();
            
            if (debug) {
                log.debug(
                    "init: pluginIdAttr set to per-digester values ["
                    + "ns=" + pluginIdAttrNs 
                    + ", name=" + pluginIdAttr + "]");
            }
        } else {
            if (debug) {
                log.debug(
                    "init: pluginIdAttr set to rule-specific values ["
                    + "ns=" + pluginIdAttrNs 
                    + ", name=" + pluginIdAttr + "]");
            }
        }
    }

    /**
     * Invoked when the Digester matches this rule against an xml element.
     * <p>
     * A new instance of the target class is created, and pushed onto the
     * stack. A new "private" PluginRules object is then created and set as
     * the digester's default Rules object. Any custom rules associated with
     * the plugin class are then loaded into that new Rules object.
     * Finally, any custom rules that are associated with the current pattern
     * (such as SetPropertiesRules) have their begin methods executed.
     * 
     * @param namespace 
     * @param name 
     * @param attributes
     *
     * @throws ClassNotFoundException
     * @throws PluginInvalidInputException
     * @throws PluginConfigurationException
     */
    public void begin(String namespace, String name,
                      org.xml.sax.Attributes attributes)
                      throws java.lang.Exception {
        Log log = digester.getLogger();
        boolean debug = log.isDebugEnabled();
        if (debug) {
            log.debug("PluginCreateRule.begin" + ": pattern=[" + pattern + "]" + 
                  " match=[" + digester.getMatch() + "]");
        }

        if (initException != null) {
            // we had a problem during initialisation that we could
            // not report then; report it now.
            throw initException;
        }
        
        String path = digester.getMatch();

        // create a new Rules object and effectively push it onto a stack of
        // rules objects. The stack is actually a linked list; using the
        // PluginRules constructor below causes the new instance to link
        // to the previous head-of-stack, then the Digester.setRules() makes
        // the new instance the new head-of-stack.
        PluginRules oldRules = (PluginRules) digester.getRules();
        PluginRules newRules = new PluginRules(path, oldRules);
        digester.setRules(newRules);
        
        // load any custom rules associated with the plugin
        PluginManager pluginManager = newRules.getPluginManager();
        Declaration currDeclaration = null;
            
        if (debug) {
            log.debug("PluginCreateRule.begin: installing new plugin: " +
                "oldrules=" + oldRules.toString() +
                ", newrules=" + newRules.toString());
        }
              
        String pluginClassName; 
        if (pluginClassAttrNs == null) {
            // Yep, this is ugly.
            //
            // In a namespace-aware parser, the one-param version will 
            // return attributes with no namespace.
            //
            // In a non-namespace-aware parser, the two-param version will 
            // never return any attributes, ever.
            pluginClassName = attributes.getValue(pluginClassAttr);
        } else {
            pluginClassName = 
                attributes.getValue(pluginClassAttrNs, pluginClassAttr);
        }

        String pluginId; 
        if (pluginIdAttrNs == null) {
            pluginId = attributes.getValue(pluginIdAttr);
        } else {
            pluginId = 
                attributes.getValue(pluginIdAttrNs, pluginIdAttr);
        }
        
        if (pluginClassName != null) {
            // The user is using a plugin "inline", ie without a previous
            // explicit declaration. If they have used the same plugin class
            // before, we have already gone to the effort of creating a 
            // Declaration object, so retrieve it. If there is no existing
            // declaration object for this class, then create one.

            currDeclaration = pluginManager.getDeclarationByClass(
                pluginClassName);

            if (currDeclaration == null) {
                currDeclaration = new Declaration(pluginClassName);
                try {
                    currDeclaration.init(digester, pluginManager);
                } catch(PluginException pwe) {
                    throw new PluginInvalidInputException(
                        pwe.getMessage(), pwe.getCause());
                }
                pluginManager.addDeclaration(currDeclaration);
            }
        } else if (pluginId != null) {
            currDeclaration = pluginManager.getDeclarationById(pluginId);
                
            if (currDeclaration == null) {
                throw new PluginInvalidInputException(
                    "Plugin id [" + pluginId + "] is not defined.");
            }
        } else if (defaultPlugin != null) {
            currDeclaration = defaultPlugin;
        } else {
            throw new PluginInvalidInputException(
                "No plugin class specified for element " +
                pattern);
        }
            
        // now load up the custom rules
        currDeclaration.configure(digester, pattern);

        // and now create an instance of the plugin class
        Class pluginClass = currDeclaration.getPluginClass();
        
        Object instance = pluginClass.newInstance();
        getDigester().push(instance);
        if (debug) {
            log.debug(
                "PluginCreateRule.begin" + ": pattern=[" + pattern + "]" + 
                " match=[" + digester.getMatch() + "]" + 
                " pushed instance of plugin [" + pluginClass.getName() + "]");
        }
        
        // and now we have to fire any custom rules which would have
        // been matched by the same path that matched this rule, had
        // they been loaded at that time.
        List rules = newRules.getDecoratedRules().match(namespace, path);
        fireBeginMethods(rules, namespace, name, attributes); 
    }

    /**
     * Process the body text of this element.
     *
     * @param text The body text of this element
     */
    public void body(String namespace, String name, String text)
        throws Exception {

        // While this class itself has no work to do in the body method,
        // we do need to fire the body methods of all dynamically-added
        // rules matching the same path as this rule. During begin, we had
        // to manually execute the dynamic rules' begin methods because they
        // didn't exist in the digester's Rules object when the match begin.
        // So in order to ensure consistent ordering of rule execution, the
        // PluginRules class deliberately avoids returning any such rules
        // in later calls to the match method, instead relying on this
        // object to execute them at the appropriate time.
        //
        // Note that this applies only to rules matching exactly the path
        // which is also matched by this PluginCreateRule. 

        String path = digester.getMatch();
        PluginRules newRules = (PluginRules) digester.getRules();
        List rules = newRules.getDecoratedRules().match(namespace, path);
        fireBodyMethods(rules, namespace, name, text);
    }

    /**
     * Invoked by the digester when the closing tag matching this Rule's
     * pattern is encountered.
     * </p>
     * 
     * @param namespace Description of the Parameter
     * @param name Description of the Parameter
     * @exception Exception Description of the Exception
     *
     * @see #begin
     */
    public void end(String namespace, String name)
                    throws Exception {


        // see body method for more info
        String path = digester.getMatch();
        PluginRules newRules = (PluginRules) digester.getRules();
        List rules = newRules.getDecoratedRules().match(namespace, path);
        fireEndMethods(rules, namespace, name);
        
        // pop the stack of PluginRules instances, which
        // discards all custom rules associated with this plugin
        digester.setRules(newRules.getParent());
        
        // and get rid of the instance of the plugin class from the
        // digester object stack.
        digester.pop();
    }

    /**
     * Return the pattern that this Rule is associated with.
     * <p>
     * In general, Rule instances <i>can</i> be associated with multiple
     * patterns. A PluginCreateRule, however, will only function correctly
     * when associated with a single pattern. It is possible to fix this, but
     * I can't be bothered just now because this feature is unlikely to be
     * used.
     * </p>
     * 
     * @return The pattern value
     */
    public String getPattern() {
        return pattern;
    }
    
    /**
     * Duplicate the processing that the Digester does when firing the
     * begin methods of rules. It would be really nice if the Digester
     * class provided a way for this functionality to just be invoked
     * directly.
     */
    public void fireBeginMethods(List rules,
                      String namespace, String name,
                      org.xml.sax.Attributes list)
                      throws java.lang.Exception {
        
        if ((rules != null) && (rules.size() > 0)) {
            Log log = digester.getLogger();
            boolean debug = log.isDebugEnabled();
            for (int i = 0; i < rules.size(); i++) {
                try {
                    Rule rule = (Rule) rules.get(i);
                    if (debug) {
                        log.debug("  Fire begin() for " + rule);
                    }
                    rule.begin(namespace, name, list);
                } catch (Exception e) {
                    throw digester.createSAXException(e);
                } catch (Error e) {
                    throw e;
                }
            }
        }
    }

    /**
     * Duplicate the processing that the Digester does when firing the
     * body methods of rules. It would be really nice if the Digester
     * class provided a way for this functionality to just be invoked
     * directly.
     */
    private void fireBodyMethods(List rules,
                    String namespaceURI, String name,
                    String text) throws Exception {

        if ((rules != null) && (rules.size() > 0)) {
            Log log = digester.getLogger();
            boolean debug = log.isDebugEnabled();
            for (int i = 0; i < rules.size(); i++) {
                try {
                    Rule rule = (Rule) rules.get(i);
                    if (debug) {
                        log.debug("  Fire body() for " + rule);
                    }
                    rule.body(namespaceURI, name, text);
                } catch (Exception e) {
                    throw digester.createSAXException(e);
                } catch (Error e) {
                    throw e;
                }
            }
        }
    }
    
    /**
     * Duplicate the processing that the Digester does when firing the
     * end methods of rules. It would be really nice if the Digester
     * class provided a way for this functionality to just be invoked
     * directly.
     */
    public void fireEndMethods(List rules,
                    String namespaceURI, String name)
                    throws Exception {

        // Fire "end" events for all relevant rules in reverse order
        if (rules != null) {
            Log log = digester.getLogger();
            boolean debug = log.isDebugEnabled();
            for (int i = 0; i < rules.size(); i++) {
                int j = (rules.size() - i) - 1;
                try {
                    Rule rule = (Rule) rules.get(j);
                    if (debug) {
                        log.debug("  Fire end() for " + rule);
                    }
                    rule.end(namespaceURI, name);
                } catch (Exception e) {
                    throw digester.createSAXException(e);
                } catch (Error e) {
                    throw e;
                }
            }
        }
    }
}