/*
 * 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.dev.cfg;

import com.google.gwt.core.ext.TreeLogger;
import com.google.gwt.core.ext.UnableToCompleteException;
import com.google.gwt.dev.util.Util;
import com.google.gwt.dev.util.xml.ReflectiveParser;
import com.google.gwt.util.tools.Utility;

import org.apache.commons.collections.map.AbstractReferenceMap;
import org.apache.commons.collections.map.ReferenceMap;

import java.io.File;
import java.io.Reader;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/**
 * The top-level API for loading module XML.
 */
public final class ModuleDefLoader {

  /**
   * Interface to provide a load strategy to the load process.
   */
  private interface LoadStrategy {
    /**
     * Perform loading on the specified module.
     * 
     * @param logger logs the process
     * @param moduleName the name of the process
     * @param moduleDef a module
     * @throws UnableToCompleteException
     */
    void load(TreeLogger logger, String moduleName, ModuleDef moduleDef)
        throws UnableToCompleteException;
  }

  /**
   * Filename suffix used for GWT Module XML files.
   */
  public static final String GWT_MODULE_XML_SUFFIX = ".gwt.xml";

  /**
   * Keep soft references to loaded modules so the VM can gc them when memory is
   * tight.
   */
  @SuppressWarnings("unchecked")
  private static final Map<String, ModuleDef> loadedModules = new ReferenceMap(
      AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT);

  /**
   * Creates a module in memory that is not associated with a
   * <code>.gwt.xml</code> file on disk.
   * 
   * @param logger logs the process
   * @param moduleName the synthetic module to create
   * @param inherits a set of modules to inherit from
   * @param refresh whether to refresh the module
   * @return the loaded module
   * @throws UnableToCompleteException
   */
  public static ModuleDef createSyntheticModule(TreeLogger logger,
      String moduleName, String[] inherits, boolean refresh)
      throws UnableToCompleteException {
    ModuleDef moduleDef = tryGetLoadedModule(logger, moduleName, refresh);
    if (moduleDef != null) {
      return moduleDef;
    }
    ModuleDefLoader loader = new ModuleDefLoader(inherits);
    ModuleDef module = loader.doLoadModule(logger, moduleName);
    /*
     * Must reset name override on synthetic modules. Otherwise they'll be
     * incorrectly affected by the last inherits tag, because they have no XML
     * which would reset the name at the end of parse.
     */
    module.setNameOverride(null);
    return module;
  }

  /**
   * Loads a new module from the class path.
   * 
   * @param logger logs the process
   * @param moduleName the module to load
   * @return the loaded module
   * @throws UnableToCompleteException
   */
  public static ModuleDef loadFromClassPath(TreeLogger logger, String moduleName)
      throws UnableToCompleteException {
    return loadFromClassPath(logger, moduleName, false);
  }

  /**
   * Loads a new module from the class path.
   * 
   * @param logger logs the process
   * @param moduleName the module to load
   * @param refresh whether to refresh the module
   * @return the loaded module
   * @throws UnableToCompleteException
   */
  public static ModuleDef loadFromClassPath(TreeLogger logger,
      String moduleName, boolean refresh) throws UnableToCompleteException {
    ModuleDef moduleDef = tryGetLoadedModule(logger, moduleName, refresh);
    if (moduleDef != null) {
      return moduleDef;
    }
    ModuleDefLoader loader = new ModuleDefLoader();
    return loader.doLoadModule(logger, moduleName);
  }

  private static ModuleDef tryGetLoadedModule(TreeLogger logger,
      String moduleName, boolean refresh) {
    ModuleDef moduleDef = loadedModules.get(moduleName);
    if (moduleDef == null || moduleDef.isGwtXmlFileStale()) {
      return null;
    } else if (refresh) {
      moduleDef.refresh(logger);
    }
    return moduleDef;
  }

  private final Set<String> alreadyLoadedModules = new HashSet<String>();

  private final ClassLoader classLoader;

  private final LoadStrategy strategy;

  /**
   * Constructs a {@link ModuleDefLoader} that loads from the class path.
   */
  private ModuleDefLoader() {
    this.classLoader = Thread.currentThread().getContextClassLoader();
    this.strategy = new LoadStrategy() {
      public void load(TreeLogger logger, String moduleName, ModuleDef moduleDef)
          throws UnableToCompleteException {
        nestedLoad(logger, moduleName, moduleDef);
      }
    };
  }

  /**
   * Constructs a {@link ModuleDefLoader} that loads a synthetic module.
   * 
   * @param inherits a set of modules to inherit from
   */
  private ModuleDefLoader(final String[] inherits) {
    this.classLoader = Thread.currentThread().getContextClassLoader();
    this.strategy = new LoadStrategy() {
      public void load(TreeLogger logger, String moduleName, ModuleDef moduleDef)
          throws UnableToCompleteException {
        for (String inherit : inherits) {
          TreeLogger branch = logger.branch(TreeLogger.TRACE,
              "Loading inherited module '" + inherit + "'", null);
          nestedLoad(branch, inherit, moduleDef);
        }
      }
    };
  }

  /**
   * Loads a new module into <code>moduleDef</code> as an included module.
   * 
   * @param logger Logs the process.
   * @param moduleName The module to load.
   * @param moduleDef The module to add the new module to.
   * @throws UnableToCompleteException
   */
  void nestedLoad(TreeLogger logger, String moduleName, ModuleDef moduleDef)
      throws UnableToCompleteException {

    if (alreadyLoadedModules.contains(moduleName)) {
      logger.log(TreeLogger.TRACE, "Module '" + moduleName
          + "' has already been loaded and will be skipped", null);
      return;
    } else {
      alreadyLoadedModules.add(moduleName);
    }

    // Find the specified module using the classpath.
    //
    String slashedModuleName = moduleName.replace('.', '/');
    String resName = slashedModuleName + ModuleDefLoader.GWT_MODULE_XML_SUFFIX;
    URL moduleURL = classLoader.getResource(resName);

    if (moduleURL != null) {
      String externalForm = moduleURL.toExternalForm();
      logger.log(TreeLogger.TRACE, "Module location: " + externalForm, null);
      try {
        if ((!(externalForm.startsWith("jar:file")))
            && (!(externalForm.startsWith("zip:file")))
            && (!(externalForm.startsWith("http://")))
            && (!(externalForm.startsWith("ftp://")))) {
          File gwtXmlFile = new File(moduleURL.toURI());
          moduleDef.addGwtXmlFile(gwtXmlFile);
        }
      } catch (URISyntaxException e) {
        logger.log(TreeLogger.ERROR, "Error parsing URI", e);
        throw new UnableToCompleteException();
      }
    }
    if (moduleURL == null) {
      String msg = "Unable to find '"
          + resName
          + "' on your classpath; could be a typo, or maybe you forgot to include a classpath entry for source?";
      logger.log(TreeLogger.ERROR, msg, null);
      throw new UnableToCompleteException();
    }

    // Extract just the directory containing the module.
    //
    String moduleDir = "";
    int i = slashedModuleName.lastIndexOf('/');
    if (i != -1) {
      moduleDir = slashedModuleName.substring(0, i) + "/";
    }

    // Parse it.
    //
    Reader r = null;
    try {
      r = Util.createReader(logger, moduleURL);
      ModuleDefSchema schema = new ModuleDefSchema(logger, this, moduleName,
          moduleURL, moduleDir, moduleDef);
      ReflectiveParser.parse(logger, schema, r);
    } catch (Throwable e) {
      logger.log(TreeLogger.ERROR, "Unexpected error while processing XML", e);
      throw new UnableToCompleteException();
    } finally {
      Utility.close(r);
    }
  }

  /**
   * This method loads a module.
   * 
   * @param logger used to log the loading process
   * @param moduleName the name of the module
   * @return the module returned -- cannot be null
   * @throws UnableToCompleteException if module loading failed
   */
  private ModuleDef doLoadModule(TreeLogger logger, String moduleName)
      throws UnableToCompleteException {
    if (!ModuleDef.isValidModuleName(moduleName)) {
      logger.log(TreeLogger.ERROR, "Invalid module name: '" + moduleName + "'",
          null);
      throw new UnableToCompleteException();
    }

    ModuleDef moduleDef = new ModuleDef(moduleName);
    strategy.load(logger, moduleName, moduleDef);

    // Do any final setup.
    //
    moduleDef.normalize(logger);

    // Add the "physical" module name: com.google.Module
    loadedModules.put(moduleName, moduleDef);

    // Add the module's effective name: some.other.Module
    loadedModules.put(moduleDef.getName(), moduleDef);
    return moduleDef;
  }
}