/*
 * 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.core.linker;

import com.google.gwt.core.ext.LinkerContext;
import com.google.gwt.core.ext.TreeLogger;
import com.google.gwt.core.ext.UnableToCompleteException;
import com.google.gwt.core.ext.linker.LinkerOrder;
import com.google.gwt.core.ext.linker.LinkerOrder.Order;
import com.google.gwt.core.ext.linker.Shardable;
import com.google.gwt.core.ext.linker.impl.SelectionScriptLinker;
import com.google.gwt.dev.About;
import com.google.gwt.dev.util.DefaultTextOutput;

/**
 * Implements the canonical GWT bootstrap sequence that loads the GWT module in
 * a separate iframe.
 */
@LinkerOrder(Order.PRIMARY)
@Shardable
public class IFrameLinker extends SelectionScriptLinker {
  /**
   * This string is inserted between script chunks. It is made default access
   * for testing.
   */
  static final String SCRIPT_CHUNK_SEPARATOR = "--></script>\n<script><!--\n";

  @Override
  public String getDescription() {
    return "Standard";
  }

  @Override
  protected String getCompilationExtension(TreeLogger logger,
      LinkerContext context) {
    return ".cache.html";
  }

  @Override
  protected String getHostedFilename() {
    return "hosted.html";
  }

  @Override
  protected String getModulePrefix(TreeLogger logger, LinkerContext context,
      String strongName) throws UnableToCompleteException {
    return getModulePrefix(logger, context, strongName, true);
  }

  @Override
  protected String getModulePrefix(TreeLogger logger, LinkerContext context,
      String strongName, int numFragments) throws UnableToCompleteException {
    return getModulePrefix(logger, context, strongName, numFragments > 1);
  }

  @Override
  protected String getModuleSuffix(TreeLogger logger, LinkerContext context) {
    DefaultTextOutput out = new DefaultTextOutput(context.isOutputCompact());

    out.print("$stats && $stats({moduleName:'" + context.getModuleName()
        + "',sessionId:$sessionId"
        + ",subSystem:'startup',evtGroup:'moduleStartup'"
        + ",millis:(new Date()).getTime(),type:'moduleEvalEnd'});");

    // Generate the call to tell the bootstrap code that we're ready to go.
    out.newlineOpt();
    out.print("if ($wnd." + context.getModuleFunctionName() + ") $wnd."
        + context.getModuleFunctionName() + ".onScriptLoad();");
    out.newline();
    out.print("--></script></body></html>");
    out.newlineOpt();

    return out.toString();
  }

  @Override
  protected String getScriptChunkSeparator(TreeLogger logger, LinkerContext context) {
    return SCRIPT_CHUNK_SEPARATOR;
  }

  @Override
  protected String getSelectionScriptTemplate(TreeLogger logger, LinkerContext context) {
    return "com/google/gwt/core/linker/IFrameTemplate.js";
  }

  protected String modifyPrimaryJavaScript(String js) {
    return js;
  }

  /**
   * This is the real implementation of <code>getModulePrefix</code> for this
   * linker. The other versions forward to this one.
   */
  private String getModulePrefix(TreeLogger logger, LinkerContext context,
      String strongName, boolean supportRunAsync)
      throws UnableToCompleteException {
    DefaultTextOutput out = new DefaultTextOutput(context.isOutputCompact());
    out.print("<html>");
    out.newlineOpt();

    // Setup the well-known variables.
    out.print("<head><meta charset=\"UTF-8\" /><script>");
    out.newlineOpt();
    out.print("var $gwt_version = \"" + About.getGwtVersionNum() + "\";");
    out.newlineOpt();
    out.print("var $wnd = parent;");
    out.newlineOpt();
    out.print("var $doc = $wnd.document;");
    out.newlineOpt();
    out.print("var $moduleName, $moduleBase;");
    out.newlineOpt();
    out.print("var $strongName = '" + strongName + "';");
    out.newlineOpt();
    if (supportRunAsync) {
      out.print("function __gwtStartLoadingFragment(frag) {");
      out.indentIn();
      out.newlineOpt();
      out.print("  return $moduleBase + '" + getFragmentSubdir(logger, context)
          + "/'  + $strongName + '/' + frag + '" + FRAGMENT_EXTENSION + "';");
      out.indentOut();
      out.newlineOpt();
      out.print("};");
      out.newlineOpt();
      out.print("function __gwtInstallCode(code) {");
      /*
       * Use a script tag on all platforms, for simplicity. It would be cleaner
       * to use window.eval, but at the time of writing that only reliably works
       * on Firefox. It would also be cleaner to use window.execScript on
       * platforms that support it (IE and Chrome). However, trying this causes
       * IE 6 (and possibly others) to emit "error 80020101", apparently due to
       * something objectionable in the compiler's output JavaScript.
       */
      out.indentIn();
      out.newlineOpt();
      out.print("var head = document.getElementsByTagName('head').item(0);");
      out.newlineOpt();
      out.print("var script = document.createElement('script');");
      out.newlineOpt();
      out.print("script.type = 'text/javascript';");
      out.newlineOpt();
      out.print("script.text = code;");
      out.newlineOpt();
      out.print("head.appendChild(script);");
      out.indentOut();
      out.newlineOpt();
      out.print("};");
      out.newlineOpt();
    }
    out.print("var $stats = $wnd.__gwtStatsEvent ? function(a) {return $wnd.__gwtStatsEvent(a);} : null,");
    out.newlineOpt();
    out.print("$sessionId = $wnd.__gwtStatsSessionId ? $wnd.__gwtStatsSessionId : null;");
    out.newlineOpt();
    out.print("$stats && $stats({moduleName:'" + context.getModuleName()
        + "',sessionId:$sessionId"
        + ",subSystem:'startup',evtGroup:'moduleStartup'"
        + ",millis:(new Date()).getTime(),type:'moduleEvalStart'});");
    out.newlineOpt();
    out.print("</script></head>");
    out.newlineOpt();
    out.print("<body>");
    out.newlineOpt();

    // Begin a script block inside the body. It's commented out so that the
    // browser won't mistake strings containing "<script>" for actual script.
    out.print("<script><!--");
    out.newline();
    return out.toString();
  }

}