/**
 * @license
 * Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 */

/*
 * PLEASE NOTE: This file is duplicated within Polymer. Please keep it in sync!
 * https://github.com/Polymer/polymer/blob/master/src/system/HTMLImports/base.js
 */

/*
	Create polyfill scope and feature detect native support.
*/
window.HTMLImports = window.HTMLImports || {flags:{}};

(function(scope) {

/**
	Basic setup and simple module executer. We collect modules and then execute
  the code later, only if it's necessary for polyfilling.
*/
var IMPORT_LINK_TYPE = 'import';
var useNative = Boolean(IMPORT_LINK_TYPE in document.createElement('link'));

/**
  Support `currentScript` on all browsers as `document._currentScript.`

  NOTE: We cannot polyfill `document.currentScript` because it's not possible
  both to override and maintain the ability to capture the native value.
  Therefore we choose to expose `_currentScript` both when native imports
  and the polyfill are in use.
*/
// NOTE: ShadowDOMPolyfill intrusion.
var hasShadowDOMPolyfill = Boolean(window.ShadowDOMPolyfill);
var wrap = function(node) {
  return hasShadowDOMPolyfill ? ShadowDOMPolyfill.wrapIfNeeded(node) : node;
};
var rootDocument = wrap(document);

var currentScriptDescriptor = {
  get: function() {
    var script = HTMLImports.currentScript || document.currentScript ||
        // NOTE: only works when called in synchronously executing code.
        // readyState should check if `loading` but IE10 is
        // interactive when scripts run so we cheat.
        (document.readyState !== 'complete' ?
        document.scripts[document.scripts.length - 1] : null);
    return wrap(script);
  },
  configurable: true
};

Object.defineProperty(document, '_currentScript', currentScriptDescriptor);
Object.defineProperty(rootDocument, '_currentScript', currentScriptDescriptor);

/**
  Add support for the `HTMLImportsLoaded` event and the `HTMLImports.whenReady`
  method. This api is necessary because unlike the native implementation,
  script elements do not force imports to resolve. Instead, users should wrap
  code in either an `HTMLImportsLoaded` hander or after load time in an
  `HTMLImports.whenReady(callback)` call.

  NOTE: This module also supports these apis under the native implementation.
  Therefore, if this file is loaded, the same code can be used under both
  the polyfill and native implementation.
 */

var isIE = /Trident|Edge/.test(navigator.userAgent);

// call a callback when all HTMLImports in the document at call time
// (or at least document ready) have loaded.
// 1. ensure the document is in a ready state (has dom), then
// 2. watch for loading of imports and call callback when done
function whenReady(callback, doc) {
  doc = doc || rootDocument;
  // if document is loading, wait and try again
  whenDocumentReady(function() {
    watchImportsLoad(callback, doc);
  }, doc);
}

// call the callback when the document is in a ready state (has dom)
var requiredReadyState = isIE ? 'complete' : 'interactive';
var READY_EVENT = 'readystatechange';
function isDocumentReady(doc) {
  return (doc.readyState === 'complete' ||
      doc.readyState === requiredReadyState);
}

// call <callback> when we ensure the document is in a ready state
function whenDocumentReady(callback, doc) {
  if (!isDocumentReady(doc)) {
    var checkReady = function() {
      if (doc.readyState === 'complete' ||
          doc.readyState === requiredReadyState) {
        doc.removeEventListener(READY_EVENT, checkReady);
        whenDocumentReady(callback, doc);
      }
    };
    doc.addEventListener(READY_EVENT, checkReady);
  } else if (callback) {
    callback();
  }
}

function markTargetLoaded(event) {
  event.target.__loaded = true;
}

// call <callback> when we ensure all imports have loaded
function watchImportsLoad(callback, doc) {
  var imports = doc.querySelectorAll('link[rel=import]');
  var loaded = 0, l = imports.length;
  function checkDone(d) {
    if ((loaded == l) && callback) {
       callback();
    }
  }
  function loadedImport(e) {
    markTargetLoaded(e);
    loaded++;
    checkDone();
  }
  if (l) {
    for (var i=0, imp; (i<l) && (imp=imports[i]); i++) {
      if (isImportLoaded(imp)) {
        loadedImport.call(imp, {target: imp});
      } else {
        imp.addEventListener('load', loadedImport);
        imp.addEventListener('error', loadedImport);
      }
    }
  } else {
    checkDone();
  }
}

// NOTE: test for native imports loading is based on explicitly watching
// all imports (see below).
// However, we cannot rely on this entirely without watching the entire document
// for import links. For perf reasons, currently only head is watched.
// Instead, we fallback to checking if the import property is available
// and the document is not itself loading.
function isImportLoaded(link) {
  return useNative ? link.__loaded ||
      (link.import && link.import.readyState !== 'loading') :
      link.__importParsed;
}

// TODO(sorvell): Workaround for
// https://www.w3.org/Bugs/Public/show_bug.cgi?id=25007, should be removed when
// this bug is addressed.
// (1) Install a mutation observer to see when HTMLImports have loaded
// (2) if this script is run during document load it will watch any existing
// imports for loading.
//
// NOTE: The workaround has restricted functionality: (1) it's only compatible
// with imports that are added to document.head since the mutation observer
// watches only head for perf reasons, (2) it requires this script
// to run before any imports have completed loading.
if (useNative) {
  new MutationObserver(function(mxns) {
    for (var i=0, l=mxns.length, m; (i < l) && (m=mxns[i]); i++) {
      if (m.addedNodes) {
        handleImports(m.addedNodes);
      }
    }
  }).observe(document.head, {childList: true});

  function handleImports(nodes) {
    for (var i=0, l=nodes.length, n; (i<l) && (n=nodes[i]); i++) {
      if (isImport(n)) {
        handleImport(n);
      }
    }
  }

  function isImport(element) {
    return element.localName === 'link' && element.rel === 'import';
  }

  function handleImport(element) {
    var loaded = element.import;
    if (loaded) {
      markTargetLoaded({target: element});
    } else {
      element.addEventListener('load', markTargetLoaded);
      element.addEventListener('error', markTargetLoaded);
    }
  }

  // make sure to catch any imports that are in the process of loading
  // when this script is run.
  (function() {
    if (document.readyState === 'loading') {
      var imports = document.querySelectorAll('link[rel=import]');
      for (var i=0, l=imports.length, imp; (i<l) && (imp=imports[i]); i++) {
        handleImport(imp);
      }
    }
  })();

}

// Fire the 'HTMLImportsLoaded' event when imports in document at load time
// have loaded. This event is required to simulate the script blocking
// behavior of native imports. A main document script that needs to be sure
// imports have loaded should wait for this event.
whenReady(function() {
  HTMLImports.ready = true;
  HTMLImports.readyTime = new Date().getTime();
  rootDocument.dispatchEvent(
    new CustomEvent('HTMLImportsLoaded', {bubbles: true})
  );
});

// exports
scope.IMPORT_LINK_TYPE = IMPORT_LINK_TYPE;
scope.useNative = useNative;
scope.rootDocument = rootDocument;
scope.whenReady = whenReady;
scope.isIE = isIE;

})(HTMLImports);