gecko-dev/browser/devtools/shared/Templater.jsm

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */


var EXPORTED_SYMBOLS = [ "Templater", "template" ];

Components.utils.import("resource://gre/modules/Services.jsm");
const Node = Components.interfaces.nsIDOMNode;

/**
 * For full documentation, see:
 * https://github.com/mozilla/domtemplate/blob/master/README.md
 */

// WARNING: do not 'use_strict' without reading the notes in _envEval();

/**
 * Begin a new templating process.
 * @param node A DOM element or string referring to an element's id
 * @param data Data to use in filling out the template
 * @param options Options to customize the template processing. One of:
 * - allowEval: boolean (default false) Basic template interpolations are
 *   either property paths (e.g. ${a.b.c.d}), or if allowEval=true then we
 *   allow arbitrary JavaScript
 * - stack: string or array of strings (default empty array) The template
 *   engine maintains a stack of tasks to help debug where it is. This allows
 *   this stack to be prefixed with a template name
 * - blankNullUndefined: By default DOMTemplate exports null and undefined
 *   values using the strings 'null' and 'undefined', which can be helpful for
 *   debugging, but can introduce unnecessary extra logic in a template to
 *   convert null/undefined to ''. By setting blankNullUndefined:true, this
 *   conversion is handled by DOMTemplate
 */
function template(node, data, options) {
  var template = new Templater(options || {});
  template.processNode(node, data);
  return template;
}

/**
 * Construct a Templater object. Use template() in preference to this ctor.
 * @deprecated Use template(node, data, options);
 */
function Templater(options) {
  if (options == null) {
    options = { allowEval: true };
  }
  this.options = options;
  if (options.stack && Array.isArray(options.stack)) {
    this.stack = options.stack;
  }
  else if (typeof options.stack === 'string') {
    this.stack = [ options.stack ];
  }
  else {
    this.stack = [];
  }
  this.nodes = [];
}

/**
 * Cached regex used to find ${...} sections in some text.
 * Performance note: This regex uses ( and ) to capture the 'script' for
 * further processing. Not all of the uses of this regex use this feature so
 * if use of the capturing group is a performance drain then we should split
 * this regex in two.
 */
Templater.prototype._templateRegion = /\$\{([^}]*)\}/g;

/**
 * Cached regex used to split a string using the unicode chars F001 and F002.
 * See Templater._processTextNode() for details.
 */
Templater.prototype._splitSpecial = /\uF001|\uF002/;

/**
 * Cached regex used to detect if a script is capable of being interpreted
 * using Template._property() or if we need to use Template._envEval()
 */
Templater.prototype._isPropertyScript = /^[_a-zA-Z0-9.]*$/;

/**
 * Recursive function to walk the tree processing the attributes as it goes.
 * @param node the node to process. If you pass a string in instead of a DOM
 * element, it is assumed to be an id for use with document.getElementById()
 * @param data the data to use for node processing.
 */
Templater.prototype.processNode = function(node, data) {
  if (typeof node === 'string') {
    node = document.getElementById(node);
  }
  if (data == null) {
    data = {};
  }
  this.stack.push(node.nodeName + (node.id ? '#' + node.id : ''));
  var pushedNode = false;
  try {
    // Process attributes
    if (node.attributes && node.attributes.length) {
      // We need to handle 'foreach' and 'if' first because they might stop
      // some types of processing from happening, and foreach must come first
      // because it defines new data on which 'if' might depend.
      if (node.hasAttribute('foreach')) {
        this._processForEach(node, data);
        return;
      }
      if (node.hasAttribute('if')) {
        if (!this._processIf(node, data)) {
          return;
        }
      }
      // Only make the node available once we know it's not going away
      this.nodes.push(data.__element);
      data.__element = node;
      pushedNode = true;
      // It's good to clean up the attributes when we've processed them,
      // but if we do it straight away, we mess up the array index
      var attrs = Array.prototype.slice.call(node.attributes);
      for (var i = 0; i < attrs.length; i++) {
        var value = attrs[i].value;
        var name = attrs[i].name;
        this.stack.push(name);
        try {
          if (name === 'save') {
            // Save attributes are a setter using the node
            value = this._stripBraces(value);
            this._property(value, data, node);
            node.removeAttribute('save');
          } else if (name.substring(0, 2) === 'on') {
            // Event registration relies on property doing a bind
            value = this._stripBraces(value);
            var func = this._property(value, data);
            if (typeof func !== 'function') {
              this._handleError('Expected ' + value +
                ' to resolve to a function, but got ' + typeof func);
            }
            node.removeAttribute(name);
            var capture = node.hasAttribute('capture' + name.substring(2));
            node.addEventListener(name.substring(2), func, capture);
            if (capture) {
              node.removeAttribute('capture' + name.substring(2));
            }
          } else {
            // Replace references in all other attributes
            var newValue = value.replace(this._templateRegion, function(path) {
              var insert = this._envEval(path.slice(2, -1), data, value);
              if (this.options.blankNullUndefined && insert == null) {
                insert = '';
              }
              return insert;
            }.bind(this));
            // Remove '_' prefix of attribute names so the DOM won't try
            // to use them before we've processed the template
            if (name.charAt(0) === '_') {
              node.removeAttribute(name);
              node.setAttribute(name.substring(1), newValue);
            } else if (value !== newValue) {
              attrs[i].value = newValue;
            }
          }
        } finally {
          this.stack.pop();
        }
      }
    }

    // Loop through our children calling processNode. First clone them, so the
    // set of nodes that we visit will be unaffected by additions or removals.
    var childNodes = Array.prototype.slice.call(node.childNodes);
    for (var j = 0; j < childNodes.length; j++) {
      this.processNode(childNodes[j], data);
    }

    if (node.nodeType === 3 /*Node.TEXT_NODE*/) {
      this._processTextNode(node, data);
    }
  } finally {
    if (pushedNode) {
      data.__element = this.nodes.pop();
    }
    this.stack.pop();
  }
};

/**
 * Handle <x if="${...}">
 * @param node An element with an 'if' attribute
 * @param data The data to use with _envEval()
 * @returns true if processing should continue, false otherwise
 */
Templater.prototype._processIf = function(node, data) {
  this.stack.push('if');
  try {
    var originalValue = node.getAttribute('if');
    var value = this._stripBraces(originalValue);
    var recurse = true;
    try {
      var reply = this._envEval(value, data, originalValue);
      recurse = !!reply;
    } catch (ex) {
      this._handleError('Error with \'' + value + '\'', ex);
      recurse = false;
    }
    if (!recurse) {
      node.parentNode.removeChild(node);
    }
    node.removeAttribute('if');
    return recurse;
  } finally {
    this.stack.pop();
  }
};

/**
 * Handle <x foreach="param in ${array}"> and the special case of
 * <loop foreach="param in ${array}">.
 * This function is responsible for extracting what it has to do from the
 * attributes, and getting the data to work on (including resolving promises
 * in getting the array). It delegates to _processForEachLoop to actually
 * unroll the data.
 * @param node An element with a 'foreach' attribute
 * @param data The data to use with _envEval()
 */
Templater.prototype._processForEach = function(node, data) {
  this.stack.push('foreach');
  try {
    var originalValue = node.getAttribute('foreach');
    var value = originalValue;

    var paramName = 'param';
    if (value.charAt(0) === '$') {
      // No custom loop variable name. Use the default: 'param'
      value = this._stripBraces(value);
    } else {
      // Extract the loop variable name from 'NAME in ${ARRAY}'
      var nameArr = value.split(' in ');
      paramName = nameArr[0].trim();
      value = this._stripBraces(nameArr[1].trim());
    }
    node.removeAttribute('foreach');
    try {
      var evaled = this._envEval(value, data, originalValue);
      this._handleAsync(evaled, node, function(reply, siblingNode) {
        this._processForEachLoop(reply, node, siblingNode, data, paramName);
      }.bind(this));
      node.parentNode.removeChild(node);
    } catch (ex) {
      this._handleError('Error with \'' + value + '\'', ex);
    }
  } finally {
    this.stack.pop();
  }
};

/**
 * Called by _processForEach to handle looping over the data in a foreach loop.
 * This works with both arrays and objects.
 * Calls _processForEachMember() for each member of 'set'
 * @param set The object containing the data to loop over
 * @param template The node to copy for each set member
 * @param sibling The sibling node to which we add things
 * @param data the data to use for node processing
 * @param paramName foreach loops have a name for the parameter currently being
 * processed. The default is 'param'. e.g. <loop foreach="param in ${x}">...
 */
Templater.prototype._processForEachLoop = function(set, template, sibling, data, paramName) {
  if (Array.isArray(set)) {
    set.forEach(function(member, i) {
      this._processForEachMember(member, template, sibling, data, paramName, '' + i);
    }, this);
  } else {
    for (var member in set) {
      if (set.hasOwnProperty(member)) {
        this._processForEachMember(member, template, sibling, data, paramName, member);
      }
    }
  }
};

/**
 * Called by _processForEachLoop() to resolve any promises in the array (the
 * array itself can also be a promise, but that is resolved by
 * _processForEach()). Handle <LOOP> elements (which are taken out of the DOM),
 * clone the template, and pass the processing on to processNode().
 * @param member The data item to use in templating
 * @param template The node to copy for each set member
 * @param siblingNode The parent node to which we add things
 * @param data the data to use for node processing
 * @param paramName The name given to 'member' by the foreach attribute
 * @param frame A name to push on the stack for debugging
 */
Templater.prototype._processForEachMember = function(member, template, siblingNode, data, paramName, frame) {
  this.stack.push(frame);
  try {
    this._handleAsync(member, siblingNode, function(reply, node) {
      data[paramName] = reply;
      if (template.nodeName.toLowerCase() === 'loop') {
        for (var i = 0; i < template.childNodes.length; i++) {
          var clone = template.childNodes[i].cloneNode(true);
          node.parentNode.insertBefore(clone, node);
          this.processNode(clone, data);
        }
      } else {
        var clone = template.cloneNode(true);
        clone.removeAttribute('foreach');
        node.parentNode.insertBefore(clone, node);
        this.processNode(clone, data);
      }
      delete data[paramName];
    }.bind(this));
  } finally {
    this.stack.pop();
  }
};

/**
 * Take a text node and replace it with another text node with the ${...}
 * sections parsed out. We replace the node by altering node.parentNode but
 * we could probably use a DOM Text API to achieve the same thing.
 * @param node The Text node to work on
 * @param data The data to use in calls to _envEval()
 */
Templater.prototype._processTextNode = function(node, data) {
  // Replace references in other attributes
  var value = node.data;
  // We can't use the string.replace() with function trick (see generic
  // attribute processing in processNode()) because we need to support
  // functions that return DOM nodes, so we can't have the conversion to a
  // string.
  // Instead we process the string as an array of parts. In order to split
  // the string up, we first replace '${' with '\uF001$' and '}' with '\uF002'
  // We can then split using \uF001 or \uF002 to get an array of strings
  // where scripts are prefixed with $.
  // \uF001 and \uF002 are just unicode chars reserved for private use.
  value = value.replace(this._templateRegion, '\uF001$$$1\uF002');
  var parts = value.split(this._splitSpecial);
  if (parts.length > 1) {
    parts.forEach(function(part) {
      if (part === null || part === undefined || part === '') {
        return;
      }
      if (part.charAt(0) === '$') {
        part = this._envEval(part.slice(1), data, node.data);
      }
      this._handleAsync(part, node, function(reply, siblingNode) {
        var doc = siblingNode.ownerDocument;
        if (reply == null) {
          reply = this.options.blankNullUndefined ? '' : '' + reply;
        }
        if (typeof reply.cloneNode === 'function') {
          // i.e. if (reply instanceof Element) { ...
          reply = this._maybeImportNode(reply, doc);
          siblingNode.parentNode.insertBefore(reply, siblingNode);
        } else if (typeof reply.item === 'function' && reply.length) {
          // NodeLists can be live, in which case _maybeImportNode can
          // remove them from the document, and thus the NodeList, which in
          // turn breaks iteration. So first we clone the list
          var list = Array.prototype.slice.call(reply, 0);
          list.forEach(function(child) {
            var imported = this._maybeImportNode(child, doc);
            siblingNode.parentNode.insertBefore(imported, siblingNode);
          }.bind(this));
        }
        else {
          // if thing isn't a DOM element then wrap its string value in one
          reply = doc.createTextNode(reply.toString());
          siblingNode.parentNode.insertBefore(reply, siblingNode);
        }

      }.bind(this));
    }, this);
    node.parentNode.removeChild(node);
  }
};

/**
 * Return node or a import of node, if it's not in the given document
 * @param node The node that we want to be properly owned
 * @param doc The document that the given node should belong to
 * @return A node that belongs to the given document
 */
Templater.prototype._maybeImportNode = function(node, doc) {
  return node.ownerDocument === doc ? node : doc.importNode(node, true);
};

/**
 * A function to handle the fact that some nodes can be promises, so we check
 * and resolve if needed using a marker node to keep our place before calling
 * an inserter function.
 * @param thing The object which could be real data or a promise of real data
 * we use it directly if it's not a promise, or resolve it if it is.
 * @param siblingNode The element before which we insert new elements.
 * @param inserter The function to to the insertion. If thing is not a promise
 * then _handleAsync() is just 'inserter(thing, siblingNode)'
 */
Templater.prototype._handleAsync = function(thing, siblingNode, inserter) {
  if (thing != null && typeof thing.then === 'function') {
    // Placeholder element to be replaced once we have the real data
    var tempNode = siblingNode.ownerDocument.createElement('span');
    siblingNode.parentNode.insertBefore(tempNode, siblingNode);
    thing.then(function(delayed) {
      inserter(delayed, tempNode);
      tempNode.parentNode.removeChild(tempNode);
    }.bind(this));
  }
  else {
    inserter(thing, siblingNode);
  }
};

/**
 * Warn of string does not begin '${' and end '}'
 * @param str the string to check.
 * @return The string stripped of ${ and }, or untouched if it does not match
 */
Templater.prototype._stripBraces = function(str) {
  if (!str.match(this._templateRegion)) {
    this._handleError('Expected ' + str + ' to match ${...}');
    return str;
  }
  return str.slice(2, -1);
};

/**
 * Combined getter and setter that works with a path through some data set.
 * For example:
 * <ul>
 * <li>_property('a.b', { a: { b: 99 }}); // returns 99
 * <li>_property('a', { a: { b: 99 }}); // returns { b: 99 }
 * <li>_property('a', { a: { b: 99 }}, 42); // returns 99 and alters the
 * input data to be { a: { b: 42 }}
 * </ul>
 * @param path An array of strings indicating the path through the data, or
 * a string to be cut into an array using <tt>split('.')</tt>
 * @param data the data to use for node processing
 * @param newValue (optional) If defined, this value will replace the
 * original value for the data at the path specified.
 * @return The value pointed to by <tt>path</tt> before any
 * <tt>newValue</tt> is applied.
 */
Templater.prototype._property = function(path, data, newValue) {
  try {
    if (typeof path === 'string') {
      path = path.split('.');
    }
    var value = data[path[0]];
    if (path.length === 1) {
      if (newValue !== undefined) {
        data[path[0]] = newValue;
      }
      if (typeof value === 'function') {
        return value.bind(data);
      }
      return value;
    }
    if (!value) {
      this._handleError('"' + path[0] + '" is undefined');
      return null;
    }
    return this._property(path.slice(1), value, newValue);
  } catch (ex) {
    this._handleError('Path error with \'' + path + '\'', ex);
    return '${' + path + '}';
  }
};

/**
 * Like eval, but that creates a context of the variables in <tt>env</tt> in
 * which the script is evaluated.
 * WARNING: This script uses 'with' which is generally regarded to be evil.
 * The alternative is to create a Function at runtime that takes X parameters
 * according to the X keys in the env object, and then call that function using
 * the values in the env object. This is likely to be slow, but workable.
 * @param script The string to be evaluated.
 * @param data The environment in which to eval the script.
 * @param frame Optional debugging string in case of failure.
 * @return The return value of the script, or the error message if the script
 * execution failed.
 */
Templater.prototype._envEval = function(script, data, frame) {
  try {
    this.stack.push(frame.replace(/\s+/g, ' '));
    if (this._isPropertyScript.test(script)) {
      return this._property(script, data);
    } else {
      if (!this.options.allowEval) {
        this._handleError('allowEval is not set, however \'' + script + '\'' +
            ' can not be resolved using a simple property path.');
        return '${' + script + '}';
      }
      with (data) {
        return eval(script);
      }
    }
  } catch (ex) {
    this._handleError('Template error evaluating \'' + script + '\'', ex);
    return '${' + script + '}';
  } finally {
    this.stack.pop();
  }
};

/**
 * A generic way of reporting errors, for easy overloading in different
 * environments.
 * @param message the error message to report.
 * @param ex optional associated exception.
 */
Templater.prototype._handleError = function(message, ex) {
  this._logError(message + ' (In: ' + this.stack.join(' > ') + ')');
  if (ex) {
    this._logError(ex);
  }
};


/**
 * A generic way of reporting errors, for easy overloading in different
 * environments.
 * @param message the error message to report.
 */
Templater.prototype._logError = function(message) {
  Services.console.logStringMessage(message);
};