elementpath.js

/**
 *  Copyright 2011 Rackspace
 *
 *  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.
 *
 */

var sprintf = require('./sprintf').sprintf;

var utils = require('./utils');
var SyntaxError = require('./errors').SyntaxError;

var _cache = {};

var RE = new RegExp(
  "(" +
  "'[^']*'|\"[^\"]*\"|" +
  "::|" +
  "//?|" +
  "\\.\\.|" +
  "\\(\\)|" +
  "[/.*:\\[\\]\\(\\)@=])|" +
  "((?:\\{[^}]+\\})?[^/\\[\\]\\(\\)@=\\s]+)|" +
  "\\s+", 'g'
);

var xpath_tokenizer = utils.findall.bind(null, RE);

function prepare_tag(next, token) {
  var tag = token[0];

  function select(context, result) {
    var i, len, elem, rv = [];

    for (i = 0, len = result.length; i < len; i++) {
      elem = result[i];
      elem._children.forEach(function(e) {
        if (e.tag === tag) {
          rv.push(e);
        }
      });
    }

    return rv;
  }

  return select;
}

function prepare_star(next, token) {
  function select(context, result) {
    var i, len, elem, rv = [];

    for (i = 0, len = result.length; i < len; i++) {
      elem = result[i];
      elem._children.forEach(function(e) {
        rv.push(e);
      });
    }

    return rv;
  }

  return select;
}

function prepare_dot(next, token) {
  function select(context, result) {
    var i, len, elem, rv = [];

    for (i = 0, len = result.length; i < len; i++) {
      elem = result[i];
      rv.push(elem);
    }

    return rv;
  }

  return select;
}

function prepare_iter(next, token) {
  var tag;
  token = next();

  if (token[1] === '*') {
    tag = '*';
  }
  else if (!token[1]) {
    tag = token[0] || '';
  }
  else {
    throw new SyntaxError(token);
  }

  function select(context, result) {
    var i, len, elem, rv = [];

    for (i = 0, len = result.length; i < len; i++) {
      elem = result[i];
      elem.iter(tag, function(e) {
        if (e !== elem) {
          rv.push(e);
        }
      });
    }

    return rv;
  }

  return select;
}

function prepare_dot_dot(next, token) {
  function select(context, result) {
    var i, len, elem, rv = [], parent_map = context.parent_map;

    if (!parent_map) {
      context.parent_map = parent_map = {};

      context.root.iter(null, function(p) {
        p._children.forEach(function(e) {
          parent_map[e] = p;
        });
      });
    }

    for (i = 0, len = result.length; i < len; i++) {
      elem = result[i];

      if (parent_map.hasOwnProperty(elem)) {
        rv.push(parent_map[elem]);
      }
    }

    return rv;
  }

  return select;
}


function prepare_predicate(next, token) {
  var tag, key, value, select;
  token = next();

  if (token[1] === '@') {
    // attribute
    token = next();

    if (token[1]) {
      throw new SyntaxError(token, 'Invalid attribute predicate');
    }

    key = token[0];
    token = next();

    if (token[1] === ']') {
      select = function(context, result) {
        var i, len, elem, rv = [];

        for (i = 0, len = result.length; i < len; i++) {
          elem = result[i];

          if (elem.get(key)) {
            rv.push(elem);
          }
        }

        return rv;
      };
    }
    else if (token[1] === '=') {
      value = next()[1];

      if (value[0] === '"' || value[value.length - 1] === '\'') {
        value = value.slice(1, value.length - 1);
      }
      else {
        throw new SyntaxError(token, 'Ivalid comparison target');
      }

      token = next();
      select = function(context, result) {
        var i, len, elem, rv = [];

        for (i = 0, len = result.length; i < len; i++) {
          elem = result[i];

          if (elem.get(key) === value) {
            rv.push(elem);
          }
        }

        return rv;
      };
    }

    if (token[1] !== ']') {
      throw new SyntaxError(token, 'Invalid attribute predicate');
    }
  }
  else if (!token[1]) {
    tag = token[0] || '';
    token = next();

    if (token[1] !== ']') {
      throw new SyntaxError(token, 'Invalid node predicate');
    }

    select = function(context, result) {
      var i, len, elem, rv = [];

      for (i = 0, len = result.length; i < len; i++) {
        elem = result[i];

        if (elem.find(tag)) {
          rv.push(elem);
        }
      }

      return rv;
    };
  }
  else {
    throw new SyntaxError(null, 'Invalid predicate');
  }

  return select;
}



var ops = {
  "": prepare_tag,
  "*": prepare_star,
  ".": prepare_dot,
  "..": prepare_dot_dot,
  "//": prepare_iter,
  "[": prepare_predicate,
};

function _SelectorContext(root) {
  this.parent_map = null;
  this.root = root;
}

function findall(elem, path) {
  var selector, result, i, len, token, value, select, context;

  if (_cache.hasOwnProperty(path)) {
    selector = _cache[path];
  }
  else {
    // TODO: Use smarter cache purging approach
    if (Object.keys(_cache).length > 100) {
      _cache = {};
    }

    if (path.charAt(0) === '/') {
      throw new SyntaxError(null, 'Cannot use absolute path on element');
    }

    result = xpath_tokenizer(path);
    selector = [];

    function getToken() {
      return result.shift();
    }

    token = getToken();
    while (true) {
      var c = token[1] || '';
      value = ops[c](getToken, token);

      if (!value) {
        throw new SyntaxError(null, sprintf('Invalid path: %s', path));
      }

      selector.push(value);
      token = getToken();

      if (!token) {
        break;
      }
      else if (token[1] === '/') {
        token = getToken();
      }

      if (!token) {
        break;
      }
    }

    _cache[path] = selector;
  }

  // Execute slector pattern
  result = [elem];
  context = new _SelectorContext(elem);

  for (i = 0, len = selector.length; i < len; i++) {
    select = selector[i];
    result = select(context, result);
  }

  return result || [];
}

function find(element, path) {
  var resultElement = findall(element, path);

  if (resultElement) {
    return resultElement[0];
  }

  return null;
}

function findtext(element, path, defvalue) {
  var resultElements = findall(element, path);

  if (resultElements) {
    return resultElements[0].text;
  }

  return defvalue;
}


exports.find = find;
exports.findall = findall;
exports.findtext = findtext;