var util = require('../util');
var Shape = require('../model/shape');

function DomXmlParser() { }

DomXmlParser.prototype.parse = function(xml, shape) {
  if (xml.replace(/^\s+/, '') === '') return {};

  var result, error;
  try {
    if (window.DOMParser) {
      try {
        var parser = new DOMParser();
        result = parser.parseFromString(xml, 'text/xml');
      } catch (syntaxError) {
        throw util.error(new Error('Parse error in document'),
          {
            originalError: syntaxError,
            code: 'XMLParserError',
            retryable: true
          });
      }

      if (result.documentElement === null) {
        throw util.error(new Error('Cannot parse empty document.'),
          {
            code: 'XMLParserError',
            retryable: true
          });
      }

      var isError = result.getElementsByTagName('parsererror')[0];
      if (isError && (isError.parentNode === result ||
          isError.parentNode.nodeName === 'body' ||
          isError.parentNode.parentNode === result ||
          isError.parentNode.parentNode.nodeName === 'body')) {
        var errorElement = isError.getElementsByTagName('div')[0] || isError;
        throw util.error(new Error(errorElement.textContent || 'Parser error in document'),
          {
            code: 'XMLParserError',
            retryable: true
          });
      }
    } else if (window.ActiveXObject) {
      result = new window.ActiveXObject('Microsoft.XMLDOM');
      result.async = false;

      if (!result.loadXML(xml)) {
        throw util.error(new Error('Parse error in document'),
          {
            code: 'XMLParserError',
            retryable: true
          });
      }
    } else {
      throw new Error('Cannot load XML parser');
    }
  } catch (e) {
    error = e;
  }

  if (result && result.documentElement && !error) {
    var data = parseXml(result.documentElement, shape);
    var metadata = getElementByTagName(result.documentElement, 'ResponseMetadata');
    if (metadata) {
      data.ResponseMetadata = parseXml(metadata, {});
    }
    return data;
  } else if (error) {
    throw util.error(error || new Error(), {code: 'XMLParserError', retryable: true});
  } else { // empty xml document
    return {};
  }
};

function getElementByTagName(xml, tag) {
  var elements = xml.getElementsByTagName(tag);
  for (var i = 0, iLen = elements.length; i < iLen; i++) {
    if (elements[i].parentNode === xml) {
      return elements[i];
    }
  }
}

function parseXml(xml, shape) {
  if (!shape) shape = {};
  switch (shape.type) {
    case 'structure': return parseStructure(xml, shape);
    case 'map': return parseMap(xml, shape);
    case 'list': return parseList(xml, shape);
    case undefined: case null: return parseUnknown(xml);
    default: return parseScalar(xml, shape);
  }
}

function parseStructure(xml, shape) {
  var data = {};
  if (xml === null) return data;

  util.each(shape.members, function(memberName, memberShape) {
    if (memberShape.isXmlAttribute) {
      if (Object.prototype.hasOwnProperty.call(xml.attributes, memberShape.name)) {
        var value = xml.attributes[memberShape.name].value;
        data[memberName] = parseXml({textContent: value}, memberShape);
      }
    } else {
      var xmlChild = memberShape.flattened ? xml :
        getElementByTagName(xml, memberShape.name);
      if (xmlChild) {
        data[memberName] = parseXml(xmlChild, memberShape);
      } else if (!memberShape.flattened && memberShape.type === 'list') {
        data[memberName] = memberShape.defaultValue;
      }
    }
  });

  return data;
}

function parseMap(xml, shape) {
  var data = {};
  var xmlKey = shape.key.name || 'key';
  var xmlValue = shape.value.name || 'value';
  var tagName = shape.flattened ? shape.name : 'entry';

  var child = xml.firstElementChild;
  while (child) {
    if (child.nodeName === tagName) {
      var key = getElementByTagName(child, xmlKey).textContent;
      var value = getElementByTagName(child, xmlValue);
      data[key] = parseXml(value, shape.value);
    }
    child = child.nextElementSibling;
  }
  return data;
}

function parseList(xml, shape) {
  var data = [];
  var tagName = shape.flattened ? shape.name : (shape.member.name || 'member');

  var child = xml.firstElementChild;
  while (child) {
    if (child.nodeName === tagName) {
      data.push(parseXml(child, shape.member));
    }
    child = child.nextElementSibling;
  }
  return data;
}

function parseScalar(xml, shape) {
  if (xml.getAttribute) {
    var encoding = xml.getAttribute('encoding');
    if (encoding === 'base64') {
      shape = new Shape.create({type: encoding});
    }
  }

  var text = xml.textContent;
  if (text === '') text = null;
  if (typeof shape.toType === 'function') {
    return shape.toType(text);
  } else {
    return text;
  }
}

function parseUnknown(xml) {
  if (xml === undefined || xml === null) return '';

  // empty object
  if (!xml.firstElementChild) {
    if (xml.parentNode.parentNode === null) return {};
    if (xml.childNodes.length === 0) return '';
    else return xml.textContent;
  }

  // object, parse as structure
  var shape = {type: 'structure', members: {}};
  var child = xml.firstElementChild;
  while (child) {
    var tag = child.nodeName;
    if (Object.prototype.hasOwnProperty.call(shape.members, tag)) {
      // multiple tags of the same name makes it a list
      shape.members[tag].type = 'list';
    } else {
      shape.members[tag] = {name: tag};
    }
    child = child.nextElementSibling;
  }
  return parseStructure(xml, shape);
}

/**
 * @api private
 */
module.exports = DomXmlParser;