Apex script for parsing and updating generated WSDL2Apex from Metadata API WSDL, uses Tooling REST API to dynamically create the modified code.

gistfile1.cls

public with sharing class MetadataServicePatcher {

	// Perhaps parse these from the WSDL in the future
	private static final Map<String, String> METADATA_TYPES = 
		new Map<String, String> { 
			'CustomSite' => 'Metadata', 
			'InstalledPackage' => 'Metadata',
			'CustomField' => 'Metadata',
			'FieldSet' => 'Metadata',
			'PicklistValue' => 'Metadata',
			'RecordType' => 'Metadata',
			'WebLink' => 'Metadata',
			'AddressSettings' => 'Metadata',
			'CaseSettings' => 'Metadata',
			'CustomObject' => 'Metadata',
			'Layout' => 'Metadata',
			'ApexPage' => 'MetadataWithContent',
			'ApexClass' => 'MetadataWithContent',
			'StaticResource' => 'MetadataWithContent'
			 };
	
	public static void patch()
	{
		// Query the current Apex Class
		ApexClass apexClass = 
			[select Id, Body 
			  from ApexClass 
			  where Name = 'MetadataServiceImported'];
			
		// Process and scan for lines to modify and/or insert
		LineReader lineReader = new LineReader(apexClass.Body);
		List<String> newLines = new List<String>();
		while(lineReader.hasNext())
		{
			// Read line
			String line = lineReader.next();
			String trimmedLine = line.trim();
			// Adjust class name?
			if(trimmedLine.contains('MetadataServiceImported'))
				line = line.replace('MetadataServiceImported', 'MetadataService');			
			// Adjust end point logic?
			if(trimmedLine.startsWith('public String endpoint_x'))
				line = '        public String endpoint_x = URL.getSalesforceBaseUrl().toExternalForm() + \'/services/Soap/m/30.0\';';
			// Adjust update_x method name?
			else if(trimmedLine.contains('update_x('))
				line = line.replace('update_x', 'updateMetadata');			
			// Adjust delete_x method name?
			else if(trimmedLine.contains('delete_x('))
				line = line.replace('delete_x', 'deleteMetadata');			
			// Adjust retrieve_x method name?
			else if(trimmedLine.contains('retrieve_x('))
				line = line.replace('retrieve_x', 'retrieve');
			// Make Metadata virtual?
			else if(trimmedLine.startsWith('public class Metadata '))
				line = line.replace('public class', 'public virtual class');				
			// Make MetadataWithContent virtual?
			else if(trimmedLine.startsWith('public class MetadataWithContent '))
				line = line.replace('public class MetadataWithContent', 'public virtual class MetadataWithContent extends Metadata');			
			// Class definition?
			else if(trimmedLine.startsWith('public class'))
			{			
				List<String> parts = trimmedLine.split(' ');
				String className = parts[2];
				if(METADATA_TYPES.containsKey(className))
				{
					// Adjust class to extend base class and add base class members (XML serialiser does not support inheritance)
					String extendsClassName = METADATA_TYPES.get(className); 
					line = line.replace('public class ' + className, 'public class ' + className + ' extends ' + extendsClassName);
					newLines.add(line);
					newLines.add('        public String type = \'' + className + '\';');
					newLines.add('        public String fullName;');
					if(extendsClassName.equals('MetadataWithContent'))
						newLines.add('        public String content;');
					// Move forward until field_order_type_info member
					while(lineReader.hasNext())
					{
						line = (String) lineReader.next();
						trimmedLine = line.trim();
						// Adjust class name?
						if(trimmedLine.contains('MetadataServiceImported'))
							line = line.replace('MetadataServiceImported', 'MetadataService');									
						else if(trimmedLine.startsWith('private String[] field_order_type_info'))
						{
							// Add type info descriptors and adjust field_order_type_info list
							newLines.add('        private String[] type_att_info = new String[]{\'xsi:type\'};');
							newLines.add('        private String[] fullName_type_info = new String[]{\'fullName\',\'http://www.w3.org/2001/XMLSchema\',\'string\',\'0\',\'1\',\'false\'};');
							if(extendsClassName.equals('MetadataWithContent'))
							{
								newLines.add('        private String[] content_type_info = new String[]{\'content\',\'http://www.w3.org/2001/XMLSchema\',\'base64Binary\',\'0\',\'1\',\'false\'};');
								line = line.replace('new String[]{', 'new String[]{\'fullName\', \'content\', ');
							}
							else
							{
								line = line.replace('new String[]{', 'new String[]{\'fullName\', ');
							}
							newLines.add(line);
							break;														
						}
						newLines.add(line);
					}
					continue;
				}
			}
			newLines.add(line);
		}
							  
		// Query for the patched ApexClass (via Tooling REST API)?			  
		Http h = new Http();	    
	    HttpRequest queryReq = new HttpRequest();
	    queryReq.setEndpoint(URL.getSalesforceBaseUrl().toExternalForm() + '/services/data/v29.0/tooling/query/?q=SELECT+Id+from+ApexClass+Where+Name=\'MetadataService\'');
	    queryReq.setHeader('Authorization', 'OAuth ' + UserInfo.getSessionId());
	    queryReq.setHeader('Content-Type', 'application/json');
	    queryReq.setMethod('GET');
	    HttpResponse queryRes = h.send(queryReq);
	    if(queryRes.getStatusCode() != 200)
	    	throw new PatchException(queryReq.getEndpoint() + ' ' + queryRes.getStatusCode() + ' ' + queryRes.getBody());			    	    
	    Map<String, Object> queryData = (Map<String, Object>) JSON.deserializeUntyped(queryRes.getBody());
	    Integer size = (Integer) queryData.get('size');			
		if(size > 0)
		{
			// Delete the patch ApexClass (via Tooling REST API)
			List<Object> records = (List<Object>) queryData.get('records');
			Map<String, Object> recordList = (Map<String, Object>) records[0];
			String classId = (String) recordList.get('Id');
		    HttpRequest deleteReq = new HttpRequest();		    
		    deleteReq.setEndpoint(URL.getSalesforceBaseUrl().toExternalForm() + '/services/data/v29.0/tooling/sobjects/ApexClass/'+classId);
		    deleteReq.setHeader('Authorization', 'OAuth ' + UserInfo.getSessionId());
		    deleteReq.setHeader('Content-Type', 'application/json');
		    deleteReq.setMethod('DELETE');
		    HttpResponse deleteRes = h.send(deleteReq);
		    if(deleteRes.getStatusCode() != 204)
		    	throw new PatchException(deleteReq.getEndpoint() + ' ' + deleteRes.getStatusCode() + ' ' + deleteRes.getBody());			    
		}
		
		// Create the patched ApexClass (via Tooling REST API)
		String patchClass = String.join(newLines, '\n');
	    JSONGenerator body = JSON.createGenerator(false);
	    body.writeStartObject();
	    body.writeStringField('Name', 'MetadataService');
	    body.writeStringField('Body', patchClass);
	    body.writeEndObject();
	    HttpRequest createReq = new HttpRequest();
	    createReq.setEndpoint(URL.getSalesforceBaseUrl().toExternalForm() + '/services/data/v29.0/tooling/sobjects/ApexClass');
	    createReq.setBody( body.getAsString() );
	    createReq.setHeader('Authorization', 'OAuth ' + UserInfo.getSessionId());
	    createReq.setHeader('Content-Type', 'application/json');
	    createReq.setMethod('POST');
	    HttpResponse createRes = h.send(createReq);
	    if(createRes.getStatusCode() != 201)
	    	throw new PatchException(createRes.getStatusCode() + ' ' + createRes.getBody());
	}
	
	public class PatchException extends Exception { }
	
	/**
	 * Utility class to iterate over lines in Apex source code
	 **/
	public class LineReader 
		implements Iterator<string>, Iterable<string>
	{		
		private String LF = '\n';
		
		private String textData;
		
		public LineReader(String textData)
		{		
			this.textData = textData;
		}
		
		public Boolean hasNext()
		{
			return textData.length() > 0 ? true : false;
		}	
		
		public String next()
		{
			String row = null;
			Integer endPos = textData.indexOf(LF);
			if(endPos == -1)
			{
				row = textData;
				textData = '';
			}
			else
			{
				row = textData.subString(0, endPos);
				textData = textData.subString(endPos + LF.length(), textData.length());				
			}
			return row;
   		}
   		
		public Iterator<String> Iterator()
		{
			return this;   
		}   		
	}
}