diff --git a/gitc_utils.py b/gitc_utils.py
index d082c8d..dd38f89 100644
--- a/gitc_utils.py
+++ b/gitc_utils.py
@@ -15,6 +15,8 @@
 
 from __future__ import print_function
 import os
+import platform
+import re
 import sys
 import time
 
@@ -22,7 +24,6 @@
 import git_config
 import wrapper
 
-
 GITC_FS_ROOT_DIR = '/gitc/manifest-rw/'
 NUM_BATCH_RETRIEVE_REVISIONID = 300
 
@@ -65,26 +66,82 @@
       sys.exit(1)
     proj.revisionExpr = gitcmd.stdout.split('\t')[0]
 
-def generate_gitc_manifest(client_dir, manifest, projects=None):
+def _manifest_groups(manifest):
+  """Returns the manifest group string that should be synced
+
+  This is the same logic used by Command.GetProjects(), which is used during
+  repo sync
+
+  @param manifest: The XmlManifest object
+  """
+  mp = manifest.manifestProject
+  groups = mp.config.GetString('manifest.groups')
+  if not groups:
+    groups = 'default,platform-' + platform.system().lower()
+  return groups
+
+def generate_gitc_manifest(gitc_manifest, manifest, paths=None):
   """Generate a manifest for shafsd to use for this GITC client.
 
-  @param client_dir: GITC client directory to install the .manifest file in.
-  @param manifest: XmlManifest object representing the repo manifest.
-  @param projects: List of projects we want to update, this must be a sublist
-                   of manifest.projects to work properly. If not provided,
-                   manifest.projects is used.
+  @param gitc_manifest: Current gitc manifest, or None if there isn't one yet.
+  @param manifest: A GitcManifest object loaded with the current repo manifest.
+  @param paths: List of project paths we want to update.
   """
+
   print('Generating GITC Manifest by fetching revision SHAs for each '
         'project.')
-  if projects is None:
-    projects = manifest.projects
+  if paths is None:
+    paths = manifest.paths.keys()
+
+  groups = [x for x in re.split(r'[,\s]+', _manifest_groups(manifest)) if x]
+
+  # Convert the paths to projects, and filter them to the matched groups.
+  projects = [manifest.paths[p] for p in paths]
+  projects = [p for p in projects if p.MatchesGroups(groups)]
+
+  if gitc_manifest is not None:
+    for path, proj in manifest.paths.iteritems():
+      if not proj.MatchesGroups(groups):
+        continue
+
+      if not proj.upstream and not git_config.IsId(proj.revisionExpr):
+        proj.upstream = proj.revisionExpr
+
+      if not path in gitc_manifest.paths:
+        # Any new projects need their first revision, even if we weren't asked
+        # for them.
+        projects.append(proj)
+      elif not path in paths:
+        # And copy revisions from the previous manifest if we're not updating
+        # them now.
+        gitc_proj = gitc_manifest.paths[path]
+        if gitc_proj.old_revision:
+          proj.revisionExpr = None
+          proj.old_revision = gitc_proj.old_revision
+        else:
+          proj.revisionExpr = gitc_proj.revisionExpr
+
   index = 0
   while index < len(projects):
     _set_project_revisions(
         projects[index:(index+NUM_BATCH_RETRIEVE_REVISIONID)])
     index += NUM_BATCH_RETRIEVE_REVISIONID
+
+  if gitc_manifest is not None:
+    for path, proj in gitc_manifest.paths.iteritems():
+      if proj.old_revision and path in paths:
+        # If we updated a project that has been started, keep the old-revision
+        # updated.
+        repo_proj = manifest.paths[path]
+        repo_proj.old_revision = repo_proj.revisionExpr
+        repo_proj.revisionExpr = None
+
+  # Convert URLs from relative to absolute.
+  for name, remote in manifest.remotes.iteritems():
+    remote.fetchUrl = remote.resolvedFetchUrl
+
   # Save the manifest.
-  save_manifest(manifest, client_dir=client_dir)
+  save_manifest(manifest)
 
 def save_manifest(manifest, client_dir=None):
   """Save the manifest file in the client_dir.
@@ -95,7 +152,7 @@
   if not client_dir:
     client_dir = manifest.gitc_client_dir
   with open(os.path.join(client_dir, '.manifest'), 'w') as f:
-    manifest.Save(f)
+    manifest.Save(f, groups=_manifest_groups(manifest))
   # TODO(sbasi/jorg): Come up with a solution to remove the sleep below.
   # Give the GITC filesystem time to register the manifest changes.
-  time.sleep(3)
\ No newline at end of file
+  time.sleep(3)