diff --git a/mercurial/state.py b/mercurial/state.py
new file mode 100644
--- /dev/null
+++ b/mercurial/state.py
@@ -0,0 +1,89 @@
+# state.py - writing and reading state files in Mercurial
+#
+# Copyright 2018 Pulkit Goyal <pulkitmgoyal@gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+"""
+This file contains class to wrap the state for commands and other
+related logic.
+
+All the data related to the command state is stored as dictionary in the object.
+The class has methods using which the data can be stored to disk in a file under
+.hg/ directory.
+
+We store the data on disk in cbor, for which we use the third party cbor library
+to serialize and deserialize data.
+"""
+
+from __future__ import absolute_import
+
+from .thirdparty import cbor
+
+from . import (
+    util,
+)
+
+class cmdstate(object):
+    """a wrapper class to store the state of commands like `rebase`, `graft`,
+    `histedit`, `shelve` etc. Extensions can also use this to write state files.
+
+    All the data for the state is stored in the form of key-value pairs in a
+    dictionary.
+
+    The class object can write all the data to a file in .hg/ directory and
+    can populate the object data reading that file.
+
+    Uses cbor to serialize and deserialize data while writing and reading from
+    disk.
+    """
+
+    def __init__(self, repo, fname, opts=None):
+        """ repo is the repo object
+        fname is the file name in which data should be stored in .hg directory
+        opts is a dictionary of data of the statefile
+        """
+        self._repo = repo
+        self.fname = fname
+        if not opts:
+            self.opts = {}
+        else:
+            self.opts = opts
+
+    def __nonzero__(self):
+        return self.exists()
+
+    def __getitem__(self, key):
+        return self.opts[key]
+
+    def load(self):
+        """load the existing evolvestate file into the class object"""
+        op = self._read()
+        self.opts.update(op)
+
+    def addopts(self, opts):
+        """add more key-value pairs to the data stored by the object"""
+        self.opts.update(opts)
+
+    def save(self):
+        """write all the evolvestate data stored in .hg/evolvestate file
+
+        we use third-party library cbor to serialize data to write in the file.
+        """
+        with self._repo.vfs(self.fname, 'wb', atomictemp=True) as fp:
+            cbor.dump(self.opts, fp)
+
+    def _read(self):
+        """reads the evolvestate file and returns a dictionary which contain
+        data in the same format as it was before storing"""
+        with self._repo.vfs(self.fname, 'rb') as fp:
+            return cbor.load(fp)
+
+    def delete(self):
+        """drop the evolvestate file if exists"""
+        util.unlinkpath(self._repo.vfs.join(self.fname), ignoremissing=True)
+
+    def exists(self):
+        """check whether the evolvestate file exists or not"""
+        return self._repo.vfs.exists(self.fname)