Adds class method to create from dict and on_sync method

pisa/appointment.py

@@ -15,14 +15,32 @@ class Appointment:
         self.cipher = cipher
         self.hash_function = hash_function
 
+    @classmethod
+    def from_dict(cls, appointment_data):
+        locator = appointment_data.get("locator")
+        start_time = appointment_data.get("start_time")    # ToDo: #4-standardize-appointment-fields
+        end_time = appointment_data.get("end_time")    # ToDo: #4-standardize-appointment-fields
+        dispute_delta = appointment_data.get("dispute_delta")
+        encrypted_blob_data = appointment_data.get("encrypted_blob")
+        cipher = appointment_data.get("cipher")
+        hash_function = appointment_data.get("hash_function")
+
+        if all([locator, start_time, end_time, dispute_delta, encrypted_blob_data, cipher, hash_function]) is not None:
+            appointment = cls(locator, start_time, end_time, dispute_delta, EncryptedBlob(encrypted_blob_data), cipher,
+                              hash_function)
+
+        else:
+            raise ValueError("Wrong appointment data, some fields are missing")
+
+        return appointment
+
     def to_dict(self):
+        # ToDO: #3-improve-appointment-structure
         appointment = {"locator": self.locator, "start_time": self.start_time, "end_time": self.end_time,
                        "dispute_delta": self.dispute_delta, "encrypted_blob": self.encrypted_blob.data,
                        "cipher": self.cipher, "hash_function": self.hash_function}
 
         return appointment
 
-        # ToDO: #3-improve-appointment-structure
-
     def to_json(self):
         return json.dumps(self.to_dict(), sort_keys=True, separators=(',', ':'))