use tokenObj in burn (#156)

* use tokenObj in burn

* refactor token serialization

* add tests

* rename

cashu/core/base.py

@@ -1,3 +1,5 @@
+import base64
+import json
 from sqlite3 import Row
 from typing import Any, Dict, List, Optional, TypedDict, Union
 
@@ -357,3 +359,37 @@ class TokenV3(BaseModel):
         if self.memo:
             return_dict.update(dict(memo=self.memo))  # type: ignore
         return return_dict
+
+    def get_proofs(self):
+        return [proof for token in self.token for proof in token.proofs]
+
+    def get_amount(self):
+        return sum([p.amount for p in self.get_proofs()])
+
+    def get_keysets(self):
+        return list(set([p.id for p in self.get_proofs()]))
+
+    @classmethod
+    def deserialize(cls, tokenv3_serialized: str):
+        """
+        Takes a TokenV3 and serializes it as "cashuA<json_urlsafe_base64>.
+        """
+        prefix = "cashuA"
+        assert tokenv3_serialized.startswith(prefix), Exception(
+            f"Token prefix not valid. Expected {prefix}."
+        )
+        token_base64 = tokenv3_serialized[len(prefix) :]
+        token = json.loads(base64.urlsafe_b64decode(token_base64))
+        return cls.parse_obj(token)
+
+    def serialize(self):
+        """
+        Takes a TokenV3 and serializes it as "cashuA<json_urlsafe_base64>.
+        """
+        prefix = "cashuA"
+        tokenv3_serialized = prefix
+        # encode the token as a base64 string
+        tokenv3_serialized += base64.urlsafe_b64encode(
+            json.dumps(self.to_dict()).encode()
+        ).decode()
+        return tokenv3_serialized