Policy json serializer (#58)

* Read/write native scripts to/from dict

* Differentiate between ints and strings for to_dict

* Add json_tag/field params to each native script

* Format with black

* Add docstring

* Add to/from_dict tests

Author: astrojarred

pycardano/nativescript.py

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass, field
-from typing import List, Union
+from typing import ClassVar, List, Union
 
 from nacl.encoding import RawEncoder
 from nacl.hash import blake2b
@@ -52,16 +52,80 @@ def hash(self) -> ScriptHash:
             )
         )
 
+    @classmethod
+    def from_dict(
+        cls: NativeScript, script: dict, top_level: bool = True
+    ) -> Union[
+        ScriptPubkey, ScriptAll, ScriptAny, ScriptNofK, InvalidBefore, InvalidHereAfter
+    ]:
+        """Parse a standard native script dictionary (potentially parsed from a JSON file)."""
+
+        types = {
+            p.json_tag: p
+            for p in [
+                ScriptPubkey,
+                ScriptAll,
+                ScriptAny,
+                ScriptNofK,
+                InvalidBefore,
+                InvalidHereAfter,
+            ]
+        }
+
+        if isinstance(script, dict):
+            native_script = []
+
+            for key, value in script.items():
+                if key == "type":
+                    native_script.insert(0, list(types.keys()).index(value))
+                elif key == "scripts":
+                    native_script.append(cls.from_dict(value, top_level=False))
+                else:
+                    native_script.append(value)
+
+        elif isinstance(script, list):  # list
+            native_script = [cls.from_dict(i, top_level=False) for i in script]
+
+        if not top_level:
+            return native_script
+        else:
+            return super(NativeScript, types[script["type"]]).from_primitive(
+                native_script[1:]
+            )
+
+    def to_dict(self) -> dict:
+        """Export to standard native script dictionary (potentially to dump to a JSON file)."""
+
+        script = {}
+
+        for value in self.__dict__.values():
+            script["type"] = self.json_tag
+
+            if isinstance(value, list):
+                script["scripts"] = [i.to_dict() for i in value]
+
+            else:
+                if isinstance(value, int):
+                    script[self.json_field] = value
+                else:
+                    script[self.json_field] = str(value)
+
+        return script
+
 
 @dataclass
 class ScriptPubkey(NativeScript):
+    json_tag: ClassVar[str] = "sig"
+    json_field: ClassVar[str] = "keyHash"
     _TYPE: int = field(default=0, init=False)
 
     key_hash: VerificationKeyHash
 
 
 @dataclass
 class ScriptAll(NativeScript):
+    json_tag: ClassVar[str] = "all"
+    json_field: ClassVar[str] = "scripts"
     _TYPE: int = field(default=1, init=False)
 
     native_scripts: List[
@@ -78,6 +142,8 @@ class ScriptAll(NativeScript):
 
 @dataclass
 class ScriptAny(NativeScript):
+    json_tag: ClassVar[str] = "any"
+    json_field: ClassVar[str] = "scripts"
     _TYPE: int = field(default=2, init=False)
 
     native_scripts: List[
@@ -94,6 +160,8 @@ class ScriptAny(NativeScript):
 
 @dataclass
 class ScriptNofK(NativeScript):
+    json_tag: ClassVar[str] = "atLeast"
+    json_field: ClassVar[str] = "required"
     _TYPE: int = field(default=3, init=False)
 
     n: int
@@ -112,13 +180,17 @@ class ScriptNofK(NativeScript):
 
 @dataclass
 class InvalidBefore(NativeScript):
+    json_tag: ClassVar[str] = "after"
+    json_field: ClassVar[str] = "slot"
     _TYPE: int = field(default=4, init=False)
 
     before: int = None
 
 
 @dataclass
 class InvalidHereAfter(NativeScript):
+    json_tag: ClassVar[str] = "before"
+    json_field: ClassVar[str] = "slot"
     _TYPE: int = field(default=5, init=False)
 
     after: int = None

test/pycardano/test_nativescript.py

@@ -7,6 +7,7 @@
 from pycardano.nativescript import (
     InvalidBefore,
     InvalidHereAfter,
+    NativeScript,
     ScriptAll,
     ScriptAny,
     ScriptNofK,
@@ -123,3 +124,75 @@ def test_full_tx():
     script = ScriptAll([before, spk1, spk2])
 
     assert tx.transaction_witness_set.native_scripts[0] == script
+
+
+def test_to_dict():
+
+    vk1 = VerificationKey.from_cbor(
+        "58206443a101bdb948366fc87369336224595d36d8b0eee5602cba8b81a024e58473"
+    )
+    vk2 = VerificationKey.from_cbor(
+        "58206443a101bdb948366fc87369336224595d36d8b0eee5602cba8b81a024e58475"
+    )
+    spk1 = ScriptPubkey(key_hash=vk1.hash())
+    spk2 = ScriptPubkey(key_hash=vk2.hash())
+    before = InvalidHereAfter(123456789)
+    after = InvalidBefore(123456780)
+
+    script_nofk = ScriptNofK(2, [before, after, spk1, spk2])
+
+    script_dict = script_nofk.to_dict()
+
+    assert script_dict == {
+        "type": "atLeast",
+        "required": 2,
+        "scripts": [
+            {"type": "before", "slot": 123456789},
+            {"type": "after", "slot": 123456780},
+            {
+                "type": "sig",
+                "keyHash": "9139e5c0a42f0f2389634c3dd18dc621f5594c5ba825d9a8883c6627",
+            },
+            {
+                "type": "sig",
+                "keyHash": "835600a2be276a18a4bebf0225d728f090f724f4c0acd591d066fa6f",
+            },
+        ],
+    }
+
+    assert NativeScript.from_dict(script_dict) == script_nofk
+
+
+def test_from_dict():
+
+    vk1 = VerificationKey.from_cbor(
+        "58206443a101bdb948366fc87369336224595d36d8b0eee5602cba8b81a024e58473"
+    )
+    vk2 = VerificationKey.from_cbor(
+        "58206443a101bdb948366fc87369336224595d36d8b0eee5602cba8b81a024e58475"
+    )
+    spk1 = ScriptPubkey(key_hash=vk1.hash())
+    spk2 = ScriptPubkey(key_hash=vk2.hash())
+    before = InvalidHereAfter(123456789)
+
+    script_all = ScriptAll([before, spk1, spk2])
+
+    script_all_dict = {
+        "type": "all",
+        "scripts": [
+            {"type": "before", "slot": 123456789},
+            {
+                "type": "sig",
+                "keyHash": "9139e5c0a42f0f2389634c3dd18dc621f5594c5ba825d9a8883c6627",
+            },
+            {
+                "type": "sig",
+                "keyHash": "835600a2be276a18a4bebf0225d728f090f724f4c0acd591d066fa6f",
+            },
+        ],
+    }
+
+    script_from_dict = NativeScript.from_dict(script_all_dict)
+    
+    assert script_from_dict == script_all
+    assert script_from_dict.to_dict() == script_all_dict