[jsonish] Flesh out encoder a bit

Initially, this is to handle disabling extras. Eventually, it could also
handle writing out to INI+JSON format.

XXX: Not sure how to handle the `allow_nan` arg, since it overlaps/
     conflicts with the `enable_extras` arg.

src/jsonish/src/jsonish/__main__.py

@@ -55,9 +55,9 @@ def main(argv=None):
     if out_file:
         path = pathlib.Path(out_file)
         with path.open("w") as fp:
-            encode_to_file(obj, fp, indent=indent)
+            encode_to_file(obj, fp, indent=indent, enable_extras=enable_extras)
     else:
-        print(encode(obj, indent=indent))
+        print(encode(obj, indent=indent, enable_extras=enable_extras))
 
 
 if __name__ == "__main__":

src/jsonish/src/jsonish/encoder.py

@@ -6,26 +6,103 @@
 """
 import datetime
 import json
-import functools
 
 from .obj import JSONObject
 
 
 __all__ = ["encode", "encode_to_file", "Encoder"]
 
 
-def default(obj):
-    if isinstance(obj, JSONObject):
-        return dict(obj)
-    if isinstance(obj, datetime.datetime):
-        return obj.isoformat()
-    raise TypeError(f"Object of type {type(obj)} is not JSON serializable")
+class Encoder(json.JSONEncoder):
+    def __init__(
+        self,
+        *,
+        skipkeys=False,
+        ensure_ascii=True,
+        check_circular=True,
+        allow_nan=True,
+        sort_keys=False,
+        indent=None,
+        separators=None,
+        default=None,
+        enable_extras=True,
+    ):
+        super().__init__(
+            skipkeys=skipkeys,
+            ensure_ascii=ensure_ascii,
+            check_circular=check_circular,
+            allow_nan=allow_nan,
+            sort_keys=sort_keys,
+            indent=indent,
+            separators=separators,
+            default=default,
+        )
+        self.enable_extras = enable_extras
 
+    def jsonish_default(self, obj):
+        if self.enable_extras:
+            if isinstance(obj, JSONObject):
+                return dict(obj)
+            if isinstance(obj, datetime.datetime):
+                return obj.isoformat()
+        # Raise TypeError
+        return super().default(obj)
 
-encode = functools.partial(json.dumps, default=default)
-encode_to_file = functools.partial(json.dump, default=default)
 
+def encode(
+    obj,
+    *,
+    cls=Encoder,
+    skipkeys=False,
+    ensure_ascii=True,
+    check_circular=True,
+    allow_nan=True,
+    sort_keys=False,
+    indent=None,
+    separators=None,
+    default=None,
+    enable_extras=True,
+):
+    instance = cls(
+        skipkeys=skipkeys,
+        ensure_ascii=ensure_ascii,
+        check_circular=check_circular,
+        allow_nan=allow_nan,
+        sort_keys=sort_keys,
+        indent=indent,
+        separators=separators,
+        default=default,
+        enable_extras=enable_extras,
+    )
+    return instance.encode(obj)
 
-class Encoder(json.JSONEncoder):
-    def default(self, obj):
-        return default(obj)
+
+def encode_to_file(
+    obj,
+    fp,
+    *,
+    cls=Encoder,
+    skipkeys=False,
+    ensure_ascii=True,
+    check_circular=True,
+    allow_nan=True,
+    sort_keys=False,
+    indent=None,
+    separators=None,
+    default=None,
+    enable_extras=True,
+):
+    instance = cls(
+        skipkeys=skipkeys,
+        ensure_ascii=ensure_ascii,
+        check_circular=check_circular,
+        allow_nan=allow_nan,
+        sort_keys=sort_keys,
+        indent=indent,
+        separators=separators,
+        default=default,
+        enable_extras=enable_extras,
+    )
+    iterable = instance.iterencode(obj)
+    for chunk in iterable:
+        fp.write(chunk)