try:
    from json import JSONEncoder
except ImportError:
    from simplejson import JSONEncoder

from datetime               import datetime, date
from decimal                import Decimal
from webob.multidict        import MultiDict
from sqlalchemy.engine.base import ResultProxy, RowProxy
from simplegeneric          import generic

#
# exceptions
#

class JsonEncodeError(Exception):
    pass


#
# encoders
#

def is_saobject(obj):
    return hasattr(obj, '_sa_class_manager')


class GenericJSON(JSONEncoder):
    def default(self, obj):
        if hasattr(obj, '__json__') and callable(obj.__json__):
            return obj.__json__()
        elif isinstance(obj, (date, datetime)):
            return str(obj)
        elif isinstance(obj, Decimal):
            return float(obj)
        elif is_saobject(obj):
            props = {}
            for key in obj.__dict__:
                if not key.startswith('_sa_'):
                    props[key] = getattr(obj, key)
            return props
        elif isinstance(obj, ResultProxy):
            return dict(rows=list(obj), count=obj.rowcount)
        elif isinstance(obj, RowProxy):
            return dict(rows=dict(obj), count=1)
        elif isinstance(obj, MultiDict):
            return obj.mixed()
        else:
            return JSONEncoder.default(self, obj)


_default = GenericJSON()

@generic
def jsonify(obj):
    return _default.default(obj)

class GenericFunctionJSON(GenericJSON):
    def default(self, obj):
        return jsonify(obj)

_instance = GenericFunctionJSON()
    

def encode(obj):
    if isinstance(obj, basestring):
        return _instance.encode(obj)
    return _instance.encode(obj)