import uuid

from sqlalchemy.dialects.postgresql import UUID
from sqlalchemy.types import CHAR, TypeDecorator


class GUID(TypeDecorator):
    """Platform-independent GUID type.
    Uses PostgreSQL's UUID type, otherwise uses
    CHAR(32), storing as stringified hex values.
    """

    impl = CHAR
    cache_ok = True

    @staticmethod
    def generate():
        return uuid.uuid4()

    def load_dialect_impl(self, dialect):
        if dialect.name == "postgresql":
            return dialect.type_descriptor(UUID())
        else:
            return dialect.type_descriptor(CHAR(32))

    def process_bind_param(self, value, dialect):
        if value is None:
            return value
        elif dialect.name == "postgresql":
            return str(value)
        else:
            if not isinstance(value, uuid.UUID):
                return "%.32x" % uuid.UUID(value).int
            else:
                # hexstring
                return "%.32x" % value.int

    def process_result_value(self, value, dialect):
        if value is not None and not isinstance(value, uuid.UUID):
            value = uuid.UUID(value)
        return value
