Adding an imported product
==========================

Currently products can be imported only from files, thus any imported product should
derive from ``ImportedFileProduct``::

    from runmacs.processor.product import ImportedFileProduct

    class NewImportedProduct(ImportedFileProduct):
        pass

Every product should specify its ``productType``, additionally, every
imported file product must implement a ``fromFilename`` classmethod, which
is supposed to return a new instance of the new imported product, if the filename
belongs to a file which actually can be represented using this product.
It the file can not be represented by this product, the classmethod should raise
a ``ValueError``.
Most likely, the product needs to store some information about the data location
in the instance as well::

    class NewImportedProduct(ImportedFileProduct):
        productType = "my_new_product"
        @classmethod
        def fromFilename(cls, filename, place, accessor):
            if not filename.endswith(".mydata"):
                raise ValueError("invalid file")
            instance = cls()
            instance._accessor = accessor
            instance.place = place
            instance.filename = filename
            return instance

Additionally, every imported product must implement ``_hash(self)``, which is supposed
to return a unique hash value computed from the contents of the file.
The ``Product`` baseclass provides a ``defaulthash`` method to help implementing this::

    class NewImportedProduct(ImportedFileProduct):
        ...
        def _hash(self):
            contents = self._accessor.files.getFileData(self.place, self.filename)
            return self.defaulthash(contents).hexdigest()