Source code for delb.transform

# Copyright (C) 2018-'22  Frank Sachsenheim
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

"""
This module offers a canonical interface with the aim to make re-use of transforming
algorithms easier.

Let's look at it with examples::

   from delb.transform import Transformation


   class ResolveCopyOf(Transformation):
       def transform(self):
           for node in self.root.css_select("*[copyOf]"):
               source_id = node["copyOf"]
               source_node = self.origin_document.xpath(
                   f'//*[@xml:id="{source_id[1:]}"]'
               ).first
               cloned_node = source_node.clone(deep=True)
               cloned_node.id = None
               node.replace_with(cloned_node)


From such defined transformations instances can be called with a (sub-)tree and an
optional document where that tree originates from::

   resolve_copy_of = ResolveCopyOf()
   tree = resolve_copy_of(tree)  # where tree is an instance of TagNode


:class:`typing.NamedTuple` are used to define options for transformations::

   from typing import NamedTuple


   class ResolveChoiceOptions(NamedTuple):
       corr: bool = True
       reg: bool = True


   class ResolveChoice(Transformation):
       options_class = ResolveChoiceOptions

       def __init__(self, options):
           super().__init__(options)
           self.keep_selector = ",".join(
               (
                   "corr" if self.options.corr else "sic",
                   "reg" if self.options.reg else "orig"
               )
            )
           self.drop_selector = ",".join(
               (
                   "sic" if self.options.corr else "corr",
                   "orig" if self.options.reg else "reg"
               )
           )

       def transform(self):
           for choice_node in self.root.css_select("choice"):
               node_to_drop = choice_node.css_select(self.drop_selector).first
               node_to_drop.detach()

               node_to_keep = choice_node.css_select(self.keep_selector).first
               node_to_keep.detach(retain_child_nodes=True)

               choice_node.detach(retain_child_nodes=True)


A transformation class that defines an ``option_class`` property can then either be used
with its defaults or with alternate options::

   resolve_choice = ResolveChoice()
   tree = resolve_choice(tree)

   resolve_choice = ResolveChoice(ResolveChoiceOptions(reg=False))
   tree = resolve_choice(tree)


Finally, concrete transformations can be chained, both as classes or instances. The
interface allows also to chain multiple chains::

   from delb.transform import TransformationSequence

   tidy_up = TransformationSequence(ResolveCopyOf, resolve_choice)
   tree = tidy_up(tree)


.. attention::
   This is an experimental feature. It might change significantly in the future or be
   removed altogether.
"""

from __future__ import annotations

from abc import ABC, abstractmethod
from typing import NamedTuple, Optional

from delb import Document, TagNode


#


class TransformationBase(ABC):
    """This base class defines the calling interface of transformations."""

    @abstractmethod
    def __call__(self, root: TagNode, document: Optional[Document] = None) -> TagNode:
        pass


class Transformation(TransformationBase):
    """This is a base class for any transformation algorithm."""

    options_class: Optional[type] = None

    def __init__(self, options: Optional[NamedTuple] = None):
        self.root: Optional[TagNode] = None
        self.document: Optional[Document] = None
        if options is None and self.options_class is not None:
            options = self.options_class()

        self.options = options

    def __call__(self, root: TagNode, document: Optional[Document] = None) -> TagNode:
        if root.document is None:
            # TODO clarify why a copy is needed for trees that aren't part of a
            #      document
            root = Document(root).root
        self.root = root
        self.origin_document = document
        self.transform()
        result = self.root
        self.root = self.document = None
        return result

    @abstractmethod
    def transform(self):
        """
        This method needs to implement the transformation logic. When it is called,
        the instance has two attributes assigned from its call:

        ``root`` is the node that the transformation was called to transform with.
        ``origin_document`` is the document that was possibly passed as second argument.
        """
        pass


class TransformationSequence(TransformationBase):
    """
    A transformation sequence can be used to combine any number of both
    :class:`Transformation` (provided as class or instantiated with options) and other
    :class:`TransformationSequence` instances or classes.
    """

    def __init__(
        self,
        *transformations: TransformationBase | type[TransformationBase],
    ):
        self.transformations = []
        for transformation in transformations:
            if isinstance(transformation, type) and issubclass(
                transformation, TransformationBase
            ):
                self.transformations.append(transformation())
            elif isinstance(transformation, TransformationBase):
                self.transformations.append(transformation)
            else:
                raise TypeError(
                    "Only subclasses of TransformationBase or instances of such are "
                    "allowed."
                )

    def __call__(self, root: TagNode, document: Optional[Document] = None) -> TagNode:
        for transformation in self.transformations:
            root = transformation(root, document=document)
        return root


__all__ = (Transformation.__name__, TransformationSequence.__name__)