"""Patching support for db.Model objects."""
from typing import Type, Set, Optional, Any, Dict

from corvus import db
from corvus import errors
from corvus.model import User
from corvus.service import transformation_service
from corvus.service import validation_service


def get_patch_fields(patch_json: Dict[str, Any]) -> Set[str]:
    """Convert json fields to python fields."""
    return {
        transformation_service.convert_key_from_json(key) for key in
        patch_json.keys()}


def perform_patch(request_user: User,
                  original_model: Type[db.Model],
                  patch_model: Type[db.Model],
                  model_attributes: Set[str],
                  patched_fields: Optional[Set[str]]) \
        -> Type[db.Model]:
    """
    Patch changed attributes onto original model.

    :param request_user:
    :param original_model: The model to apply the patches to
    :param patch_model: The model to pull the patch information from
    :param model_attributes: The attributes that are valid for patching
    :param patched_fields: The explicitly passed fields for patching
    :return: Thd patched original_model
    """
    change_set = validation_service.determine_change_set(
        original_model, patch_model, model_attributes, patched_fields)
    model_validation = validation_service.validate_model(
        request_user, original_model, change_set)
    if model_validation.success:
        for attribute, value in change_set.items():
            setattr(original_model, attribute, value)
        db.session.commit()
    else:
        raise errors.ValidationError(
            'Restricted attributes modified. Invalid Patch Set.')
    return original_model


def versioning_aware_patch(request_user: User,
                           original_model: Type[db.Model],
                           patch_model: Type[db.Model],
                           model_attributes: Set[str],
                           patched_fields: Optional[Set[str]]) \
        -> Type[db.Model]:
    """
    Account for version numbers in the model.

    Versions must match to perform the patching. Otherwise a simultaneous edit
    error has occurred. If the versions match and the patch moves forward, bump
    the version on the model by 1 to prevent other reads from performing a
    simultaneous edit.

    :param patched_fields:
    :param request_user:
    :param original_model: The model to apply the patches to
    :param patch_model: The model to pull the patch information from
    :param model_attributes: The attributes that are valid for patching
    :return: Thd patched original_model
    """
    if original_model.version == patch_model.version:
        patch_model.version = patch_model.version + 1
        return perform_patch(
            request_user,
            original_model,
            patch_model,
            model_attributes,
            patched_fields)
    raise errors.ValidationError(
        'Versions do not match. Concurrent edit in progress.')


def patch(
        request_user: User,
        original_model: Type[db.Model],
        patch_model: Type[db.Model],
        patched_fields: Optional[Set[str]] = None) -> Type[db.Model]:
    """
    Patch the original model with the patch model data.

    :param request_user:
    :param original_model: The model to apply the patches to
    :param patch_model: The model to pull the patch information from
    :param patched_fields:
    :return: The patched original_model
    """
    if type(original_model) is type(patch_model):
        model_attributes = validation_service.get_changable_attribute_names(
            original_model)
        if patch_model.id is not None and original_model.id != patch_model.id:
            raise errors.ValidationError('Cannot change ids through patching')
        if 'version' in model_attributes:
            return versioning_aware_patch(
                request_user,
                original_model,
                patch_model,
                model_attributes,
                patched_fields)
        return perform_patch(
            request_user,
            original_model,
            patch_model,
            model_attributes,
            patched_fields)
    raise errors.ValidationError(
        'Model types "{}" and "{}" do not match'.format(
            original_model.__class__.__name__,
            patch_model.__class__.__name__
        ))