from typing import Any, Optional
from alembic.operations import Operations, MigrateOperation
class ReplaceableObject:
    def __init__(self, name: str, sqltext: str) -> None:
        self.name = name
        self.sqltext = sqltext
class ReversibleOp(MigrateOperation):
    """This is the base of our “replaceable” operation, which includes not just a base operation for emitting
    CREATE and DROP instructions on a ReplaceableObject, it also assumes a certain model of “reversibility” which
    makes use of references to other migration files in order to refer to the “previous” version of an object.

    https://alembic.sqlalchemy.org/en/latest/cookbook.html#replaceable-objects
    """
    def __init__(self, target: ReplaceableObject) -> None:
        self.target = target
    @classmethod
    def invoke_for_target(cls, operations: Operations, target: ReplaceableObject):
        op = cls(target)
        return operations.invoke(op)
    def reverse(self):
        raise NotImplementedError
    @classmethod
    def _get_object_from_version(cls, operations: Operations, ident: str) -> Any:
        version, objectname = ident.split(".")
        module = operations.get_context().script.get_revision(version).module
        return getattr(module, objectname)
    @classmethod
    def replace(
            cls,
            operations: Operations,
            target: ReplaceableObject,
            replaces: Optional[str] = None,
            replace_with: Optional[str] = None,
    ) -> None:
        if replaces is None and replace_with is None:
            raise TypeError("replaces or replace_with is required")
        old_obj = cls._get_object_from_version(
            operations,
            replaces if replaces is not None else replace_with,
        )
        drop_old = cls(old_obj).reverse()
        create_new = cls(target)
        operations.invoke(drop_old)
        operations.invoke(create_new)
"""To create usable operations from this base, we will build a series of stub classes and use 
[Operations.register_operation()](https://alembic.sqlalchemy.org/en/latest/ops.html#alembic.operations.Operations.register_operation)
 to make them part of the op.* namespace"""
@Operations.register_operation("create_view", "invoke_for_target")
@Operations.register_operation("replace_view", "replace")
class CreateViewOp(ReversibleOp):
    def reverse(self):
        return DropViewOp(self.target)
@Operations.register_operation("drop_view", "invoke_for_target")
class DropViewOp(ReversibleOp):
    def reverse(self):
        return CreateViewOp(self.target)
@Operations.implementation_for(CreateViewOp)
def create_view(operations: Operations, operation: ReversibleOp) -> None:
    operations.execute(f"CREATE VIEW {operation.target.name} AS {operation.target.sqltext}")
@Operations.implementation_for(DropViewOp)
def drop_view(operations: Operations, operation: ReversibleOp) -> None:
    operations.execute(f"DROP VIEW {operation.target.name}")

"""adjust view 

Revision ID: 24627210e3e6
Revises: bcf089c643e3
Create Date: 2021-07-16 17:03:05.673405

"""
from alembic import op
import sqlalchemy as sa
from sqlalchemy import orm
from fun_stuff import alembic_utils
# revision identifiers, used by Alembic.
revision = '24627210e3e6'
down_revision = 'bcf089c643e3'
branch_labels = None
depends_on = None
new_view = alembic_utils.ReplaceableObject(
    name="E_CrazyFunView",
    sqltext="""SELECT * FROM WowTable""",
)
old_view = alembic_utils.ReplaceableObject(
    name="E_CrazyFunView",
    sqltext="""SELECT * FROM NotWowTable""",
)
def upgrade():
    op.drop_view(old_view)
    op.create_view(new_view)
def downgrade():
    op.drop_view(new_view)
    op.create_view(old_view)

Traceback (most recent call last):
  File "/usr/local/bin/alembic", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.8/site-packages/alembic/config.py", line 588, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/usr/local/lib/python3.8/site-packages/alembic/config.py", line 582, in main
    self.run_cmd(cfg, options)
  File "/usr/local/lib/python3.8/site-packages/alembic/config.py", line 559, in run_cmd
    fn(
  File "/usr/local/lib/python3.8/site-packages/alembic/command.py", line 461, in history
    _display_history(config, script, base, head)
  File "/usr/local/lib/python3.8/site-packages/alembic/command.py", line 429, in _display_history
    for sc in script.walk_revisions(
  File "/usr/local/lib/python3.8/site-packages/alembic/script/base.py", line 277, in walk_revisions
    for rev in self.revision_map.iterate_revisions(
  File "/usr/local/lib/python3.8/site-packages/alembic/script/revision.py", line 793, in iterate_revisions
    revisions, heads = fn(
  File "/usr/local/lib/python3.8/site-packages/alembic/script/revision.py", line 1393, in _collect_upgrade_revisions
    targets: Collection["Revision"] = self._parse_upgrade_target(
  File "/usr/local/lib/python3.8/site-packages/alembic/script/revision.py", line 1193, in _parse_upgrade_target
    return self.get_revisions(target)
  File "/usr/local/lib/python3.8/site-packages/alembic/script/revision.py", line 527, in get_revisions
    resolved_id, branch_label = self._resolve_revision_number(
  File "/usr/local/lib/python3.8/site-packages/alembic/script/revision.py", line 747, in _resolve_revision_number
    self._revision_map
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py", line 1113, in __get__
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File "/usr/local/lib/python3.8/site-packages/alembic/script/revision.py", line 189, in _revision_map
    for revision in self._generator():
  File "/usr/local/lib/python3.8/site-packages/alembic/script/base.py", line 136, in _load_revisions
    script = Script._from_filename(self, vers, file_)
  File "/usr/local/lib/python3.8/site-packages/alembic/script/base.py", line 999, in _from_filename
    module = util.load_python_file(dir_, filename)
  File "/usr/local/lib/python3.8/site-packages/alembic/util/pyfiles.py", line 92, in load_python_file
    module = load_module_py(module_id, path)
  File "/usr/local/lib/python3.8/site-packages/alembic/util/pyfiles.py", line 108, in load_module_py
    spec.loader.exec_module(module)  # type: ignore
  File "<frozen importlib._bootstrap_external>", line 843, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/src/employees/alembic/versions/24627210e3e6_swap_old_with_new.py", line 13, in <module>
    from fun_stuff import alembic_utils
  File "/src/fun_stuff/alembic_utils.py", line 67, in <module>
    class CreateViewOp(ReversibleOp):
  File "/usr/local/lib/python3.8/site-packages/alembic/operations/base.py", line 163, in register
    exec(func_text, globals_, lcl)
  File "<string>", line 1, in <module>
NameError: name 'fun_stuff' is not defined