"""Schema 7: an anchor is a peg.

`[:xform :anchor]` is gone from the transform. `T(a)·M·T(-a)` is a transform
conjugated by a translation — "do M in a frame shifted by a" — and a parent
already is a shifted frame, so an anchor was a peg written inline: one that could
not be selected, keyed, shared between nodes, or placed above a measured channel.
A pivot nobody chose is now derived from what the node draws, per drag, and stored
nowhere; a pivot to keep is a peg, an ordinary `:group` parent.

Nothing is converted, as in schema 6. Every project is marked 7, and one that
still carries an anchor is refused when it is opened, by name and with what to do
about it — `node/problems` in the frontend.

Not converted rather than not worth converting. Dropping an anchor is in fact
pixel-exact wherever rotation and scale are the identity, since the anchor
cancels out of the composition there — and that is everywhere a freeze, a drop or
a new drawing wrote one. It is NOT exact on anything a hand has since turned or
scaled, where the composed translation is `a + p - M·a`, and it cannot be made
exact at all where `pos` is dense, because tier 2 is content-addressed and not
rewritable here. A conversion would therefore be silent and right for most nodes
and silent and wrong for exactly the ones somebody had hand-placed, which is the
worse failure: a refusal names the document and says what to do.
"""

from django.db import migrations, models


def forwards(apps, schema_editor):
    apps.get_model("clips", "Project").objects.update(schema_version=7)


class Migration(migrations.Migration):
    dependencies = [("clips", "0015_tracing_images")]

    operations = [
        migrations.AlterField(
            model_name="project",
            name="schema_version",
            field=models.PositiveIntegerField(default=7),
        ),
        migrations.RunPython(forwards, migrations.RunPython.noop),
    ]