"""Schema 2: a document holds symbols, not timelines, and no symbol is reserved.

Three renames, each in the stored transit and nowhere else:

  clip/<cid>/timeline/...          ->  clip/<cid>/symbol/...
  a node leaf's  :kind :symbol     ->  :kind :instance
  a feature leaf's :timeline key   ->  :symbol

A leaf value is transit's map form, ["^ ", k1, v1, k2, v2, ...]. Only TOP-LEVEL
pairs are rewritten, and only literal ones: transit caches a repeated keyword as
"^N", and a rename that met a cache reference where it expected the keyword would
be guessing. Every saved leaf at the time of writing had these as literals; if one
does not, the migration stops rather than writing a document that decodes to
something else.

Renaming a cached keyword in place is safe because the cache is positional: the
literal keeps its slot, so any later "^N" that referred to it now refers to the
new name, which is what it meant.
"""

import re

from django.db import migrations, models

PATH = re.compile(r"^(clip/[^/]+/)timeline(/|$)")


def _rename_pair(value, key, old, new, path):
    if not (isinstance(value, list) and value[:1] == ["^ "]):
        return value
    out = list(value)
    for i in range(1, len(out) - 1, 2):
        if out[i] != key:
            continue
        if old is None:
            out[i] = new
        elif out[i + 1] == old:
            out[i + 1] = new
        elif isinstance(out[i + 1], str) and out[i + 1].startswith("^") and out[i + 1] != "^ ":
            raise RuntimeError(f"leaf {path!r} has a cached {key} value; migrate it by hand")
    return out


def forwards(apps, schema_editor):
    Leaf = apps.get_model("clips", "Leaf")
    Project = apps.get_model("clips", "Project")
    for leaf in Leaf.objects.all():
        path = PATH.sub(r"\1symbol\2", leaf.path)
        value = leaf.value
        parts = path.split("/")
        if len(parts) == 6 and parts[2] == "symbol" and parts[4] == "node":
            value = _rename_pair(value, "~:kind", "~:symbol", "~:instance", leaf.path)
        if len(parts) == 4 and parts[2] == "feature":
            value = _rename_pair(value, "~:timeline", None, "~:symbol", leaf.path)
        if path != leaf.path or value != leaf.value:
            leaf.path = path
            leaf.value = value
            leaf.version += 1
            leaf.save(update_fields=["path", "value", "version"])
    Project.objects.update(schema_version=2)


class Migration(migrations.Migration):
    dependencies = [
        ("clips", "0006_project_schema_version"),
    ]

    operations = [
        migrations.AlterField(
            model_name="project",
            name="schema_version",
            field=models.PositiveIntegerField(default=2),
        ),
        migrations.RunPython(forwards, migrations.RunPython.noop),
    ]