"""trigger_leaves_the_stored_title — a snippet's and lesson's title is its name (milestone 427)

Revision ID: 0108
Revises: 0107
Create Date: 2026-09-23

Snippets and lessons stored their title as `subject — trigger`, because the
join is what makes these kinds rank on the situation they apply to (#2485) and
the stored title WAS the embedded one. Every surface that shows a title then
showed the trigger too: menu lines, lists and search rows ran to 1,500–3,000
characters, and an injected repeat spent all of it again.

The trigger's home is `data` (decision #4157), and since this milestone the
join happens at embed time (`embeddings.document_title`). This revision
rewrites the rows already stored.

EXACT-SUFFIX, READ FROM THE ROW'S OWN MIRROR. A title is only rewritten when
it ends with `' — ' || <that row's trigger>`, so a subject that legitimately
contains an em dash is never cut, and a row whose title and mirror disagree —
hand-edited through the generic note door — is left alone. Such a row still
embeds correctly (`document_title` is idempotent) and merely shows its old
title; that is the right way round for a data migration to fail.

NO RE-EMBED, AND `updated_at` IS NOT TOUCHED. The embedded text is identical
before and after, so the vectors are already right. The startup backfill
re-embeds any row whose `updated_at` is newer than its vectors, and a raw
UPDATE that leaves `updated_at` alone is what keeps this from queueing the
whole snippet corpus for work that would produce the same numbers. There is
no database trigger on `updated_at`; it is set by the ORM only.
"""
from alembic import op

revision = "0108"
down_revision = "0107"
branch_labels = None
depends_on = None

# kind → the `data` key its trigger is mirrored under (embeddings._TRIGGER_DATA_KEYS).
_KINDS = (("snippet", "when_to_use"), ("lesson", "when_to_apply"))
_SEP = " — "


def upgrade() -> None:
    for note_type, key in _KINDS:
        op.execute(f"""
            UPDATE notes
               SET title = btrim(left(title, length(title) - length('{_SEP}' || (data->>'{key}'))))
             WHERE note_type = '{note_type}'
               AND coalesce(btrim(data->>'{key}'), '') <> ''
               AND right(title, length('{_SEP}' || (data->>'{key}'))) = '{_SEP}' || (data->>'{key}')
        """)


def downgrade() -> None:
    # Recompose, on the same condition inverted: only where the trigger is not
    # already on the end, so a downgrade run twice cannot double it.
    for note_type, key in _KINDS:
        op.execute(f"""
            UPDATE notes
               SET title = title || '{_SEP}' || (data->>'{key}')
             WHERE note_type = '{note_type}'
               AND coalesce(btrim(data->>'{key}'), '') <> ''
               AND right(title, length('{_SEP}' || (data->>'{key}'))) <> '{_SEP}' || (data->>'{key}')
        """)