"""Chunked embeddings: one note_embeddings row per chunk (#280)

Revision ID: 0077
Revises: 0076
Create Date: 2026-08-09

The embedding model reads at most 512 tokens and fastembed truncates the rest
silently, so the old one-row-per-note shape permanently lost everything past
~400 words of a record. A note now stores one row per chunk of
`embeddings.chunk_document`: PK (note_id, chunk_index), plus the chunk's text
(inspectability + future "matched section" surfacing) and the chunker version
that produced it (so later shape changes re-embed by version comparison
instead of repeating this wipe).

Embeddings are DERIVED data (0067 precedent): rows are cleared here and the
startup backfill regenerates the whole corpus at the new shape on next boot.
The HNSW index is untouched — it indexes chunk rows exactly as it indexed
note rows.
"""
from alembic import op


revision = "0077"
down_revision = "0076"
branch_labels = None
depends_on = None


def upgrade() -> None:
    # Derived data — the version-aware startup backfill re-embeds everything
    # at the chunked shape. Old whole-document rows would be indistinguishable
    # from properly-chunked single-chunk notes, so they cannot be carried over.
    op.execute("DELETE FROM note_embeddings")

    # Empty table, so NOT NULL columns need no defaults and the PK swap is
    # instant.
    op.execute("ALTER TABLE note_embeddings ADD COLUMN chunk_index integer NOT NULL")
    op.execute("ALTER TABLE note_embeddings ADD COLUMN chunk_text text NOT NULL")
    op.execute("ALTER TABLE note_embeddings ADD COLUMN chunker_version integer NOT NULL")
    op.execute("ALTER TABLE note_embeddings DROP CONSTRAINT note_embeddings_pkey")
    op.execute(
        "ALTER TABLE note_embeddings ADD PRIMARY KEY (note_id, chunk_index)"
    )


def downgrade() -> None:
    # Same reasoning in reverse: chunk rows make no sense to a whole-document
    # reader, so clear and let the old backfill regenerate.
    op.execute("DELETE FROM note_embeddings")
    op.execute("ALTER TABLE note_embeddings DROP CONSTRAINT note_embeddings_pkey")
    op.execute("ALTER TABLE note_embeddings DROP COLUMN chunk_index")
    op.execute("ALTER TABLE note_embeddings DROP COLUMN chunk_text")
    op.execute("ALTER TABLE note_embeddings DROP COLUMN chunker_version")
    op.execute("ALTER TABLE note_embeddings ADD PRIMARY KEY (note_id)")