"""sources_meta + saved_chats.sources_version: the KB-generation stamp (phase 53)

Revision ID: 0010
Revises: 0009
Create Date: 2026-08-30

Phase 53 (invalidate saved chats on sources sync, TODO-derived
2026-08-30): a saved answer can silently predate the current index,
because neither sync path (the admin Sync button,
``scripts/import_docs.py``) records *when the KB last changed*. ONE
migration carries the whole feature (A13 — one feature, one atomic,
reversible schema change):

* ``sources_meta`` — a **single-row** counter (``id INTEGER PK
  DEFAULT 1``, the ``kb_overview`` phase-31 precedent) holding the
  current **generation** of the knowledge base. The seed row
  (id 1, version 0) is inserted here — not lazily on first bump — so
  ``app.rag.sources_meta.current_sources_version`` is a plain PK read.
  ``version`` is bumped exactly once per KB-changing sync (task 02,
  change-gated on ``added + updated + pruned > 0``); a failed sync
  never bumps.
* ``saved_chats.sources_version`` — ``INTEGER NOT NULL DEFAULT 0``:
  the generation the conversation was saved against, stamped by the
  chats API at save time (task 03). Pre-0010 rows come back stamped 0
  (the pre-counter KB) and go stale on the first bump.
"""
from __future__ import annotations

import sqlalchemy as sa

from alembic import op

revision = "0010"
down_revision = "0009"
branch_labels = None
depends_on = None


def upgrade() -> None:
    op.create_table(
        "sources_meta",
        sa.Column("id", sa.Integer(), primary_key=True, server_default=sa.text("1")),
        sa.Column("version", sa.Integer(), nullable=False, server_default=sa.text("0")),
        sa.Column(
            "updated_at",
            sa.DateTime(timezone=True),
            nullable=False,
            server_default=sa.func.now(),
        ),
    )
    # Seed the single row (id 1, version 0): "the pre-counter KB".
    op.execute(
        "INSERT INTO sources_meta (id, version, updated_at) VALUES (1, 0, now())"
    )
    op.add_column(
        "saved_chats",
        sa.Column(
            "sources_version", sa.Integer(), nullable=False, server_default=sa.text("0")
        ),
    )


def downgrade() -> None:
    # Safe order: drop the stamp column first, then the counter table.
    op.drop_column("saved_chats", "sources_version")
    op.drop_table("sources_meta")