"""documents.page_count: the rendered page-strip's page count (phase 148, task 01)

Revision ID: 0026
Revises: 0025
Create Date: 2026-10-01

Phase 148 (pictorial PDFs show their PAGES in the sources — task 01,
storage only):

* ``documents.page_count`` — INTEGER NULLABLE, NO server default, NO
  index: the number of rendered page PNGs persisted in
  ``settings.pdf_page_dir`` (``BOR_PDF_PAGE_DIR``) as
  ``<doc-id>-p{N}.png`` (N 1-based) for ONE page-qualifying document —
  the PDF's page count. Set ONLY by the importer's PDF branch (task 01):
  a qualifying PDF (the phase-133 fallback class — unusable text layer,
  — or the phase-140 pictorial class — the sparse-page pass described
  ≥1 page) gets every page rendered at index time, and this column
  records the page count (a per-page render failure leaves a GAP — the
  file is simply absent, the route of task 02 404s that N, the viewer's
  note covers it). NULL for every other document (text documents,
  images, text-heavy PDFs) and for a qualifying PDF whose render/write
  failed (fail-soft — the render is a display concern, it never gates
  indexing); the prune cleanup deletes the copies with the row.

  A display fact, never a query surface: the page-bytes route (task 02)
  looks the document up by its uuid4 id FIRST (the unguessable id is the
  credential — the phase-124 image-route trust model) and reads this
  column from the ROW, so it carries no index of its own (the
  ``file_hash`` convention, 0025).

One additive, fully reversible migration (A13); no other schema change.
The render/persist/cleanup logic itself (task 01) is importer code —
this revision only carries the column.
"""
from __future__ import annotations

import sqlalchemy as sa

from alembic import op

revision = "0026"
down_revision = "0025"
branch_labels = None
depends_on = None


def upgrade() -> None:
    # No index (a display fact, never a query surface — the page route
    # reads it from the row after the uuid4 id lookup) and no server
    # default (NULL is the meaningful state for every non-qualifying
    # document and every fail-soft miss).
    op.add_column("documents", sa.Column("page_count", sa.Integer(), nullable=True))


def downgrade() -> None:
    # The page_count column is the only 0026 artefact — dropping it
    # leaves 0025's schema byte-identical (A13, fully reversible). The
    # rendered copies are re-derivable from the source files on the
    # next sync, so no data is lost by the drop.
    op.drop_column("documents", "page_count")