"""A library can hold articles as well as questions.

Collections were questions only, so the reading side of the site had no way to
put anything aside — the bookmark on an article had nowhere to write. Its own
table rather than a nullable column beside `question_id`, so a row cannot claim
to be both kinds or neither.

Revision ID: c5d6e7f8091a
Revises: b4c5d6e7f809
"""
import sqlalchemy as sa
from alembic import op

revision = "c5d6e7f8091a"
down_revision = "b4c5d6e7f809"
branch_labels = None
depends_on = None


def upgrade():
    # `Base.metadata.create_all()` still runs at startup and creates missing
    # tables, so on a box that has already booted this code the table is here
    # before the migration is. Checked rather than assumed, or the upgrade
    # fails on exactly the machines that are up to date.
    if "user_collection_articles" in sa.inspect(op.get_bind()).get_table_names():
        return
    op.create_table(
        "user_collection_articles",
        sa.Column("id", sa.Integer(), primary_key=True, index=True),
        sa.Column("collection_id", sa.Integer(),
                  sa.ForeignKey("user_collections.id", ondelete="CASCADE"), nullable=False),
        sa.Column("article_id", sa.Integer(),
                  sa.ForeignKey("articles.id", ondelete="CASCADE"), nullable=False),
        sa.UniqueConstraint("collection_id", "article_id", name="uq_collection_article"),
    )
    op.create_index("ix_user_collection_articles_collection",
                    "user_collection_articles", ["collection_id"])


def downgrade():
    if "user_collection_articles" not in sa.inspect(op.get_bind()).get_table_names():
        return
    op.drop_index("ix_user_collection_articles_collection", table_name="user_collection_articles")
    op.drop_table("user_collection_articles")