"""A share link may open a folder

Revision ID: 0108_folder_links
Revises: 0107_link_token_at_rest
Create Date: 2026-10-15

A `/watch` link opened one file. Now it may open one of its owner's own folders instead: the link's
page lists what is in the folder when it is opened. `folder_id` sits beside `job_id`, exactly one of
the two set; a folder's links go with the folder.

The downgrade has nowhere to keep a folder link, so it deletes them: they stop opening.
"""

import sqlalchemy as sa
from alembic import op

revision: str = "0108_folder_links"
down_revision: str | None = "0107_link_token_at_rest"
branch_labels: str | None = None
depends_on: str | None = None


def upgrade() -> None:
    op.add_column(
        "download_links",
        sa.Column("folder_id", sa.Integer(), sa.ForeignKey("file_folders.id", ondelete="CASCADE")),
    )
    op.create_index("ix_download_links_folder_id", "download_links", ["folder_id"])
    op.alter_column("download_links", "job_id", nullable=True)
    op.create_check_constraint(
        "ck_download_link_target", "download_links", "(job_id IS NULL) <> (folder_id IS NULL)"
    )


def downgrade() -> None:
    op.execute("DELETE FROM download_links WHERE folder_id IS NOT NULL")
    op.drop_constraint("ck_download_link_target", "download_links", type_="check")
    op.alter_column("download_links", "job_id", nullable=False)
    op.drop_index("ix_download_links_folder_id", table_name="download_links")
    op.drop_column("download_links", "folder_id")