-- Kernel-owned web-push subscriptions. A subscription is always scoped to the
-- structure that registered it, and send-time fanout re-checks structure
-- visibility before delivery.
CREATE TABLE notification_subscriptions (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    structure_id INTEGER NOT NULL,
    user_id INTEGER NOT NULL,
    endpoint TEXT NOT NULL,
    client_id TEXT,
    subscription TEXT NOT NULL,
    content_encoding TEXT,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY(structure_id) REFERENCES structures(id),
    FOREIGN KEY(user_id) REFERENCES users(id),
    UNIQUE(structure_id, endpoint)
);

CREATE INDEX idx_notification_subscriptions_structure
    ON notification_subscriptions (structure_id, user_id);