CREATE TABLE IF NOT EXISTS notification_preferences (
    user_id INTEGER PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
    language VARCHAR(2) NOT NULL DEFAULT 'de' CHECK (language IN ('de', 'en')),
    friend_request BOOLEAN NOT NULL DEFAULT TRUE,
    direct_message BOOLEAN NOT NULL DEFAULT TRUE,
    event_invitation BOOLEAN NOT NULL DEFAULT TRUE
);
CREATE TABLE IF NOT EXISTS push_notifications (
    id UUID PRIMARY KEY,
    device_id BIGINT NOT NULL REFERENCES push_devices(id) ON DELETE CASCADE,
    session_id INTEGER NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
    recipient_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    actor_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    kind VARCHAR(32) NOT NULL CHECK (kind IN ('friend_request', 'direct_message', 'event_invitation')),
    object_id BIGINT NOT NULL,
    event_key TEXT NOT NULL,
    token_hash VARCHAR(64) NOT NULL,
    state VARCHAR(16) NOT NULL DEFAULT 'pending' CHECK (state IN ('pending', 'sent', 'dropped', 'failed')),
    attempts SMALLINT NOT NULL DEFAULT 0,
    created_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
    expires_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP + INTERVAL '1 hour',
    available_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
    UNIQUE(device_id, event_key)
);
CREATE INDEX IF NOT EXISTS idx_push_notifications_pending
    ON push_notifications(available_at) WHERE state='pending';