CREATE TABLE IF NOT EXISTS direct_messages (
    id SERIAL PRIMARY KEY,
    sender_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    recipient_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    body TEXT NOT NULL,
    read_at TIMESTAMP,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    CHECK (sender_id <> recipient_id)
);

CREATE INDEX IF NOT EXISTS idx_direct_messages_conversation
ON direct_messages (sender_id, recipient_id, created_at);

CREATE INDEX IF NOT EXISTS idx_direct_messages_unread
ON direct_messages (recipient_id, read_at);