CREATE TABLE IF NOT EXISTS users (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    username VARCHAR(100) UNIQUE NOT NULL,
    created_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP NOT NULL
);

CREATE TABLE IF NOT EXISTS chats (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    first_user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    second_user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    created_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP NOT NULL,
    UNIQUE(first_user_id, second_user_id),
    CHECK (first_user_id != second_user_id)
);

CREATE TABLE IF NOT EXISTS messages (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    sender_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    recipient_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    chat_id UUID NOT NULL REFERENCES chats(id) ON DELETE CASCADE,
    content TEXT NOT NULL,
    created_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP NOT NULL
);


CREATE INDEX IF NOT EXISTS idx_messages_chat_id ON messages(chat_id);
CREATE INDEX IF NOT EXISTS idx_messages_sender_id ON messages(sender_id);
CREATE INDEX IF NOT EXISTS idx_messages_chat_created ON messages(chat_id, created_at);