CREATE TABLE shop_invitations (
                                  id BIGINT PRIMARY KEY,
                                  shop_id BIGINT NOT NULL REFERENCES shops(id),
                                  player_id BIGINT NOT NULL,
                                  status VARCHAR(20) NOT NULL DEFAULT 'pending',
                                  invited_by BIGINT NOT NULL,
                                  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
                                  responded_at TIMESTAMPTZ,

                                  CONSTRAINT chk_invitation_status CHECK (status IN ('pending', 'accepted', 'rejected', 'cancelled')),
                                  UNIQUE(shop_id, player_id, status) WHERE status = 'pending'
);

CREATE INDEX idx_invitations_shop ON shop_invitations(shop_id);
CREATE INDEX idx_invitations_player ON shop_invitations(player_id) WHERE status = 'pending';
CREATE INDEX idx_invitations_player_status ON shop_invitations(player_id, status, created_at DESC);
CREATE INDEX idx_invitations_shop_status ON shop_invitations(shop_id, status, created_at DESC);