Trouble with single trigger using UUID as key, should I use two triggers?

I'm running into a foreign key constraint when running a BEFORE trigger 
for audit purposes.  My initial goal was to do this in one BEFORE 
trigger, but I'm leaning towards executing using two different 
triggers.  I'm seeking a second opinion!  My initial thought was 
creating a trigger that runs before the data is written to the primary 
table; specifically on updates, as I want to increment the version_count 
before the data is written to the primary table.  Because the audit_id 
(UUID generated) has not been written to the primary table, I get a 
foreign key constraint problem when it tries to first write to the audit 
table.  I understand the error is because audit_id doesn't exist in the 
primary table.  If I were using a SERIAL/SEQUENCE, I could use the 
NEXTVAL function; but I need to use UUID the key and audit_id.

Knowing that, I think my only option is to create an AFTER trigger for 
the INSERT.  Then create a BEFORE trigger when doing UPDATES and 
DELETES.  Before I go this path, I through I'd see if anyone has any 
additional options I should consider; or would this be the suggested 
path?  Thoughts?

-JA-


--Example INSERT
INSERT INTO departments (department_legacyid, department_name) VALUES 
('ACT', 'Accounting');
INSERT INTO departments (department_legacyid, department_name) VALUES 
('HRM', 'Human Resources');
INSERT INTO departments (department_legacyid, department_name) VALUES 
('CSR', 'Customer Service');

--ERROR
ERROR: insert or update on table "departments_audit" violates foreign 
key constraint "departments_audit_audit_id_fkey" DETAIL: Key 
(audit_id)=(241451bd-796e-5add-95b0-18f6098bc08f) is not present in 
table "departments". CONTEXT: SQL statement "INSERT INTO 
departments_audit (audit_id, audit_lastaction, department_legacyid, 
department_name ) VALUES (NEW.audit_id, 'INSERT', 
NEW.department_legacyid, NEW.department_name )" PL/pgSQL function 
process_departments_audit() line 10 at SQL statement SQL state: 23503

--Primary Table
CREATE TABLE IF NOT EXISTS departments (
   row_id                UUID NOT NULL DEFAULT 
uuid_generate_v5(uuid_ns_dns(), 'location1.local'),
   row_created           TIMESTAMP WITHOUT TIME ZONE NOT NULL DEFAULT 
CURRENT_TIMESTAMP,
   audit_id              UUID NOT NULL DEFAULT 
uuid_generate_v5(uuid_ns_dns(), 'location1.local'),
   version_count         INTEGER NOT NULL DEFAULT 1,
   version_timestamp TIMESTAMP WITHOUT TIME ZONE NOT NULL DEFAULT 
CURRENT_TIMESTAMP,
   department_legacyid   VARCHAR(255) NOT NULL,
   department_name       VARCHAR(255) NOT NULL,
   PRIMARY KEY (row_id)
);

--Creating index on audit_ID to ensure there is only one unique record 
in primary table
CREATE UNIQUE INDEX departments_ref_idx ON departments(audit_id);

--Audit Table
CREATE TABLE IF NOT EXISTS departments_audit (
   row_id                UUID NOT NULL DEFAULT 
uuid_generate_v5(uuid_ns_dns(), 'location1.local'),
   row_created           TIMESTAMP WITHOUT TIME ZONE NOT NULL DEFAULT 
CURRENT_TIMESTAMP,
   audit_id              UUID NOT NULL DEFAULT 
uuid_generate_v5(uuid_ns_dns(), 'location1.local'),
   audit_lastaction      CHARACTER VARYING DEFAULT 'NOT DEFINED',
   version_count         INTEGER NOT NULL DEFAULT 1,
version_timestamp TIMESTAMP WITHOUT TIME ZONE NOT NULL DEFAULT 
CURRENT_TIMESTAMP,
   department_legacyid   VARCHAR(255) NOT NULL,
   department_name       VARCHAR(255) NOT NULL,
   PRIMARY KEY (row_id),
   FOREIGN KEY (audit_id) REFERENCES departments(audit_id)
);

-- Creating audit trigger for departments
CREATE OR REPLACE FUNCTION process_departments_audit() RETURNS TRIGGER 
AS $departments_audit$
   BEGIN
     IF (TG_OP = 'DELETE') THEN
       --Nothing yet
     ELSEIF (TG_OP = 'UPDATE') THEN
       --Nothing yet
       NEW.version_count = OLD.version_count + 1;
     ELSEIF (TG_OP = 'INSERT') THEN
       INSERT INTO departments_audit (audit_id,
                                      audit_lastaction,
                                      department_legacyid,
                                      department_name
                                     )
                              VALUES (NEW.audit_id,
                                      'INSERT',
                                      NEW.department_legacyid,
                                      NEW.department_name
                                     );
     END IF;
     RETURN NULL;
   END;
$departments_audit$ LANGUAGE plpgsql;

--Applying trigger BEFORE data is written to primary table
CREATE TRIGGER department_audit
   BEFORE INSERT OR UPDATE OR DELETE ON departments
     FOR EACH ROW EXECUTE PROCEDURE process_departments_audit();