mkdir -p /tmp/test_inv/{tools,inventory/vars/{template,g1/g2/g3},group_vars}
cd /tmp/test_inv
git clone https://github.com/jtyr/ansible-yaml_inventory.git tools/yaml_inventory
ln -s ./tools/yaml_inventory/yaml_inventory.py ./hosts
cat > ./site.yaml <<END
---

- hosts: all
  connection: local
  gather_facts: no
  tasks:
    - debug:
        msg: Host from the group {{ xxx }} are using template {{ yyy + ((' and ' + zzz) if zzz is defined else '') }}
END
cat > ./inventory/main.yaml <<END
---

g1:
  g2:
    :templates:
      - template-app1
    :hosts:
      - g2h1
    g3:
      :templates:
        - template-app1
        - template-app2
      :hosts:
        - g3h1
END
cat > ./inventory/vars/g1/g2/all <<END
---

xxx: G2
END
cat > ./inventory/vars/g1/g2/g3/all <<END
---

xxx: G3
END
cat > ./inventory/vars/template/app1 <<END
---

yyy: APP1
END
cat > ./inventory/vars/template/app2 <<END
---

zzz: APP2
END
ansible-playbook -i hosts -l g2h1 site.yaml
ansible-playbook -i hosts -l g3h1 site.yaml