Change codes for readability

Change codes for readability

- Adjust include file order.
- Add some blank lines for readability.
- Apply early-return policy to reduce indentation depth.
- Extract duplicated codes into function.
- Remove unnecessary local variables.
- Move parameter checking logics to another function.

Change-Id: I45b86175e90e559c7eccf263f21841042bec1d96
Signed-off-by: Junghyun Yeon <jungh.yeon@samsung.com>