refactor and lint code

[ubogdan]

Describe the PR

• reduce code complexity
• improve code testing and coverage

Relation issue
NONE

Additional context
NONE

[codecov]

Codecov Report

Merging #978 (04c12f5) into master (b19e9cf) will increase coverage by 2.41%.
The diff coverage is 94.68%.

@@            Coverage Diff             @@
##           master     #978      +/-   ##
==========================================
+ Coverage   88.15%   90.57%   +2.41%     
==========================================
  Files           8        8              
  Lines        1874     1909      +35     
==========================================
+ Hits         1652     1729      +77     
+ Misses        127      104      -23     
+ Partials       95       76      -19     

Impacted Files	Coverage Δ
swagger.go	100.00% <ø> (ø)
types.go	100.00% <ø> (ø)
packages.go	77.55% <81.25%> (+0.85%)	⬆️
parser.go	89.32% <96.01%> (+2.50%)	⬆️
operation.go	92.89% <96.77%> (+3.28%)	⬆️
debug.go	100.00% <0.00%> (+50.00%)	⬆️

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[ubogdan]

@sdghchj Need a review, please.

[sdghchj]

LGTM