feat(transformer): add transformer impl

[shenxiangzhuang]

Close #33

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.11%. Comparing base (b5dbfed) to head (37fe7fa).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #35      +/-   ##
==========================================
+ Coverage   86.63%   92.11%   +5.48%     
==========================================
  Files           7        8       +1     
  Lines         217      368     +151     
==========================================
+ Hits          188      339     +151     
  Misses         29       29              

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