Country filter v1

[raysonkoh]

Fixes #108
Basic implementation of country filter c/COUNTRY_CODE command. Tested working with GUI on country filter c/SG.

@tankangliang note that when u add the country field to Client, you need to update the client.getCountry() method as I am hardcoding the return country.

Better tests and user feedback messages will be done in a separate issue.

[codecov-io]

Codecov Report

Merging #121 into master will decrease coverage by 0.82%.
The diff coverage is 65.00%.

@@             Coverage Diff              @@
##             master     #121      +/-   ##
============================================
- Coverage     72.10%   71.28%   -0.83%     
- Complexity      410      440      +30     
============================================
  Files            76       81       +5     
  Lines          1269     1379     +110     
  Branches        127      143      +16     
============================================
+ Hits            915      983      +68     
- Misses          320      345      +25     
- Partials         34       51      +17     

Impacted Files	Coverage Δ	Complexity Δ
.../seedu/address/logic/parser/AddressBookParser.java	56.41% <0.00%> (-28.78%)	13.00 <0.00> (ø)
...c/main/java/seedu/address/model/client/Client.java	95.23% <0.00%> (-2.33%)	21.00 <0.00> (ø)
...main/java/seedu/address/model/country/Country.java	60.00% <22.22%> (-21.82%)	6.00 <2.00> (+3.00)	⬇️
...u/address/logic/commands/CountryFilterCommand.java	46.15% <46.15%> (ø)	2.00 <2.00> (?)
...ent/ClientCountryMatchesInputCountryPredicate.java	50.00% <50.00%> (ø)	2.00 <2.00> (?)
...edu/address/logic/commands/CountryNoteCommand.java	70.58% <70.58%> (ø)	4.00 <4.00> (?)
src/main/java/seedu/address/model/note/Note.java	75.00% <75.00%> (-25.00%)	2.00 <2.00> (+1.00)	⬇️
...va/seedu/address/model/country/CountryManager.java	85.71% <76.92%> (-14.29%)	11.00 <8.00> (+6.00)	⬇️
...in/java/seedu/address/logic/parser/ParserUtil.java	93.47% <80.00%> (-3.75%)	17.00 <3.00> (+3.00)	⬇️
...eedu/address/logic/commands/ClientFindCommand.java	100.00% <100.00%> (ø)	6.00 <0.00> (ø)
... and 11 more

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[rtshkmr]

this PR is required for other PRs to be made, hence it got expedited. Should be okay after the minor changes that @tankangliang suggested. Thanks man!

[tankangliang]

The rest of the code looks good!

[qwoprocks]

Hmmm I was thinking that this CountryManager class holds all Country objects, while every other class should be holding references to these objects instead of any new Country() object. That way, the class themselves should be able to check if the Country has any notes, and this method would not be needed.

[raysonkoh]

My idea is that whenever you are interacting with the existing Country instances (other than just getting country notes), you should only do it via CountryManager. I think this layer of abstraction is good especially for logging/debugging in the future since Model only needs to operate on CountryManager and I would be able to log all Country method calls.

For classes like the CountryNoteParser or CountryFilterParser they should not be holding references to the existing Country as they do not have a reference to CountryManager. Only Model has a reference to CountryManager. So when a Command executes on a Model, then they are able to check for duplicate notes, etc.

Also, Country has a hasCountryNote method, but I purposely made it protected so that only CountryManager can call that method. Other classes should only be able to call the constructor and getCountryNote method of Country only.