Merge pull request #52 from JQChong/update-find-doc

Update find doc

Author: JQChong

docs/DeveloperGuide.md

@@ -173,6 +173,34 @@ The following activity diagram summarizes what happens when a user executes a bl
     * Pros: Able to directly set blacklist status without checking current status.
     * Cons: More commands to remember.
 
+### Find persons by tag feature
+This feature is built on the current `find` command, which is used to be limited to only finding persons by names. With this change, the format of the `find` command is now modified to `find n/[NAME] t/[TAG]`.
+This command returns the persons with attributes that matches at least one of the attributes of interest (See User Guide for more details).
+Note that users are only required to provide at least one of the parameters to use this command. In other words, commands such as `find n/Alex` and `find t/autistic` are valid commands.
+
+To facilitate the implementation of this feature, two new predicate classes are introduced, namely `PersonTagContainsKeywordsPredicate` and `ReturnTruePredicate`. The former class is to check whether any of the `tag`s contain the keywords. The latter predicate always returns `true`. 
+
+The introduction of `ReturnTruePredicate` may seem pointless, but it is of great use. The key here is to realize that if X is a boolean variable, then X `and` `true` simplifies to X. If both `name` and `tag` keywords are given, the `FindCommand` class will receive `NameContainsKeywordsPredicate` and `PersonTagContainsKeywordsPredicate`. If, say, only `name` keywords are given, then `ReturnTruePredicate` will instead be supplied to `FindCommand`.
+As such, the filter will now solely depend on `NameContainsKeywordsPredicate` since the second predicate always returns true.
+
+The following sequence diagram shows how the `find` command works:
+![FindSequenceDiagram](images/FindSequenceDiagram.png)
+
+The following activity diagram shows what happens when `find` command is executed.
+![FindActivityDiagram](images/FindActivityDiagram.png)
+
+#### Design considerations:
+
+##### Aspect: Command design
+
+* **Alternative 1 (current choice):** `find` command alone supports finding by names and tags.
+    * Pros: More intuitive to use since most commands have similar format. Makes further extensions easier as developers only need to define a new predicate class.
+    * Cons: Can make debugging harder since further extensions are centralized into one class.
+
+* **Alternative 2:** Find by names and find by tags are separate commands.
+    * Pros: Easier to debug as one command is meant for one criterion.
+    * Cons: It is now not possible to combine both criteria together. More commands to remember. Due to similarity of the commands, they can be confused from one another.
+    
 ### \[Proposed\] Undo/redo feature
 
 #### Proposed Implementation

docs/diagrams/FindActivityDiagram.puml

@@ -0,0 +1,10 @@
+@startuml
+start
+:User executes find command;
+repeat
+    :Check if the next person matches the keywords;
+repeat while () is ([has next person])
+-> [else];
+:Display results;
+end
+@enduml

docs/diagrams/FindSequenceDiagram.puml

@@ -0,0 +1,67 @@
+@startuml
+!include style.puml
+
+box Logic LOGIC_COLOR_T1
+participant ":LogicManager" as LogicManager LOGIC_COLOR
+participant ":AddressBookParser" as AddressBookParser LOGIC_COLOR
+participant ":FindCommandParser" as FindCommandParser LOGIC_COLOR
+participant ":FindCommand" as FindCommand LOGIC_COLOR
+participant ":CommandResult" as CommandResult LOGIC_COLOR
+end box
+
+box Model MODEL_COLOR_T1
+participant ":Model" as Model MODEL_COLOR_T1
+end box
+
+[-> LogicManager : execute("find n/Alex t/friends")
+activate LogicManager
+
+LogicManager -> AddressBookParser : parseCommand("find n/Alex t/friends")
+activate AddressBookParser
+
+create FindCommandParser
+AddressBookParser -> FindCommandParser
+activate FindCommandParser
+
+FindCommandParser --> AddressBookParser
+deactivate FindCommandParser
+
+AddressBookParser -> FindCommandParser : parse("n/Alex t/friends")
+activate FindCommandParser
+
+create FindCommand
+FindCommandParser -> FindCommand
+deactivate FindCommand
+
+FindCommand --> FindCommandParser
+deactivate FindCommand
+
+FindCommandParser --> AddressBookParser
+deactivate AddressBookParser
+
+AddressBookParser --> LogicManager
+deactivate AddressBookParser
+
+LogicManager -> FindCommand : execute()
+activate FindCommand
+
+FindCommand -> Model : updateFilteredPersonList
+activate Model
+
+Model --> FindCommand
+deactivate Model
+
+create CommandResult
+FindCommand -> CommandResult
+activate CommandResult
+
+CommandResult --> FindCommand
+deactivate CommandResult
+
+FindCommand --> LogicManager : result
+deactivate FindCommand
+
+[<--LogicManager
+deactivate LogicManager
+
+@enduml