docs: Add FindFreeTimeSequenceDiagram to DG

docs/DeveloperGuide.md

@@ -163,11 +163,40 @@ Classes used by multiple components are in the `seedu.addressbook.commons` packa
 
 This section describes some noteworthy details on how certain features are implemented.
 
+### Finding free time between friends based on allocated module timings
+
+Finding free time between students is done through `find_free_time d/Wed st/1200 et/1400`.
+
+`LogicManager` first calls `AddressBookParser` which then runs `parse_command` and then calls
+`FindFreeTimeCommandParser` which then parses the arguments, validates them, and then creates
+a new `FindFreeTimeCommand` instance. The arguments passed in is then used within a newly `IsFreePredicate`
+instance within the `FindFreeTimeCommand` instance, and the `LogicManager` then executes it.
+
+This then calls the existing `updateFilteredStudentList`with the `IsFreePredicate` within the `Model` instance.
+
+The following is the sequence diagram for this example.
+
+<img src="diagrams/FindFreeTimeSequenceDiagram.png" />
+
+#### Design Considerations
+
+Well, it was rather straightforward to implement this design because it has extreme similarities to the `FindCommand`
+that already existed within the AB3. Only tough parts were the filtering of conditions to ensure the
+time range stated doesn't overlap with the module timings of the students within the list.
+
+* **Alternative 1 (current choice):** Re-use code from `FindCommand` sequence.
+    * Pros: Easy to implement.
+    * Cons: Had to reconfigure the code to match our usecase.
+
+In short, this was the straightforward options with no backlash as it was a insanely easy command to create
+considering that existing groundwork has been laid. No issues has been faced with the implementation of the design
+other than rough hiccups (i.e allowing end time to be earlier than start time)
+
 ### Adding a ModuleTiming to a Student
 
 Adding a class to a student in ModContacts is done by the command `add_timing i/1 m/CS2103T d/Mon st/0800 et/1200`
 
-The entry point for this command is when the `LogicManager` parses the command, gets a `AddStudentModuleCommand`, 
+The entry point for this command is when the `LogicManager` parses the command, gets a `AddStudentModuleCommand`,
 and then executes it.
 
 `AddStudentModuleCommand` performs some validations, then adds the `ModuleTiming` to the designated

docs/diagrams/FindFreeTimeSequenceDiagram.puml

@@ -0,0 +1,71 @@
+@startuml
+'Belongs to @taufiq, Copied from author of AddModuleTimingSequenceDiagram
+!include style.puml
+skinparam ArrowFontStyle plain
+
+box Logic LOGIC_COLOR_T1
+participant ":LogicManager" as LogicManager LOGIC_COLOR
+participant ":AddressBookParser" as AddressBookParser LOGIC_COLOR
+participant ":FindFreeTimeCommandParser" as FindFreeTimeCommandParser LOGIC_COLOR
+participant "d:FindFreeTimeCommand" as FindFreeTimeCommand LOGIC_COLOR
+participant "r:CommandResult" as CommandResult LOGIC_COLOR
+end box
+
+box Model MODEL_COLOR_T1
+participant "m:Model" as Model MODEL_COLOR
+end box
+
+[-> LogicManager : execute("find_free_time d/Wed st/1200 et/1400")
+activate LogicManager
+
+LogicManager -> AddressBookParser : parseCommand("find_free_time d/Wed st/1200 et/1400")
+activate AddressBookParser
+
+create FindFreeTimeCommandParser
+AddressBookParser -> FindFreeTimeCommandParser
+activate FindFreeTimeCommandParser
+
+FindFreeTimeCommandParser --> AddressBookParser
+deactivate FindFreeTimeCommandParser
+
+AddressBookParser -> FindFreeTimeCommandParser : parse("d/Wed st/1200 et/1400")
+activate FindFreeTimeCommandParser
+
+create FindFreeTimeCommand
+FindFreeTimeCommandParser -> FindFreeTimeCommand
+activate FindFreeTimeCommand
+
+FindFreeTimeCommand --> FindFreeTimeCommandParser :
+deactivate FindFreeTimeCommand
+
+FindFreeTimeCommandParser --> AddressBookParser : d
+deactivate FindFreeTimeCommandParser
+'Hidden arrow to position the destroy marker below the end of the activation bar.
+FindFreeTimeCommandParser -[hidden]-> AddressBookParser
+destroy FindFreeTimeCommandParser
+
+AddressBookParser --> LogicManager : d
+deactivate AddressBookParser
+
+LogicManager -> FindFreeTimeCommand : execute(m)
+activate FindFreeTimeCommand
+
+FindFreeTimeCommand -> Model : updateFilteredStudentList(freePredicate)
+activate Model
+
+Model --> FindFreeTimeCommand
+deactivate Model
+
+create CommandResult
+FindFreeTimeCommand -> CommandResult
+activate CommandResult
+
+CommandResult --> FindFreeTimeCommand
+deactivate CommandResult
+
+FindFreeTimeCommand --> LogicManager : r
+deactivate FindFreeTimeCommand
+
+[<--LogicManager
+deactivate LogicManager
+@enduml