Merge branch 'master' into DG-additions

docs/DeveloperGuide.md

@@ -20,6 +20,8 @@ title: Developer Guide
     * [Help feature](#help-feature)
     * [Birthday Reminder feature](#birthday-reminder-feature)
     * [Mailing List feature](#mailing-list-feature)
+    * [Command History feature](#command-history-feature)
+    * [Command Assistant feature](#command-assistant-feature)
 
 * [Documentation, logging, testing, configuration, dev-ops](#documentation-logging-testing-configuration-dev-ops)
 * [Appendix: Requirements](#appendix-requirements)
@@ -388,6 +390,8 @@ Step 4. The user decides to view the usage of `add` to learn to add a contact, a
 
 Step 5. CONNECTIONS will display a detailed help message on the usage of the `add` command in `ResultDisplay`.
 
+![HelpSequenceDiagram](images/HelpCommandDiagram.png)
+
 
 ### Birthday Reminder feature
 
@@ -469,6 +473,74 @@ Step 10. The headers and rows are written to the CSV file that is specified by t
     * Cons: Additional calls to logic and model are needed to get the required information.
 
 
+### Command History feature
+
+#### Implementation
+
+The operation is exposed in `CommandBox` and `CommandHistory`.
+
+The user keystroke will be read in `CommandBox#handleKeyStroke`, which will call the appropriate method in `CommandHistory` to retrieve the previous and next commands. The retrieved commands are passed into `CommandBox#commandTextField` to be displayed.
+
+Given below is an example usage scenario and how the Command History mechanism behaves at each step.
+
+Step 1. The user launches the application for the first time. All contacts are displayed by default.
+
+Step 2. The user executes `find n/David t/friend t/football` to search for a matching contact.
+
+Step 3. User wants to retrieve previous command and presses the `UP` key.
+
+Step 4. `CommandBox#handleKeyStroke` reads the `UP` keystroke and calls `CommandHistory#getPreviousCommand`.
+
+Step 5. `CommandHistory` retrieves the previous command and returns it.
+
+Step 6. `CommandBox` displays the previous command in the Command Box.
+
+![CommandHistoryActivityDiagram](images/CommandHistoryActivityDiagram.png)
+
+#### Design considerations:
+
+**Aspect: Implementation of Command History:**
+
+* **Option 1 (current choice):** Generate `CommandHistory` as a Singleton class.
+    * Pros: Ensures that there is only one set of history that is tracked.
+    * Cons: Complicates testing as different versions of history cannot be created.
+
+* **Option 2:** Generate `CommandHistory` as a normal class.
+    * Pros: Makes testing easier as multiple `CommandHistory` objects can be created with different history to test different conditions.
+    * Cons: Possible conflicting history if `CommandHistory` is not updated properly.
+
+### Command Assistant feature
+
+#### Implementation
+
+The operation is exposed in `SystemCommand`, specifically in `SystemCommand#execute`.
+
+The user keystroke will be read in `CommandBox#handleKeyStroke`. The user input will be evaluated by `SystemCommand#execute` to determine the appropriate help message to display.
+
+Given below is an example usage scenario and how the Command Assistant mechanism behaves at each step.
+
+Step 1. The user launches the application for the first time. All contacts are displayed by default.
+
+Step 2. The user enters `find ` to search for a matching contact.
+
+Step 3. `CommandBox#handleKeyStroke` reads `find ` input string and calls `SystemCommand#execute`.
+
+Step 4. `SystemCommand` evaluates the user input and returns the appropriate help message.
+
+Step 5. CONNECTIONS will display a help message in `ResultDisplay`.
+
+#### Design considerations:
+
+**Aspect: Implementation of Command Assistant:**
+
+* **Option 1:** Create a `AssistantCommand` class which extends from `Command` to handle the features of `Command Assistant`.
+    * Pros: Simplifies implementation as only an additional subclass needs to be created.
+    * Cons: Creates an additional command that users may be able to utilise, which they are not supposed to.
+
+* **Option 2 (current choice):** Create a new type of command called `SystemCommand` that does not extend from `Command`.
+    * Pros: Prevents potential issues such as users using an additional command which they are not supposed to use.
+    * Cons: Requires additional code to interface with `Logic`, 'MainWindow` and `CommandBox`.
+
 ### [Proposed] Partial data recovery feature
 Allows the user to recover partial data if the data file becomes corrupted. 
 

docs/diagrams/CommandHistoryActivityDiagram.puml

@@ -0,0 +1,36 @@
+@startuml
+'https://plantuml.com/activity-diagram-beta
+
+start
+:UI receives keystroke;
+switch()
+case ([keystroke `UP`])
+  :Attempts to retrieves previous command;
+  if () then ([has command history])
+    if () then ([has previous command])
+      :Displays previous command;
+    else ([no previous command])
+      :Displays last command in history;
+    endif
+  else ([no command history])
+    :Displays nothing;
+  endif
+case ([keystroke `DOWN`])
+  :Attempts to retrieves next command;
+  if () then ([has command history])
+    if () then ([has next command])
+      :Displays next command;
+    else ([no next command])
+      :Displays nothing;
+    endif
+  else ([no command history])
+    :Displays nothing;
+  endif
+case ([other keystrokes])
+  :Retrieves Command Assistant;
+endswitch
+
+
+stop
+
+@enduml

docs/diagrams/HelpCommandDiagram.puml

@@ -0,0 +1,69 @@
+@startuml
+!include style.puml
+
+box UI UI_COLOR
+participant "UI" as UI UI_COLOR
+end box
+
+box Logic LOGIC_COLOR_T1
+participant ":LogicManager" as LogicManager LOGIC_COLOR
+participant ":AddressBookParser" as AddressBookParser LOGIC_COLOR
+participant ":HelpCommandParser" as HelpCommandParser LOGIC_COLOR
+participant "h:HelpCommand" as HelpCommand LOGIC_COLOR
+participant ":CommandResult" as CommandResult LOGIC_COLOR
+end box
+
+UI -> LogicManager : execute("help add")
+activate LogicManager
+
+LogicManager -> AddressBookParser : parseCommand("help add")
+activate AddressBookParser
+
+create HelpCommandParser
+AddressBookParser -> HelpCommandParser
+activate HelpCommandParser
+
+HelpCommandParser --> AddressBookParser
+deactivate HelpCommandParser
+
+AddressBookParser -> HelpCommandParser : parse("add")
+activate HelpCommandParser
+
+create HelpCommand
+HelpCommandParser -> HelpCommand
+activate HelpCommand
+
+HelpCommand --> HelpCommandParser : h
+deactivate HelpCommand
+
+HelpCommandParser --> AddressBookParser  : h
+deactivate HelpCommandParser
+'Hidden arrow to position the destroy marker below the end of the activation bar.
+HelpCommandParser -[hidden]-> AddressBookParser
+destroy HelpCommandParser
+
+AddressBookParser --> LogicManager  : h
+deactivate AddressBookParser
+
+LogicManager -> HelpCommand : execute()
+activate HelpCommand
+
+create CommandResult
+HelpCommand -> CommandResult
+activate CommandResult
+CommandResult -> HelpCommand
+deactivate CommandResult
+
+
+HelpCommand --> LogicManager : result
+deactivate HelpCommand
+
+UI <--LogicManager: result
+deactivate LogicManager
+'Hidden arrow to position the destroy marker below the end of the activation bar.
+HelpCommand -[hidden]-> LogicManager
+destroy HelpCommand
+
+
+
+@enduml