Add support for --fullscreen, --maximized (#6139)

## Summary of the Pull Request

Adds two new flags to the `wt.exe` alias:

* `--maximized,-M`: Launch the new Terminal window maximized. This flag cannot be combined with `--fullscreen`.
* `--fullscreen,-F`: Launch the new Terminal window fullscreen. This flag cannot be combined with `--maximized`.

## References
* This builds on the work done in #6060.
* The cmdline args megathread: #4632

## PR Checklist
* [x] Closes #5801
* [x] I work here
* [ ] Tests added/passed
* [n/a] Requires documentation to be updated

## Detailed Description of the Pull Request / Additional comments

* I had to move the commandline arg parsing up a layer from `TerminalPage` to `AppLogic`, because `AppLogic` controls the Terminal's settings, including launch mode settings. This seems like a reasonable change, to put both the settings from the file and the commandline in the same place.
  - **Most of the diff is that movement of code**

* _"What happens when you try to pass both flags, like `wtd -M -F new-tab`?"_:
![image](https://user-images.githubusercontent.com/18356694/82679939-3cffde00-9c11-11ea-8d88-03ec7db83e59.png)

## Validation Steps Performed
* Ran a bunch of commandlines to see what happened.

src/cascadia/TerminalApp/AppActionHandlers.cpp

@@ -232,7 +232,7 @@ namespace winrt::TerminalApp::implementation
     void TerminalPage::_HandleToggleFullscreen(const IInspectable& /*sender*/,
                                                const TerminalApp::ActionEventArgs& args)
     {
-        _ToggleFullscreen();
+        ToggleFullscreen();
         args.Handled(true);
     }
 }

src/cascadia/TerminalApp/AppCommandlineArgs.cpp

@@ -157,6 +157,7 @@ int AppCommandlineArgs::_handleExit(const CLI::App& command, const CLI::Error& e
 // - <none>
 void AppCommandlineArgs::_buildParser()
 {
+    // -v,--version: Displays version info
     auto versionCallback = [this](int64_t /*count*/) {
         if (const auto appLogic{ winrt::TerminalApp::implementation::AppLogic::Current() })
         {
@@ -173,6 +174,20 @@ void AppCommandlineArgs::_buildParser()
     };
     _app.add_flag_function("-v,--version", versionCallback, RS_A(L"CmdVersionDesc"));
 
+    // Maximized and Fullscreen flags
+    //   -M,--maximized: Maximizes the window on launch
+    //   -F,--fullscreen: Fullscreens the window on launch
+    auto maximizedCallback = [this](int64_t /*count*/) {
+        _launchMode = winrt::TerminalApp::LaunchMode::MaximizedMode;
+    };
+    auto fullscreenCallback = [this](int64_t /*count*/) {
+        _launchMode = winrt::TerminalApp::LaunchMode::FullscreenMode;
+    };
+    auto maximized = _app.add_flag_function("-M,--maximized", maximizedCallback, RS_A(L"CmdMaximizedDesc"));
+    auto fullscreen = _app.add_flag_function("-F,--fullscreen", fullscreenCallback, RS_A(L"CmdFullscreenDesc"));
+    maximized->excludes(fullscreen);
+
+    // Subcommands
     _buildNewTabParser();
     _buildSplitPaneParser();
     _buildFocusTabParser();
@@ -410,6 +425,10 @@ void AppCommandlineArgs::_resetStateToDefault()
     _focusTabIndex = -1;
     _focusNextTab = false;
     _focusPrevTab = false;
+
+    // DON'T clear _launchMode here! This will get called once for every
+    // subcommand, so we don't want `wt -F new-tab ; split-pane` clearing out
+    // the "global" fullscreen flag (-F).
 }
 
 // Function Description:
@@ -604,3 +623,8 @@ void AppCommandlineArgs::ValidateStartupCommands()
         _startupActions.push_front(*newTabAction);
     }
 }
+
+std::optional<winrt::TerminalApp::LaunchMode> AppCommandlineArgs::GetLaunchMode() const noexcept
+{
+    return _launchMode;
+}

src/cascadia/TerminalApp/AppCommandlineArgs.h

@@ -38,6 +38,8 @@ class TerminalApp::AppCommandlineArgs final
     const std::string& GetExitMessage();
     bool ShouldExitEarly() const noexcept;
 
+    std::optional<winrt::TerminalApp::LaunchMode> GetLaunchMode() const noexcept;
+
 private:
     static const std::wregex _commandDelimiterRegex;
 
@@ -76,6 +78,8 @@ class TerminalApp::AppCommandlineArgs final
     int _focusTabIndex{ -1 };
     bool _focusNextTab{ false };
     bool _focusPrevTab{ false };
+
+    std::optional<winrt::TerminalApp::LaunchMode> _launchMode{ std::nullopt };
     // Are you adding more args here? Make sure to reset them in _resetStateToDefault
 
     std::deque<winrt::TerminalApp::ActionAndArgs> _startupActions;

src/cascadia/TerminalApp/AppLogic.cpp

@@ -242,6 +242,17 @@ namespace winrt::TerminalApp::implementation
 
         _root->SetSettings(_settings, false);
         _root->Loaded({ this, &AppLogic::_OnLoaded });
+        _root->Initialized([this](auto&&, auto&&) {
+            // GH#288 - When we finish initialization, if the user wanted us
+            // launched _fullscreen_, toggle fullscreen mode. This will make sure
+            // that the window size is _first_ set up as something sensible, so
+            // leaving fullscreen returns to a reasonable size.
+            const auto launchMode = this->GetLaunchMode();
+            if (launchMode == LaunchMode::FullscreenMode)
+            {
+                _root->ToggleFullscreen();
+            }
+        });
         _root->Create();
 
         _ApplyTheme(_settings->GlobalSettings().GetTheme());
@@ -529,7 +540,13 @@ namespace winrt::TerminalApp::implementation
             LoadSettings();
         }
 
-        return _settings->GlobalSettings().GetLaunchMode();
+        // GH#4620/#5801 - If the user passed --maximized or --fullscreen on the
+        // commandline, then use that to override the value from the settings.
+        const auto valueFromSettings = _settings->GlobalSettings().GetLaunchMode();
+        const auto valueFromCommandlineArgs = _appArgs.GetLaunchMode();
+        return valueFromCommandlineArgs.has_value() ?
+                   valueFromCommandlineArgs.value() :
+                   valueFromSettings;
     }
 
     // Method Description:
@@ -934,31 +951,108 @@ namespace winrt::TerminalApp::implementation
         }
     }
 
-    int32_t AppLogic::SetStartupCommandline(array_view<const winrt::hstring> actions)
+    // Method Description:
+    // - Sets the initial commandline to process on startup, and attempts to
+    //   parse it. Commands will be parsed into a list of ShortcutActions that
+    //   will be processed on TerminalPage::Create().
+    // - This function will have no effective result after Create() is called.
+    // - This function returns 0, unless a there was a non-zero result from
+    //   trying to parse one of the commands provided. In that case, no commands
+    //   after the failing command will be parsed, and the non-zero code
+    //   returned.
+    // Arguments:
+    // - args: an array of strings to process as a commandline. These args can contain spaces
+    // Return Value:
+    // - the result of the first command who's parsing returned a non-zero code,
+    //   or 0. (see AppLogic::_ParseArgs)
+    int32_t AppLogic::SetStartupCommandline(array_view<const winrt::hstring> args)
     {
-        if (_root)
+        const auto result = _ParseArgs(args);
+        if (result == 0)
         {
-            return _root->SetStartupCommandline(actions);
+            _appArgs.ValidateStartupCommands();
+            _root->SetStartupActions(_appArgs.GetStartupActions());
         }
-        return 0;
+
+        return result;
     }
 
-    winrt::hstring AppLogic::ParseCommandlineMessage()
+    // Method Description:
+    // - Attempts to parse an array of commandline args into a list of
+    //   commands to execute, and then parses these commands. As commands are
+    //   successfully parsed, they will generate ShortcutActions for us to be
+    //   able to execute. If we fail to parse any commands, we'll return the
+    //   error code from the failure to parse that command, and stop processing
+    //   additional commands.
+    // Arguments:
+    // - args: an array of strings to process as a commandline. These args can contain spaces
+    // Return Value:
+    // - 0 if the commandline was successfully parsed
+    int AppLogic::_ParseArgs(winrt::array_view<const hstring>& args)
     {
-        if (_root)
+        auto commands = ::TerminalApp::AppCommandlineArgs::BuildCommands(args);
+
+        for (auto& cmdBlob : commands)
         {
-            return _root->ParseCommandlineMessage();
+            // On one hand, it seems like we should be able to have one
+            // AppCommandlineArgs for parsing all of them, and collect the
+            // results one at a time.
+            //
+            // On the other hand, re-using a CLI::App seems to leave state from
+            // previous parsings around, so we could get mysterious behavior
+            // where one command affects the values of the next.
+            //
+            // From https://cliutils.github.io/CLI11/book/chapters/options.html:
+            // > If that option is not given, CLI11 will not touch the initial
+            // > value. This allows you to set up defaults by simply setting
+            // > your value beforehand.
+            //
+            // So we pretty much need the to either manually reset the state
+            // each command, or build new ones.
+            const auto result = _appArgs.ParseCommand(cmdBlob);
+
+            // If this succeeded, result will be 0. Otherwise, the caller should
+            // exit(result), to exit the program.
+            if (result != 0)
+            {
+                return result;
+            }
         }
-        return { L"" };
+
+        // If all the args were successfully parsed, we'll have some commands
+        // built in _appArgs, which we'll use when the application starts up.
+        return 0;
     }
 
+    // Method Description:
+    // - If there were any errors parsing the commandline that was used to
+    //   initialize the terminal, this will return a string containing that
+    //   message. If there were no errors, this message will be blank.
+    // - If the user requested help on any command (using --help), this will
+    //   contain the help message.
+    // - If the user requested the version number (using --version), this will
+    //   contain the version string.
+    // Arguments:
+    // - <none>
+    // Return Value:
+    // - the help text or error message for the provided commandline, if one
+    //   exists, otherwise the empty string.
+    winrt::hstring AppLogic::ParseCommandlineMessage()
+    {
+        return winrt::to_hstring(_appArgs.GetExitMessage());
+    }
+
+    // Method Description:
+    // - Returns true if we should exit the application before even starting the
+    //   window. We might want to do this if we're displaying an error message or
+    //   the version string, or if we want to open the settings file.
+    // Arguments:
+    // - <none>
+    // Return Value:
+    // - true iff we should exit the application before even starting the window
     bool AppLogic::ShouldExitEarly()
     {
-        if (_root)
-        {
-            return _root->ShouldExitEarly();
-        }
-        return false;
+        return _appArgs.ShouldExitEarly();
     }
 
     winrt::hstring AppLogic::ApplicationDisplayName() const

src/cascadia/TerminalApp/AppLogic.h

@@ -76,6 +76,9 @@ namespace winrt::TerminalApp::implementation
 
         std::atomic<bool> _settingsReloadQueued{ false };
 
+        ::TerminalApp::AppCommandlineArgs _appArgs;
+        int _ParseArgs(winrt::array_view<const hstring>& args);
+
         fire_and_forget _ShowDialog(const winrt::Windows::Foundation::IInspectable& sender, winrt::Windows::UI::Xaml::Controls::ContentDialog dialog);
         void _ShowLoadErrorsDialog(const winrt::hstring& titleKey, const winrt::hstring& contentKey, HRESULT settingsLoadedResult);
         void _ShowLoadWarningsDialog();

src/cascadia/TerminalApp/Resources/en-US/Resources.resw

@@ -259,6 +259,12 @@
   <data name="CmdVersionDesc" xml:space="preserve">
     <value>Display the application version</value>
   </data>
+  <data name="CmdMaximizedDesc" xml:space="preserve">
+    <value>Launch the window maximized</value>
+  </data>
+  <data name="CmdFullscreenDesc" xml:space="preserve">
+    <value>Launch the window in fullscreen mode</value>
+  </data>
   <data name="NewTabSplitButton.[using:Windows.UI.Xaml.Automation]AutomationProperties.HelpText" xml:space="preserve">
     <value>Press the button to open a new terminal tab with your default profile. Open the flyout to select which profile you want to open.</value>
   </data>