Prefer std::string over std::wstring. (#179)

In the past, FTXUI switched from std::string to std::wstring to support
fullwidth characters. The reasons was that fullwidth characters can be
stored inside a single wchar_t.

Then FTXUI added support for combining characters. A single glygh
doesn't even fit a wchar_t. Instead, a glyph can be arbitrary large.

The usage of wstring doesn't really fit the new model and have several
drawbacks:
1. It doesn't simplify the implementation of FTXUI, because of combining
   characters.
2. It reduces drawing performance by 2x.
3. It increase Screen's memory allocation by 2x.

This patch converts FTXUI to use std::string internally. It now exposes
std::string based API. The std::wstring API remains, but is now
deprecated.

Tests and examples haven't been update to show the breakage is limited.
They will be updated in a second set of patches.

Bug: https://github.com/ArthurSonzogni/FTXUI/issues/153
Co-authored-by: Tushar Maheshwari <tushar27192@gmail.com>

src/ftxui/component/input.cpp

@@ -8,21 +8,24 @@
 #include "ftxui/component/component.hpp"          // for Make, Input
 #include "ftxui/component/component_base.hpp"     // for ComponentBase
 #include "ftxui/component/component_options.hpp"  // for InputOption
+#include "ftxui/component/deprecated.hpp"         // for Input
 #include "ftxui/component/event.hpp"  // for Event, Event::ArrowLeft, Event::ArrowRight, Event::Backspace, Event::Custom, Event::Delete, Event::End, Event::Home, Event::Return
 #include "ftxui/component/mouse.hpp"  // for Mouse, Mouse::Left, Mouse::Pressed
 #include "ftxui/component/screen_interactive.hpp"  // for Component
-#include "ftxui/dom/elements.hpp"  // for operator|, Element, text, reflect, dim, flex, focus, inverted, hbox, size, frame, select, underlined, Decorator, EQUAL, HEIGHT
+#include "ftxui/dom/deprecated.hpp"                // for text
+#include "ftxui/dom/elements.hpp"  // for operator|, Element, reflect, text, dim, flex, focus, inverted, hbox, size, frame, select, underlined, Decorator, EQUAL, HEIGHT
 #include "ftxui/screen/box.hpp"    // for Box
-#include "ftxui/util/ref.hpp"      // for StringRef, Ref, ConstStringRef
+#include "ftxui/screen/string.hpp"  // for to_wstring, to_string
+#include "ftxui/util/ref.hpp"  // for WideStringRef, Ref, ConstStringRef, StringRef
 
 namespace ftxui {
 
 // An input box. The user can type text into it.
-class InputBase : public ComponentBase {
+class WideInputBase : public ComponentBase {
  public:
-  InputBase(StringRef content,
-            ConstStringRef placeholder,
-            Ref<InputOption> option)
+  WideInputBase(WideStringRef content,
+                ConstStringRef placeholder,
+                Ref<InputOption> option)
       : content_(content), placeholder_(placeholder), option_(option) {}
 
   int& cursor_position() { return *(option_->cursor_position); }
@@ -132,7 +135,7 @@ class InputBase : public ComponentBase {
 
     // Content
     if (event.is_character()) {
-      content_->insert(cursor_position(), 1, event.character());
+      content_->insert(cursor_position(), 1, to_wstring(event.character())[0]);
       cursor_position()++;
       option_->on_change();
       return true;
@@ -165,7 +168,7 @@ class InputBase : public ComponentBase {
 
   bool Focusable() const final { return true; }
 
-  StringRef content_;
+  WideStringRef content_;
   ConstStringRef placeholder_;
 
   Box input_box_;
@@ -173,6 +176,43 @@ class InputBase : public ComponentBase {
   Ref<InputOption> option_;
 };
 
+// An input box. The user can type text into it.
+// For convenience, the std::string version of Input simply wrap a
+// WideInputBase.
+// TODO(arthursonzogni): Provide an implementation handling std::string natively
+// and adds better support for combining characters.
+class InputBase : public ComponentBase {
+ public:
+  InputBase(StringRef content,
+            ConstStringRef placeholder,
+            Ref<InputOption> option)
+      : content_(std::move(content)),
+        wrapped_content_(to_wstring(*content_)),
+        wrapped_input_(&wrapped_content_,
+                       std::move(placeholder),
+                       std::move(option)) {}
+
+  Element Render() override {
+    wrapped_content_ = to_wstring(*content_);
+    return wrapped_input_.Render();
+  }
+
+  bool OnEvent(Event event) override {
+    wrapped_content_ = to_wstring(*content_);
+    if (wrapped_input_.OnEvent(event)) {
+      content_ = to_string(wrapped_content_);
+      return true;
+    }
+    return false;
+  }
+
+  bool Focusable() const final { return true; }
+
+  StringRef content_;
+  std::wstring wrapped_content_;
+  WideInputBase wrapped_input_;
+};
+
 /// @brief An input box for editing text.
 /// @param content The editable content.
 /// @param placeholder The text displayed when content is still empty.
@@ -184,8 +224,8 @@ class InputBase : public ComponentBase {
 ///
 /// ```cpp
 /// auto screen = ScreenInteractive::FitComponent();
-/// std::wstring content= L"";
-/// std::wstring placeholder = L"placeholder";
+/// std::string content= "";
+/// std::string placeholder = "placeholder";
 /// Component input = Input(&content, &placeholder);
 /// screen.Loop(input);
 /// ```
@@ -201,6 +241,34 @@ Component Input(StringRef content,
   return Make<InputBase>(content, placeholder, std::move(option));
 }
 
+/// @brief . An input box for editing text.
+/// @param content The editable content.
+/// @param placeholder The text displayed when content is still empty.
+/// @param option Additional optional parameters.
+/// @ingroup component
+/// @see InputBase
+///
+/// ### Example
+///
+/// ```cpp
+/// auto screen = ScreenInteractive::FitComponent();
+/// std::string content= "";
+/// std::string placeholder = "placeholder";
+/// Component input = Input(&content, &placeholder);
+/// screen.Loop(input);
+/// ```
+///
+/// ### Output
+///
+/// ```bash
+/// placeholder
+/// ```
+Component Input(WideStringRef content,
+                ConstStringRef placeholder,
+                Ref<InputOption> option) {
+  return Make<WideInputBase>(content, placeholder, std::move(option));
+}
+
 }  // namespace ftxui
 
 // Copyright 2020 Arthur Sonzogni. All rights reserved.