PDFViewer: Add a toolbar

The toolbar has an option to toggle the sidebar, a number input to
set the current page, and two buttons to go up and down by one page

Userland/Applications/PDFViewer/NumericInput.cpp

@@ -0,0 +1,90 @@
+/*
+ * Copyright (c) 2021, Matthew Olsson <mattco@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "NumericInput.h"
+#include "ctype.h"
+
+NumericInput::NumericInput()
+{
+    set_text("0");
+
+    on_change = [&] {
+        auto number_opt = text().to_int();
+        if (number_opt.has_value()) {
+            set_current_number(number_opt.value(), false);
+            return;
+        }
+
+        StringBuilder builder;
+        bool first = true;
+        for (auto& ch : text()) {
+            if (isdigit(ch) || (first && ((ch == '-' && m_min_number < 0) || ch == '+')))
+                builder.append(ch);
+            first = false;
+        }
+
+        auto new_number_opt = builder.to_string().to_int();
+        if (!new_number_opt.has_value()) {
+            m_needs_text_reset = true;
+            set_text(builder.to_string());
+            return;
+        } else {
+            m_needs_text_reset = false;
+        }
+
+        set_text(builder.to_string());
+        set_current_number(new_number_opt.value(), false);
+    };
+
+    on_up_pressed = [&] {
+        if (m_current_number < m_max_number)
+            set_current_number(m_current_number + 1);
+    };
+
+    on_down_pressed = [&] {
+        if (m_current_number > m_min_number)
+            set_current_number(m_current_number - 1);
+    };
+
+    on_focusout = [&] { on_focus_lost(); };
+    on_return_pressed = [&] { on_focus_lost(); };
+    on_escape_pressed = [&] { on_focus_lost(); };
+}
+
+void NumericInput::set_min_number(i32 number)
+{
+    m_min_number = number;
+    if (m_current_number < number)
+        set_current_number(number);
+}
+
+void NumericInput::set_max_number(i32 number)
+{
+    m_max_number = number;
+    if (m_current_number > number)
+        set_current_number(number);
+}
+
+void NumericInput::on_focus_lost()
+{
+    if (m_needs_text_reset) {
+        set_text(String::number(m_current_number));
+        m_needs_text_reset = false;
+    }
+    if (on_number_changed)
+        on_number_changed(m_current_number);
+}
+
+void NumericInput::set_current_number(i32 number, bool call_change_handler)
+{
+    if (number == m_current_number)
+        return;
+
+    m_current_number = clamp(number, m_min_number, m_max_number);
+    set_text(String::number(m_current_number));
+    if (on_number_changed && call_change_handler)
+        on_number_changed(m_current_number);
+}