Improve color-coding for user disambiguation

See also: https://github.com/quotient-im/libQuotient/wiki/User-color-coding-standard-draft-proposal

src/neochatuser.cpp

@@ -5,9 +5,35 @@
  */
 #include "neochatuser.h"
 
+#include <PlatformTheme> // Kirigami
+
 #include "csapi/profile.h"
 
+NeoChatUser::NeoChatUser(QString userId, Connection *connection)
+    : User(userId, connection)
+{
+    m_theme = static_cast<Kirigami::PlatformTheme *>(qmlAttachedPropertiesObject<Kirigami::PlatformTheme>(this, true));
+    Q_ASSERT(m_theme);
+
+    connect(m_theme, &Kirigami::PlatformTheme::colorsChanged, this, &NeoChatUser::polishColor);
+}
+
 QColor NeoChatUser::color()
 {
-    return QColor::fromHslF(hueF(), 0.7, 0.5, 1);
+    return m_color;
+}
+
+void NeoChatUser::setColor(QColor color)
+{
+    if (m_color == color)
+        return;
+
+    m_color = color;
+    emit colorChanged(m_color);
+}
+
+void NeoChatUser::polishColor()
+{
+    // https://github.com/quotient-im/libQuotient/wiki/User-color-coding-standard-draft-proposal
+    setColor(QColor::fromHslF(hueF(), 1 - m_theme->alternateBackgroundColor().saturationF(), -0.7 * m_theme->alternateBackgroundColor().lightnessF() + 0.9, m_theme->textColor().alphaF()));
 }

src/neochatuser.h

@@ -10,17 +10,30 @@
 #include "room.h"
 #include "user.h"
 
+namespace Kirigami
+{
+class PlatformTheme;
+}
+
 using namespace Quotient;
 
 class NeoChatUser : public User
 {
     Q_OBJECT
-    Q_PROPERTY(QColor color READ color CONSTANT)
+    Q_PROPERTY(QColor color READ color WRITE setColor NOTIFY colorChanged)
 public:
-    NeoChatUser(QString userId, Connection *connection)
+    NeoChatUser(QString userId, Connection *connection);
-        : User(userId, connection)
-    {
-    }
 
+public Q_SLOTS:
     QColor color();
+    void setColor(QColor color);
+
+Q_SIGNALS:
+    void colorChanged(QColor color);
+
+private:
+    Kirigami::PlatformTheme *m_theme = nullptr;
+    QColor m_color;
+
+    void polishColor();
 };