Add "syntax highlighter" to set code block background; color setting

Maybe can add real syntax highlighting later; but this is an available
hook to set the block background, as a workaround for Qt's lack of a
dynamic means of applying CSS to Markdown.

src/codeblockhighlighter.cpp

@@ -0,0 +1,19 @@
+#include "codeblockhighlighter.h"
+#include "settings.h"
+
+CodeBlockHighlighter::CodeBlockHighlighter(QTextDocument *parent)
+  : QSyntaxHighlighter(parent)
+{
+}
+
+void CodeBlockHighlighter::highlightBlock(const QString &text)
+{
+    Q_UNUSED(text) // TODO reuse kate syntax highlighters?
+    QTextBlockFormat fmt = currentBlock().blockFormat();
+    if (fmt.hasProperty(QTextFormat::BlockCodeFence)) {
+        fmt.setBackground(QColor(Settings::instance()->stringOrDefault(
+                                     Settings::styleGroup, Settings::codeBlockBackground, "#EEE")));
+        QTextCursor cur(currentBlock());
+        cur.setBlockFormat(fmt);
+    }
+}

src/codeblockhighlighter.h

@@ -0,0 +1,16 @@
+#ifndef CODEBLOCKHIGHLIGHTER_H
+#define CODEBLOCKHIGHLIGHTER_H
+
+#include <QSyntaxHighlighter>
+
+class CodeBlockHighlighter : public QSyntaxHighlighter
+{
+    Q_OBJECT
+public:
+    CodeBlockHighlighter(QTextDocument *parent);
+
+protected:
+    void highlightBlock(const QString &text) override;
+};
+
+#endif // CODEBLOCKHIGHLIGHTER_H

src/colorswatch.cpp

@@ -0,0 +1,34 @@
+#include "colorswatch.h"
+
+#include <QColorDialog>
+#include <QPainter>
+
+ColorSwatch::ColorSwatch(QWidget *parent) :
+    QWidget(parent),
+    m_color(QPalette().window().color())
+{
+    setFixedSize(24, 24);
+}
+
+void ColorSwatch::setColor(QColor color)
+{
+    if (!color.isValid())
+        return;
+    m_color = color;
+    update();
+}
+
+void ColorSwatch::paintEvent(QPaintEvent *event)
+{
+    Q_UNUSED(event)
+    QPainter painter(this);
+    painter.fillRect(rect(), m_color);
+    painter.setPen(QPalette().buttonText().color());
+    painter.drawRect(rect().adjusted(0, 0, -1, -1));
+}
+
+void ColorSwatch::mouseReleaseEvent(QMouseEvent *event)
+{
+    Q_UNUSED(event)
+    setColor(QColorDialog::getColor(m_color, parentWidget(), tr("Code block background")));
+}

src/colorswatch.h

@@ -0,0 +1,24 @@
+#ifndef COLORSWATCH_H
+#define COLORSWATCH_H
+
+#include <QWidget>
+
+class ColorSwatch : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit ColorSwatch(QWidget *parent = nullptr);
+    QColor color() { return m_color; }
+    void setColor(QColor color);
+
+signals:
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+    void mouseReleaseEvent(QMouseEvent *event) override;
+
+private:
+    QColor m_color;
+};
+
+#endif // COLORSWATCH_H

src/mainwindow.cpp

@@ -60,6 +60,7 @@ MainWindow::MainWindow(QWidget *parent) :
     ui->setupUi(this);
     m_mainWidget = ui->browser;
     m_mainWidget->setDocument(m_document);
+    m_highlighter = new CodeBlockHighlighter(m_document);
     connect(m_mainWidget, &QTextEdit::currentCharFormatChanged,
             this, &MainWindow::currentCharFormatChanged);
     connect(m_mainWidget, &QTextEdit::cursorPositionChanged,

src/mainwindow.h

@@ -27,6 +27,7 @@
 #include <QTextBrowser>
 #include <QUrl>
 #include "markdownbrowser.h"
+#include "codeblockhighlighter.h"
 #include "ipfsagent.h"
 #include "linkdialog.h"
 #include "thumbnailscene.h"
@@ -135,6 +136,7 @@ private slots:
     Ui::MainWindow *ui;
     MarkdownBrowser *m_mainWidget;
     Document *m_document;
+    CodeBlockHighlighter *m_highlighter;
     QJsonDocument m_jsonDocument;
     ThumbnailScene *m_thumbs = nullptr;
     LinkDialog *m_linkDialog = nullptr;

src/nb.pro

@@ -14,6 +14,8 @@ no_kio: DEFINES += NETTEBOOK_NO_KIO
 
 SOURCES += \
     cidfinder.cpp \
+    codeblockhighlighter.cpp \
+    colorswatch.cpp \
     datepickerdialog.cpp \
     document.cpp \
     ipfsagent.cpp \
@@ -33,6 +35,8 @@ SOURCES += \
 
 HEADERS += \
     cidfinder.h \
+    codeblockhighlighter.h \
+    colorswatch.h \
     datepickerdialog.h \
     document.h \
     ipfsagent.h \

src/settings.cpp

@@ -28,6 +28,8 @@ const QString Settings::journalGroup(QLatin1String("Journal"));
 const QString Settings::journalDirectory(QLatin1String("journalDirectory"));
 const QString Settings::journalFilenameFormat(QLatin1String("journalFilenameFormat"));
 const QString Settings::journalUsesTemplates(QLatin1String("journalUsesTemplates"));
+const QString Settings::styleGroup(QLatin1String("Style"));
+const QString Settings::codeBlockBackground(QLatin1String("codeBlockBackground"));
 
 Settings* Settings::instance()
 {

src/settings.h

@@ -43,6 +43,8 @@ class Settings : public QSettings
     static const QString journalDirectory;
     static const QString journalFilenameFormat;
     static const QString journalUsesTemplates;
+    static const QString styleGroup;
+    static const QString codeBlockBackground;
 
 protected:
     Settings(QObject* parent = nullptr);

src/settingsdialog.cpp

@@ -15,6 +15,7 @@ SettingsDialog::SettingsDialog(QWidget *parent) :
     ui->journalDirectory->setText(settings->stringOrDefault(settings->journalGroup, settings->journalDirectory, QLatin1String("~/journal")));
     ui->journalFilenameFormat->setText(settings->stringOrDefault(settings->journalGroup, settings->journalFilenameFormat, QLatin1String("$date-$topics.md")));
     ui->useJournalTemplates->setChecked(settings->boolOrDefault(settings->journalGroup, settings->journalUsesTemplates, true));
+    ui->codeBackgroundColorSwatch->setColor(QColor(settings->stringOrDefault(settings->styleGroup, settings->codeBlockBackground, "#EEE")));
     adjustSize();
 }
 
@@ -31,6 +32,7 @@ void SettingsDialog::on_SettingsDialog_accepted()
     settings->setString(settings->journalGroup, settings->journalDirectory, ui->journalDirectory->text());
     settings->setString(settings->journalGroup, settings->journalFilenameFormat, ui->journalFilenameFormat->text());
     settings->setBool(settings->journalGroup, settings->journalUsesTemplates, ui->useJournalTemplates->checkState());
+    settings->setString(settings->styleGroup, settings->codeBlockBackground, ui->codeBackgroundColorSwatch->color().name());
 }
 
 void SettingsDialog::on_journalDirectoryChooseButton_clicked()

src/settingsdialog.ui

@@ -20,6 +20,9 @@
   <layout class="QVBoxLayout" name="verticalLayout">
    <item>
     <widget class="QTabWidget" name="tabWidget">
+     <property name="currentIndex">
+      <number>0</number>
+     </property>
      <widget class="QWidget" name="writingTab">
       <attribute name="title">
        <string>Writing</string>
@@ -96,6 +99,23 @@
        </item>
       </layout>
      </widget>
+     <widget class="QWidget" name="styleTab">
+      <attribute name="title">
+       <string>Style</string>
+      </attribute>
+      <layout class="QFormLayout" name="formLayout_2">
+       <item row="0" column="0">
+        <widget class="QLabel" name="codeBlockBackgroundLabel">
+         <property name="text">
+          <string>Code block background</string>
+         </property>
+        </widget>
+       </item>
+       <item row="0" column="1">
+        <widget class="ColorSwatch" name="codeBackgroundColorSwatch" native="true"/>
+       </item>
+      </layout>
+     </widget>
     </widget>
    </item>
    <item>
@@ -110,6 +130,14 @@
    </item>
   </layout>
  </widget>
+ <customwidgets>
+  <customwidget>
+   <class>ColorSwatch</class>
+   <extends>QWidget</extends>
+   <header>colorswatch.h</header>
+   <container>1</container>
+  </customwidget>
+ </customwidgets>
  <resources>
   <include location="resources/resources.qrc"/>
  </resources>