1 files changed, 91 insertions, 12 deletions

diff --git a/src/htmlbuilder.cpp b/src/htmlbuilder.cpp
index ccb9171..c8f039f 100644
--- a/src/htmlbuilder.cpp
+++ b/src/htmlbuilder.cpp
@@ -18,25 +18,92 @@
 
 #include "htmlbuilder.h"
 
+#include <QCoreApplication>
+#include <QGuiApplication>
 #include <QRegularExpression>
 
 namespace {
 
-const char *kStyle = R"CSS(
-body { font-family: sans-serif; font-size: 10pt; margin: 12px; }
+/// The stylesheet, with every colour supplied by the caller.
+///
+/// %1 background, %2 text, %3 quote, %4 border, %5 dim.
+const char *kStyleTemplate = R"CSS(
+body { font-family: sans-serif; font-size: 10pt; margin: 12px;
+       background: %1; color: %2; }
 pre.plain { white-space: pre-wrap; word-wrap: break-word;
             font-family: monospace; margin: 0; }
-span.quote { color: #4a6f8a; }
-.message { border-top: 1px solid #bbb; padding: 10px 0; }
+span.quote { color: %3; }
+.message { border-top: 1px solid %4; padding: 10px 0; }
 .message:first-child { border-top: none; }
-.msg-header { font-size: 9pt; color: #555; margin-bottom: 8px; }
-.msg-header .who { font-weight: bold; color: #000; }
-.stub { font-size: 9pt; color: #666; padding: 4px 0;
-        border-top: 1px solid #ddd; }
+.msg-header { font-size: 9pt; color: %5; margin-bottom: 8px; }
+.msg-header .who { font-weight: bold; color: %2; }
+.stub { font-size: 9pt; color: %5; padding: 4px 0;
+        border-top: 1px solid %4; }
 )CSS";
 
+/// Mixes two colours, `weight` being how much of `a` survives.
+///
+/// Blending is what makes the derived colours theme-correct. A fixed grey is
+/// only "subtle" against the background it was chosen for: #555 reads as a
+/// quiet label on white and nearly vanishes on near-black.
+QColor blend(const QColor &a, const QColor &b, qreal weight)
+{
+    const qreal inverse = 1.0 - weight;
+    return QColor::fromRgbF(a.redF() * weight + b.redF() * inverse,
+                            a.greenF() * weight + b.greenF() * inverse,
+                            a.blueF() * weight + b.blueF() * inverse);
+}
+
 } // namespace
 
+HtmlBuilder::Palette HtmlBuilder::paletteFrom(const QPalette &palette)
+{
+    // Base and Text, not Window and WindowText: the pane is a content surface
+    // like a text edit, and on many themes Base differs from Window.
+    const QColor background = palette.color(QPalette::Base);
+    const QColor text = palette.color(QPalette::Text);
+
+    Palette result;
+    result.background = background;
+    result.text = text;
+
+    // Both derived from the pair, so they land at the right contrast whichever
+    // way round the theme is.
+    result.dim = blend(text, background, 0.6);
+    result.border = blend(text, background, 0.25);
+
+    // The quote colour keeps its hue, since "this is quoted" is carried by the
+    // colour being different rather than by it being dimmer, but it is pulled
+    // toward the background so it stays readable on a dark theme instead of
+    // glowing.
+    const QColor quoteHue(0x4a, 0x6f, 0x8a);
+    result.quote = background.lightnessF() < 0.5
+        ? blend(quoteHue.lighter(160), background, 0.75)
+        : blend(quoteHue, background, 0.85);
+
+    return result;
+}
+
+HtmlBuilder::Palette HtmlBuilder::defaultPalette()
+{
+    if (const QGuiApplication *app =
+            qobject_cast<QGuiApplication *>(QCoreApplication::instance()))
+        return paletteFrom(app->palette());
+
+    // No GUI application: only reachable from a test that did not pass a
+    // palette. A default-constructed QPalette is light, which matches what
+    // this code did before it was themed at all.
+    return paletteFrom(QPalette());
+}
+
+QString HtmlBuilder::styleSheet(const Palette &palette)
+{
+    return QString::fromUtf8(kStyleTemplate)
+        .arg(palette.background.name(), palette.text.name(),
+             palette.quote.name(), palette.border.name(),
+             palette.dim.name());
+}
+
 QString HtmlBuilder::renderPlain(const QString &text)
 {
     QString out;
@@ -61,12 +128,12 @@ QString HtmlBuilder::renderPlain(const QString &text)
     return out;
 }
 
-QString HtmlBuilder::document(const QString &bodyHtml)
+QString HtmlBuilder::document(const QString &bodyHtml, const Palette &palette)
 {
     return QStringLiteral(
         "<!DOCTYPE html><html><head><meta charset=\"utf-8\">"
         "<style>%1</style></head><body>%2</body></html>")
-        .arg(QString::fromUtf8(kStyle), bodyHtml);
+        .arg(styleSheet(palette), bodyHtml);
 }
 
 QString HtmlBuilder::namespaceCids(const QString &html, const QString &prefix)
@@ -218,14 +285,26 @@ QString HtmlBuilder::renderStub(const ParsedMessage &message)
 
 QString HtmlBuilder::build(const ParsedMessage &message, Mode mode)
 {
+    return build(message, mode, defaultPalette());
+}
+
+QString HtmlBuilder::build(const ParsedMessage &message, Mode mode,
+                           const Palette &palette)
+{
     ThreadRenderItem item;
     item.message = message;
     item.expanded = true;
-    return document(renderBody(item, mode));
+    return document(renderBody(item, mode), palette);
 }
 
 QString HtmlBuilder::buildThread(const QList<ThreadRenderItem> &items, Mode mode)
 {
+    return buildThread(items, mode, defaultPalette());
+}
+
+QString HtmlBuilder::buildThread(const QList<ThreadRenderItem> &items, Mode mode,
+                                 const Palette &palette)
+{
     QString body;
 
     for (int i = 0; i < items.size(); ++i) {
@@ -246,5 +325,5 @@ QString HtmlBuilder::buildThread(const QList<ThreadRenderItem> &items, Mode mode
                  renderBody(item, mode));
     }
 
-    return document(body);
+    return document(body, palette);
 }