feat(dialog-sdk): add Python syntax highlighter and runtime language swapping

pj_plugins/dialog_protocol/src/python_syntax_highlighter.hpp

@@ -0,0 +1,104 @@
+#pragma once
+
+#include <QRegularExpression>
+#include <QSyntaxHighlighter>
+#include <QTextCharFormat>
+
+namespace PJ {
+
+/// Minimal Python syntax highlighter for QPlainTextEdit code editors.
+class PythonSyntaxHighlighter : public QSyntaxHighlighter {
+ public:
+  explicit PythonSyntaxHighlighter(QTextDocument* parent) : QSyntaxHighlighter(parent) {
+    // Keywords
+    QTextCharFormat keyword_fmt;
+    keyword_fmt.setForeground(QColor("#0000ff"));
+    keyword_fmt.setFontWeight(QFont::Bold);
+    const char* keywords[] = {"and",      "as",       "assert",   "break",    "class",   "continue",
+                              "def",      "del",      "elif",     "else",     "except",  "False",
+                              "finally",  "for",      "from",     "global",   "if",      "import",
+                              "in",       "is",       "lambda",   "None",     "nonlocal", "not",
+                              "or",       "pass",     "raise",    "return",   "True",    "try",
+                              "while",    "with",     "yield"};
+    for (const char* kw : keywords) {
+      rules_.append({QRegularExpression("\\b" + QString(kw) + "\\b"), keyword_fmt});
+    }
+
+    // Decorators
+    rules_.append({QRegularExpression("@\\w+"), keyword_fmt});
+
+    // Numbers
+    QTextCharFormat number_fmt;
+    number_fmt.setForeground(QColor("#098658"));
+    rules_.append({QRegularExpression("\\b[0-9]+(\\.[0-9]+)?([eE][+-]?[0-9]+)?\\b"), number_fmt});
+
+    // Strings (single and double quoted, single-line)
+    string_fmt_.setForeground(QColor("#a31515"));
+    rules_.append({QRegularExpression("\"[^\"]*\""), string_fmt_});
+    rules_.append({QRegularExpression("'[^']*'"), string_fmt_});
+
+    // Single-line comments
+    comment_fmt_.setForeground(QColor("#008000"));
+    comment_fmt_.setFontItalic(true);
+    rules_.append({QRegularExpression("#[^\n]*"), comment_fmt_});
+
+    // Built-in functions
+    QTextCharFormat builtin_fmt;
+    builtin_fmt.setForeground(QColor("#795e26"));
+    const char* builtins[] = {"print",     "len",       "range",  "type",    "int",    "float",
+                              "str",       "list",      "dict",   "tuple",   "set",    "enumerate",
+                              "zip",       "map",       "filter", "sorted",  "abs",    "min",
+                              "max",       "sum",       "isinstance", "hasattr", "getattr"};
+    for (const char* bi : builtins) {
+      rules_.append({QRegularExpression("\\b" + QString(bi) + "\\b"), builtin_fmt});
+    }
+  }
+
+ protected:
+  void highlightBlock(const QString& text) override {
+    // Apply single-line rules first.
+    for (const auto& rule : rules_) {
+      auto it = rule.pattern.globalMatch(text);
+      while (it.hasNext()) {
+        auto match = it.next();
+        setFormat(static_cast<int>(match.capturedStart()), static_cast<int>(match.capturedLength()),
+                  rule.format);
+      }
+    }
+
+    // Multi-line strings: """ ... """ and ''' ... '''
+    // State 0 = normal, 1 = inside """, 2 = inside '''
+    handleTripleQuote(text, "\"\"\"", 1);
+    handleTripleQuote(text, "'''", 2);
+  }
+
+ private:
+  void handleTripleQuote(const QString& text, const QString& delimiter, int state) {
+    qsizetype start_index = 0;
+    if (previousBlockState() != state) {
+      start_index = text.indexOf(delimiter);
+    }
+    while (start_index >= 0) {
+      qsizetype end_index = text.indexOf(delimiter, start_index + 3);
+      qsizetype length;
+      if (end_index == -1) {
+        setCurrentBlockState(state);
+        length = text.length() - start_index;
+      } else {
+        length = end_index - start_index + 3;
+      }
+      setFormat(static_cast<int>(start_index), static_cast<int>(length), string_fmt_);
+      start_index = text.indexOf(delimiter, start_index + length);
+    }
+  }
+
+  struct Rule {
+    QRegularExpression pattern;
+    QTextCharFormat format;
+  };
+  QList<Rule> rules_;
+  QTextCharFormat string_fmt_;
+  QTextCharFormat comment_fmt_;
+};
+
+}  // namespace PJ

pj_plugins/dialog_protocol/src/widget_binding.cpp

@@ -24,6 +24,7 @@
 #include <pj_plugins/host_qt/chart_preview_widget.hpp>
 #include <pj_plugins/host_qt/widget_binding.hpp>
 #include "lua_syntax_highlighter.hpp"
+#include "python_syntax_highlighter.hpp"
 #include <set>
 
 namespace PJ {
@@ -65,12 +66,19 @@ static void apply_to_widget(QWidget* w, std::string_view name, const PJ::WidgetD
       if (pte->toPlainText() != new_text) {
         pte->setPlainText(new_text);
       }
-      // Install syntax highlighter on first use.
+      // Install or swap syntax highlighter when the language changes.
       if (auto lang = view.codeLanguage(name)) {
-        if (!pte->property("_pj_code_lang").isValid()) {
-          pte->setProperty("_pj_code_lang", QString::fromStdString(*lang));
+        QString current = pte->property("_pj_code_lang").toString();
+        QString requested = QString::fromStdString(*lang);
+        if (current != requested) {
+          pte->setProperty("_pj_code_lang", requested);
+          if (auto* old = pte->document()->findChild<QSyntaxHighlighter*>()) {
+            delete old;
+          }
           if (*lang == "lua") {
             new PJ::LuaSyntaxHighlighter(pte->document());
+          } else if (*lang == "python") {
+            new PJ::PythonSyntaxHighlighter(pte->document());
           }
         }
       }