Show UnsavedDocumentsDialog when closing window or quitting application

so user can save and or discard docs more efficiently.

pglab/querytool/SqlDocument.h

@@ -0,0 +1,60 @@
+#ifndef SQLDOCUMENT_H
+#define SQLDOCUMENT_H
+
+#include <QList>
+#include <QObject>
+#include <QString>
+
+class QTextDocument;
+class QWidget;
+class SqlSyntaxHighlighter;
+
+/** Owns the text of a SQL script together with its file state.
+ * Several query tools (editors) can show the same document, they all
+ * use the same QTextDocument.
+ */
+class SqlDocument : public QObject {
+	Q_OBJECT
+public:
+	explicit SqlDocument(QObject *parent = nullptr);
+	~SqlDocument() override;
+
+	QTextDocument *textDocument() const { return m_document; }
+	SqlSyntaxHighlighter *highlighter() const { return m_highlighter; }
+
+	QString fileName() const { return m_fileName; }
+	bool isNew() const { return m_new; }
+	bool isModified() const;
+	void setModified(bool modified);
+
+	/// Empties the document and makes it a new unnamed document.
+	void clear();
+	bool load(const QString &filename);
+	/// Save the document under its current name, a file save dialog will be shown if this is a new document
+	bool save(QWidget *parent);
+	/// Saves the document under a new name and continue editing the document under this new name.
+	bool saveAs(QWidget *parent);
+	/// Save the document under a new name but continue editing the document under its old name.
+	bool saveCopyAs(QWidget *parent);
+
+	void addEditor(QWidget *editor);
+	void removeEditor(QWidget *editor);
+	const QList<QWidget*> &editors() const { return m_editors; }
+
+signals:
+	void modifiedChanged(bool modified);
+	void fileNameChanged();
+
+private:
+	QTextDocument *m_document;
+	SqlSyntaxHighlighter *m_highlighter;
+	QString m_fileName;
+	bool m_new = true;
+	QList<QWidget*> m_editors;
+
+	void setFileName(const QString &filename);
+	bool saveSqlTo(const QString &filename);
+	QString promptUserForSaveSqlFilename(QWidget *parent);
+};
+
+#endif // SQLDOCUMENT_H