store history using sqlite, add suggestion with open

src/history.h

@@ -0,0 +1,49 @@
+#pragma once
+
+#include <QList>
+#include <QSqlDatabase>
+#include <QString>
+#include <QStringList>
+#include <QUrl>
+
+// Browsing history in history.sqlite under AppDataLocation. Two tables:
+// "visits" is an append-only log of every page load; "urls" holds one row per
+// URL with its latest title and visit time, and is what completion searches.
+//
+// Queries run synchronously on the GUI thread. That is fine for SQLite at
+// browser-history sizes, with WAL so a write never waits on a full fsync.
+class History
+{
+public:
+    struct Entry {
+        QString url;
+        QString title;
+    };
+
+    History();
+    ~History();
+
+    History(const History &) = delete;
+    History &operator=(const History &) = delete;
+
+    bool isOpen() const { return m_open; }
+
+    void addVisit(const QUrl &url, const QString &title);
+    // Pages often set their title after the load finished.
+    void updateTitle(const QUrl &url, const QString &title);
+
+    // Most recently visited first. Every word must appear in the URL or the
+    // title, case-insensitively.
+    QList<Entry> search(const QStringList &words, int limit) const;
+
+    bool clear();
+
+    // Whether a URL belongs in history at all: no internal or data pages.
+    static bool isRecordable(const QUrl &url);
+
+private:
+    bool exec(const QString &sql);
+
+    QSqlDatabase m_db;
+    bool m_open = false;
+};