fixed and optimized the autocompletion

src/common/UsernameSet.hpp

@@ -0,0 +1,73 @@
+#pragma once
+
+#include <QString>
+#include <functional>
+#include <set>
+#include <unordered_map>
+
+namespace chatterino {
+class Prefix
+{
+public:
+    Prefix(const QString &string);
+    bool operator==(const Prefix &other) const;
+    bool isStartOf(const QString &string) const;
+
+private:
+    QChar first;
+    QChar second;
+
+    friend struct std::hash<Prefix>;
+};
+}  // namespace chatterino
+
+namespace std {
+template <>
+struct hash<chatterino::Prefix> {
+    size_t operator()(const chatterino::Prefix &prefix) const
+    {
+        return (size_t(prefix.first.unicode()) << 16) |
+               size_t(prefix.second.unicode());
+    }
+};
+}  // namespace std
+
+namespace chatterino {
+class UsernameSet
+{
+public:
+    static constexpr int PrefixLength = 2;
+
+    using Iterator = std::set<QString>::iterator;
+    using ConstIterator = std::set<QString>::const_iterator;
+
+    class Range
+    {
+    public:
+        Range(ConstIterator start, ConstIterator end);
+
+        ConstIterator begin();
+        ConstIterator end();
+
+    private:
+        ConstIterator start_;
+        ConstIterator end_;
+    };
+
+    ConstIterator begin() const;
+    ConstIterator end() const;
+    Range subrange(const Prefix &prefix) const;
+
+    std::set<QString>::size_type size() const;
+
+    std::pair<Iterator, bool> insert(const QString &value);
+    std::pair<Iterator, bool> insert(QString &&value);
+
+private:
+    void insertPrefix(const QString &string);
+
+    std::set<QString> items;
+    std::unordered_map<Prefix, QString> firstKeyForPrefix;
+};
+
+}  // namespace chatterino