Implement unicode on console, move readline into driver

luprex/cpp/drv/readline.hpp

@@ -0,0 +1,53 @@
+
+#ifndef READLINE_HPP
+#define READLINE_HPP
+
+#include <string>
+#include <string_view>
+
+using CodepointString = std::basic_string<char32_t>;
+
+class ReadlineDevice {
+public:
+    using print_callback = void (*)(const CodepointString &text);
+
+private:
+    print_callback print_cb_;
+    CodepointString desired_command_;
+    CodepointString current_command_;
+    CodepointString desired_prompt_;
+    CodepointString current_prompt_;
+    char32_t readline_lastc_;
+
+    void echo_command();
+    void erase_command();
+
+public:
+    ReadlineDevice();
+
+    // The callback must be set before using the readline device.
+    void set_print_callback(print_callback cb);
+    
+    // change the prompt.
+    void set_prompt(const CodepointString &prompt);
+
+    // Use this to print anything on the console.
+    void print(const CodepointString &cps);
+
+    // Whenever the user types a character, call 'putcode'. If the code is
+    // newline, this returns the line of text that was entered, including the
+    // newline.  Otherwise returns empty string. Backspace is handled here.
+    CodepointString putcode(char32_t codepoint);
+
+    // This can be used to convert a codepoint string into a
+    // UTF8-string.
+    static std::string to_utf8(const CodepointString &cps);
+
+    // This can be used to convert UTF8 to a codepoint string.
+    // Some of the bytes may not be consumed.  Returns the Codepoint
+    // string and the number of bytes consumed.
+    static CodepointString from_utf8(std::string_view source, int *consumed);
+};
+
+
+#endif // READLINE_HPP