#pragma once

#include <Gosu/Fwd.hpp>
#include <Gosu/Platform.hpp>
#include <memory>
#include <string>

namespace Gosu
{
    /// TextInput instances are invisible objects that build a text string from input, using the
    /// current operating system's keyboard layout or input method editor (IME).
    /// To start processing keyboard text input, you need to create a new TextInput instance and
    /// pass it to your window's Input object via set_text_input.
    /// Until you call this function again with a nullptr value, the TextInput object will then
    /// build a text that can be accessed via TextInput::text().
    /// A TextInput object has no built-in UI. It is up to you to actually draw a text field.
    /// TextInput only provides a portable base for your own GUI to build upon.
    class TextInput
    {
        struct Impl;
        // Non-movable (const) to avoid dangling references to TextInput instances.
        const std::unique_ptr<Impl> m_impl;

    public:
        TextInput();
        virtual ~TextInput();

        std::string text() const;

        /// Replaces the current text by the given string and positions the cursor at the end of the
        /// text, with an empty selection.
        void set_text(const std::string& text);

        /// Index of the character that comes after the caret. When the text is empty, this is
        /// always 0. For ease of use in C++, this counts bytes, not codepoints, in the UTF-8
        /// encoded string.
        unsigned caret_pos() const;
        /// Sets the caret position as returned by caret_pos.
        /// You usually also want to use set_selection_start.
        void set_caret_pos(unsigned pos);

        /// If there is a selection, the selection_start() member yields its beginning, using the
        /// same indexing scheme as caret_pos. If there is no selection, selection_start() is equal
        /// to caret_pos().
        unsigned selection_start() const;
        /// Sets the start of the selection as returned by selection_start.
        void set_selection_start(unsigned pos);

#ifndef GOSU_IS_IPHONE
        // Platform-specific communication with Gosu::Input.
        bool feed_sdl_event(void* event);
#endif

        /// Overridable filter that is applied to all new text that is entered.
        /// Allows for context-sensitive filtering/extending/... of new characters.
        /// The return value will be inserted at caret_pos.
        virtual std::string filter(std::string text) const { return text; }

        /// Replaces the current selection (if any) and inserts the given string at the current
        /// caret position.
        /// The filter method will not be applied before appending the string.
        void insert_text(std::string text);

        /// Deletes the current selection, if any, or the next character.
        void delete_forward();

        /// Deletes the current selection, if any, or the previous character.
        void delete_backward();
    };
}