ui_text_editor.c

typedef struct UITextEditor
{
    int text_capacity;
    int text_length;
    char *text;
    int cursor;
}
UITextEditor;

void
ui_text_editor_init(UITextEditor *editor)
{
    memset(editor, 0, sizeof(UITextEditor));
    editor->text_capacity = 256;
    editor->text = calloc(editor->text_capacity, 1);
}

void
_ui_text_editor_ensure_capacity(UITextEditor *editor, size_t length, bool copy)
{
    length++;
    if (length >= editor->text_capacity) {
        editor->text_capacity = editor->text_capacity * 2;
        char *_text = realloc(editor->text, editor->text_capacity);
        if (copy) {
            memcpy(_text, editor->text, editor->text_length);
            _text[editor->text_length] = 0;
        }
        free(editor->text);
        editor->text = _text;
    }
}

void
ui_text_editor_insert(UITextEditor *editor, const char *string)
{
    size_t length = strlen(string);
    if (length == 0) {
        return;
    }

    _ui_text_editor_ensure_capacity(editor, editor->text_length + length, true);

    if (editor->cursor != editor->text_length)
    {
        memmove(editor->text + editor->cursor + length,
                editor->text + editor->cursor,
                editor->text_length - editor->cursor);
    }

    memmove(editor->text + editor->cursor,
            string,
            length);
    editor->cursor += length;
    editor->text_length += length;
    editor->text[editor->text_length] = 0;
}

void
ui_text_editor_remove(UITextEditor *editor, int from, int length)
{
    if (length <= 0) {
        printf("ui_text_editor_remove: length <= 0\n");
        return;
    }

    if (from < 0) {
        printf("ui_text_editor_remove: from < 0\n");
        return;
    }

    if (from >= editor->text_length) {
        printf("ui_text_editor_remove: from >= editor->text_length\n");
        return;
    }

    int to = from + length;

    if (to > editor->text_length) {
        printf("ui_text_editor_remove: from + length > editor->text_length\n");
        return;
    }

    if (to != editor->text_length)
    {
        memmove(editor->text + from,
                editor->text + to,
                editor->text_length - to);
    }
    editor->text_length -= length;
    editor->cursor = from;
    editor->text[editor->text_length] = 0;
}

bool
ui_text_editor_event(UITextEditor *editor, SDL_Event *event)
{
    switch (event->type)
    {
    case SDL_TEXTINPUT:
        ui_text_editor_insert(editor, event->text.text);
        return true;

    case SDL_KEYDOWN:
        switch (event->key.keysym.sym)
        {
        case SDLK_RIGHT:
            editor->cursor = MIN(editor->text_length, editor->cursor + 1);
            return true;
        case SDLK_LEFT:
            editor->cursor = MAX(0, editor->cursor - 1);
            return true;
        case SDLK_BACKSPACE:
            ui_text_editor_remove(editor, editor->cursor - 1, 1);
            return true;
        case SDLK_DELETE:
            ui_text_editor_remove(editor, editor->cursor, 1);
            return true;
        }
        break;

    }
    return false;
}