Harfbuzz hb_shape return the isolated glyph

Question

I am using harfbuzz hb_shape() fubction to get the final glyph index but I am getting the isolated glyph without any gsub applied on it if I comment the .hb_buffer_set_direction function.And if I don't comment it then I am getting glyph out of the arabic range. Can anyone help me how to fix it. And why it is hapeening? Below is sample code:-

           FT_Library    library;
            FT_Face       face;
            FT_Error      error;
            char*         fontfilepath;

        fontfilepath      = "D:/Amiri-Bold.ttf";
        error = FT_Init_FreeType( &library );
        error = FT_New_Face( library, fontfilepath, 0, &face );
        hb_font_t* hb_font = hb_ft_font_create(face, NULL);
        hb_buffer_t* hb_buffer = hb_buffer_create();
        const uint16_t* textt = (const uint16_t*) tempdata;
        hb_buffer_set_script(hb_buffer, HB_SCRIPT_ARABIC); // Set script to Arabic
        hb_buffer_set_language(hb_buffer, hb_language_from_string("ara", -1));
        hb_buffer_set_direction(hb_buffer, HB_DIRECTION_RTL); // Set direction to Right-To-Left for Arabic
        hb_buffer_add_utf16(hb_buffer, textt, -1, 0, -1);
        hb_shape(hb_font, hb_buffer, NULL, 0);
        unsigned int glyph_count;
        hb_glyph_info_t *glyph_info = hb_buffer_get_glyph_infos(hb_buffer, &glyph_count);

        // Now, glyph_info contains an array of glyph indexes
        for (unsigned int ii = 0; ii < glyph_count; ii++) {

            char str[7];
            // Get the glyph index from FreeType directly
            FT_UInt glyph_index;// = FT_Get_Char_Index(face, glyph_info[ii].codepoint);
            glyph_index = FT_Get_Char_Index(face, glyph_info[ii].codepoint);
            sprintf(str, "%04X", glyph_index);

            vContentStream->PutBlock((CBytePtr)/*"0037"*/str, 4);
        }