/*
  StarForth — Steady-State Virtual Machine Runtime

  Copyright (c) 2023–2025 Robert A. James
  All rights reserved.

  Licensed under the StarForth License, Version 1.0
*/

/* scroll_words.c — REPL scrollback entry points (FABRIC.md item 4.4q).
 * Kernel-only; no-op on hosted builds. */

#include "include/scroll_words.h"
#include "../../include/log.h"
#include "../../include/word_registry.h"

#ifdef __STARKERNEL__
#include "starkernel/console.h"

/* SCROLL-BACK ( n -- ) -- move the REPL scrollback view back n lines.
 * Relies on vm_pop()'s own underflow guard (sets vm->error, logs, returns
 * 0) rather than a separate dsp precheck -- this codebase has more than
 * one dsp convention across older word_source files (some treat it as a
 * top-of-stack index, some as a raw count); vm_pop() is the one this word
 * actually calls, so deferring to its own check sidesteps the mismatch
 * entirely instead of risking silently picking the wrong one. */
static void scroll_word_back(VM *vm) {
    cell_t n = vm_pop(vm);
    if (vm->error) return;
    if (n < 0) n = 0;
    console_fb_scroll_back((uint32_t)n);
}

/* SCROLL-FWD ( n -- ) -- move the REPL scrollback view forward n lines
 * (toward live). Same underflow-handling rationale as SCROLL-BACK above. */
static void scroll_word_fwd(VM *vm) {
    cell_t n = vm_pop(vm);
    if (vm->error) return;
    if (n < 0) n = 0;
    console_fb_scroll_fwd((uint32_t)n);
}
#endif /* __STARKERNEL__ */

void register_scroll_words(VM *vm)
{
#ifdef __STARKERNEL__
    register_word(vm, "SCROLL-BACK", scroll_word_back);
    register_word(vm, "SCROLL-FWD", scroll_word_fwd);
#else
    (void) vm;
#endif
}