# Dockerfile.kernel-build — reproducible Linux toolchain image for building the
# self-written KHY OS kernel ISO from any host (notably native Windows, where the
# ELF/multiboot2/GRUB toolchain is unavailable). Used by `khy os build` when the
# Docker backend is selected (KHY_KERNEL_BUILD_BACKEND=docker, or auto when WSL2
# is absent). The kernel source is bind-mounted at /kernel at run time, e.g.:
#
#   docker build -f kernel/Dockerfile.kernel-build -t khyos-kernel-build:latest kernel
#   docker run --rm -v "<host-kernel-dir>:/kernel" -w /kernel khyos-kernel-build make -C /kernel iso
#
# The image is build-only: it carries exactly the toolchain the Makefile needs
# (nasm, gcc, binutils/ld, grub-mkrescue + xorriso, plus MoonBit), nothing else.
# QEMU is intentionally NOT installed — running the ISO is a host concern.
FROM debian:bookworm-slim

# Avoid interactive tzdata prompts during apt.
ENV DEBIAN_FRONTEND=noninteractive

# GNU/ELF kernel toolchain. Mirrors the apt package set `khy os build` prints:
#   build-essential → gcc + ld (binutils) + make
#   nasm           → ELF64 assembler for boot/*.asm
#   grub-pc-bin grub-common xorriso → grub-mkrescue + ISO packaging
#   curl ca-certificates → fetch the MoonBit toolchain
RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        build-essential \
        nasm \
        binutils \
        grub-pc-bin \
        grub-common \
        xorriso \
        mtools \
        curl \
        ca-certificates \
    && rm -rf /var/lib/apt/lists/*

# MoonBit toolchain (provides `moon`, plus ~/.moon/include + ~/.moon/lib/runtime.c
# that the Makefile's MoonBit objects compile against). Installed for root; the
# Makefile resolves these via $(HOME)/.moon, so run the container as root (default).
RUN curl -fsSL https://cli.moonbitlang.com/install/unix.sh | bash
ENV PATH="/root/.moon/bin:${PATH}"

# Kernel source is provided at run time via a bind mount; no COPY so the image
# stays source-agnostic and cache-friendly across edits.
WORKDIR /kernel

# Default to a full ISO build; override the command to target a specific rule.
CMD ["make", "-C", "/kernel", "iso"]