#!/bin/bash
# ============================================================================
# DarkForge Linux — Kernel Build Script
# ============================================================================
# Downloads, configures, and compiles the Linux kernel for DarkForge.
#
# Prerequisites (Arch Linux):
#   sudo pacman -S base-devel bc flex bison libelf perl openssl
#
# Usage:
#   cd /path/to/project-root
#   bash kernel/build-kernel.sh
#
# Output:
#   kernel/vmlinuz              — Compressed kernel (bzImage)
#   kernel/vmlinuz.efi          — Copy with .efi extension for EFISTUB
#   kernel/System.map           — Symbol map
#   kernel/modules/             — Kernel modules (if any)
#   build/linux-<version>/      — Full kernel source tree (for module builds)
#
# Notes:
#   - Runs as regular user (no sudo needed for compile)
#   - Uses the config at kernel/config
#   - Applies 'make olddefconfig' to fill in defaults for unspecified options
#   - Builds with -j32 (16C/32T)
# ============================================================================

set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
PROJECT_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"

# --- Configuration -----------------------------------------------------------
KERNEL_VERSION="6.19.9"
KERNEL_MAJOR="6.19"
KERNEL_URL="https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-${KERNEL_VERSION}.tar.xz"
KERNEL_SIGN_URL="${KERNEL_URL}.sign"
BUILD_DIR="${PROJECT_ROOT}/build"
KERNEL_SRC="${BUILD_DIR}/linux-${KERNEL_VERSION}"
CONFIG_FILE="${SCRIPT_DIR}/config"
JOBS=32

RED='\033[0;31m'; GREEN='\033[0;32m'; YELLOW='\033[1;33m'; CYAN='\033[0;36m'; NC='\033[0m'
info() { echo -e "${CYAN}>>> $1${NC}"; }
ok()   { echo -e "${GREEN}>>> $1${NC}"; }
warn() { echo -e "${YELLOW}!!! $1${NC}"; }
die()  { echo -e "${RED}!!! $1${NC}"; exit 1; }

# --- Preflight ---------------------------------------------------------------
info "DarkForge Kernel Builder — Linux ${KERNEL_VERSION}"
echo ""

# Check required tools
for tool in gcc make flex bison bc perl; do
    command -v "$tool" >/dev/null 2>&1 || die "Missing: $tool — install with pacman"
done

# Check for libelf headers (needed for CONFIG_BPF_SYSCALL, etc.)
if ! pkg-config --exists libelf 2>/dev/null; then
    warn "libelf not found — install with: sudo pacman -S libelf"
    warn "Continuing anyway (may fail if CONFIG_BPF_SYSCALL=y)"
fi

# Check for openssl headers (needed for module signing)
if ! pkg-config --exists openssl 2>/dev/null && ! [ -f /usr/include/openssl/opensslv.h ]; then
    warn "OpenSSL headers not found — install with: sudo pacman -S openssl"
fi

# --- Download kernel source --------------------------------------------------
mkdir -p "${BUILD_DIR}"

TARBALL="${BUILD_DIR}/linux-${KERNEL_VERSION}.tar.xz"
if [ -f "$TARBALL" ]; then
    info "Kernel tarball already downloaded: ${TARBALL}"
else
    info "Downloading Linux ${KERNEL_VERSION}..."
    # Try cdn.kernel.org first, then mirrors
    for url in \
        "https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-${KERNEL_VERSION}.tar.xz" \
        "https://mirrors.edge.kernel.org/pub/linux/kernel/v6.x/linux-${KERNEL_VERSION}.tar.xz" \
        "https://mirror.aarnet.edu.au/pub/ftp.kernel.org/linux/kernel/v6.x/linux-${KERNEL_VERSION}.tar.xz"; do
        if curl --connect-timeout 15 -fL# -o "$TARBALL" "$url" 2>&1; then
            ok "Downloaded from ${url}"
            break
        else
            warn "Failed: ${url}"
            rm -f "$TARBALL"
        fi
    done
fi

[ -f "$TARBALL" ] || die "Failed to download kernel tarball"

# Verify tarball is valid
if ! xz -t "$TARBALL" 2>/dev/null; then
    die "Kernel tarball is corrupt — delete ${TARBALL} and re-run"
fi

# --- Extract kernel source ---------------------------------------------------
if [ -d "$KERNEL_SRC" ] && [ -f "$KERNEL_SRC/Makefile" ]; then
    info "Kernel source already extracted: ${KERNEL_SRC}"
else
    info "Extracting Linux ${KERNEL_VERSION}..."
    tar -xf "$TARBALL" -C "${BUILD_DIR}"
    [ -d "$KERNEL_SRC" ] || die "Expected directory ${KERNEL_SRC} not found after extraction"
    ok "Extracted to ${KERNEL_SRC}"
fi

# --- Apply DarkForge config --------------------------------------------------
info "Applying DarkForge kernel config..."

# Copy our config
cp "$CONFIG_FILE" "${KERNEL_SRC}/.config"

# Update version target in config header comment (informational only)
# The actual version comes from the kernel source, not the config

# Run olddefconfig to fill in all unspecified options with defaults
# This is critical — our config only specifies ~176 options out of thousands
cd "$KERNEL_SRC"
make olddefconfig

ok "Config applied — $(grep -c '=y\|=m' .config) options enabled"

# Verify critical options survived olddefconfig
CRITICAL_OPTS=(
    "CONFIG_EFI_STUB=y"
    "CONFIG_BLK_DEV_NVME=y"
    "CONFIG_EXT4_FS=y"
    "CONFIG_PREEMPT=y"
    "CONFIG_MODULES=y"
    "CONFIG_DRM=y"
    "CONFIG_R8169=y"
    "CONFIG_EFI=y"
)
FAIL=0
for opt in "${CRITICAL_OPTS[@]}"; do
    key="${opt%%=*}"
    if ! grep -q "^${opt}$" .config; then
        warn "CRITICAL: ${opt} not set in final config!"
        FAIL=1
    fi
done
if [ "$FAIL" -eq 1 ]; then
    die "Critical config options missing after olddefconfig — review .config"
fi
ok "All critical config options verified"

# --- Compile -----------------------------------------------------------------
info "Compiling Linux ${KERNEL_VERSION} with -j${JOBS}..."
info "This will take a few minutes on 16C/32T..."
echo ""

# Set DarkForge compiler flags for kernel build
# Note: kernel has its own CFLAGS handling; -march is passed via KCFLAGS
# The kernel's CONFIG_MZEN4 handles most CPU-specific codegen
KCFLAGS="-march=znver4 -pipe"
# znver4 because znver5 may not be fully supported by all kernel assembly
# TODO: test znver5 when compiler+kernel support is confirmed

START_TIME=$(date +%s)

make -j${JOBS} KCFLAGS="$KCFLAGS" bzImage 2>&1 | tail -20

END_TIME=$(date +%s)
ELAPSED=$((END_TIME - START_TIME))

if [ -f "arch/x86/boot/bzImage" ]; then
    ok "Kernel compiled in ${ELAPSED}s"
else
    die "Kernel compilation failed — check output above"
fi

# Build modules (for any =m options)
info "Building kernel modules..."
make -j${JOBS} modules 2>&1 | tail -5
ok "Modules built"

# --- Install outputs ---------------------------------------------------------
info "Installing kernel outputs..."

# Copy bzImage
cp arch/x86/boot/bzImage "${SCRIPT_DIR}/vmlinuz"
cp arch/x86/boot/bzImage "${SCRIPT_DIR}/vmlinuz.efi"
ok "Kernel: ${SCRIPT_DIR}/vmlinuz ($(du -h "${SCRIPT_DIR}/vmlinuz" | cut -f1))"

# Copy System.map
cp System.map "${SCRIPT_DIR}/System.map"

# Install modules to a staging directory
MODULES_DIR="${SCRIPT_DIR}/modules"
rm -rf "$MODULES_DIR"
make INSTALL_MOD_PATH="$MODULES_DIR" modules_install 2>&1 | tail -3
ok "Modules installed to ${MODULES_DIR}"

# Verify the kernel is a valid EFI application
if file "${SCRIPT_DIR}/vmlinuz" | grep -q "bzImage"; then
    ok "Kernel is a valid bzImage"
elif file "${SCRIPT_DIR}/vmlinuz" | grep -q "EFI\|PE32"; then
    ok "Kernel is a valid EFI binary"
else
    warn "Kernel type: $(file "${SCRIPT_DIR}/vmlinuz")"
    warn "May not boot via EFISTUB — verify manually"
fi

# --- Summary -----------------------------------------------------------------
echo ""
echo "============================================================================"
echo -e "${GREEN}  DarkForge Kernel Build Complete${NC}"
echo "============================================================================"
echo ""
echo "  Version:    Linux ${KERNEL_VERSION}-darkforge"
echo "  Kernel:     ${SCRIPT_DIR}/vmlinuz"
echo "  Kernel EFI: ${SCRIPT_DIR}/vmlinuz.efi"
echo "  System.map: ${SCRIPT_DIR}/System.map"
echo "  Modules:    ${MODULES_DIR}/"
echo "  Source:     ${KERNEL_SRC}/"
echo ""
echo "  Compile time: ${ELAPSED}s"
echo "  Kernel size:  $(du -h "${SCRIPT_DIR}/vmlinuz" | cut -f1)"
echo ""
echo "  Next steps:"
echo "    1. Rebuild ISO: sudo bash src/iso/build-iso-arch.sh"
echo "    2. Test in QEMU: see tests/run-tests.sh"
echo "    3. For real hardware: copy vmlinuz.efi to ESP as /EFI/Linux/vmlinuz.efi"
echo ""
echo "============================================================================"