#! /bin/bash
#
# gentoostrap
# Build a Gentoo system in /mnt
# Copyright (C) 2020 Vintage Salt <rehashedsalt@cock.li>
#
# Distributed under terms of the MIT license.
#
set -e

# Read-only set-once variables
declare -r _name="$(basename -- "$0")"
# Options
declare -i _optchroot
declare _optdest="/mnt"
declare _optprofile="desktop"
declare -i _opthelp
declare -i _optverbose
# Working variables
declare -a _args
declare _return

# Helper functions
log() {
	# Print a line to the terminal if _optverbose is greater than $2
	# $2 defaults to 0
	# loglevel 0: Daily-use messages
	# loglevel 1: Detailed but not quite debugging
	# loglevel 2: Definitely debugging
	[ -z "$1" ] && return 1
	if (( _optverbose >= ${2:-0} )); then
		printf "%s\\n" "$1"
	fi
}
warn() {
	# Print a yellow line to the terminal, respecting _optverbose
	[ -z "$1" ] && return 1
	if (( _optverbose >= ${2:-0} )); then
		if [ -t 1 ]; then
			printf "\\e[33m%s\\e[0m\\n" "$1"
		else
			printf "WARN: %s\\n" "$1"
		fi
	fi
}
error() {
	# Print a red line to the terminal, exit if $2 is specified
	[ -z "$1" ] && return 1
	if [ -t 2 ]; then
		printf "\\e[31m%s\\e[0m\\n" "$1" 1>&2
	else
		printf "ERROR: %s\\n" "$1" 1>&2
	fi
	[ -z "$2" ] && return
	exit "${2:-1}"
}
has() {
	# Parse out all arguments and try to find them in path
	# If an argument cannot be found, set _return and fail
	for prog in "$@"; do
		if ! command -v "$prog" > /dev/null 2>&1; then
			_return="$prog"
			return 1
		fi
	done
	return 0
}

# Helper functions
cleanup() {
	[ -z "$1" ] && warn "No argument passed to cleanup"
	rm -rf "$1" || warn "Failed to remove $1: $?"
}

# Core program functions
printhelp() {
	cat << EOF
Usage: $_name [OPTION]...

  -h			Print this help text
  -c			Perform the Gentoo half of installation. Must be invoked from a chroot
  -v			Print more status messages. Stacks

Copyright (c) 2020 rehashedsalt@cock.li
Licensed under the MIT license
EOF
}
build-gentoo() {
	# Build Gentoo

	# First, get a link to a stage3 tarball
	stage3="http://distfiles.gentoo.org/releases/amd64/autobuilds/current-stage3-amd64-systemd/$(
		curl -s http://distfiles.gentoo.org/releases/amd64/autobuilds/current-stage3-amd64-systemd/ \
			| grep -oe 'stage3-amd64-systemd-20.*\.tar\.xz' \
			| sed 's/^stage3.*">//g' \
			| sort \
			| uniq \
			| head -n 1
		)"
	stage3file="/tmp/tmp.$USER.$_name.stage3.tar.xz"
	stage3sig="/tmp/tmp.$USER.$_name.stage3.tar.xz.DIGESTS"
	for file in "$stage3file" "$stage3sig"; do
		touch "$file"
		chmod 0600 "$file"
	done
	trap "cleanup $stage3file" EXIT
	# We grab the checksums first to verify the integrity of any tarball leftover from a previous run
	log "Downloading stage3 signature"
	curl -s "$stage3.DIGESTS" -o "$stage3sig"
	if ! [ -f "$stage3file" ]; then
		log "Downloading stage3"
		curl -s "$stage3" -o "$stage3file"
	elif ! grep "$stage3sig" -e "$(sha512sum "$stage3file" | awk '{print $1}')" > /dev/null 2>&1; then
		log "Checksum verification failed; downloading new stage3"
		curl -s "$stage3" -o "$stage3file"
	fi
	# At this point, we should have a new stage3 that matches our signature; die if not
	if ! grep "$stage3sig" -e "$(sha512sum "$stage3file" | awk '{print $1}')" > /dev/null 2>&1; then
		error "stage3 checksum verification failed" 50
	fi
	log "Decompressing tarball; this will prompt for root privileges"
	sudo tar xf "$stage3file" -C "$_optdest"

	# Now we do some pre-chroot configuration
	pushd "$_optdest" > /dev/null 2>&1
	# These is a very generic make.conf to get the system up and running
	# We use march of x86-64 to ensure compatibility if we're bootstrapping on a host other than the target
	cat <<-EOF > "$_optdest/etc/portage/make.conf"
	COMMON_FLAGS="-march=x86-64 -mtune=generic -O2 -pipe"
	CFLAGS="\${COMMON_FLAGS}"
	CXXFLAGS="\${COMMON_FLAGS}"
	GENTOO_MIRRORS="http://distfiles.gentoo.org"
	MAKEOPTS="$(nproc)"
	EOF
	# Configure default ebuild repositories
	mkdir -p "$_optdest/etc/portage/repos.conf"
	cp "$_optdest/usr/share/portage/config/repos.conf" \
		"$_optdest/etc/portage/repos.conf/gentoo.conf"
	# DNS
	cat <<-EOF > "$_optdest/etc/resolv.conf"
	nameserver 8.8.8.8
	nameserver 8.8.4.4
	EOF
	# Timezone
	cp /etc/timezone "$_optdest/etc/timezone"
	# Locale
	cat <<-EOF > "$_optdest/etc/locale.gen"
	en_US ISO-8859-1
	en_US.UTF-8 UTF-8
	EOF

	# Now we need to pivot into a chroot and finish configuration natively
	# Buuuut... since we're using systemd, we get to just spawn a systemd-nspawn container
	popd
	cp "$0" "$_optdest/gentoostrap.sh"
	sudo systemd-nspawn --directory="$_optdest" /gentoostrap.sh -c
}
build-gentoo-chroot() {
	# Build Gentoo, but from within the chroot environment
	log "Building Gentoo from within chroot"

	# Sync repositories
	log "Getting ebuild repositories"
	emerge-webrsync

	# Get the stable plasma/systemd profile and select it
	profile=$(
		eselect profile list \
			| grep -ie 'stable' \
			| grep -ie "$profile" \
			| sort \
			| uniq \
			| head -n 1 \
			| grep -oP '\[\K[^\]]+'
		) || error "Error finding profile: $profile" 51
	[ -z "$profile" ] && error "Could not find profile: $profile" 52
	log "Setting profile $profile"
	eselect profile set "$profile"

	# BEHOLD!
	emerge -DNuv @world
	# Configure timezone
	emerge --config sys-libs/timezone-data
	# Locales
	locale-gen
	eselect locale set en_US.utf8
	env-update
	. /etc/profile

	# Build a kernel
}

# Main
main() {
	# Parse out arguments
	while [ -n "$1" ]; do
		# Parse out flags
		while getopts ":chv" opt; do
			case $opt in
				c)
					_optchroot=1
					;;
				h)
					_opthelp=1
					;;
				v)
					_optverbose+=1
					;;
				:)
					error "Option requires argument: -$OPTARG" 2
					;;
				*)
					error "Invalid option: -$OPTARG" 2
					;;
			esac
		done
		# Store arguments
		shift $((OPTIND - 1))
		if [ -n "$1" ]; then
			_args+=("$1")
			shift
		fi
		unset OPTIND
	done
	# Early hook for help
	[ -n "$_opthelp" ] && printhelp && exit 0
	# Validate critical options
	# TODO: That
	# Validate core program dependencies
	log "Validating dependencies" 2
	if ! has basename curl systemd-nspawn tar; then
		error "Failed to find program: $_return" 1
	fi

	# Do the do
	if [ -z "$_optchroot" ]; then
		build-gentoo
	else
		build-gentoo-chroot
	fi
	exit 0
}

main "$@"