#!/usr/bin/env bash

OS_NAME="Void Linux USB"
GRUB_PREFIX="/boot/efi/LOADER/grub"
CFG_CUSTOM_BEFORE="custom_before.cfg"
CFG_CUSTOM_AFTER="custom_after.cfg"
LINUX_CMDLINE="root=/dev/loop0 ro"

DEFAULT_LINUX=/boot/vmlinu?
if [ ! -f "$DEFAULT_LINUX" ]; then
  # in cases where it’s a .gz or .xz or whatever
  DEFAULT_LINUX=$(find /boot -type l -name "vmlinu*" 2>/dev/null | sort | head -n1)
fi
DEFAULT_LINUX="$(sed 's|^/boot/||' <<< "$DEFAULT_LINUX")"

DEFAULT_INITRAMFS=/boot/initramfs.img
if [ ! -f "$DEFAULT_INITRAMFS" ]; then
  # hope to find anything named initramfs or initrd
  DEFAULT_INITRAMFS=$(find /boot -type l -name "init*" 2>/dev/null | sort | head -n1)
fi
DEFAULT_INITRAMFS="$(sed 's|^/boot/||' <<< "$DEFAULT_INITRAMFS")"

function make_menuentry {
  # $1 is the kernel path

  # We don’t want duplicate entries for /boot/vmlinuz symlink
  if [ -L "$1" ]; then
    return 0
  fi

  # exclude garbage globbing results
  if [ ! -f "$1" ]; then
    return 0
  fi

  LINUX="$(basename "$1")"
  LINUX_VERSION="$(sed 's/^kernel//;s/^vm//;s/^linuz//;s/^linux//;s/^-//' <<< "$LINUX")"
  if grep -e ".gz$" -e ".xz$" -e ".bz$" -e ".bz2$" -e ".lzma$" -e ".lz$" -e ".img$" >/dev/null 2>&1 <<< "$LINUX"; then
    LINUX_VERSION="$(sed 's/[^.]*$//;s/.$//' <<< "$LINUX_VERSION")"
  fi

  INITRAMFS="$(basename "$(find /boot -name "init*$LINUX_VERSION*" 2>/dev/null | sort | head -n1)")"

  # user output
  echo "  -> Found $LINUX (version $LINUX_VERSION, initramfs $INITRAMFS)"

  # grub.cfg
  echo "
  menuentry 'Linux $LINUX_VERSION' {
    echo    'Loading $LINUX...'
    linux   /$LINUX $LINUX_CMDLINE
    echo    'Loading initial ramdisk...'
    initrd  /$INITRAMFS
  }" >> "$GRUB_PREFIX/grub.cfg"
}

# user output
echo "Generating grub config..."

# grub.cfg
echo "# This file is auto-generated by $0.
# Changes will be overwritten automatically.
# If you want to add custom entries or other changes, add them to
# $GRUB_PREFIX/$CFG_CUSTOM_BEFORE or
# $GRUB_PREFIX/$CFG_CUSTOM_AFTER

search --fs-uuid --set=root $(blkid --output value --match-tag UUID "$(grep " /boot " /proc/mounts | sed -e 's/ .*//')")

set menu_color_normal=white/black
set menu_color_highlight=black/light-gray

timeout=5

if [ -f  \${config_directory}/$CFG_CUSTOM_BEFORE ]; then
  source \${config_directory}/$CFG_CUSTOM_BEFORE
elif [ -z \"\${config_directory}\" -a -f  \$prefix/$CFG_CUSTOM_BEFORE ]; then
  source \$prefix/$CFG_CUSTOM_BEFORE
fi

menuentry '$OS_NAME' {
  echo 'Loading Linux...'
  linux /$DEFAULT_LINUX $LINUX_CMDLINE
  echo 'Loading initial ramdisk...'
  initrd /$DEFAULT_INITRAMFS
}

submenu 'Choose kernel version...' {" > "$GRUB_PREFIX/grub.cfg"

for FILE in /boot/{vm,}linu{x,z}* /boot/kernel*; do
  make_menuentry "$FILE"
done

# grub.cfg
echo "
}

if [ -f  \${config_directory}/$CFG_CUSTOM_AFTER ]; then
  source \${config_directory}/$CFG_CUSTOM_AFTER
elif [ -z \"\${config_directory}\" -a -f  \$prefix/$CFG_CUSTOM_AFTER ]; then
  source \$prefix/$CFG_CUSTOM_AFTER
fi" >> "$GRUB_PREFIX/grub.cfg"

# user output
echo "done"