action

#!/usr/bin/env bash

set -euo pipefail
shopt -s dotglob nullglob
trap 'echo "${0} line ${LINENO} Status: ${?}"' ERR

CACHE_DIR=$HOME/.apt-cache
CACHE_TAR=$CACHE_DIR/root.tar.zstd
CACHE_LOG=$CACHE_DIR/log
CACHE_FILES=$CACHE_DIR/files
APT_CACHE_KEY=$(echo "$INPUTS_PACKAGES|$INPUTS_VERSION" | md5sum | awk '{print $1}')

do_pre() {
  echo "APT_CACHE_KEY=$APT_CACHE_KEY" >>$GITHUB_ENV
}

do_post() {
  if [[ -e $CACHE_TAR ]]; then
    echo Cache hit, restoring from cache.
    sudo tar xf $CACHE_TAR -C /
  else
    echo Cache miss, installing and caching packages.
    mkdir -p $CACHE_DIR
    sudo apt update
    sudo DEBIAN_FRONTEND=noninteractive apt --yes install $INPUTS_PACKAGES | tee $CACHE_LOG
    local installed
    installed=$(cat $CACHE_LOG | grep Unpacking | awk '{print $2}')
    if [[ -z $installed ]]; then
      echo WARNING: no packages installed.
      # create empty tar file to ensure cache hit flow
      tar cf $CACHE_TAR --zstd -T /dev/null
    else
      # collect list of regular files installed by packages, trim leading /
      echo "$installed" | xargs dpkg -L |
        while IFS='\n' read -r f; do [[ -f "$f" ]] && echo "${f:1}"; done >$CACHE_FILES
      tar cf $CACHE_TAR --zstd -C / -T $CACHE_FILES
    fi
  fi
}

do_$@