#                is used. Then it is $INSTALL_ROOT/releases/<datestamp>
# CURRENT_DIR  = if -c argument is used, this is set to the $INSTALL_ROOT/current which is
#                symlinked to INSTALL_DIR
# VERBOSE      = is set if the package was called with -v for verbose output
function main() {
    set_install_dir

    if ! slug_already_current ; then

      create_pid
      wait_for_others

      kill_others

      set_owner

      unpack_payload

      if [ "$UNPACK_ONLY" == "1" ] ; then
          echo "Unpacking complete, not moving symlinks or restarting because unpack only was specified."
      else
          create_symlinks

          set +e # don't exit on errors to allow us to clean up
          if ! run_post_install ; then
              revert_symlinks
              log "Installation failed."
              exit 1
          else
              clean_out_old_releases
              log "Installation complete."
          fi
      fi

    else
        echo "This slug is already installed in 'current'. Specify -f to force reinstall. Exiting."
    fi
}

# check if this slug is already running and exit unless `force` specified
# Note: this only works with RELEASE_ID is used
function slug_already_current(){
    local this_slug=$(basename $0 .slug)
    local current=$(basename "$(readlink ${INSTALL_ROOT}/current)")
    log "'current' symlink points to slug: ${current}"

    if [ "$this_slug" == "$current" ] ; then
        if [ "$FORCE" == "1" ] ; then
        log "Force was specified. Proceeding with install after renaming live directory to allow running service to shutdown correctly."
            local real_dir=$(readlink ${INSTALL_ROOT}/current)
            if [ -f ${real_dir}.old ] ; then
                # remove that .old directory, if needed
                rm -rf ${real_dir}.old
            fi
            mv ${real_dir} ${real_dir}.old
            mkdir -p ${real_dir}
        else
            return 0;
        fi
    fi
    return 1;
}

# deletes the PID file for this installation
function delete_pid(){
    rm -f ${INSTALL_ROOT}/$$.pid 2> /dev/null
}

# write out metadata for future installs
function save_environment(){
    local METADATA=$1
    echo -n "" > ${METADATA} # empty file

    # just piping env to a file doesn't quote the variables. This does
    # filter out multiline junk, _, and functions. _ is a readonly variable.
    env | grep -v "^_=" | grep -v "^[^=(]*()=" | egrep "^[^ ]+=" | while read ENVVAR ; do
        local NAME=${ENVVAR%%=*}
        # sed is to preserve variable values with dollars (for escaped variables or $() style command replacement),
        # and command replacement backticks
        # Escaped parens captures backward reference \1 which gets replaced with backslash and \1 to esape them in the saved
        # variable value
        local VALUE=$(eval echo '$'$NAME | sed 's/\([$`]\)/\\\1/g')
        echo "export $NAME=\"$VALUE\"" >> ${METADATA}