check_for_upgrade.sh

# Migrate .zsh-update file to $ZSH_CACHE_DIR
if [[ -f ~/.zsh-update && ! -f "${ZSH_CACHE_DIR}/.zsh-update" ]]; then
    mv ~/.zsh-update "${ZSH_CACHE_DIR}/.zsh-update"
fi

# Cancel update if:
# - the automatic update is disabled.
# - the current user doesn't have write permissions nor owns the $ZSH directory.
# - git is unavailable on the system.
if [[ "$DISABLE_AUTO_UPDATE" = true ]] \
   || [[ ! -w "$ZSH" || ! -O "$ZSH" ]] \
   || ! command -v git &>/dev/null; then
    return
fi


function current_epoch() {
    zmodload zsh/datetime
    echo $(( EPOCHSECONDS / 60 / 60 / 24 ))
}

function update_last_updated_file() {
    echo "LAST_EPOCH=$(current_epoch)" >! "${ZSH_CACHE_DIR}/.zsh-update"
}

function update_ohmyzsh() {
    ZSH="$ZSH" sh "$ZSH/tools/upgrade.sh"
    update_last_updated_file
}

() {
    emulate -L zsh

    local epoch_target mtime option LAST_EPOCH

    # Remove lock directory if older than a day
    zmodload zsh/datetime
    zmodload -F zsh/stat b:zstat
    if mtime=$(zstat +mtime "$ZSH/log/update.lock" 2>/dev/null); then
        if (( (mtime + 3600 * 24) < EPOCHSECONDS )); then
            command rm -rf "$ZSH/log/update.lock"
        fi
    fi

    # Check for lock directory
    if ! command mkdir "$ZSH/log/update.lock" 2>/dev/null; then
        return
    fi

    # Remove lock directory on exit. `return 1` is important for when trapping a SIGINT:
    #  The return status from the function is handled specially. If it is zero, the signal is
    #  assumed to have been handled, and execution continues normally. Otherwise, the shell
    #  will behave as interrupted except that the return status of the trap is retained.
    trap "rm -rf '$ZSH/log/update.lock'; return 1" EXIT INT QUIT

    # Create or update .zsh-update file if missing or malformed
    if ! source "${ZSH_CACHE_DIR}/.zsh-update" 2>/dev/null || [[ -z "$LAST_EPOCH" ]]; then
        update_last_updated_file
        return
    fi

    # Number of days before trying to update again
    epoch_target=${UPDATE_ZSH_DAYS:-13}
    # Test if enough time has passed until the next update
    if (( ( $(current_epoch) - $LAST_EPOCH ) < $epoch_target )); then
        return
    fi

    # Ask for confirmation before updating unless disabled
    if [[ "$DISABLE_UPDATE_PROMPT" = true ]]; then
        update_ohmyzsh
    else
        # input sink to swallow all characters typed before the prompt
        # and add a newline if there wasn't one after characters typed
        while read -t -k 1 option; do true; done
        [[ "$option" != ($'\n'|"") ]] && echo

        echo -n "[oh-my-zsh] Would you like to update? [Y/n] "
        read -r -k 1 option
        [[ "$option" != $'\n' ]] && echo
        case "$option" in
            [yY$'\n']) update_ohmyzsh ;;
            [nN]) update_last_updated_file ;;
        esac
    fi
}

unset -f current_epoch update_last_updated_file update_ohmyzsh