OpenXcom nightly auto-update script

run

#!/usr/bin/env bash
# Runs and auto-updates OpenXcom nightlies in a portable environment
# By default, this script will try to download and use the latest
# nightly.  If it finds a newer version than you already have, it will
# prompt you (with a zenity popup) to ask if you actually want to
# download it.
#
# If you want to stick to a particular version and don't want the popup
# telling you to update, you can change the $here/versions/greatest
# symlink to point to a specific AppImage rather than the default
# $here/versions/latest (which refers to the latest known version)
#
# If you want to launch a specific version in the portable environment,
# you can also pass that AppImage as an argument to this script.
#
# Another way to skip the update prompt is to define the environment
# variable OPENXCOM_UPDATE_LATEST.  If defined, OpenXcom will be updated
# without prompting you first, except if the variable is set to "no", in
# which case OpenXcom will NOT be updated (which is similar to passing
# $here/versions/latest as an argument to the script)
#
# Old versions stick around in the versions directory, and you may want
# to delete them periodically to save disk space (though the AppImages
# currently only take up <10MiB).  However, you may want the ability to
# revert to old versions if you encounter bugs in the nightlies, so old
# AppImages are never automatically deleted.
#
# Configuration, Data, and User directories (described in the OpenXcom
# README) for AppImages run with this script are found at $here/config,
# $here/data, and $here/user respectively.

# ~requires zenity

here="$(dirname "$(realpath "$0")")"

function nightlies {
    # Outputs nightly AppImages available for download, sorted by
    # modified date, most recent first.

    curl -fL 'https://openxcom.org/git-builds' |
        grep -o "https://[^\"]*/OpenXcom_\w*_$(arch | tr _ -).AppImage"
}

function confirm_download {
    # Ask if it's ok to download OpenXcom

    if [ -L "$here/versions/latest" ]; then
        local title="Update OpenXcom?"
        local info="A new OpenXcom nightly is available!\n$1"
    else
        # The latest symlink doesn't exist yet, so this is the first
        # installation, not an "update".
        local title="Download OpenXcom?"
        local info="The latest OpenXcom nightly is\n$1"
    fi

    local body="$info\nDo you want to download it?"
    zenity --question --title="$title" --text="$body"
}

function save_to {
    # Download $1, writing it to the path $2
    curl --create-dirs -f -o "$2" "$1" |
        zenity --progress --no-cancel --pulsate --auto-close \
        --text="Downloading..."

    return "${PIPESTATUS[0]}"
}

function update_latest {
    # Update the versions/latest symlink to the latest available
    # version, downloading it if necessary.
    # The return value of update_latest is not meaningful -- success
    # does not imply that the versions/latest symlink actually exists.

    if [ "$OPENXCOM_UPDATE_LATEST" = "no" ]; then
        return
    fi

    echo "Checking for updates..." >&2
    local latest_url="$(nightlies | head -n 1)"
    if [ -z "$latest_url" ]; then
        # Probably just a problem with the user's internet connection,
        # but could also indicate a bug in the nightlies function.
        zenity --notification --window-icon=error \
            --text="Failed to check for OpenXcom updates"
        return
    fi

    local latest_name="$(basename "$latest_url")"
    local latest_path="$here/versions/$latest_name"
    if [ ! -x "$latest_path" ]; then
        if [ -z "$OPENXCOM_UPDATE_LATEST" ]; then
            confirm_download "$latest_name" || return
        fi

        echo "Downloading $latest_url..." >&2
        if save_to "$latest_url" "$latest_path"; then
            chmod +x "$latest_path"
        else
            rm -- "$latest_path" &> /dev/null
            zenity --notification --window-icon=error \
                --text="Failed to download $latest_name"
        fi
    fi

    if [ -x "$latest_path" ]; then
        # If the download succeeds or we didn't need to download because
        # the file already exists, update latest symlink to point to it.
        ln -fs "$latest_name" "$here/versions/latest"
    fi
}

function exec_app {
    mkdir -p "$here/user" "$here/data" "$here/config"
    DESKTOPINTEGRATION=no exec -- "$(realpath "$1")" \
        -user "$here/user" \
        -data "$here/data" \
        -config "$here/config"
}

function prepend {
    while read -r line; do
        echo "$1$line"
    done
}

if [ -n "$1" ]; then
    exec_app "$1"
else
    mkdir -p "$here/versions"
    greatest="$here/versions/greatest"

    if [ ! -L "$greatest" ]; then
        ln -s "latest" "$greatest"
    fi

    if [ "$(basename "$(readlink "$greatest")")" = "latest" ]; then
        update_latest
    fi

    if [ ! -x "$greatest" ]; then
        zenity --error --no-wrap \
            --text="The <tt>versions/greatest</tt> symlink\nis broken."
    fi

    exec_app "$greatest"
fi