depend.sh

#!/bin/bash

usage() {
	echo "$0 {-d|-g|-p {tag}|-x} {target image Dockerfile} [known image tags]" >&2
}

find_parent() {
	awk '
		BEGIN {
			ec = 1;
		}

		$1 == "FROM" && parent {
			ec = 2;
			exit;
		}

		$1 == "FROM" {
			split($0, a);
			parent = $2;
			ec = 0
			print parent;
		}

		END {
			exit ec
		}' "$1"
}

contains() {
	needle=$1
	shift
	echo "$@" | grep -q -E "\<$needle\>"
}

#
# You cannot use a colon (:) in a target or prerequisite name in a
# Makefile. Change colons to @-signs, which docker does not allow as part
# of an name or tag. The Makefile will have to translate them back before
# invoking `docker pull' to fetch the base images.
#
make_friendly_name() {
	echo "$1" | sed 's/:/@/g'
}

untag() {
	echo "${1%:*}"
}

noop() {
	:
}

depfiles_own_image() {
	local target_image=$1
	local make_friendly_parent=$(make_friendly_name "$2")
	local untagged_parent=$(untag "$2")

	echo "$target_image@latest: $make_friendly_parent"
	echo ".PHONY: $target_image.dependants $untagged_parent.dependants"
	echo "$untagged_parent.dependants: $target_image"
	echo "$untagged_parent.dependants: $target_image.dependants"
}

depfiles_ext_image() {
	local target_image="$1"
	local make_friendly_parent=$(make_friendly_name "$2")

	echo "$target_image@latest: $make_friendly_parent"
}

list_ext_image() {
	local make_friendly_parent=$(make_friendly_name "$2")
	echo "$make_friendly_parent"
}

graph_own_image() {
	local untagged_parent=$(untag "$2")
	cat <<-EOF
	"$1" [shape=box]
	"$untagged_parent" [shape=box]
	"$1" -> "$untagged_parent"

EOF
}

graph_ext_image() {
	cat <<-EOF
	"$1" [shape=box]
	"$2" [shape=house; style=filled; fillcolor="#a0a0a0"]
	"$1" -> "$2"
EOF
}

require_parent_tag() {
	local target_image=$1
	local parent_image=$2

	if ! echo "$parent_image" | grep ":${required_parent_tag}\$"; then
		echo "FROM in Dockerfile for $target_image must specify a parent with the tag '$required_parent_tag'" >&2
		exit 1
	fi
}

while getopts ":dgp:x" c; do
	case $c in
		d)
			own_image_function=depfiles_own_image
			ext_image_function=depfiles_ext_image
			;;
		x)
			own_image_function=noop
			ext_image_function=list_ext_image
			;;
		g)
			own_image_function=graph_own_image
			ext_image_function=graph_ext_image
			;;
		p)
			own_image_function=require_parent_tag
			required_parent_tag=$OPTARG
			ext_image_function=noop
			;;
		\?)
			echo "Unrecognized option -$OPTARG" >&2
			exit 1
			;;
		:)
			echo "Option -$OPTARG requires an argument" >&2
			exit 1
			;;
	esac
done

shift "$(dc -e"$OPTIND 1 - p")"

if [ -z "$own_image_function" ] || [ $# -lt 2 ]; then
	usage
	exit 1
fi

target_dockerfile=$1
target_image=$(dirname "$target_dockerfile")
shift
known_images="$*"

parent_image_tag=$(find_parent "$target_dockerfile")
ec=$?
case $ec in
	0) ;;
	1)
		echo "Failed to find a parent docker image in $target_dockerfile" >&2
		exit $ec
		;;
	2)
		echo "Found multiple parent docker images in $target_dockerfile" >&2
		exit $ec
		;;
esac

if contains "$parent_image_tag" "$known_images"; then
	$own_image_function "$target_image" "$parent_image_tag"
else
	$ext_image_function "$target_image" "$parent_image_tag"
fi