#!/usr/bin/env bash
# Decide which images CI should build. Prints GITHUB_OUTPUT lines:
#
#   images=["node-agent",...]   JSON array consumed by the build job's matrix
#   any=true|false              whether there is anything to build at all
#
# Rules, first match wins:
#   1. workflow_dispatch naming one image  -> that image
#   2. tag push (<image>/vX.Y.Z)           -> the image named in the tag
#   3. shared build plumbing changed       -> every image
#   4. anything else                       -> images with changed files
#
# When the diff base is unknown (first push, force-push, shallow clone) this builds
# everything. Rebuilding too much is the safe direction to fail.
set -euo pipefail
cd "$(dirname "$0")/.."

# A change to any of these can affect how every image is built.
SHARED_PATHS='^(hack/|Makefile|\.hadolint\.yaml|\.gitea/workflows/)'

all_images() {
	local dockerfile
	for dockerfile in images/*/Dockerfile; do
		# Guards against the glob staying literal when there are no images.
		[ -f "$dockerfile" ] || continue
		basename "$(dirname "$dockerfile")"
	done
}

# Names on stdin -> ["a","b"]. Built by hand so the runner needs no jq.
as_json() {
	local out='' name
	while IFS= read -r name; do
		[ -n "$name" ] || continue
		out="${out:+$out,}\"$name\""
	done
	printf '[%s]' "$out"
}

emit() {
	local names=$1 reason=$2 any=false
	[ -n "$names" ] && any=true
	echo "selected (${reason}): ${names:-<none>}" >&2
	printf 'images=%s\n' "$(printf '%s\n' "$names" | as_json)"
	printf 'any=%s\n' "$any"
	exit 0
}

require_image() {
	[ -f "images/$1/Dockerfile" ] || {
		echo "no such image: images/$1/Dockerfile does not exist" >&2
		exit 1
	}
}

# 1. Explicit request via workflow_dispatch.
case "${DISPATCH_IMAGE:-}" in
	'') ;;
	all) emit "$(all_images)" 'workflow_dispatch: all' ;;
	*)
		require_image "$DISPATCH_IMAGE"
		emit "$DISPATCH_IMAGE" "workflow_dispatch: $DISPATCH_IMAGE"
		;;
esac

# 2. Release tag: <image>/vX.Y.Z.
if [ "${GITHUB_REF_TYPE:-}" = tag ]; then
	image=${GITHUB_REF_NAME%/*}
	require_image "$image"
	emit "$image" "tag ${GITHUB_REF_NAME}"
fi

# 3 and 4 both need a usable diff base.
base=${BASE_SHA:-}
if [ -z "$base" ] || [[ $base =~ ^0+$ ]] || ! git cat-file -e "${base}^{commit}" 2>/dev/null; then
	emit "$(all_images)" 'diff base unavailable, building everything'
fi

changed=$(git diff --name-only "$base" HEAD)

if printf '%s\n' "$changed" | grep -qE "$SHARED_PATHS"; then
	emit "$(all_images)" 'shared build plumbing changed'
fi

# Map changed paths back to image names, dropping any that no longer exist so a
# deleted image directory does not fail the build.
selected=$(
	printf '%s\n' "$changed" |
		sed -n 's#^images/\([^/]*\)/.*#\1#p' |
		sort -u |
		while IFS= read -r i; do
			[ -f "images/$i/Dockerfile" ] && echo "$i"
		done
)

emit "$selected" 'changed paths'