#!/usr/bin/env bash
# Decide which images CI should build. Prints GITHUB_OUTPUT lines:
#
#   images=node-agent other-image   space-separated, fed straight to build-images.sh
#   any=true|false                  whether there is anything to build at all
#
# Space-separated rather than a JSON matrix on purpose. Gitea resolves a job's matrix
# when it parses the workflow — before `needs` outputs exist — so a dynamic
# `fromJSON(needs...)` matrix yields one job whose name is the raw, uninterpolated
# expression. See jobparser.nameWithMatrix in the Gitea source, and
# https://github.com/go-gitea/gitea/issues/28207. Looping inside one job gives an
# honest job name and collapsible per-image log sections instead.
#
# 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
}

emit() {
	local names=$1 reason=$2 any=false flat
	# Collapse the newline-separated list onto one line for the workflow output.
	flat=$(printf '%s\n' "$names" | tr '\n' ' ' | sed -e 's/  */ /g' -e 's/^ //' -e 's/ $//')
	[ -n "$flat" ] && any=true
	echo "selected (${reason}): ${flat:-<none>}" >&2
	printf 'images=%s\n' "$flat"
	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'