#!/bin/bash
set -eo pipefail
shopt -s dotglob

# make sure we can GTFO
trap 'echo >&2 Ctrl+C captured, exiting; exit 1' SIGINT

usage() {
	cat <<-EOUSAGE
		usage: $0 [PR number] [repo[:tag]]
		   ie: $0 1024
		       $0 9001 debian php django
	EOUSAGE
}

# TODO flags parsing
allFiles=
listTarballContents=1
findCopies='20%'

if [ "$#" -eq 0 ]; then
	usage >&2
	exit 1
fi
pull="$1" # PR number
shift

#dir="$(dirname "$(readlink -f "$BASH_SOURCE")")"

tempDir="$(mktemp -d)"
trap "rm -rf '$tempDir'" EXIT
cd "$tempDir"

git clone --quiet --depth 1 \
	https://github.com/docker-library/official-images.git \
	oi

git -C oi fetch --quiet --depth 1 \
	origin "pull/$pull/merge":pull

images=( "$@" )
if [ "${#images[@]}" -eq 0 ]; then
	images=( $(git -C oi/library diff --name-only master...pull -- . | xargs -n1 basename) )
fi

export BASHBREW_CACHE="${BASHBREW_CACHE:-${XDG_CACHE_HOME:-$HOME/.cache}/bashbrew}"
export BASHBREW_LIBRARY="$PWD/oi/library"

# TODO something less hacky than "git archive" hackery, like a "bashbrew archive" or "bashbrew context" or something
template='
{{- range $.Entries -}}
	{{- $from := $.DockerFrom . -}}
	git -C "$BASHBREW_CACHE/git" archive --format=tar
	{{- " " -}}
	{{- "--prefix=" -}}
	{{- $.RepoName -}}
	_
	{{- .Tags | last -}}
	{{- "/" -}}
	{{- " " -}}
	{{- .GitCommit -}}
	{{- ":" -}}
	{{- (eq .Directory ".") | ternary "" .Directory -}}
	{{- "\n" -}}
{{- end -}}
'

copy-tar() {
	local src="$1"; shift
	local dst="$1"; shift

	if [ "$allFiles" ]; then
		mkdir -p "$dst"
		cp -al "$src"/*/ "$dst/"
		return
	fi

	# "Dockerfile*" at the end here ensures we capture "Dockerfile.builder" style repos in a useful way too (busybox, hello-world)
	for d in "$src"/*/Dockerfile*; do
		dDir="$(dirname "$d")"
		dDirName="$(basename "$dDir")"

		IFS=$'\n'
		files=(
			"$(basename "$d")"
			$(awk '
				toupper($1) == "COPY" || toupper($1) == "ADD" {
					for (i = 2; i < NF; i++) {
						print $i
					}
				}
			' "$d")

			# some extra files which are likely interesting if they exist, but no big loss if they do not
			' *.manifest' # debian/ubuntu "package versions" list
			' *.ks' # fedora "kickstart" (rootfs build script)
			' build*.txt' # ubuntu "build-info.txt", debian "build-command.txt"

			# usefulness yet to be proven:
			#' *.log'
			#' {MD5,SHA1,SHA256}SUMS'
			#' *.{md5,sha1,sha256}'

			# (the space prefix is removed below and is used to ignore non-matching globs so that bad "Dockerfile" entries appropriately lead to failure)
		)
		unset IFS

		mkdir -p "$dst/$dDirName"

		for origF in "${files[@]}"; do
			f="${origF# }" # trim off leading space (indicates we don't care about failure)
			[ "$f" = "$origF" ] && failureMatters=1 || failureMatters=

			globbed=( $(cd "$dDir" && eval "echo $f") )

			for g in "${globbed[@]}"; do
				if [ -z "$failureMatters" ] && [ ! -e "$dDir/$g" ]; then
					continue
				fi

				mkdir -p "$(dirname "$dst/$dDirName/$g")"
				cp -alT "$dDir/$g" "$dst/$dDirName/$g"

				if [ "$listTarballContents" ]; then
					case "$g" in
						*.tar.*|*.tgz)
							tar -tf "$dst/$dDirName/$g" | sort > "$dst/$dDirName/$g  'tar -t'"
							;;
					esac
				fi
			done
		done
	done
}

mkdir temp
git -C temp init --quiet

for image in "${images[@]}"; do
	if script="$(bashbrew cat -f "$template" "$image")"; then
		mkdir tar
		( eval "$script" | tar -xiC tar )
		copy-tar tar temp
		rm -rf tar
	fi
done
git -C temp add . || :
git -C temp commit --quiet --allow-empty -m 'initial' || :

git -C oi checkout --quiet pull

git -C temp rm --quiet -rf . || :
script="$(bashbrew cat -f "$template" "${images[@]}")"
mkdir tar
( eval "$script" | tar -xiC tar )
copy-tar tar temp
rm -rf tar
git -C temp add .

git -C temp diff --minimal --find-copies="$findCopies" --find-copies-harder --irreversible-delete --staged