#!/bin/bash
 set -e
 
 # hello-world                      latest              ef872312fe1b        3 months ago        910 B
 # hello-world                      latest              ef872312fe1bbc5e05aae626791a47ee9b032efa8f3bda39cc0be7b56bfe59b9   3 months ago        910 B
 
 # debian                           latest              f6fab3b798be        10 weeks ago        85.1 MB
 # debian                           latest              f6fab3b798be3174f45aa1eb731f8182705555f89c9026d8c1ef230cbf8301dd   10 weeks ago        85.1 MB
 

 if ! command -v curl &> /dev/null; then
 	echo >&2 'error: "curl" not found!'
 	exit 1
 fi
 

 usage() {
 	echo "usage: $0 dir image[:tag][@image-id] ..."
 	echo "   ie: $0 /tmp/hello-world hello-world"
 	echo "       $0 /tmp/debian-jessie debian:jessie"
 	echo "       $0 /tmp/old-hello-world hello-world@ef872312fe1bbc5e05aae626791a47ee9b032efa8f3bda39cc0be7b56bfe59b9"
 	echo "       $0 /tmp/old-debian debian:latest@f6fab3b798be3174f45aa1eb731f8182705555f89c9026d8c1ef230cbf8301dd"
 	[ -z "$1" ] || exit "$1"
 }
 
 dir="$1" # dir for building tar in
 shift || usage 1 >&2
 
 [ $# -gt 0 -a "$dir" ] || usage 2 >&2
 mkdir -p "$dir"
 

 # hacky workarounds for Bash 3 support (no associative arrays)
 images=()
 rm -f "$dir"/tags-*.tmp
 # repositories[busybox]='"latest": "...", "ubuntu-14.04": "..."'

 
 while [ $# -gt 0 ]; do
 	imageTag="$1"
 	shift
 	image="${imageTag%%[:@]*}"
 	tag="${imageTag#*:}"
 	imageId="${tag##*@}"
 	[ "$imageId" != "$tag" ] || imageId=
 	[ "$tag" != "$imageTag" ] || tag='latest'
 	tag="${tag%@*}"

 	imageFile="${image//\//_}" # "/" can't be in filenames :)
 

 	token="$(curl -sSL -o /dev/null -D- -H 'X-Docker-Token: true' "https://index.docker.io/v1/repositories/$image/images" | tr -d '\r' | awk -F ': *' '$1 == "X-Docker-Token" { print $2 }')"

 	if [ -z "$imageId" ]; then
 		imageId="$(curl -sSL -H "Authorization: Token $token" "https://registry-1.docker.io/v1/repositories/$image/tags/$tag")"
 		imageId="${imageId//\"/}"
 	fi

 	ancestryJson="$(curl -sSL -H "Authorization: Token $token" "https://registry-1.docker.io/v1/images/$imageId/ancestry")"
 	if [ "${ancestryJson:0:1}" != '[' ]; then
 		echo >&2 "error: /v1/images/$imageId/ancestry returned something unexpected:"
 		echo >&2 "  $ancestryJson"
 		exit 1
 	fi

 	IFS=','
 	ancestry=( ${ancestryJson//[\[\] \"]/} )
 	unset IFS

 	if [ -s "$dir/tags-$imageFile.tmp" ]; then
 		echo -n ', ' >> "$dir/tags-$imageFile.tmp"

 	else
 		images=( "${images[@]}" "$image" )
 	fi

 	echo -n '"'"$tag"'": "'"$imageId"'"' >> "$dir/tags-$imageFile.tmp"

 	echo "Downloading '$imageTag' (${#ancestry[@]} layers)..."
 	for imageId in "${ancestry[@]}"; do
 		mkdir -p "$dir/$imageId"
 		echo '1.0' > "$dir/$imageId/VERSION"

 		curl -sSL -H "Authorization: Token $token" "https://registry-1.docker.io/v1/images/$imageId/json" -o "$dir/$imageId/json"

 		# TODO figure out why "-C -" doesn't work here
 		# "curl: (33) HTTP server doesn't seem to support byte ranges. Cannot resume."
 		# "HTTP/1.1 416 Requested Range Not Satisfiable"
 		if [ -f "$dir/$imageId/layer.tar" ]; then
 			# TODO hackpatch for no -C support :'(
 			echo "skipping existing ${imageId:0:12}"
 			continue
 		fi
 		curl -SL --progress -H "Authorization: Token $token" "https://registry-1.docker.io/v1/images/$imageId/layer" -o "$dir/$imageId/layer.tar" # -C -
 	done
 	echo
 done
 
 echo -n '{' > "$dir/repositories"
 firstImage=1

 for image in "${images[@]}"; do

 	imageFile="${image//\//_}" # "/" can't be in filenames :)
 

 	[ "$firstImage" ] || echo -n ',' >> "$dir/repositories"
 	firstImage=
 	echo -n $'\n\t' >> "$dir/repositories"

 	echo -n '"'"$image"'": { '"$(cat "$dir/tags-$imageFile.tmp")"' }' >> "$dir/repositories"

 done
 echo -n $'\n}\n' >> "$dir/repositories"
 

 rm -f "$dir"/tags-*.tmp
 

 echo "Download of images into '$dir' complete."
 echo "Use something like the following to load the result into a Docker daemon:"
 echo "  tar -cC '$dir' . | docker load"