#!/usr/bin/env bash

# Receives files as arguments, scans them for lines like
# #> FETCH dd16fb1d67bfab79a72f5e8390735c49e3e8e70b4945a15ab1f81ddb78658fb3
# #>  FROM http://ftp.gnu.org/gnu/make/make-4.4.1.tar.gz
# #>    AS make.tar.gz
# or
#   #local = "/downloads/make.tar.gz";
#   url = "http://ftp.gnu.org/gnu/make/make-4.4.1.tar.gz";
#   sha256 = "dd16fb1d67bfab79a72f5e8390735c49e3e8e70b4945a15ab1f81ddb78658fb3";
# downloads to ./downloads if file's not present there yet, verifies hash,
# copies file over to $DESTDIR.

set -ue

: ${DESTDIR:=stage/downloads}  # final location of putting the file
: ${ONLY:=all}  # allow to limit to just a single file
mkdir -p downloads   # first cached there, so that stage can be cleaned freely

fetch() {
	hash=$1; url=$2; filename=${3:-$(basename "$url")}
	if [[ -e "downloads/$filename" ]]; then
		pushd downloads >/dev/null
			echo "$hash $filename" | sha256sum -c
		popd >/dev/null
	else
		mkdir -p downloads/.tmp$$
		pushd downloads/.tmp$$ >/dev/null
			wget -nv --show-progress "$url" -O "$filename"
			echo "$hash $filename" | sha256sum -c --quiet
		popd >/dev/null
		mv "downloads/.tmp$$/$filename" downloads/
		rm -d downloads/.tmp$$
	fi
	if [[ "${DESTDIR:-}" != downloads ]]; then
		mkdir -p "$DESTDIR"
		cp -a --reflink=auto "downloads/$filename" \
			"$DESTDIR/$filename"
	fi
}

REGEX_MAGIC='^#> '
REGEX_FETCH='^#> FETCH'
REGEX_FROM='^#>  FROM'
REGEX_AS='^#>    AS'
NIX_REGEX_FETCH='^[[:blank:]]*sha256[[:blank:]]*=[[:blank:]]*"(.*)";$'
NIX_REGEX_FROM='^[[:blank:]]*url[[:blank:]]*=[[:blank:]]*"(.*)";$'
NIX_REGEX_AS='^[[:blank:]]*#[[:blank:]]local[[:blank:]]*=[[:blank:]]*/downloads/(.*);$'
process_commands_in() {
	hash=''; url=''; filename=''
	while read -r line; do
		if [[ "$line" =~ $REGEX_MAGIC ]]; then
			if [[ "$line" =~ $REGEX_FETCH ]]; then
				hash="${line##"#> FETCH"}"
			elif [[ "$line" =~ $REGEX_FROM ]]; then
				url="${line##'#>  FROM '}"
			elif [[ "$line" =~ $REGEX_AS ]]; then
				filename="${line##'#>    AS '}"
			else
				echo "### $0: malformed line '$line' in '$1'"
				exit 2
			fi
		elif [[ "$line" =~ $NIX_REGEX_FETCH ]]; then
		     hash=${BASH_REMATCH[1]}
		elif [[ "$line" =~ $NIX_REGEX_FROM ]]; then
		     url=${BASH_REMATCH[1]}
		elif [[ "$line" =~ $NIX_REGEX_AS ]]; then
			filename=${BASH_REMATCH[1]}
		else
			if [[ -n "$hash" && -n "$url" ]]; then
				filename=${filename:-$(basename $url)}
				if [[ "$ONLY" == all || \
						"$ONLY" == "$filename" ]]; then
					fetch "$hash" "$url" "$filename"
				fi
			fi
			hash=''; url=''; filename=''
		fi
	done < $1
}

[[ $# == 0 ]] && files='recipes/*.sh recipes/*/*.sh' || files="$@"
for f in $files; do
	process_commands_in $f
done