#!/bin/sh

die() {
	echo "$@" >&2
	exit 1
}

have_binary() {
	type "$1" > /dev/null 2> /dev/null
}

check_writeable() {
	printf "" > "$1" && rm "$1"
}

download() {
	dl_url="$1"
	dl_output="$2"

	test "$#" -eq "2" || die "download requires exactly two arguments, was given $@"

	if ! check_writeable "$dl_output"; then
		die "download error: cannot write to $dl_output"
	fi

	if have_binary wget; then
		printf '==> Using wget to download "%s" to "%s"\n' "$dl_url" "$dl_output"
		wget "$dl_url" -O "$dl_output" || return
	elif have_binary curl; then
		printf '==> Using curl to download "%s" to "%s"\n' "$dl_url" "$dl_output"
		curl --silent "$dl_url" > "$dl_output" || return
	elif have_binary fetch; then
		printf '==> Using fetch to download "%s" to "%s"\n' "$dl_url" "$dl_output"
		fetch "$dl_url" -o "$dl_output" || return
	else
		die "no binary found to download $dl_url. exiting."
	fi
	echo "==> download complete!"
}

unarchive() {
	ua_archivetype="$1"
	ua_infile="$2"
	ua_outfile="$3"
	ua_distname="$4"

	if ! check_writeable "$ua_outfile"; then
		die "unarchive error: cannot write to $ua_outfile"
	fi

	case "$ua_archivetype" in
		tar.gz)
			if have_binary tar; then
				echo "==> using 'tar' to extract binary from archive"
				cat "$ua_infile" | tar -O -z -x "$ua_distname/$ua_distname" > "$ua_outfile"
			else
				die "no binary on system for extracting tar files"
			fi
			;;
		zip)
			if have_binary unzip; then
				echo "==> using 'unzip' to extract binary from archive"
				unzip -p "$ua_infile" "$ua_distname/$ua_distname" > "$ua_outfile"
			else
				die "no installed method for extracting .zip archives"
			fi
			;;
		*)
			die "unrecognized archive type '$ua_archivetype'"
	esac

	chmod +x "$ua_outfile"
}

get_go_vars() {
	if [ ! -z "$GOOS" ] && [ ! -z "$GOARCH" ]; then
		printf "%s-%s" "$GOOS" "$GOARCH"
	elif have_binary go; then
		printf "%s-%s" "$(go env GOOS)" "$(go env GOARCH)"
	else
		die "no way of determining system GOOS and GOARCH\nPlease manually set GOOS and GOARCH then retry."
	fi
}

mkurl() {
	m_root="$1"
	m_name="$2"
	m_vers="$3"
	m_archive="$4"
	m_govars=$(get_go_vars) || die "could not get go env vars"

	echo "https://ipfs.io$m_root/$m_name/$m_vers/${m_name}_${m_vers}_$m_govars.$m_archive"
}

distroot="$1"
distname="$2"
outpath="$3"
version="$4"

if [ -z "$distroot" ] || [ -z "$distname" ] || [ -z "$outpath" ] || [ -z "$version" ]; then
	die "usage: dist_get <distroot> <distname> <outpath> <version>"
fi

case $version in
	v*)
		# correct input
		;;
	*)
		echo "invalid version '$version'" >&2
		die "versions must begin with 'v', for example: v0.4.0"
		;;
esac

# TODO: don't depend on the go tool being installed to detect this
goenv=$(get_go_vars) || die "could not get go env vars"

case $goenv in
	linux-*)
		archive="tar.gz"
		;;
	darwin-*)
		archive="tar.gz"
		;;
	windows-*)
		archive="zip"
		;;
	freebsd-*)
		archive="tar.gz"
		;;
	openbsd-*)
		archive="tar.gz"
		;;
	*)
		echo "unrecognized system environment: $goenv" >&2
		die "currently only linux, darwin, windows and freebsd are supported by this script"
esac


mkdir -p bin/tmp

url=$(mkurl "$distroot" "$distname" "$version" "$archive")
tmpfi="bin/tmp/$distname.$archive"

download "$url" "$tmpfi"
if [ $? -ne 0 ]; then
	die "failed to download $url to $tmpfi"
fi

unarchive "$archive" "$tmpfi" "$outpath" "$distname"
if [ $? -ne 0 ]; then
	die "failed to extract archive $tmpfi"
fi
