#!/bin/bash

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

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

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

download() {
	local url="$1"
	local output="$2"

	if [ -z "$url" ] || [ -z "$output" ]; then
		die "download takes exactly two arguments. was given '$@'"
	fi

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

	if have_binary wget; then
		printf 'Using wget to download "%s" to "%s"\n' "$url" "$output"
		wget "$url" -O "$output"
	elif have_binary curl; then
		printf 'Using curl to download "%s" to "%s"\n' "$url" "$output"
		curl --silent "$url" > "$output"
	elif have_binary fetch; then
		printf 'Using fetch to download "%s" to "%s"\n' "$url" "$output"
		fetch "$url" -o "$output"
	else
		die "no binary found to download $url. exiting."
	fi
}

unarchive() {
	local archivetype="$1"
	local infile="$2"
	local outfile="$3"
	local distname="$4"

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

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

	chmod +x "$outfile"
}

get_go_vars() {
	if [ ! -z "$GOOS" ] && [ ! -z "$GOARCH" ]; then
		printf "%s-%s" "$GOOS" "$GOARCH"
	fi

	if 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() {
	local name="$1"
	local vers="$2"
	local archive="$3"

	local govars=$(get_go_vars)

	echo "http://dist.ipfs.io/$name/$vers/${name}_${vers}_$govars.$archive"
}

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

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

if [ ${version:0:1} != "v" ]; then
	echo "invalid version '$version'" >&2
	die "versions must begin with 'v', for example: v0.4.0"
fi

# TODO: don't depend on the go tool being installed to detect this
goenv=$(get_go_vars)

case $goenv in
	linux-*)
		archive="tar.gz"
		;;
	darwin-*)
		archive="tar.gz"
		;;
	windows-*)
		archive="zip"
		;;
	freebsd-*)
		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=$(mkurl "$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 exract archive $tmpfi"
fi