#!/usr/bin/env bash

# Installs the latest Go release into $TARGETDIR (default: ~/.local)
# without requiring root access. Assumes the following suggested
# environment variables (which need to be set or changed in this script
# or after install completes):
#
#     PATH="~/.local/bin:~/.local/bin/go/bin:$PATH"
#     GOOS=linux
#     GOARCH=amd64
#     GOPATH="~/.local/go"
#     GOBIN="~/.local/go/bin"
#
# Note that the downloaded tar file is not removed and can be found in
# either $DOWNLOADS or /tmp.

true "${TARGETDIR:="$HOME/.local"}"

# change this to your target (detecting not always reliable)
declare GOOS=linux
declare GOARCH=amd64

lookup_file() {
	curl -sSL "https://go.dev/dl/?mode=json" |
		jq -r '.[0].files[]
       | select(.os == "'"$GOOS"'")
       | select(.arch == "'"$GOARCH"'")
       | .filename'
}

fetch() {
	local filename
	filename="$(lookup_file)"
	[[ -z "$filename" ]] && echo "unable to fetch filename" 1>&2 && return 1
	local path="/tmp/$filename"
	[[ -n "$DOWNLOADS" ]] && [[ -d "$DOWNLOADS" ]] && path="$DOWNLOADS/$filename"
	curl -L "https://go.dev/dl/$filename" -o "$path"
	echo "$path"
}

install_latest_go() {
	local dir="$1" path
	[[ -z "$dir" ]] && dir="$TARGETDIR"
	[[ -z "$dir" ]] && dir="$HOME/.local"
	mkdir -p "$dir" 2>/dev/null
	path="$(fetch)"
	[[ -z "$path" ]] && echo "unable to fetch go tarball" 1>&2 && return 1
	rm -rf "$dir/go" && tar -C "$dir" -xzf "$path" # rm is required by instructions
	echo "Add $dir/go/bin to your path and optionally set GOBIN=~/.local/bin" 1>&2
}

install_latest_go "$@"