update-gem-binary-links

#!/bin/bash

# Dynamically updates versioned symlinks in /usr/local/bin for independent Ruby gems.
# Maps target binaries to their active Gentoo package ruby_targets using /var/db/pkg.
# This script was composed with significant help from Google AI.

shopt -s nullglob || exit

LINK_DIR="/usr/local/bin"
SELECTOR_PATH="/write/libexec/ruby/gem-binary-exec.bash"
TARGET_BINARIES=(irb pry)

GENFUN_MODULES="rc portage"
source /lib/gentoo/functions.sh || exit

function remove_links {
	local link

	for link; do
		einfo "Removing link: ${link}"
		rm -f -- "${link}"
	done
}

function process_binary {
	local binary=$1 link pkg target targets use_files IFS=' '
	local -A created_links=() || exit

	if [[ ! -f /usr/bin/${binary} ]]; then
		ewarn "/usr/bin/${binary} doesn't exist."
		remove_links "${LINK_DIR}/${binary}"[0-9][0-9]
		return
	fi

	readarray -t pkg < <(qfile -qC "/usr/bin/${binary}")
	[[ ${pkg[1]+.} ]] && die "The ${binary} binary represents too many packages."

	use_files=(/var/db/pkg/"${pkg}"-[0-9]*/USE)
	[[ ${use_files+.} ]] || die "No USE files found with ${pkg}."

	readarray -t targets < <(grep -Poe '(?<=ruby_targets_ruby)[0-9][0-9]' "${use_files[@]}" | sort -u)
	[[ ${targets+.} ]] || die "No active Ruby target found with '${pkg}'."

	for target in "${targets[@]}"; do
		link=${LINK_DIR}/${binary}${target}
		einfo "Creating link: ${link} (${pkg})"
		ln -sf "${SELECTOR_PATH}" "${link}"
		created_links[${link}]=.
	done

	for link in "${LINK_DIR}/${binary}"[0-9][0-9]; do
		[[ ${created_links[${link}]+.} ]] || remove_links "${link}"
	done
}

function main {
	[[ -d ${LINK_DIR} ]] || die "Specified link directory not a directory: ${LINK_DIR}"
	[[ -e ${SELECTOR_PATH} ]] || die "Specified selector doesn't exist: ${SELECTOR_PATH}"

	local binary

	for binary in "${TARGET_BINARIES[@]}"; do
		process_binary "${binary}"
	done
}

main