#!/usr/bin/env bash
#
# Copyright 2014 David Vazgenovich Shakaryan
# Distributed under the terms of the MIT License.
#
# rbpm (ruby path mangler)
# https://git.potato.am/rbpm.git/
# Manage multiple Ruby installations with no black magic.
#
# In order to prevent environment pollution, the output of this script
# is a list of commands which must be sourced. This can be achieved
# through a simple shell function:
#
#     rbpm() { source <(/path/to/rbpm.sh "${@}"); }
#
# Placing the above function inside ~/.bashrc (or equivalent) will load
# it upon starting your shell.

RBPM_VERSION='0.3'

: ${RUBIES_PATH:="${HOME}/.rubies"}

_echo() {
 	echo "echo '${@//\'/\'\\\'\'}'"
}

_export() {
 	echo "export PATH='${PATH//\'/\'\\\'\'}'"
 	echo 'hash -r'
}

_warn() {
 	echo "echo 'rbpm: ${@//\'/\'\\\'\'}' 1>&2"
}

_die() {
 	[[ -n "${@}" ]] && _warn "${@}"

 	echo 'false'
 	exit 1
}

_populate_dirs() {
 	[[ -d "${RUBIES_PATH}" ]] \
 	 	|| _die "directory ${RUBIES_PATH} does not exist"

 	mapfile -td $'\0' dirs < <(shopt -s nullglob;
 	 	printf '%s\0' "${RUBIES_PATH}"/* | sort -zV)

 	[[ -n "${dirs}" ]] || _die "directory ${RUBIES_PATH} is empty"
}

_populate_selected() {
 	local dir dirs

 	mapfile -td : dirs < <(printf %s "${PATH}")

 	for dir in "${dirs[@]}"; do
 	 	if [[ "${dir}" == "${RUBIES_PATH}/"* ]]; then
 	 	 	dir="${dir%/bin}"
 	 	 	selected+=("${dir##*/}")
 	 	fi
 	done

 	[[ "${#selected[@]}" -ne 0 ]] || return 1
 	[[ "${#selected[@]}" -eq 1 ]] \
 	 	|| _warn 'warning: multiple managed paths found in PATH'
}

_clear() {
 	local dir dirs cdirs

 	mapfile -td : dirs < <(printf %s "${PATH}")

 	for dir in "${dirs[@]}"; do
 	 	if [[ "${dir}" == "${RUBIES_PATH}/"* ]]; then
 	 	 	_echo "removing ${dir} from PATH"
 	 	else
 	 	 	cdirs+=("${dir}")
 	 	fi
 	done

 	[[ "${#cdirs[@]}" -ne "${#dirs[@]}" ]] || return 1

 	PATH="$(IFS=':'; echo "${cdirs[*]}")"
}

_add() {
 	_echo "adding ${1}/bin to PATH"

 	PATH="${1}/bin:${PATH}"
}

rbpm_ls() {
 	local dir dirs selected str

 	_populate_dirs
 	_populate_selected

 	for dir in "${dirs[@]}"; do
 	 	str="  ${dir##*/}"

 	 	[[ "${dir##*/}" == "${selected}" ]] && str="${str/ /*}"

 	 	_echo "${str}"
 	done
}

rbpm_get() {
 	local dir selected

 	_populate_selected || _die 'no managed path found in PATH'

 	for dir in "${selected[@]}"; do
 	 	_echo "${dir}"
 	done
}

rbpm_set() {
 	[[ -n "${1}" ]] || _die 'set command requires an argument'

 	local dir dirs match match_start

 	_populate_dirs

 	for dir in "${dirs[@]}"; do
 	 	[[ "${dir##*/}" == *"${1}"* ]] || continue

 	 	match="${dir}"

		# match from start of version is preferred. we assume the
		# version is at the beginning of the directory name or
		# immediately following a hyphen. this avoids unintuitive
		# behaviour like `2.1' matching `2.2.1' over `2.1.0'.
 	 	if [[ "${dir##*/}" == "${1}"* ||
			"${dir##*/}" == *-"${1}"* ]]; then
 	 	 	match_start="${dir}"
 	 	fi
 	done

 	[[ -n "${match}" ]] || _die 'no matching ruby found'
 	[[ -n "${match_start}" ]] && match="${match_start}"

 	_clear
 	_add "${match}"
 	_export
}

rbpm_clear() {
 	_clear || _die 'no managed path found in PATH'
 	_export
}

rbpm_version() {
 	_echo "rbpm ${RBPM_VERSION}"
}

rbpm_help() {
 	_echo 'Usage: rbpm <command> [args]'
 	_echo
 	_echo 'Commands:'
 	_echo '  ls       List all available rubies'
 	_echo '  get      Display currently selected ruby'
 	_echo '  set      Select specified ruby'
 	_echo '  clear    Unselect any selected rubies'
 	_echo '  version  Display rbpm version'
}

case "${1}" in
 	'ls')
 	 	rbpm_ls ;;
 	'get')
 	 	rbpm_get ;;
 	'set')
 	 	rbpm_set "${2}" ;;
 	'clear')
 	 	rbpm_clear ;;
 	'version')
 	 	rbpm_version ;;
 	*)
 	 	rbpm_help ;;
esac