#!/usr/bin/env bash
#
# Copyright 2014 David Vazgenovich Shakaryan
# Distributed under the terms of the MIT License.
#
# gbpm
# https://git.potato.am/gbpm.git/
# Manage multiple Python/Ruby/etc. installations with no black magic.
#
# Output must be executed: gbpm() { . <(/path/to/gbpm.sh "${@}"); }

GBPM_VERSION='0.4'

: ${GBPM_OPTS_PATH:="${HOME}/.pythons"}

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

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

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

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

	echo 'false'
	exit 1
}

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

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

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

_populate_selected() {
	local dir dirs

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

	selected=()
	for dir in "${dirs[@]}"; do
		if [[ "${dir}" == "${GBPM_OPTS_PATH}/"* ]]; then
			dir="${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}" == "${GBPM_OPTS_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}"
}

cmd_ls() {
	local dir dirs selected str

	_populate_dirs
	_populate_selected

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

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

		_echo "${str}"
	done
}

cmd_get() {
	local dir selected

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

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

cmd_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}"

		# exact match
		if [[ "${dir##*/}" == "${1}" ]]; then
			unset match_start
			break
		fi

		# 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 `3.2.1' over `2.1.0'.
		if [[ "${dir##*/}" == "${1}"* ||
			"${dir##*/}" == *-"${1}"* ]]; then
			match_start="${dir}"
		fi
	done

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

	_clear
	_add "${match}"
	_export
}

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

cmd_version() {
	_echo "gbpm ${GBPM_VERSION}"
}

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

case "${1}" in
	'ls')
		cmd_ls ;;
	'get')
		cmd_get ;;
	'set')
		cmd_set "${2}" ;;
	'clear')
		cmd_clear ;;
	'version')
		cmd_version ;;
	*)
		cmd_help ;;
esac