#!/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_CMD:='gbpm'}
: ${GBPM_LABEL:='version'}
: ${GBPM_LABEL_PL:="${GBPM_LABEL}s"}
: ${GBPM_PATH:="${HOME}/.pythons"}

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

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

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

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

	echo 'false'
	exit 1
}

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

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

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

_populate_selected() {
	local dir dirs

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

	selected=()
	for dir in "${dirs[@]}"; do
		if [[ "${dir}" == "${GBPM_PATH}/"* ]]; then
			dir="${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_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() {
	[[ "${#}" -eq 0 ]] && _die 'set command requires an argument'

	local dir dirs bn prefix pri match match_pri

	_populate_dirs

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

		[[ "${bn}" == *"${1}"* ]] || continue

		# lower depth (i.e. fewer hyphens before match) is preferred,
		# e.g. `2' matches `python-2.0' over `python-3.0-2'.
		#
		# priority at the same depth, using `2.1' as an example:
		# - from start/hyphen to end (python-2.1)
		# - from start/hyphen to hyphen (python-2.1-2)
		# - from start/hyphen to dot (python-2.1.3)
		# - from start/hyphen (python-2.11)
		# - other (python-3.2.1)
		#
		# at the same priority, the last match (i.e. greatest
		# version-sorted string) is used, e.g. `3' matches
		# `python-3.14' over `python-3.2'.

		prefix="${bn%%${1}*}"
		pri="${prefix//[^-]}"
		pri="$((${#pri} * 5))"
		if [[ "${prefix}" == @(|*-) ]]; then
			case "${bn#*${1}}" in
				'') ;;
				-*) ((pri++)) ;;
				.*) ((pri += 2)) ;;
				*) ((pri += 3)) ;;
			esac
		else
			((pri += 4))
		fi

		[[ "${pri}" -le "${match_pri:-${pri}}" ]] || continue

		match="${dir}"
		match_pri="${pri}"
	done

	[[ -n "${match}" ]] || _die "no matching ${GBPM_LABEL} found"

	_clear
	_add "${match}"
	_export
}

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

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

cmd_help() {
	_echo "Usage: ${GBPM_CMD} <command> [args]"
	_echo
	_echo 'Commands:'
	_echo "  ls       List available ${GBPM_LABEL_PL}"
	_echo "  get      Print currently selected ${GBPM_LABEL}"
	_echo "  set      Select specified ${GBPM_LABEL}"
	_echo "  clear    Clear any selected ${GBPM_LABEL_PL}"
	_echo "  version  Print ${GBPM_CMD} version"
}

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