# Functions for opening and closing file descriptors
#
# Copyright (C) 2013  Patrick "P. J." McDermott
#
# This file is part of the ProteanOS Development Kit.
#
# The ProteanOS Development Kit is free software: you can redistribute
# it and/or modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# The ProteanOS Development Kit is distributed in the hope that it
# will be useful, but WITHOUT ANY WARRANTY; without even the implied
# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with the ProteanOS Development Kit.  If not, see
# <http://www.gnu.org/licenses/>.

[ "x${_FD_SM+set}" = 'xset' ] && return 0
_FD_SM=1

use output
use locale

_FD_MIN=3
# Shells and the file descriptors they reserve for the user:
#   * Debian Almquist Shell
#     - The shell doesn't understand any file descriptor greater than 9.
#     - File descriptors starting at 10 are used for I/O redirection.
#   * BusyBox ash
#     - File descriptors starting at 10 are used for job control and I/O
#       redirection.
#   * GNU Bash:
#     - GNU Readline uses file descriptor 255 in interactive shells.
#     - File descriptors starting at 10 are used for I/O redirection.
#   * MirOS Korn Shell
#     - File descriptors starting at either 10 or 24 are used for the shell's
#       tty_fd and shl_dbg_fd.
#   * Solaris ksh
#     - The shell doesn't understand any file descriptor greater than 9.
_FD_MAX=9

FD=

fopen()
{
	local path="${1}"
	local mode="${2}"
	local i=
	local fd=

	case "${mode}" in
		'r')  mode='<' ;;
		'w')  mode='>' ;;
		'a')  mode='>>';;
		'rw') mode='<>';;
		*) return 125;;
	esac

	# Find first available file descriptor.
	i=${_FD_MIN}
	while [ ${i} -le ${_FD_MAX} ]; do
		if [ "x$(eval echo "\${_fd_${i}+set}")" != 'xset' ]; then
			fd=${i}
			break
		fi
		i=$(($i + 1))
	done
	if [ "x${fd:+set}" != 'xset' ]; then
		error 2 "$(get_msg 'emfile')"
		return
	fi

	if eval "exec ${fd}${mode}'${path}'"; then
		eval "_fd_${fd}='${mode}${path}'"
		FD="${fd}"
		return 0
	else
		error 2 "$(get_msg 'cant_fopen')"
	fi
}

fclose()
{
	local fd="${1}"

	# Make sure the file descriptor is open.
	if [ "x$(eval echo "\${_fd_${fd}+set}")" != 'xset' ]; then
		error 2 "$(get_msg 'ebadf')"
	fi

	eval "exec ${fd}>&-"
	unset "_fd_${fd}"

	return 0
}