#!/bin/sh
#
# A POSIX shell help2man implementation. Supports most options but does not
# output identical manuals. Written in a few hours this is still in "alpha"
# status. Please let me know if there are any issues.
#
# Copyright (c) 2019-2021 Dylan Araps
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

args() {
    while _arg=$1; do
        case $1 in -[a-zA-Z]) shift; esac

        case $_arg in
            -n|--name=*) _arg_name=${1##--name=}
                : "${_arg_name:?"$_arg requires an argument"}" ;;

            -s|--section=*) _arg_section=${1##--section=}
                : "${_arg_section:?"$_arg requires an argument"}" ;;

            -m|--manual=*) _arg_manual=${1##--manual=}
                : "${_arg_manual:?"$_arg requires an argument"}" ;;

            -S|--source=*) _arg_source=${1##--source=}
                : "${_arg_source:?"$_arg requires an argument"}" ;;

            -i|--include=*|-I|--opt-include=*) _arg_include=${1##--include=}
                : "${_arg_include:?"$_arg requires an argument"}" ;;

            -o|--output=*) _arg_output=${1##--output=}
                : "${_arg_output:?"$_arg requires an argument"}" ;;

            --version)
                cat <<EOF
GNU ${0##*/} 1.47.16

Copyright (c) Dylan Araps 2021

This version output must spoof
GNU help2man so build systems
automatically work with it.
EOF
                exit 0
            ;;

            -h|--help-option=*) _arg_help_option=${1##--help-option=}
                : "${_arg_help_option:?"$_arg requires an argument"}" ;;

            -v|--version-option=*) _arg_version_option=${1##--version-option=}
                : "${_arg_version_option:?"$_arg requires an argument"}" ;;

            --version-string=*) _arg_version_string=${1##--version-string=}
                : "${_arg_version_string:?"$_arg requires an argument"}" ;;

            --no-discard-stderr)
                cmd_stderr=1
            ;;

            -p|--info-page=*|-N|--no-info|-l|--libtool|-L|--locale=*)
                # Not implemented.
            ;;

            -*)
                cat <<EOF
${0##*/} generates a man page out of '--help' and '--version' output.

Usage: ${0##*/} [OPTION]... EXECUTABLE

 -n, --name=STRING       description for the NAME paragraph
 -s, --section=SECTION   section number for manual page (1, 6, 8)
 -m, --manual=TEXT       name of manual (User Commands, ...)
 -S, --source=TEXT       source of program (FSF, Debian, ...)
 -L, --locale=STRING     select locale (default "C")
 -i, --include=FILE      include material from 'FILE'
 -I, --opt-include=FILE  include material from 'FILE' if it exists
 -o, --output=FILE       send output to 'FILE'
 -p, --info-page=TEXT    name of Texinfo manual
 -N, --no-info           suppress pointer to Texinfo manual
 -l, --libtool           exclude the 'lt-' from the program name
     --help              print this help, then exit
     --version           print version number, then exit

EXECUTABLE should accept '--help' and '--version' options and produce output on
stdout although alternatives may be specified using:

 -h, --help-option=STRING     help option string
 -v, --version-option=STRING  version option string
 --version-string=STRING      version string
 --no-discard-stderr          include stderr when parsing option output

Report bugs to <dylan.araps@gmail.com>.
EOF
                exit 0
            ;;

            *)
                exe=$1
                break
            ;;
        esac

        shift
    done
}

fnr() {
    # Replace all occurrences of substrings with substrings. This
    # function takes pairs of arguments iterating two at a time
    # until everything has been replaced.
    _fnr=$1
    shift 1

    while :; do case $_fnr-$# in
        *"$1"*) _fnr=${_fnr%"$1"*}${2}${_fnr##*"$1"} ;;
           *-2) break ;;
             *) shift 2
    esac done
}

clean() {
    _trim=${1#${1%%[![:space:]]*}}
    _trim=${_trim%${_trim##*[![:space:]]}}
    fnr "$_trim" "	" " " "  " " "
}

get_help() {
    case $cmd_stderr in
        1) cmd_help=$("$exe" "${_arg_help_option:---help}" 2>&1) ;;
        *) cmd_help=$("$exe" "${_arg_help_option:---help}")
    esac || :
    cmd_help=${cmd_help:?cannot get --help info from "$exe"}
}

get_version() {
    case $cmd_stderr in
        1) cmd_version_raw=${_arg_version_string:-\
                $("$exe" "${_arg_version_option:---version}" 2>&1)} ;;
        *) cmd_version_raw=${_arg_version_string:-\
                $("$exe" "${_arg_version_option:---version}")}
    esac || :

    read -r cmd_name cmd_version _junk <<EOF
$cmd_version_raw
EOF

    case $cmd_name in GNU)
        cmd_name="$cmd_name $cmd_version"
        cmd_version=$_junk
    esac
    cmd_version_raw="$cmd_name $cmd_version"
    cmd_name=${cmd_name##GNU }
    cmd_NAME=$(tr '[:lower:]' '[:upper:]' <<EOF
$cmd_name
EOF
    )
}

get_sections() {
    while IFS= read -r line || [ "$line" ]; do
        case $line in
            *[Uu][Ss][Aa][Gg][Ee]:*)
                sect_usage=$sect_usage${line#[Uu][Ss][Aa][Gg][Ee]: }$nl.P$nl
            ;;

            *[Oo][Rr]:*)
                sect_usage=$sect_usage${line#[Oo][Rr]: }$nl.P$nl
            ;;

            *"$cmd_name $cmd_version"*)
                # Skip lines containing what is probably the version string.
                # Some utilities do not provide --version and so --help includes
                # such information.
            ;;

            *"Report bugs"*|Report[[:space:]]*[[:space:]]bugs)
                sect_bug=$line
            ;;

            [[:space:]]*[[:space:]]-*|-*)
                read -r __arg1 __desc __junk <<EOF
$line
EOF
                case $__desc in -*)
                    __arg1="$__arg1 $__desc"
                    __desc=
                esac

                clean "$__desc${__junk:+ $__junk}"
                sect_opt="$sect_opt$nl.TP$nl$__arg1$nl$_fnr "
            ;;

            [[:space:]]*)
                clean "$line"
                sect_opt="$sect_opt$_fnr "
            ;;

            [[:print:]]*)
                clean "$line"
                sect_desc="$sect_desc$_fnr "
            ;;
        esac
    done <<EOF
$cmd_help
EOF
}

get_includes() {
    case $_arg_include in '') return 0; esac
    exec 3<"$_arg_include"

    while read -r line <&3 || [ "$line" ] || {
        case $_hdr in *?*)
            fnr "$_hdr" ' ' _
            export "HELP_$_fnr=.SH \"$_hdr\"$nl$_buf"
        esac
        break
    }; do
        case $line in
            '['*']')
                case $_hdr in *?*)
                    fnr "$_hdr" ' ' _
                    export "HELP_$_fnr=.SH \"$_hdr\"$nl$_buf"
                esac

                fnr "$line" '[' '' ']' ''
                _hdr=$_fnr
                _buf=
            ;;

            *?*) _buf=$_buf$line$nl ;;
        esac
    done
}

main() {
    set -e
    nl="
"

    args "$@"
    get_help
    get_version
    cmd_date=$(date +'%B %Y')
    get_sections
    get_includes

: "${HELP_NAME:=".SH NAME$nl$cmd_name ${_arg_name:+"\\- $_arg_name"}"}"
: "${HELP_SYNOPSIS:="${sect_usage:+".SH SYNOPSIS$nl$sect_usage"}"}"
: "${HELP_DESCRIPTION:="${sect_desc:+".SH DESCRIPTION$nl$sect_desc"}"}"
: "${HELP_OPTIONS:="${sect_opt:+".SH OPTIONS$nl$sect_opt"}"}"
: "${HELP_REPORTING_BUGS:="${sect_bug:+".SH \"REPORTING BUGS\"$nl$sect_bug"}"}"

    cat <<EOF > "${_arg_output:-/dev/stdout}"
.\\" DO NOT MODIFY THIS FILE!  It was generated by ${0##*/} 1.48.3.
.TH $cmd_NAME "${_arg_section:-1}" "$cmd_date"\
 "${_arg_source:-$cmd_version_raw}" "${_arg_manual:-User Commands}"
${HELP_NAME:+"$nl$HELP_NAME"}\
${HELP_SYNOPSIS:+"$nl$HELP_SYNOPSIS"}\
${HELP_DESCRIPTION:+"$nl$HELP_DESCRIPTION"}\
${HELP_OPTIONS:+"$nl$HELP_OPTIONS"}\
${HELP_REPORTING_BUGS:+"$nl$HELP_REPORTING_BUGS"}\
${HELP_SEE_ALSO:+"$nl$HELP_SEE_ALSO"}
EOF
}

main "$@"