#!/bin/sh

# Forked from https://github.com/chambln/pandoc-rss
# MIT/X Consortium License

# © 2020 Gregory Chamberlain <greg@cosine.blue>

# 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.

SHARE=${0%/*}/../share/${0##*/}
TEMPLATES_DIR=$SHARE/data/templates
DOMAIN=${PWD##*/}
EMAIL=${EMAIL:-webmaster@$DOMAIN}

usage ()
{
    cat <<EOF
Usage: ${0##*/} [OPTIONS] [FILE]...
  -s                Produce standalone XML
  -t TITLE         'Example Feed'
  -d DESCRIPTION   'Short description of the feed'
  -l LINK           http://example.net
  -f FORMAT         blog/%s.html  =>  http://example.net/blog/%s.html
  -w WEBMASTER     'webmaster@example.net (Real Name)'
  -c COPYRIGHT     'Year © Name, CC BY-SA 4.0'
  -n LANGUAGE       en-GB
EOF
}

get_language_code ()
{
    [ -n "$LANG" ] || exit 1
    code=${LANG%%.*}
    primary_code=${code%%_*}
    subcode=${code#$primary_code}
    subcode=${subcode#_}
    printf %s\\n "$primary_code${subcode:+-$subcode}"
}

is_valid_language_code ()
{
    arg=$(printf %s "$1" | tr [A-Z] [a-z])
    while IFS=' 	' read -r code _
    do
        [ x"$code" = x"#" ] && continue
        [ x"$code" = x"$arg" ] && return 0
    done < $SHARE/data/language-codes
    return 1
}

get_user_fullname ()
{
    while IFS=':' read -r user _ _ _ gecos _
    do
        if [ x"$user" = x"$LOGNAME" ]
        then
            user_fullname="${gecos%%,*}"
            [ -n "$user_fullname" ] || exit 1
            printf %s\\n "$user_fullname"
            return 0
        fi
    done < /etc/passwd
    return 1
}

get_user_contact ()
{
    user_fullname="${NAME:-$(get_user_fullname)}"
    printf '%s\n' "$EMAIL${user_fullname:+ ($user_fullname)}"
}

get_metadata_value ()
{
    key=$1
    shift
    value=$(pandoc --template="$TEMPLATES_DIR/$key.value" "$@")
    [ -n "$value" ] || return 1
    printf %s\\n "$value"
}

get_date ()
{
    input_file=$1
    shift
    if date=$(get_metadata_value date "$input_file")
    then
	if [ -f /opt/homebrew/bin/gdate ]; then
	    date_cmd=/opt/homebrew/bin/gdate
	elif [ -f /usr/bin/date ]; then
	    date_cmd=/usr/bin/date
	else
	    date_cmd=/bin/date
	fi

        $date_cmd --utc --date "$date" +'%a, %d %b %Y %T +0000'
    fi
}

generate_feed_item ()
{
    input_file=$1
    shift

    case $guid_format in
        *%s*)
            filename=${input_file##*/}
            basename=${filename%.*}
            guid=$(printf "$guid_format" "$basename")
            set -- -V "guid:$guid" "$@"
    esac

    if date=$(get_date "$input_file")
    then
        set -- -V "date:$date" "$@"
    fi

    if $omit_body
    then
        set -- -V body: "$@"
    fi

    pandoc --template="$TEMPLATES_DIR/item.xml" --no-highlight "$@" "$input_file"
}

generate_feed_items ()
{
    for input_file do
        generate_feed_item "$input_file"
    done
}

print_xml_element ()
{
    [ -n "$2" ] || return 1
    printf '<%s>%s</%s>\n' "$1" "$2" "$1"
}

generate_standalone_feed ()
{
    if [ -z "$channel_language" ]
    then
        if language_code=$(get_language_code)
        then
            channel_language=$language_code
        fi
    fi

    if ! is_valid_language_code "$channel_language"
    then
        >&2 printf 'Invalid language code: ‘%s’\n' "$channel_language"
        >&2 printf 'See %s\n' "$SHARE"/data/language-codes
        exit 1
    fi

    echo '<?xml version="1.0" encoding="UTF-8" ?>'
    echo '<rss version="2.0">'
    echo '<channel>'
    print_xml_element title "$channel_title"
    print_xml_element link "$channel_link"
    print_xml_element description "$channel_description"
    print_xml_element language "$channel_language"
    print_xml_element webMaster "${channel_webmaster:=$(get_user_contact)}"
    print_xml_element copyright "$channel_copyright"
    print_xml_element docs https://www.rssboard.org/rss-specification
    echo '<generator>pandoc-rss</generator>'
    generate_feed_items "$@"
    echo '</channel>'
    echo '</rss>'
}

channel_title=$DOMAIN
channel_link=https://$DOMAIN
channel_description="Posts from $DOMAIN"
unset channel_webmaster
unset channel_copyright
unset channel_language
omit_body=false
guid_optarg=auto
standalone=false
while getopts t:l:d:w:c:n:of:hs OPT
do
    case "$OPT" in
        t)  channel_title=$OPTARG ;;
        l)  channel_link=${OPTARG%/} ;;
        d)  channel_description=$OPTARG ;;
        w)  channel_webmaster=$OPTARG ;;
        c)  channel_copyright=$OPTARG ;;
        n)  channel_language=$OPTARG ;;
        o)  omit_body=true ;;
        f)  guid_optarg=$OPTARG ;;
        s)  standalone=true ;;
        ?)  usage; exit 2 ;;
    esac
done
shift $((OPTIND - 1))

case $guid_optarg in
    auto) guid_optarg=%s.html
esac
case $guid_optarg in
    omit)      guid_format= ;;
    *://*%s*)  guid_format=$guid_optarg ;;
    *%s*)      [ "$channel_link" ] &&
                   guid_format=$channel_link/${guid_optarg#/} ;;
    *)         >&2 printf 'Invalid guid format ‘%s’\n' "$guid_optarg"
               exit 1
esac

if $standalone
then
    generate_standalone_feed "$@"
else
    generate_feed_items "$@"
fi