#!/bin/sh
# SHATOM: generate a feed from a directory of files
# Copyright (C) 2020--2022 Case Duckworth <acdw@acdw.net>
# Licensed under the Good Choices License.  See COPYING for details.

### Entry point

usage() {
	cat <<EOF
SHATOM: generate a web feed from directories, recursively
USAGE:	shatom -h
	shatom [-c CONFIG] [-C DIR] [VAR=VALUE...] DIRECTORY...

FLAGS:
 -h	Show this help and exit.

OPTIONS:
 -c CONFIG	Specify shatom's configuration path, a shell
		script overriding functions in shatom itself.
		Default: \$PWD/shatom.conf.sh
 -C DIR	Change the current working directory to DIR
		before executing the rest of the script.

PARAMETERS:
 VAR=VALUE...	Override configuration variables for this
		invocation of shatom.  These are eval'd, so
		be careful!
 DIRECTORY...	Directory(s) containing feed content.  These
		can be files as well, but really directories
		makes more sense, don't you think?
EOF
	exit "${1:-0}"
}

main() {
	# Command-line flags
	while getopts hc:C: opt; do
		case "$opt" in
		h) usage ;;
		c) CONFIG="$OPTARG" ;;
		C) cd "$OPTARG" || exit 2 ;;
		*) usage 1 ;;
		esac
	done
	shift $((OPTIND - 1))

	# Configuration file
	if [ -f "${CONFIG:=$PWD/shatom.conf.sh}" ]; then
		# shellcheck source=/dev/null
		. "$CONFIG"
	fi

	# Command-line variable assignment
	for arg; do
		case "$arg" in
		*=*) eval "$arg" ;;
		*) break ;;
		esac
	done

	# Finally, default values for variables
	FEED_TITLE="${FEED_TITLE:-example}"
	FEED_SUBTITLE="${FEED_SUBTITLE:-an example}"
	FEED_AUTHOR="${FEED_AUTHOR:-nobody}"
	FEED_COPYRIGHT="${FEED_COPYRIGHT:-Copyright (C) $(date +%Y) $FEED_AUTHOR}"
	FEED_URL="${FEED_URL:-https://example.com/feed.xml}"
	FEED_ID="${FEED_ID:-${FEED_URL#*//}}"
	FEED_UPDATED="${FEED_UPDATED:-$(date -u +'%F %TZ')}"
	SITE_URL="${SITE_URL:-https://example.com/}"

	# Add PWD if no directories are given.
	if [ $# -eq 0 ]; then
		set -- .
	fi

	# Do the damn thing already
	feed_header
	for DIR; do
		recent_files "$DIR" -type f |
			while read -r item; do
				skip_item "$item" && continue
				feed_item "$item"
			done
	done
	feed_footer
}

### Library functions

## File-listing functions

recent_files() {
	# requires stat(1)
	dir="$1"
	shift

	find "$dir" "$@" \
		-exec stat -c '%Y %n' '{}' + |
		sort -k1,1 -nr |
		cut -d' ' -f2-
}

## Feed-level functions
# by default, generate Atom feeds
# (https://datatracker.ietf.org/doc/html/rfc4287), but an RSS configuration file
# is included in rss.conf.sh.

feed_header() {
	cat <<END
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title>$FEED_TITLE</title>
<subtitle>$FEED_SUBTITLE</subtitle>
<link href="$FEED_URL" rel="self" />
<link href="$SITE_URL" />
<id>$FEED_ID</id>
<generator uri="https://git.sr.ht/~acdw/shatom" version="infinite">shatom</generator>
<rights>$FEED_COPYRIGHT</rights>
<updated>$FEED_UPDATED</updated>
END
}

feed_footer() {
	cat <<END
</feed>
END
}

feed_item() {
	ITEM_URL="$(item_url "$1")"
	cat <<END
<entry>
<id>$ITEM_URL</id>
<link rel="alternate" href="$ITEM_URL" />
<title>$(item_title "$1")</title>
<summary>$(item_summary "$1")</summary>
<updated>$(item_updated "$1")</updated>
<author>$(item_author)</author>
<content type="text"><![CDATA[$(item_content "$1")]]></content>
</entry>
END
}

## Item-level functions
# These can all be, and in fact should be, changed in the configuration file.

skip_item() {
	return 1
}

item_url() {
	basename="${1#$DIRECTORY}"
	echo "$FEED_URL/$basename"
}

item_title() {
	basename="${1#$DIRECTORY}"
	echo "$basename"
}

item_summary() {
	return 1
}

item_author() {
	echo "$FEED_AUTHOR"
}

item_content() {
	cat "$1"
}

item_updated() {
	# requires stat(1)
	stat -c %y "$1"
}

### Execution section

test -n "$DEBUG" && set -x
test -n "$SOURCE" || main "$@"