fix: set env vars like described in the manpage

Also remove the mention of AGENDA_NEXT, since we don't actually set
that...

agenda

@@ -149,6 +149,18 @@ __edit() {
 		fi
 	done
 
+	# These values are (potentially) used by the AGENDA_EDITOR and AGENDA_TEMPLATE
+	# processes.
+	AGENDA_FILE=$file
+	AGENDA_DATE=$base
+	AGENDA_NAME=$opt_t
+	AGENDA_SLUG=$slug
+	AGENDA_FILE=$file
+	AGENDA_LAST=$(__agenda_last "$file" "$opt_t")
+
+	# Make shellcheck happy...
+	export AGENDA_FILE AGENDA_DATE AGENDA_NAME AGENDA_SLUG AGENDA_FILE AGENDA_LAST
+
 	if ! [ -f "$file" ]; then
 		if [ "$opt_c" = "yes" ]; then
 			__agenda_create "$file" "$opt_b" "$opt_t" "$slug" "$base"
@@ -159,7 +171,6 @@ __edit() {
 	fi
 
 	if [ "$opt_E" = "no" ]; then
-		export AGENDA_FILE="$file"
 		exec $AGENDA_EDITOR "$file"
 	else
 		echo "$file"
@@ -305,26 +316,10 @@ __agenda_create() {
 	tmp_err=$(mktemp)
 
 	if [ "$backlog" = "no" ]; then
-		local last
-		while read -r REPLY; do
-			if [ "$REPLY" = "$file" ]; then
-				break
-			else
-				last=$REPLY
-			fi
-		done < <(
-			{
-				echo "$file"
-				find "$AGENDA_DIR/$name" -type f
-			} | sort
-		)
-
 		# Capture exit code of the template command.
 		local code
 		set +e
-		AGENDA_DATE=$date AGENDA_NAME=$name AGENDA_SLUG=$slug \
+		"$AGENDA_TEMPLATE" > "$tmp" 2> "$tmp_err"
-		AGENDA_FILE=$file AGENDA_LAST=${last:-} \
-			"$AGENDA_TEMPLATE" > "$tmp" 2> "$tmp_err"
 		code=$?
 		set -e
 
@@ -362,6 +357,26 @@ __agenda_default_template() {
 	esac
 }
 
+__agenda_last() {
+	local file=$1 name=$2
+
+	local last
+	while read -r REPLY; do
+		if [ "$REPLY" = "$file" ]; then
+			break
+		else
+			last=$REPLY
+		fi
+	done < <(
+		{
+			echo "$file"
+			find "$AGENDA_DIR/$name" -type f
+		} | sort
+	)
+
+	echo "${last:-}"
+}
+
 # https://stackoverflow.com/a/49035906
 __slugify() {
     echo "$1" \

agenda.1

@@ -190,12 +190,6 @@ The file path of the agenda note.
 The last agenda file. Can be empty if no previous agenda note exists.
 .PP
 .RE
-\#
-\fBAGENDA_NEXT\fP
-.RS 4
-The next agenda file. Can be empty if no next agenda note exists.
-.PP
-.RE
 \#=============================================================================
 .SH "SEE ALSO"
 \fBxdg-user-dir(1)\fP