Implement mu_msgset_first and mu_msgset_last

* include/mailutils/msgset.h (mu_msgset_first, mu_msgset_last): New prototypes.
* libmailutils/msgset/Makefile.am: Add new files.
* libmailutils/msgset/first.c: New file.
* libmailutils/msgset/last.c: New file.
* libmailutils/tests/msgset.c: New options for testing the new functions.
* libmailutils/tests/msgset.at: Test new functions.

@@ -66,6 +66,9 @@ int mu_msgset_negate (mu_msgset_t msgset, mu_msgset_t *pnset);
 int mu_msgset_count (mu_msgset_t mset, size_t *pcount);
 int mu_msgset_is_empty (mu_msgset_t mset);
 
+int mu_msgset_first (mu_msgset_t msgset, size_t *ret);
+int mu_msgset_last (mu_msgset_t msgset, size_t *ret);
+  
 typedef int (*mu_msgset_msgno_action_t) (size_t _n, void *_call_data);
 typedef int (*mu_msgset_message_action_t) (size_t _n, mu_message_t _msg,
 					   void *_call_data);

@@ -27,12 +27,14 @@ libmsgset_la_SOURCES = \
  getitr.c\
  getlist.c\
  getmbox.c\
+ first.c\
  foreachnum.c\
  foreachmsgno.c\
  foreachuid.c\
  foreachmsg.c\
  free.c\
  isempty.c\
+ last.c\
  locate.c\
  negate.c\
  parse.c\

+/* GNU Mailutils -- a suite of utilities for electronic mail
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   GNU Mailutils 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, or (at your option)
+   any later version.
+
+   GNU Mailutils 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 GNU Mailutils.  If not, see <http://www.gnu.org/licenses/>. */
+
+#include <config.h>
+#include <mailutils/types.h>
+#include <mailutils/errno.h>
+#include <mailutils/list.h>
+#include <mailutils/msgset.h>
+#include <mailutils/sys/msgset.h>
+
+int
+mu_msgset_first (mu_msgset_t msgset, size_t *ret)
+{
+  int rc;
+  struct mu_msgrange const *range;
+
+  if (mu_msgset_is_empty (msgset))
+    return EINVAL;
+  if (!ret)
+    return MU_ERR_OUT_PTR_NULL;
+  rc = mu_msgset_aggregate (msgset);
+  if (rc)
+    return rc;
+  rc = mu_list_head (msgset->list, (void **) &range);
+  if (rc == 0)
+    *ret = range->msg_beg;
+  return rc;
+}

+/* GNU Mailutils -- a suite of utilities for electronic mail
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   GNU Mailutils 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, or (at your option)
+   any later version.
+
+   GNU Mailutils 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 GNU Mailutils.  If not, see <http://www.gnu.org/licenses/>. */
+
+#include <config.h>
+#include <mailutils/types.h>
+#include <mailutils/errno.h>
+#include <mailutils/list.h>
+#include <mailutils/msgset.h>
+#include <mailutils/sys/msgset.h>
+
+int
+mu_msgset_last (mu_msgset_t msgset, size_t *ret)
+{
+  int rc;
+  struct mu_msgrange const *range;
+
+  if (mu_msgset_is_empty (msgset))
+    return EINVAL;
+  if (!ret)
+    return MU_ERR_OUT_PTR_NULL;
+  rc = mu_msgset_aggregate (msgset);
+  if (rc)
+    return rc;
+  rc = mu_list_tail (msgset->list, (void **) &range);
+  if (rc == 0)
+    *ret = range->msg_end;
+  return rc;
+}

@@ -171,5 +171,17 @@ MSGSET([subtract an open range with smaller left boundary],
 [3
 ])
 
+MSGSET([first],
+[msgset-first],
+[-msgset='3,10:20' -first],
+[3
+])
+
+MSGSET([last],
+[msgset-last],
+[-msgset='3,10:20' -last],
+[20
+])
+
 dnl ------------------------------------------------------------------
 m4_popdef([MSGSET])
\ No newline at end of file

@@ -73,12 +73,36 @@ parse_msgset (const char *arg)
   return msgset;
 }
 
+static void
+print_all (mu_msgset_t msgset)
+{
+  MU_ASSERT (mu_msgset_print (mu_strout, msgset));
+  mu_printf ("\n");
+}
+
+static void
+print_first (mu_msgset_t msgset)
+{
+  size_t n;
+  MU_ASSERT (mu_msgset_first (msgset, &n));
+  printf ("%zu\n", n);
+}
+
+static void
+print_last (mu_msgset_t msgset)
+{
+  size_t n;
+  MU_ASSERT (mu_msgset_last (msgset, &n));
+  printf ("%zu\n", n);
+}
+
 int
 main (int argc, char **argv)
 {
   int i;
   char *msgset_string = NULL;
   mu_msgset_t msgset;
+  void (*print) (mu_msgset_t) = print_all;
 
   mu_set_program_name (argv[0]);
   for (i = 1; i < argc; i++)
@@ -88,7 +112,7 @@ main (int argc, char **argv)
       if (strcmp (arg, "-h") == 0 || strcmp (arg, "-help") == 0)
 	{
 	  mu_printf ("usage: %s [-msgset=SET] [-add=X[:Y]] [-del=X[:Y]] "
-		     "[-addset=SET] [-delset=SET] ...\n",
+		     "[-addset=SET] [-delset=SET] [-first] [-last]...\n",
 		     mu_program_name);
 	  return 0;
 	}
@@ -142,14 +166,17 @@ main (int argc, char **argv)
 	      mu_msgset_free (tset);
 	    }
 	}
+      else if (strcmp (arg, "-first") == 0)
+	print = print_first;
+      else if (strcmp (arg, "-last") == 0)
+	print = print_last;
       else
       	{
 	  mu_error ("unknown option %s", arg);
 	  return 1;
 	}
     }
-  MU_ASSERT (mu_msgset_print (mu_strout, msgset));
-  mu_printf ("\n");
+  print (msgset);
   mu_msgset_free (msgset);
   
   return 0;