cli: add options --offset and --limit to notmuch search

Add options --offset=[-]N and --limit=M to notmuch search to determine the
first result and maximum number of results to display.

Option --limit=M limits the maximum number of results to display to M.

Option --offset=[-]N skips the first N results; with the leading '-' skip
until the Nth result from the end.

Note that --offset with a negative N for thread or summary output requires
counting the number of matching threads in advance.

Signed-off-by: Jani Nikula <jani@nikula.org>

4 files changed, 87 insertions, 14 deletions

diff --git a/NEWS b/NEWS
index 88f7b204..f224d02c 100644
--- a/NEWS
+++ b/NEWS
@@ -23,6 +23,11 @@ Add search terms to  "notmuch dump"
   search/show/tag. The output file argument of dump is deprecated in
   favour of using stdout.
 
+Add "notmuch search" --offset and --limit options
+
+  The search command now takes options --offset=[-]N and --limit=N to limit
+  the number of results shown.
+
 Optimizations
 -------------
 
diff --git a/notmuch-search.c b/notmuch-search.c
index 6f04d9a4..36686d19 100644
--- a/notmuch-search.c
+++ b/notmuch-search.c
@@ -194,13 +194,22 @@ static int
 do_search_threads (const search_format_t *format,
 		   notmuch_query_t *query,
 		   notmuch_sort_t sort,
-		   output_t output)
+		   output_t output,
+		   int offset,
+		   int limit)
 {
     notmuch_thread_t *thread;
     notmuch_threads_t *threads;
     notmuch_tags_t *tags;
     time_t date;
     int first_thread = 1;
+    int i;
+
+    if (offset < 0) {
+	offset += notmuch_query_count_threads (query);
+	if (offset < 0)
+	    offset = 0;
+    }
 
     threads = notmuch_query_search_threads (query);
     if (threads == NULL)
@@ -208,17 +217,22 @@ do_search_threads (const search_format_t *format,
 
     fputs (format->results_start, stdout);
 
-    for (;
-	 notmuch_threads_valid (threads);
-	 notmuch_threads_move_to_next (threads))
+    for (i = 0;
+	 notmuch_threads_valid (threads) && (limit < 0 || i < offset + limit);
+	 notmuch_threads_move_to_next (threads), i++)
     {
 	int first_tag = 1;
 
+	thread = notmuch_threads_get (threads);
+
+	if (i < offset) {
+	    notmuch_thread_destroy (thread);
+	    continue;
+	}
+
 	if (! first_thread)
 	    fputs (format->item_sep, stdout);
 
-	thread = notmuch_threads_get (threads);
-
 	if (output == OUTPUT_THREADS) {
 	    format->item_id (thread, "thread:",
 			     notmuch_thread_get_thread_id (thread));
@@ -271,12 +285,21 @@ do_search_threads (const search_format_t *format,
 static int
 do_search_messages (const search_format_t *format,
 		    notmuch_query_t *query,
-		    output_t output)
+		    output_t output,
+		    int offset,
+		    int limit)
 {
     notmuch_message_t *message;
     notmuch_messages_t *messages;
     notmuch_filenames_t *filenames;
     int first_message = 1;
+    int i;
+
+    if (offset < 0) {
+	offset += notmuch_query_count_messages (query);
+	if (offset < 0)
+	    offset = 0;
+    }
 
     messages = notmuch_query_search_messages (query);
     if (messages == NULL)
@@ -284,10 +307,13 @@ do_search_messages (const search_format_t *format,
 
     fputs (format->results_start, stdout);
 
-    for (;
-	 notmuch_messages_valid (messages);
-	 notmuch_messages_move_to_next (messages))
+    for (i = 0;
+	 notmuch_messages_valid (messages) && (limit < 0 || i < offset + limit);
+	 notmuch_messages_move_to_next (messages), i++)
     {
+	if (i < offset)
+	    continue;
+
 	message = notmuch_messages_get (messages);
 
 	if (output == OUTPUT_FILES) {
@@ -394,6 +420,8 @@ notmuch_search_command (void *ctx, int argc, char *argv[])
     const search_format_t *format = &format_text;
     int i, ret;
     output_t output = OUTPUT_SUMMARY;
+    int offset = 0;
+    int limit = -1; /* unlimited */
 
     argc--; argv++; /* skip subcommand argument */
 
@@ -412,6 +440,22 @@ notmuch_search_command (void *ctx, int argc, char *argv[])
 		fprintf (stderr, "Invalid value for --sort: %s\n", opt);
 		return 1;
 	    }
+	} else if (STRNCMP_LITERAL (argv[i], "--offset=") == 0) {
+	    char *p;
+	    opt = argv[i] + sizeof ("--offset=") - 1;
+	    offset = strtol (opt, &p, 10);
+	    if (*opt == '\0' || p == opt || *p != '\0') {
+		fprintf (stderr, "Invalid value for --offset: %s\n", opt);
+		return 1;
+	    }
+	} else if (STRNCMP_LITERAL (argv[i], "--limit=") == 0) {
+	    char *p;
+	    opt = argv[i] + sizeof ("--limit=") - 1;
+	    limit = strtoul (opt, &p, 10);
+	    if (*opt == '\0' || p == opt || *p != '\0') {
+		fprintf (stderr, "Invalid value for --limit: %s\n", opt);
+		return 1;
+	    }
 	} else if (STRNCMP_LITERAL (argv[i], "--format=") == 0) {
 	    opt = argv[i] + sizeof ("--format=") - 1;
 	    if (strcmp (opt, "text") == 0) {
@@ -478,11 +522,11 @@ notmuch_search_command (void *ctx, int argc, char *argv[])
     default:
     case OUTPUT_SUMMARY:
     case OUTPUT_THREADS:
-	ret = do_search_threads (format, query, sort, output);
+	ret = do_search_threads (format, query, sort, output, offset, limit);
 	break;
     case OUTPUT_MESSAGES:
     case OUTPUT_FILES:
-	ret = do_search_messages (format, query, output);
+	ret = do_search_messages (format, query, output, offset, limit);
 	break;
     case OUTPUT_TAGS:
 	ret = do_search_tags (notmuch, format, query);
diff --git a/notmuch.1 b/notmuch.1
index bba479e1..cda777b6 100644
--- a/notmuch.1
+++ b/notmuch.1
@@ -214,11 +214,26 @@ when sorting by
 .B newest\-first
 the threads will be sorted by the newest message in each thread.
 
-.RE
-.RS 4
 By default, results will be displayed in reverse chronological order,
 (that is, the newest results will be displayed first).
+.RE
+
+.RS 4
+.TP 4
+.BR \-\-offset=[\-]N
+
+Skip displaying the first N results. With the leading '\-', start at the Nth
+result from the end.
+.RE
+
+.RS 4
+.TP 4
+.BR \-\-limit=N
 
+Limit the number of displayed results to N.
+.RE
+
+.RS 4
 See the
 .B "SEARCH SYNTAX"
 section below for details of the supported syntax for <search-terms>.
diff --git a/notmuch.c b/notmuch.c
index e004c6c5..394371d9 100644
--- a/notmuch.c
+++ b/notmuch.c
@@ -222,6 +222,15 @@ static command_t commands[] = {
       "\t\t(oldest-first) or reverse chronological order\n"
       "\t\t(newest-first), which is the default.\n"
       "\n"
+      "\t--offset=[-]N\n"
+      "\n"
+      "\t\tSkip displaying the first N results. With the leading '-',\n"
+      "\t\tstart at the Nth result from the end.\n"
+      "\n"
+      "\t--limit=N\n"
+      "\n"
+      "\t\tLimit the number of displayed results to N.\n"
+      "\n"
       "\tSee \"notmuch help search-terms\" for details of the search\n"
       "\tterms syntax." },
     { "show", notmuch_show_command,