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

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

Option --first=[-]N skips the first N results; with the leading '-' skip
until the Nth result from the end (showing a total of N results if within
bounds of the total number of results and not limited with --maxitems).

Note that --first with a negative N for thread or summary output requires
counting the number of matching threads in advance, which is a heavy
operation.

Signed-off-by: Jani Nikula <jani@nikula.org>
---
 notmuch-search.c |   67 ++++++++++++++++++++++++++++++++++++++++++++---------
 1 files changed, 55 insertions(+), 12 deletions(-)

diff --git a/notmuch-search.c b/notmuch-search.c
index 6f04d9a..ceef6ac 100644
--- a/notmuch-search.c
+++ b/notmuch-search.c
@@ -194,13 +194,20 @@ 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 first,
+		   unsigned int maxitems)
 {
     notmuch_thread_t *thread;
     notmuch_threads_t *threads;
     notmuch_tags_t *tags;
     time_t date;
     int first_thread = 1;
+    unsigned int i, start;
+
+    if (first < 0)
+	first += notmuch_query_count_threads (query);
+    start = first < 0 ? 0 : first;
 
     threads = notmuch_query_search_threads (query);
     if (threads == NULL)
@@ -208,17 +215,23 @@ 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) &&
+	     (!maxitems || i < start + maxitems);
+	 notmuch_threads_move_to_next (threads), i++)
     {
 	int first_tag = 1;
 
+	thread = notmuch_threads_get (threads);
+
+	if (i < start) {
+	    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 +284,20 @@ 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 first,
+		    unsigned int maxitems)
 {
     notmuch_message_t *message;
     notmuch_messages_t *messages;
     notmuch_filenames_t *filenames;
     int first_message = 1;
+    unsigned int i, start;
+
+    if (first < 0)
+	first += notmuch_query_count_messages(query);
+
+    start = first < 0 ? 0 : first;
 
     messages = notmuch_query_search_messages (query);
     if (messages == NULL)
@@ -284,10 +305,14 @@ 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) &&
+	     (!maxitems || i < start + maxitems);
+	 notmuch_messages_move_to_next (messages), i++)
     {
+	if (i < start)
+	    continue;
+
 	message = notmuch_messages_get (messages);
 
 	if (output == OUTPUT_FILES) {
@@ -394,6 +419,8 @@ notmuch_search_command (void *ctx, int argc, char *argv[])
     const search_format_t *format = &format_text;
     int i, ret;
     output_t output = OUTPUT_SUMMARY;
+    unsigned int maxitems = 0;
+    int first = 0;
 
     argc--; argv++; /* skip subcommand argument */
 
@@ -412,6 +439,22 @@ 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], "--first=") == 0) {
+	    char *p;
+	    opt = argv[i] + sizeof ("--first=") - 1;
+	    first = strtol(opt, &p, 10);
+	    if (*opt == '\0' || p == opt || *p != '\0') {
+		fprintf (stderr, "Invalid value for --first: %s\n", opt);
+		return 1;
+	    }
+	} else if (STRNCMP_LITERAL (argv[i], "--maxitems=") == 0) {
+	    char *p;
+	    opt = argv[i] + sizeof ("--maxitems=") - 1;
+	    maxitems = strtoul(opt, &p, 10);
+	    if (*opt == '\0' || p == opt || *p != '\0') {
+		fprintf (stderr, "Invalid value for --maxitems: %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 +521,11 @@ 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, first, maxitems);
 	break;
     case OUTPUT_MESSAGES:
     case OUTPUT_FILES:
-	ret = do_search_messages (format, query, output);
+	ret = do_search_messages (format, query, output, first, maxitems);
 	break;
     case OUTPUT_TAGS:
 	ret = do_search_tags (notmuch, format, query);
-- 
1.7.5.4