DatabaseCommands: add "window" parameter to "search"/"find"

NEWS

@@ -1,6 +1,7 @@
 ver 0.20 (not yet released)
 * protocol
   - "commands" returns playlist commands only if playlist_directory configured
+  - "search"/"find" have a "window" parameter
 * output
   - pulse: set channel map to WAVE-EX
 

doc/protocol.xml

@@ -1558,6 +1558,7 @@ OK
               <arg choice="req"><replaceable>TYPE</replaceable></arg>
               <arg choice="req"><replaceable>WHAT</replaceable></arg>
               <arg choice="opt"><replaceable>...</replaceable></arg>
+              <arg choice="opt">window <replaceable>START</replaceable>:<replaceable>END</replaceable></arg>
             </cmdsynopsis>
           </term>
           <listitem>
@@ -1602,6 +1603,13 @@ OK
             <para>
               <varname>WHAT</varname> is what to find.
             </para>
+
+            <para>
+              <varname>window</varname> can be used to query only a
+              portion of the real response.  The parameter is two
+              zero-based record numbers; a start number and an end
+              number.
+            </para>
           </listitem>
         </varlistentry>
         <varlistentry id="command_findadd">
@@ -1794,6 +1802,7 @@ OK
               <arg choice="req"><replaceable>TYPE</replaceable></arg>
               <arg choice="req"><replaceable>WHAT</replaceable></arg>
               <arg choice="opt"><replaceable>...</replaceable></arg>
+              <arg choice="opt">window <replaceable>START</replaceable>:<replaceable>END</replaceable></arg>
             </cmdsynopsis>
           </term>
           <listitem>

src/command/DatabaseCommands.cxx

@@ -32,6 +32,7 @@
 #include "util/Error.hxx"
 #include "SongFilter.hxx"
 #include "protocol/Result.hxx"
+#include "protocol/ArgParser.hxx"
 #include "BulkEdit.hxx"
 
 #include <string.h>
@@ -70,6 +71,16 @@ handle_match(Client &client, unsigned argc, char *argv[], bool fold_case)
 {
 	ConstBuffer<const char *> args(argv + 1, argc - 1);
 
+	unsigned window_start = 0, window_end = std::numeric_limits<int>::max();
+	if (args.size >= 2 && strcmp(args[args.size - 2], "window") == 0) {
+		if (!check_range(client, &window_start, &window_end,
+				 args.back()))
+			return CommandResult::ERROR;
+
+		args.pop_back();
+		args.pop_back();
+	}
+
 	SongFilter filter;
 	if (!filter.Parse(args, fold_case)) {
 		command_error(client, ACK_ERROR_ARG, "incorrect arguments");
@@ -79,7 +90,8 @@ handle_match(Client &client, unsigned argc, char *argv[], bool fold_case)
 	const DatabaseSelection selection("", true, &filter);
 
 	Error error;
-	return db_selection_print(client, selection, true, false, error)
+	return db_selection_print(client, selection, true, false,
+				  window_start, window_end, error)
 		? CommandResult::OK
 		: print_error(client, error);
 }

src/db/DatabasePrint.cxx

@@ -147,27 +147,49 @@ PrintPlaylistFull(Client &client, bool base,
 
 bool
 db_selection_print(Client &client, const DatabaseSelection &selection,
-		   bool full, bool base, Error &error)
+		   bool full, bool base,
+		   unsigned window_start, unsigned window_end,
+		   Error &error)
 {
 	const Database *db = client.GetDatabase(error);
 	if (db == nullptr)
 		return false;
 
+	unsigned i = 0;
+
 	using namespace std::placeholders;
 	const auto d = selection.filter == nullptr
 		? std::bind(full ? PrintDirectoryFull : PrintDirectoryBrief,
 			    std::ref(client), base, _1)
 		: VisitDirectory();
-	const auto s = std::bind(full ? PrintSongFull : PrintSongBrief,
+	VisitSong s = std::bind(full ? PrintSongFull : PrintSongBrief,
 				std::ref(client), base, _1);
 	const auto p = selection.filter == nullptr
 		? std::bind(full ? PrintPlaylistFull : PrintPlaylistBrief,
 			    std::ref(client), base, _1, _2)
 		: VisitPlaylist();
 
+	if (window_start > 0 || window_end < std::numeric_limits<int>::max())
+		s = [s, window_start, window_end, &i](const LightSong &song,
+						      Error &error2){
+			const bool in_window = i >= window_start && i < window_end;
+			++i;
+			return !in_window || s(song, error2);
+		};
+
 	return db->Visit(selection, d, s, p, error);
 }
 
+bool
+db_selection_print(Client &client, const DatabaseSelection &selection,
+		   bool full, bool base,
+		   Error &error)
+{
+	return db_selection_print(client, selection, full, base,
+				  0, std::numeric_limits<int>::max(),
+				  error);
+}
+
 static bool
 PrintSongURIVisitor(Client &client, const LightSong &song)
 {

src/db/DatabasePrint.hxx

@@ -37,6 +37,12 @@ bool
 db_selection_print(Client &client, const DatabaseSelection &selection,
 		   bool full, bool base, Error &error);
 
+bool
+db_selection_print(Client &client, const DatabaseSelection &selection,
+		   bool full, bool base,
+		   unsigned window_start, unsigned window_end,
+		   Error &error);
+
 bool
 PrintUniqueTags(Client &client, unsigned type, uint32_t group_mask,
 		const SongFilter *filter,