queue/Print: implement sorting

src/command/QueueCommands.cxx

@@ -24,6 +24,7 @@
 #include "protocol/RangeArg.hxx"
 #include "db/DatabaseQueue.hxx"
 #include "db/Selection.hxx"
+#include "tag/ParseName.hxx"
 #include "song/Filter.hxx"
 #include "SongLoader.hxx"
 #include "song/DetachedSong.hxx"
@@ -286,6 +287,19 @@ handle_playlistid(Client &client, Request args, Response &r)
 	return CommandResult::OK;
 }
 
+static TagType
+ParseSortTag(const char *s)
+{
+	if (StringIsEqualIgnoreCase(s, "Last-Modified"))
+		return TagType(SORT_TAG_LAST_MODIFIED);
+
+	TagType tag = tag_name_parse_i(s);
+	if (tag == TAG_NUM_OF_ITEM_TYPES)
+		throw ProtocolError(ACK_ERROR_ARG, "Unknown sort tag");
+
+	return tag;
+}
+
 static CommandResult
 handle_playlist_match(Client &client, Request args, Response &r,
 		      bool fold_case)
@@ -298,6 +312,21 @@ handle_playlist_match(Client &client, Request args, Response &r,
 		args.pop_back();
 	}
 
+	TagType sort = TAG_NUM_OF_ITEM_TYPES;
+	bool descending = false;
+	if (args.size >= 2 && StringIsEqual(args[args.size - 2], "sort")) {
+		const char *s = args.back();
+		if (*s == '-') {
+			descending = true;
+			++s;
+		}
+
+		sort = ParseSortTag(s);
+
+		args.pop_back();
+		args.pop_back();
+	}
+
 	SongFilter filter;
 	try {
 		filter.Parse(args, fold_case);
@@ -311,6 +340,8 @@ handle_playlist_match(Client &client, Request args, Response &r,
 	QueueSelection selection;
 	selection.filter = &filter;
 	selection.window = window;
+	selection.sort = sort;
+	selection.descending = descending;
 
 	playlist_print_find(r, client.GetPlaylist(), selection);
 	return CommandResult::OK;

src/queue/Print.cxx

@@ -24,11 +24,14 @@
 #include "SongPrint.hxx"
 #include "song/DetachedSong.hxx"
 #include "song/LightSong.hxx"
+#include "tag/Sort.hxx"
 #include "client/Response.hxx"
 #include "PlaylistError.hxx"
 
 #include <fmt/format.h>
 
+#include <algorithm>
+
 /**
  * Send detailed information about a range of songs in the queue to a
  * client.
@@ -101,10 +104,70 @@ queue_print_changes_position(Response &r, const Queue &queue,
 			      i, queue.PositionToId(i));
 }
 
+[[gnu::pure]]
+static std::vector<unsigned>
+CollectQueue(const Queue &queue, const QueueSelection &selection) noexcept
+{
+	std::vector<unsigned> v;
+
+	for (unsigned i = 0; i < queue.GetLength(); i++)
+		if (selection.MatchPosition(queue, i))
+			v.emplace_back(i);
+
+	return v;
+}
+
+static void
+PrintSortedQueue(Response &r, const Queue &queue,
+		 const QueueSelection &selection)
+{
+	/* collect all matching songs */
+	auto v = CollectQueue(queue, selection);
+
+	auto window = selection.window;
+	if (!window.CheckClip(v.size()))
+		throw PlaylistError::BadRange();
+
+	/* sort them */
+	const auto sort = selection.sort;
+	const auto descending = selection.descending;
+
+	if (sort == TagType(SORT_TAG_LAST_MODIFIED))
+		std::stable_sort(v.begin(), v.end(),
+				 [&queue, descending](unsigned a_pos, unsigned b_pos){
+					 if (descending)
+						 std::swap(a_pos, b_pos);
+
+					 const auto &a = queue.Get(a_pos);
+					 const auto &b = queue.Get(b_pos);
+
+					 return a.GetLastModified() < b.GetLastModified();
+				 });
+	else
+		std::stable_sort(v.begin(), v.end(),
+				 [&queue, sort, descending](unsigned a_pos,
+							    unsigned b_pos){
+					 const auto &a = queue.Get(a_pos);
+					 const auto &b = queue.Get(b_pos);
+
+					 return CompareTags(sort, descending,
+							    a.GetTag(),
+							    b.GetTag());
+				 });
+
+	for (unsigned i = window.start; i < window.end; ++i)
+		queue_print_song_info(r, queue, v[i]);
+}
+
 void
 PrintQueue(Response &r, const Queue &queue,
 	   const QueueSelection &selection)
 {
+	if (selection.sort != TAG_NUM_OF_ITEM_TYPES) {
+		PrintSortedQueue(r, queue, selection);
+		return;
+	}
+
 	auto window = selection.window;
 
 	if (!window.CheckClip(queue.GetLength()))

src/queue/Selection.hxx

@@ -20,6 +20,7 @@
 #pragma once
 
 #include "protocol/RangeArg.hxx"
+#include "tag/Type.h"
 
 struct Queue;
 class SongFilter;
@@ -36,6 +37,18 @@ struct QueueSelection {
 
 	RangeArg window = RangeArg::All();
 
+	/**
+	 * Sort the result by the given tag.  #TAG_NUM_OF_ITEM_TYPES
+	 * means don't sort.  #SORT_TAG_LAST_MODIFIED sorts by
+	 * "Last-Modified" (not technically a tag).
+	 */
+	TagType sort = TAG_NUM_OF_ITEM_TYPES;
+
+	/**
+	 * If #sort is set, this flag can reverse the sort order.
+	 */
+	bool descending = false;
+
 	[[gnu::pure]]
 	bool MatchPosition(const Queue &queue,
 			   unsigned position) const noexcept;