Fixed|Doom: Updated IDMUS cheat handling re custom episodes

The IDMUS cheat now respects custom episodes while also attempting
to interpret the given arguments in a vanilla compatible manner.
Obviously this is somewhat limited by the inflexible mechanics of
the cheat mechanism and the fixed/predefined semantics.

These changes mean that it is no longer possible to play music that
is not associated with a map using the IDMUS cheat. (However, these
can still be played using the "playmusic" command, which is a far
more flexible method in any case).

IssueID #1914

doomsday/plugins/common/include/g_defs.h

@@ -30,6 +30,18 @@
  */
 ded_t &Defs();
 
+/**
+ * Returns the total number of 'playable' episodes. A playable episode is one whos
+ * starting map is defined, and for which map data exists.
+ */
+int PlayableEpisodeCount();
+
+/**
+ * Returns the unique identifier of the first playable episode. If no playable episodes
+ * are defined a zero-length string is returned.
+ */
+de::String FirstPlayableEpisodeId();
+
 /**
  * Translates a map warp number for the @em current episode to a unique map identifier.
  *
@@ -44,7 +56,7 @@ ded_t &Defs();
  * @return The unique identifier of the map. If no game session is in progress or the
  * warp number is not found, the URI "Maps:" is returned.
  */
-de::Uri TranslateMapWarpNumber(de::String const &episodeId, uint warpNumber);
+de::Uri TranslateMapWarpNumber(de::String const &episodeId, int warpNumber);
 
 extern "C" {
 #endif

doomsday/plugins/common/src/g_defs.cpp

@@ -58,7 +58,38 @@ void GetDefState(char const *def, int *val)
     if(*val < 0) *val = 0;
 }
 
-de::Uri TranslateMapWarpNumber(String const &episodeId, uint warpNumber)
+int PlayableEpisodeCount()
+{
+    int count = 0;
+    DictionaryValue::Elements const &episodesById = Defs().episodes.lookup("id").elements();
+    for(auto const &pair : episodesById)
+    {
+        Record const &episodeDef = *pair.second->as<RecordValue>().record();
+        de::Uri startMap(episodeDef.gets("startMap"), RC_NULL);
+        if(P_MapExists(startMap.compose().toUtf8().constData()))
+        {
+            count += 1;
+        }
+    }
+    return count;
+}
+
+String FirstPlayableEpisodeId()
+{
+    DictionaryValue::Elements const &episodesById = Defs().episodes.lookup("id").elements();
+    for(auto const &pair : episodesById)
+    {
+        Record const &episodeDef = *pair.second->as<RecordValue>().record();
+        de::Uri startMap(episodeDef.gets("startMap"), RC_NULL);
+        if(P_MapExists(startMap.compose().toUtf8().constData()))
+        {
+            return episodeDef.gets("id");
+        }
+    }
+    return ""; // Not found.
+}
+
+de::Uri TranslateMapWarpNumber(String const &episodeId, int warpNumber)
 {
     if(Record const *rec = Defs().episodes.tryFind("id", episodeId))
     {

doomsday/plugins/doom/src/m_cheat.cpp

@@ -30,6 +30,7 @@
 #include "d_net.h"
 #include "dmu_lib.h"
 #include "g_eventsequence.h"
+#include "g_defs.h"
 #include "gamesession.h"
 #include "hu_msg.h"
 #include "p_user.h"
@@ -54,16 +55,35 @@ CHEAT_FUNC(Music)
 
     player_t *plr = &players[player];
 
-    int musnum;
-    if(gameModeBits & GM_ANY_DOOM2)
-        musnum = (args[0] - '0') * 10 + (args[1] - '0');
+    int const numEpisodes = PlayableEpisodeCount();
+    if(!numEpisodes) return false;
+
+    // The number of episodes determines how to interpret the arguments.
+    /// @note Logic here aims to be somewhat vanilla compatible, yet offer
+    /// a limited degree of support for custom episodes. The "playmusic"
+    /// cmd is a far more flexible method of changing music.
+    String episodeId;
+    int warpNumber;
+    if(numEpisodes > 1)
+    {
+        episodeId  = String::number(args[0]);
+        warpNumber = args[1];
+    }
     else
-        musnum = (args[0] - '1') * 9  + (args[1] - '0');
+    {
+        episodeId  = FirstPlayableEpisodeId();
+        warpNumber = (args[0] - '0') * 10 + (args[1] - '0');
+    }
 
-    if(S_StartMusicNum(musnum, true))
+    // Lookup and try to enqueue the Music for the referenced episode and map.
+    de::Uri const mapUri = TranslateMapWarpNumber(episodeId, warpNumber);
+    if(Record const *mapInfo = Defs().mapInfos.tryFind("id", mapUri.compose()))
     {
-        P_SetMessage(plr, LMF_NO_HIDE, STSTR_MUS);
-        return true;
+        if(S_StartMusic(mapInfo->gets("music").toUtf8().constData(), true /*loop it*/))
+        {
+            P_SetMessage(plr, LMF_NO_HIDE, STSTR_MUS);
+            return true;
+        }
     }
 
     P_SetMessage(plr, LMF_NO_HIDE, STSTR_NOMUS);