From a3569eabfc4e72c136c01c176dee70a3bc16638c Mon Sep 17 00:00:00 2001
From: Spencer Williams <spnw@plexwave.org>
Date: Wed, 30 Jul 2025 13:08:29 -0400
Subject: Add Lua filter support

---
 Makefile  |  2 +-
 README.md | 30 ++++++++++++++++++++++++++++++
 mpc-bar.m | 41 ++++++++++++++++++++++++++++++++++++++---
 3 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 1440a9b..2c35264 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 TARGET = mpc-bar
 CFLAGS = -O2 -fobjc-arc -Wall
-LDFLAGS = -lmpdclient -framework Cocoa
+LDFLAGS = -lmpdclient -llua -framework Cocoa
 OUTPUT_OPTION=-MMD -MP -o $@
 BINDIR = /usr/local/bin
 
diff --git a/README.md b/README.md
index d643c90..ee3ae01 100644
--- a/README.md
+++ b/README.md
@@ -29,4 +29,34 @@ format = [%name%: &[[%artist%|%performer%|%composer%|%albumartist%] - ]%title%]|
 idle_message = No song playing
 show_queue = true                       # Show queue/position info while playing? (true/false)
 show_queue_idle = (value of show_queue) # Show queue/position info while idle? (true/false)
+# lua_filter = ~/.mpc-bar-filter.lua    # Path to a Lua filter script
 ```
+
+## Lua filter
+Sometimes, especially with Internet radio, your MPD status can end up
+a lot longer than it needs to be.  MPC Bar lets you write a filter
+script in Lua to massage the status into a more manageable form.
+Here's an example:
+
+```lua
+local subs =
+  {
+    {"^Groove Salad: a nicely chilled plate of ambient beats and grooves.", "[Groove Salad]"},
+    {"^Drone Zone: Atmospheric ambient space music. Serve Best Chilled. Safe with most medications.", "[Drone Zone]"},
+    {" %[SomaFM%]:", ""},
+  }
+
+function filter(s)
+  for _, sub in ipairs(subs) do
+    s = s:gsub(sub[1], sub[2])
+  end
+  return s
+end
+```
+
+MPC Bar expects a global function called `filter`, which takes the
+original MPD status and returns a new status to be used instead.
+
+Currently there is no provision for error reporting.  If your code has
+an error, MPC Bar will just use the original status.  You might want
+to test on your own with the standalone `lua` interpreter.
diff --git a/mpc-bar.m b/mpc-bar.m
index 91597ab..1a06a6d 100644
--- a/mpc-bar.m
+++ b/mpc-bar.m
@@ -20,6 +20,9 @@
 #include "mpc/song_format.h"
 
 #include <assert.h>
+#include <lua/lauxlib.h>
+#include <lua/lua.h>
+#include <lua/lualib.h>
 #include <mpd/client.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -27,7 +30,7 @@
 
 #import <Cocoa/Cocoa.h>
 
-#define VERSION "0.4"
+#define VERSION "0.5.0"
 #define TITLE_MAX_LENGTH 96
 #define SLEEP_INTERVAL 0.2
 
@@ -46,7 +49,7 @@ static NSString *formatTime(unsigned int t) {
 }
 
 struct config {
-  const char *host, *password, *format, *idle_message;
+  const char *host, *password, *format, *idle_message, *lua_filter;
   int show_queue, show_queue_idle;
   unsigned port;
 };
@@ -69,6 +72,8 @@ static int handler(void *userdata, const char *section, const char *name,
     c->show_queue = (strcmp(value, "false") != 0);
   } else if (MATCH("display", "show_queue_idle")) {
     c->show_queue_idle = (strcmp(value, "false") != 0);
+  } else if (MATCH("display", "lua_filter")) {
+    c->lua_filter = strdup(value);
   } else {
     return 0;
   }
@@ -95,6 +100,9 @@ static int handler(void *userdata, const char *section, const char *name,
 
   NSMenu *songMenu;
   NSMapTable *songMap;
+
+  lua_State *L;
+  const char *luaFilterPath;
 }
 - (void)initConfig {
   config.host = "localhost";
@@ -121,6 +129,28 @@ static int handler(void *userdata, const char *section, const char *name,
     config.show_queue_idle = config.show_queue;
   }
 }
+- (void)initLua {
+  if (config.lua_filter) {
+    L = luaL_newstate();
+    luaL_openlibs(L);
+    luaFilterPath = [[utf8String(config.lua_filter) stringByStandardizingPath]
+        cStringUsingEncoding:NSUTF8StringEncoding];
+  }
+}
+- (const char *)runLuaFilterOn:(const char *)s {
+  if (luaL_dofile(L, luaFilterPath) != LUA_OK) {
+    return s;
+  }
+  lua_getglobal(L, "filter");
+  if (!lua_isfunction(L, -1)) {
+    return s;
+  }
+  lua_pushstring(L, s);
+  if (lua_pcall(L, 1, 1, 0) != LUA_OK) {
+    return s;
+  }
+  return lua_tostring(L, -1);
+}
 - (void)connect {
   assert(connection == NULL);
 
@@ -237,7 +267,11 @@ static int handler(void *userdata, const char *section, const char *name,
       [menuButton setImage:nil];
 
     char *s = format_song(song, config.format);
-    [output appendString:utf8String(s)];
+    if (L) {
+      [output appendString:utf8String([self runLuaFilterOn:s])];
+    } else {
+      [output appendString:utf8String(s)];
+    }
     free(s);
   } else {
     // FIXME: There's no point calling utf8String more than once, as
@@ -442,6 +476,7 @@ cleanup:
   if (self = [super init]) {
     [self initConfig];
     [self readConfigFile];
+    [self initLua];
     [self connect];
     [self initSongMenu];
     [self initControlMenu];
-- 
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