module/alsa: add ‘percent’ tag - volume level as a percentage

Fixes part of #10

CHANGELOG.md

@@ -6,6 +6,11 @@
 
 ## Unreleased
 ### Added
+
+* alsa: `percentage` tag. This is an integer tag that represents the
+  current volume as a percentage value.
+
+
 ### Deprecated
 ### Removed
 ### Fixed

doc/yambar-modules.5.scd

@@ -145,6 +145,9 @@ Monitors an alsa soundcard for volume and mute/unmute changes.
 |  volume
 :  range
 :  Volume level, with min and max as start and end range values
+|  percent
+:  range
+:  Volume level, as a percentage
 |  muted
 :  bool
 :  True if muted, otherwise false

modules/alsa.c

@@ -43,13 +43,18 @@ content(struct module *mod)
 {
     struct private *m = mod->private;
 
+    int percent = m->vol_max - m->vol_min > 0
+        ? 100 * m->vol_cur / (m->vol_max - m->vol_min)
+        : 0;
+
     mtx_lock(&mod->lock);
     struct tag_set tags = {
         .tags = (struct tag *[]){
             tag_new_int_range(mod, "volume", m->vol_cur, m->vol_min, m->vol_max),
+            tag_new_int_range(mod, "percent", percent, 0, 100),
             tag_new_bool(mod, "muted", m->muted),
         },
-        .count = 2,
+        .count = 3,
     };
     mtx_unlock(&mod->lock);