From 6316c8cb7b2b92098907943223ffe1a748359146 Mon Sep 17 00:00:00 2001
From: Madison Lynch <madi@mxdi.xyz>
Date: Fri, 2 Jan 2026 04:33:17 -0800
Subject: [PATCH] Code refactor + Improved memory safety

---
 Makefile                 |   1 +
 components/dyn_battery.c | 124 +++++++++++++++++++++++++++++++++++++++
 config.def.h             |   1 +
 slstatus.h               |   3 +
 4 files changed, 129 insertions(+)
 create mode 100644 components/dyn_battery.c

diff --git a/Makefile b/Makefile
index 7a18274..d1b24dd 100644
--- a/Makefile
+++ b/Makefile
@@ -11,6 +11,7 @@ COM =\
 	components/cpu\
 	components/datetime\
 	components/disk\
+	components/dyn_battery\
 	components/entropy\
 	components/hostname\
 	components/ip\
diff --git a/components/dyn_battery.c b/components/dyn_battery.c
new file mode 100644
index 0000000..cc87fc1
--- /dev/null
+++ b/components/dyn_battery.c
@@ -0,0 +1,124 @@
+/* Written by Lukas Lynch <madi@mxdi.xyz> */
+/* Only Linux is supported */
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <dirent.h>
+
+#include "../util.h"
+#include "../slstatus.h"
+
+#define BAT_PREFIX "BAT"
+#define BAT_DIR "/sys/class/power_supply"
+
+static bool err;
+static const char *err_str = "err";
+
+/**
+* Calculates the number of digits in a given positive integer.
+*/
+static size_t
+count_digits(const unsigned int input) {
+    size_t count = 0;
+    unsigned int n = input;
+
+    while(n/10 != 0)
+        count++;
+
+    return count+1;
+}
+
+/**
+* Counts number of batteries detected by system.
+*
+* @return Unsigned integer denoting the number of detected batteries
+* @author Lukas Lynch
+*/
+static unsigned int
+count_batteries(void) {
+    const size_t bat_prefix_s = strlen(BAT_PREFIX);
+    DIR *dir = opendir(BAT_DIR);
+    if(!dir) {
+        fprintf(stderr, "dyn_battery: Failed to open %s\n", BAT_DIR);
+        err = true;
+        return 0;
+    }
+
+    unsigned int batc = 0;
+    struct dirent *entry;
+    while((entry = readdir(dir)))
+        if(
+            strlen(entry->d_name) > bat_prefix_s &&
+            strncmp(entry->d_name, BAT_PREFIX, bat_prefix_s) == 0
+        ) batc++;
+
+    (void) closedir(dir);
+    return batc;
+}
+
+/**
+* Displays the status and capacity of a dynamic amount of batteries (i.e.
+* laptops may have secondary external batteries).
+*
+* @param  fmt format string to use for each battery display. ordered key:
+*             %u: battery number || %s: battery state || %s battery capacity
+* @return string containing the status and capacities of all detected batteries
+* @author Lukas Lynch
+*/
+const char *
+dyn_battery(const char *fmt) {
+    err = false;
+    const size_t fmt_s = strlen(fmt);
+    const unsigned int batc = count_batteries();
+
+    if(err) // err set by count_batteries()
+        return err_str;
+
+    if(batc == 0) 
+        return NULL;
+
+    // We need the amount of digits in bat_c for displaying it in strings
+    const size_t batc_digits = count_digits(batc);
+
+    char buf[
+          (batc * (fmt_s - 2)) // bat count * (format string - "%u" format specifier)
+        + (batc * batc_digits) // bat count * digits in bat count
+        + 1                    // NULL byte
+    ];
+
+    // Fill buffer with 0s, otherwise displacement calculations below can fail
+    memset(buf, 0, sizeof(buf));
+
+    /*
+    * The displacement variable will be updated with the current string length,
+    * which is independent from the buffer size, in order to allow us to write
+    * to the buffer without overwriting.
+    */
+    unsigned int displacement = 0;
+    for(unsigned int i=0; i<batc; i++) {
+        // Length of BAT_PREFIX + number of digits in bat count + 1 (NULL byte)
+        char bat[strlen(BAT_PREFIX) + batc_digits + 1];
+        (void) sprintf(bat, "%s%u", BAT_PREFIX, i);
+
+        // Add battery info to output buffer
+        displacement += sprintf(
+            buf + displacement, // Write into buffer after previous writes
+            fmt,                // Format string specified by config.h
+            i,
+            battery_state(bat), // See components/battery.c
+            battery_perc(bat)   // See components/battery.c
+        );
+
+        // Add space between battery entries
+        buf[displacement++] = ' ';
+    }
+
+    // Remove extra space after last battery entry
+    buf[--displacement] = '\0';
+
+    return bprintf("%s", buf);
+}
+
+#undef BAT_DIR
+#undef BAT_PREFIX
\ No newline at end of file
diff --git a/config.def.h b/config.def.h
index 100093e..7f26909 100644
--- a/config.def.h
+++ b/config.def.h
@@ -26,6 +26,7 @@ static const char unknown_str[] = "n/a";
  * disk_perc           disk usage in percent           mountpoint path (/)
  * disk_total          total disk space in GB          mountpoint path (/)
  * disk_used           used disk space in GB           mountpoint path (/)
+ * dyn_battery         displays the name, state and    format string (%u, %s, %s)
  * entropy             available entropy               NULL
  * gid                 GID of current user             NULL
  * hostname            hostname                        NULL
diff --git a/slstatus.h b/slstatus.h
index 394281c..6beeaec 100644
--- a/slstatus.h
+++ b/slstatus.h
@@ -21,6 +21,9 @@ const char *disk_perc(const char *path);
 const char *disk_total(const char *path);
 const char *disk_used(const char *path);
 
+/* dyn_battery */
+const char *dyn_battery(const char *fmt);
+
 /* entropy */
 const char *entropy(const char *unused);
 
-- 
2.52.0