feat: add threshold persistence after hibernation

Creates an additional systemd service that enables the charging
threshold to persist after the system goes into hibernation.

Also addresses parts of the following issues by adding checks for the
required systemd version,
    - #3
    - #5

README.md

@@ -12,12 +12,13 @@ DESCRIPTION
     -c, --capacity      print the current battery level
     -h, --help          print this help document
     -p, --persist       persist the current charging threshold setting between
-                        restarts (requires sudo permissions)
+                        restarts (requires superuser permissions)
     -r, --reset         prevents the charging threshold from persisting between
                         restarts
-    -s, --status        print the charging status
+    -s, --status        print charging status
     -t, --threshold     print the current charging threshold limit
                         specify a value between 1 and 100 to set a new threshold
+                        (the latter requires superuser permissions)
                         e.g. bat --threshold 80
 ```
 
@@ -31,7 +32,7 @@ This has only shown to work on ASUS laptops. For Dell systems, see [smbios-utils
 
 ## Installation
 
-Precompiled binaries (Linux x86-64) are available from the [GitHub releases page](https://github.com/leveson/bat/releases), the latest of which can be downloaded from [here](https://github.com/leveson/bat/releases/download/0.4.1/bat).
+Precompiled binaries (Linux x86-64) are available from the [GitHub releases page](https://github.com/leveson/bat/releases), the latest of which can be downloaded from [here](https://github.com/leveson/bat/releases/download/0.5/bat).
 
 After downloading the binary, give it permission to execute on your system by running the following command. For example, assuming the binary is located in the user's Downloads folder:
 
@@ -57,7 +58,7 @@ $ bat --threshold
 
 # Set a new charging threshold, say 80%.
 # (requires superuser permissions).
-$ bat --threshold 80
+$ sudo bat --threshold 80
 
 # Persist the current charging threshold setting between restarts
 # (requires superuser permissions).
@@ -68,4 +69,4 @@ $ sudo bat --persist
 
 Linux kernel version later than 5.4 which is the [earliest version to expose the battery charging threshold variable](https://github.com/torvalds/linux/commit/7973353e92ee1e7ca3b2eb361a4b7cb66c92abee).
 
-To persist threshold settings between restarts, the application relies on [Bash](https://www.gnu.org/software/bash/) and [systemd](https://systemd.io/) which are bundled with most Linux distributions.
+To persist the threshold setting between restarts, the application relies on [systemd](https://systemd.io/), particularly a version later than 244, and [Bash](https://www.gnu.org/software/bash/) which are bundled with most Linux distributions. 

bat.go

@@ -26,12 +26,13 @@ DESCRIPTION
     -c, --capacity      print the current battery level
     -h, --help          print this help document
     -p, --persist       persist the current charging threshold setting between
-                        restarts (requires sudo permissions)
+                        restarts (requires superuser permissions)
     -r, --reset         prevents the charging threshold from persisting between
                         restarts
     -s, --status        print charging status
     -t, --threshold     print the current charging threshold limit
                         specify a value between 1 and 100 to set a new threshold
+                        (the latter requires superuser permissions)
                         e.g. bat --threshold 80
 
 REFERENCE
@@ -48,7 +49,7 @@ func hasRequiredKernelVer() bool {
     if err != nil {
         log.Fatal(err)
     }
-    re := regexp.MustCompile(`[0-9]+\.[0-9]+`)
+    re := regexp.MustCompile(`\d+\.\d+`)
     ver := string(re.Find(out))
     maj, _ := strconv.Atoi(strings.Split(ver, ".")[0])
     min, _ := strconv.Atoi(strings.Split(ver, ".")[1])
@@ -67,6 +68,22 @@ func hasRequiredKernelVer() bool {
     return false
 }
 
+// hasRequiredSystemdVer returns true if the systemd version of the
+// system in question is later than 244 and returns false otherwise.
+func hasRequiredSystemdVer() bool {
+    cmd := exec.Command("systemctl", "--version")
+    out, err := cmd.Output()
+    if err != nil {
+        log.Fatal(err)
+    }
+    re := regexp.MustCompile(`\d+`)
+    ver, _ := strconv.Atoi(string(re.Find(out)))
+    if ver < 244 {
+        return false
+    }
+    return true
+}
+
 // page invokes the less pager on a specified string.
 func page(out string) {
     cmd := exec.Command("less")
@@ -79,12 +96,19 @@ func page(out string) {
 }
 
 // persist persists the prevailing battery charging threshold level
-// between restarts by creating or updating a systemd service with the
-// name `bat.service`.
+// between restarts and hibernation by creating or updating the systemd
+// services `bat-boot.service` and `bat-sleep.service`.
 func persist() {
-    service := fmt.Sprintf(
+    if !hasRequiredSystemdVer() {
+        fmt.Println("Requires systemd version 244 or later.")
+        os.Exit(1)
+    }
+
+    // Write systemd service that will persist the threshold after
+    // restarts.
+    bootUnit := fmt.Sprintf(
         `[Unit]
-Description=Set the battery charging threshold
+Description=Persist the battery charging threshold between restarts
 After=multi-user.target
 StartLimitBurst=0
 
@@ -97,27 +121,62 @@ ExecStart=/bin/bash -c 'echo %s > /sys/class/power_supply/BAT?/charge_control_en
 WantedBy=multi-user.target
         `,
         scat("/sys/class/power_supply/BAT?/charge_control_end_threshold"))
-    f, err := os.Create("/etc/systemd/system/bat.service")
+    bootService, err := os.Create("/etc/systemd/system/bat-boot.service")
     if err != nil {
         if strings.HasSuffix(err.Error(), ": permission denied") {
             fmt.Println("This command requires sudo permissions.")
             os.Exit(1)
         }
         log.Fatal(err)
     }
-    defer f.Close()
-    f.WriteString(service)
-    cmd := exec.Command("systemctl", "enable", "bat.service")
+    defer bootService.Close()
+    bootService.WriteString(bootUnit)
+
+    // Enable the service.
+    cmd := exec.Command("systemctl", "enable", "bat-boot.service")
+    err = cmd.Run()
+    if err != nil {
+        log.Fatal(err)
+    }
+
+    // Write systemd service that will persist the threshold after
+    // hibernation.
+    sleepUnit := fmt.Sprintf(
+        `[Unit]
+Description=Persist the battery charging threshold after hibernation 
+Before=sleep.target
+StartLimitBurst=0
+
+[Service]
+Type=oneshot
+Restart=on-failure
+ExecStart=/bin/bash -c 'echo %s > /sys/class/power_supply/BAT?/charge_control_end_threshold'
+
+[Install]
+WantedBy=sleep.target
+        `,
+        scat("/sys/class/power_supply/BAT?/charge_control_end_threshold"))
+    sleepService, err := os.Create("/etc/systemd/system/bat-sleep.service")
+    if err != nil {
+        log.Fatal(err)
+    }
+    defer sleepService.Close()
+    sleepService.WriteString(sleepUnit)
+
+    // Enable the service.
+    cmd = exec.Command("systemctl", "enable", "bat-sleep.service")
     err = cmd.Run()
     if err != nil {
         log.Fatal(err)
     }
 }
 
 // reset disables the systemd service that persists the charging
-// threshold between restarts.
+// threshold between restarts and hibernation.
 func reset() {
-    err := os.Remove("/etc/systemd/system/bat.service")
+    // Delete service that persists the charging threshold between
+    // restarts.
+    err := os.Remove("/etc/systemd/system/bat-boot.service")
     if err != nil {
         switch {
         case strings.HasSuffix(err.Error(), ": permission denied"):
@@ -129,15 +188,31 @@ func reset() {
             log.Fatal(err)
         }
     }
-    cmd := exec.Command("systemctl", "disable", "bat.service")
+    cmd := exec.Command("systemctl", "disable", "bat-boot.service")
     var stdErr bytes.Buffer
     cmd.Stderr = &stdErr
     err = cmd.Run()
     if err != nil {
-        switch msg := strings.TrimSpace(stdErr.String()); {
-        case strings.HasSuffix(msg, ": Unit file bat.service does not exist."):
-            break
-        default:
+        msg := strings.TrimSpace(stdErr.String())
+        if !strings.HasSuffix(msg, " file bat-boot.service does not exist.") {
+            log.Fatal(err)
+        }
+    }
+
+    // Delete the service that persists the charging threshold after
+    // hibernation.
+    err = os.Remove("/etc/systemd/system/bat-sleep.service")
+    if err != nil {
+        if !strings.HasSuffix(err.Error(), ": no such file or directory") {
+            log.Fatal(err)
+        }
+    }
+    cmd = exec.Command("systemctl", "disable", "bat-sleep.service")
+    cmd.Stderr = &stdErr
+    err = cmd.Run()
+    if err != nil {
+        msg := strings.TrimSpace(stdErr.String())
+        if !strings.HasSuffix(msg, " file bat-sleep.service does not exist.") {
             log.Fatal(err)
         }
     }