refactor: minor restructure and basic housekeeping

  - Document main package.
  - Update Go version to 1.18.
  - Unify cli and docs packages.
  - Rename persist package to services to allow for more idiomatic
    names.
  - Simplify error handling.
  - Separate the task of fetching the kernel version and asserting that
    it is compatible with the application.
  - Simplify logic that checks whether the kernel version is compatible
    with the application.
  - Replace `fmt.Sprint` calls with the more performant
    `strconv.FormatInt(int64(t, 10))` for writing to the threshold
    variable.
  - Create a new test suite for the threshold package including fuzz
    tests.
  - Update documentation year.
  - Fix grammar errors in the README.
  - Delete the superficial `main_test.go`.

.gitignore

@@ -2,6 +2,9 @@ bat
 !bat/
 *.zip
 
+# Development
+.vscode
+
 # Binaries for programs and plugins
 *.exe
 *.exe~

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2021 Tshaka Eric Lekholoane
+Copyright (c) 2022 Tshaka Eric Lekholoane
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -31,17 +31,17 @@ DESCRIPTION
 
 ## About
 
-The goal is to replicate the functionality of the [ASUS Battery Health Charging](https://www.asus.com/us/support/FAQ/1032726/) utility for ASUS laptops on Windows which aims prolong the battery's life-span <a href="https://electrek.co/2017/09/01/tesla-battery-expert-recommends-daily-battery-pack-charging/"><sup>1</sup></a> <a href="https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries"><sup>2</sup></a>.
+The goal is to replicate the functionality of the [ASUS Battery Health Charging](https://www.asus.com/us/support/FAQ/1032726/) utility for ASUS laptops on Windows which aims to prolong the battery's life-span <a href="https://electrek.co/2017/09/01/tesla-battery-expert-recommends-daily-battery-pack-charging/"><sup>1</sup></a> <a href="https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries"><sup>2</sup></a>.
 
 ## Disclaimer
 
-This has been reported to work with some ASUS and [Lenovo ThinkPad](https://github.com/tshakalekholoane/bat/discussions/23) laptops only. For Dell systems, see [smbios-utils](https://github.com/dell/libsmbios), particularly the `smbios-battery-ctl` command, or install it using your package manager. For other manufacturers there is also [TLP](https://linrunner.de/tlp/).
+This has been reported to only work with some ASUS and [Lenovo ThinkPad](https://github.com/tshakalekholoane/bat/discussions/23) laptops only. For Dell systems, see [smbios-utils](https://github.com/dell/libsmbios), particularly the `smbios-battery-ctl` command, or install it using your package manager. For other manufacturers there is also [TLP](https://linrunner.de/tlp/).
 
 There have also been some [problems setting the charging threshold inside of a virtual machine](https://github.com/tshakalekholoane/bat/issues/3#issuecomment-858581495).
 
 ## Installation
 
-Precompiled binaries (Linux x86-64) are available from the [GitHub releases page](https://github.com/tshakalekholoane/bat/releases), the latest of which can be downloaded from [here](https://github.com/tshakalekholoane/bat/releases/download/0.8.4/bat).
+Precompiled binaries (Linux x86-64) are available from the [GitHub releases page](https://github.com/tshakalekholoane/bat/releases), the latest of which can be downloaded from [here](https://github.com/tshakalekholoane/bat/releases/download/0.9/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:
 
@@ -65,17 +65,17 @@ $ go build ./cmd/bat/
 # Print the current battery charging threshold.
 $ bat --threshold
 
-# Set a new charging threshold, say 80%.
-# (requires superuser permissions).
+# Set a new charging threshold, say 80% (requires superuser 
+# permissions).
 $ sudo bat --threshold 80
 
-# Persist the current charging threshold setting between restarts
+# Persist the current charging threshold setting between restarts 
 # (requires superuser permissions).
 $ sudo bat --persist
 ```
 
 ## Requirements
 
-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).
+Linux kernel version later than 5.4-rc1 which is the [earliest version to expose the battery charging threshold variable](https://github.com/torvalds/linux/commit/7973353e92ee1e7ca3b2eb361a4b7cb66c92abee).
 
 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. 

cmd/bat/main.go

@@ -1,3 +1,4 @@
+// Binary bat is a battery management utility for Linux laptops.
 package main
 
 import "tshaka.co/bat/internal/cli"

go.mod

@@ -1,3 +1,3 @@
 module tshaka.co/bat
 
-go 1.17
+go 1.18

internal/cli/cli.go

@@ -2,55 +2,82 @@
 package cli
 
 import (
+	_ "embed"
 	"errors"
 	"fmt"
 	"io"
 	"log"
 	"os"
+	"os/exec"
 	"strconv"
 	"strings"
 	"syscall"
 
-	"tshaka.co/bat/internal/docs"
 	"tshaka.co/bat/internal/file"
-	"tshaka.co/bat/internal/persist"
+	"tshaka.co/bat/internal/services"
 	"tshaka.co/bat/internal/threshold"
 )
 
-// common error messages
+// Common error messages.
 const (
 	incompat = "This program is most likely not compatible with your system. " +
 		"See\nhttps://github.com/tshakalekholoane/bat#disclaimer for details."
 	permissionDenied = "Permission denied. Try running this command using sudo."
 )
 
+// Documentation.
+var (
+	//go:embed help.txt
+	help string
+	//go:embed version.txt
+	version string
+)
+
 // errPermissionDenied indicates that the user has insufficient
 // permissions to perform an action.
 var errPermissionDenied = syscall.EACCES
 
-// context is a helper function that returns an io.Writer and a status
-// code the program should exit with after performing an action.
-func context(fatal bool) (io.Writer, int) {
-	var out io.Writer = os.Stdout
-	var code int
+// context is a helper function that returns an io.Writer and exit code,
+// os.Stderr and 1 if fatal is true and os.Stdout and 0 otherwise.
+func context(fatal bool) (out io.Writer, code int) {
 	if fatal {
 		out = os.Stderr
 		code = 1
+	} else {
+		out = os.Stdout
+	}
+	return
+}
+
+// page filters the string doc through the less pager.
+func page(doc string) {
+	cmd := exec.Command(
+		"less",
+		"--no-init",
+		"--quit-if-one-screen",
+		"--IGNORE-CASE",
+		"--RAW-CONTROL-CHARS",
+	)
+	cmd.Stdin = strings.NewReader(doc)
+	cmd.Stdout = os.Stdout
+	if err := cmd.Run(); err != nil {
+		log.Fatalln(err)
 	}
-	return out, code
+	os.Exit(0)
 }
 
-// reportf formats according to a format specifier and writes to either
-// standard error or standard output depending on the context.
-func reportf(fatal bool, format string, a ...interface{}) {
+// reportf formats a according to a format specifier and prints it to
+// standard error if fatal is true or to standard output otherwise.
+func reportf(fatal bool, format string, a ...any) {
 	out, code := context(fatal)
 	fmt.Fprintf(out, format, a...)
 	os.Exit(code)
 }
 
-// reportln formats using the default formats for its operands, appends
-// a new line and, writes to standard output.
-func reportln(fatal bool, a ...interface{}) {
+// reportln formats a using the default formats for its operands,
+// appends a new line and, writes to standard error if fatal is true or
+// standard output otherwise.
+func reportln(fatal bool, a ...any) {
 	reportf(fatal, "%v\n", a...)
 }
 
@@ -69,25 +96,20 @@ func show(v string) {
 // Run executes the application.
 func Run() {
 	if len(os.Args) == 1 {
-		docs.Usage()
-		os.Exit(0)
+		page(help)
 	}
+
 	switch os.Args[1] {
 	case "-c", "--capacity":
 		show("capacity")
 	case "-h", "--help":
-		err := docs.Usage()
-		if err != nil {
-			log.Fatalln(err)
-		}
-		os.Exit(0)
+		page(help)
 	case "-p", "--persist":
-		err := persist.WriteServices()
-		if err != nil {
+		if err := services.Write(); err != nil {
 			switch {
-			case errors.Is(err, persist.ErrBashNotFound):
-				reportln(true, "Cannot find Bash on your system.")
-			case errors.Is(err, persist.ErrIncompatSystemd):
+			case errors.Is(err, services.ErrBashNotFound):
+				reportln(true, "Could not find Bash on your system.")
+			case errors.Is(err, services.ErrIncompatSystemd):
 				reportln(true, "Requires systemd version 244-rc1 or later.")
 			case errors.Is(err, file.ErrNotFound):
 				reportln(true, incompat)
@@ -99,8 +121,7 @@ func Run() {
 		}
 		reportln(false, "Persistence of the current charging threshold enabled.")
 	case "-r", "--reset":
-		err := persist.DeleteServices()
-		if err != nil {
+		if err := services.Delete(); err != nil {
 			if errors.Is(err, errPermissionDenied) {
 				reportln(true, permissionDenied)
 			}
@@ -121,11 +142,10 @@ func Run() {
 				}
 				log.Fatal(err)
 			}
-			if t < 1 || t > 100 {
+			if !threshold.IsValid(t) {
 				reportln(true, "Number should be between 1 and 100.")
 			}
-			err = threshold.Set(t)
-			if err != nil {
+			if err := threshold.Set(t); err != nil {
 				switch {
 				case errors.Is(err, threshold.ErrIncompatKernel):
 					reportln(true, "Requires Linux kernel version 5.4 or later.")
@@ -145,11 +165,7 @@ func Run() {
 			show("charge_control_end_threshold")
 		}
 	case "-v", "--version":
-		err := docs.Version()
-		if err != nil {
-			log.Fatal(err)
-		}
-		os.Exit(0)
+		page(version)
 	default:
 		reportf(
 			true,

internal/docs/help.txt → internal/cli/help.txt

@@ -47,4 +47,4 @@ SUPPORT
 REFERENCE
     https://wiki.archlinux.org/title/Laptop/ASUS#Battery_charge_threshold
 
-                                13 DECEMBER 2021
+                                  28 MAY 2022

internal/cli/version.txt

@@ -0,0 +1,3 @@
+bat 0.9
+Copyright (c) 2022 Tshaka Eric Lekholoane.
+MIT Licence.

internal/file/file.go

@@ -1,4 +1,4 @@
-// Package file implements a helper function that returns the value of a
+// Package file contains helpers related to reading the contents of a
 // /sys/class/power_supply/BAT?/ variable.
 package file
 
@@ -11,19 +11,18 @@ import (
 var ErrNotFound = errors.New("file: virtual file not found")
 
 // Contents returns the contents of a virtual file in
-// /sys/class/power_supply/BAT?/ as a sequence of bytes.
-func Contents(v string) ([]byte, error) {
-	v = "/sys/class/power_supply/BAT?/" + v
-	matches, err := filepath.Glob(v)
+// /sys/class/power_supply/BAT?/ as a slice of bytes.
+func Contents(f string) ([]byte, error) {
+	matches, err := filepath.Glob("/sys/class/power_supply/BAT?/" + f)
 	if err != nil {
 		return nil, err
 	}
 	if len(matches) == 0 {
 		return nil, ErrNotFound
 	}
-	f, err := os.ReadFile(matches[0])
+	val, err := os.ReadFile(matches[0])
 	if err != nil {
 		return nil, err
 	}
-	return f, nil
+	return val, nil
 }