Initial commit

.gitignore

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+.idea/
+dist/
+vendor/
+*.sh
+brightness
+brightness.test

.gitlab-ci.yml

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+image: golang:latest
+
+stages:
+  - validate
+  - build
+
+fmt:
+  stage: validate
+  script:
+    - gofmt -l -s -e .
+    - exit $(gofmt -l -s -e . | wc -l)
+
+vet:
+  stage: validate
+  script:
+    - go vet -composites=false ./...
+
+test:
+  stage: validate
+  script:
+    - go test -race -v ./...

LICENSE

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+MIT License
+
+Copyright (c) 2020 Trevor Slocum <trevor@rocketnine.space>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# brightness
+[![CI status](https://gitlab.com/tslocum/brightness/badges/master/pipeline.svg)](https://gitlab.com/tslocum/brightness/commits/master)
+[![Donate](https://img.shields.io/liberapay/receives/rocketnine.space.svg?logo=liberapay)](https://liberapay.com/rocketnine.space)
+
+Backlight utility
+
+## Install
+
+```bash
+go get gitlab.com/tslocum/brightness
+```
+
+## Usage
+
+### Set
+
+```bash
+brightness 60
+brightness 80%
+```
+
+### Decrease
+
+```bash
+brightness -10
+brightness -20%
+```
+
+### Increase
+
+```bash
+brightness 10
+brightness +20%
+```
+
+## Support
+
+Please share issues and suggestions [here](https://gitlab.com/tslocum/brightness/issues).

go.mod

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+module gitlab.com/tslocum/brightness
+
+go 1.15

main.go

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+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strconv"
+)
+
+// TODO specify minimum brightness
+// TODO override max brightness
+// TODO TUI mode
+// TODO widget mode
+
+var (
+	acpiBacklight = regexp.MustCompile(`acpi_video[0-9]+$`)
+)
+
+const backlightsDirectory = "/sys/class/backlight"
+
+const (
+	commandSet = 1
+	commandSub = 2
+	commandAdd = 3
+)
+
+func init() {
+	log.SetFlags(0)
+	log.SetPrefix("")
+}
+
+type backlight struct {
+	identifier string
+	current    int
+	max        int
+
+	fallback bool
+}
+
+func (b *backlight) setBrightness(brightness int) error {
+	f, err := os.OpenFile(b.currentBrightnessPath(), os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	_, err = f.WriteString(fmt.Sprintf("%d\n", brightness))
+	return err
+}
+
+func (b *backlight) currentBrightnessPath() string {
+	return filepath.Join(backlightsDirectory, b.identifier, "brightness")
+}
+
+func (b *backlight) maxBrightnessPath() string {
+	return filepath.Join(backlightsDirectory, b.identifier, "max_brightness")
+}
+
+func identifyBacklights() ([]*backlight, error) {
+	var backlights []*backlight
+
+	// Locate backlight interfaces. Issues are commonly reported when the ACPI
+	// backlight interface is used instead of other interfaces present on the
+	// system. As a result, ACPI interfaces are only used when no other
+	// interfaces are available.
+	err := filepath.Walk(backlightsDirectory, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		} else if path == backlightsDirectory {
+			return nil
+		}
+
+		backlight := &backlight{
+			identifier: filepath.Base(path),
+			fallback:   acpiBacklight.MatchString(path),
+		}
+		backlights = append(backlights, backlight)
+		return nil
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to list backlight interfaces: %s", err)
+	}
+
+	// Fetch current and max brightness
+	for _, backlight := range backlights {
+		v, err := ioutil.ReadFile(backlight.currentBrightnessPath())
+		if err != nil {
+			return nil, fmt.Errorf("failed to read current brightness of %s: %s", backlight.identifier, err)
+		}
+		backlight.current, err = strconv.Atoi(string(bytes.TrimSpace(v)))
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse current brightness of %s: %s", backlight.identifier, err)
+		}
+
+		v, err = ioutil.ReadFile(backlight.maxBrightnessPath())
+		if err != nil {
+			return nil, fmt.Errorf("failed to read maximum brightness of %s: %s", backlight.identifier, err)
+		}
+		backlight.max, err = strconv.Atoi(string(bytes.TrimSpace(v)))
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse maximum brightness of %s: %s", backlight.identifier, err)
+		}
+	}
+
+	return backlights, nil
+}
+
+func main() {
+	backlights, err := identifyBacklights()
+	if err != nil {
+		log.Fatalf("failed to identify backlight interfaces: %s", err)
+	}
+
+	mainIndex := -1
+	if len(backlights) == 1 {
+		mainIndex = 0
+	} else {
+		for i, backlight := range backlights {
+			if backlight.fallback {
+				continue
+			}
+
+			if mainIndex != -1 {
+				mainIndex = -1
+				break
+			}
+			mainIndex = i
+		}
+	}
+
+	if mainIndex == -1 {
+		// TODO
+		log.Fatal("multiple backlight interfaces were found, please specify which interface to use with --interface")
+	}
+
+	backlight := backlights[mainIndex]
+
+	var v string
+	var command string
+	if len(os.Args) > 1 {
+		command = os.Args[1]
+		if len(os.Args) > 2 {
+			v = os.Args[2]
+		}
+	}
+
+	var cmd int
+	switch command {
+	case "set":
+		cmd = commandSet
+	case "add", "inc", "up":
+		cmd = commandAdd
+	case "sub", "dec", "down":
+		cmd = commandSub
+	case "current":
+		log.Printf("%d", backlight.current)
+		return
+	case "max":
+		log.Printf("%d", backlight.max)
+		return
+	case "":
+		log.Printf("%d/%d", backlight.current, backlight.max)
+		return
+	default:
+		if len(os.Args) > 2 {
+			log.Fatalf("unrecognized command %s", command)
+		}
+
+		v = command
+		if v[0] == '-' {
+			cmd = commandSub
+			v = v[1:]
+		} else if v[0] == '+' {
+			cmd = commandAdd
+			v = v[1:]
+		} else {
+			cmd = commandSet
+		}
+	}
+
+	pct := v[len(v)-1] == '%'
+	if pct {
+		v = v[:len(v)-1]
+	}
+	setValue, err := strconv.ParseFloat(v, 64)
+	if err != nil {
+		log.Fatalf("unrecognized command %s", command)
+	}
+
+	if pct {
+		setValue = float64(backlight.max) * (setValue / 100)
+	}
+
+	value := backlight.current
+	switch cmd {
+	case commandSet:
+		value = int(setValue)
+	case commandSub:
+		value -= int(setValue)
+	case commandAdd:
+		value += int(setValue)
+	}
+
+	err = backlight.setBrightness(value)
+	if err != nil {
+		log.Fatalf("failed to set brightness of %s to %d: %s", backlight.identifier, value, err)
+	}
+}