From e7cfaf764d5ec6c88b0cb076191ac02412cbde69 Mon Sep 17 00:00:00 2001
From: Rasmus Dahlberg <rasmus@mullvad.net>
Date: Sun, 27 Mar 2022 17:57:55 +0200
Subject: add a basic leveled logger

Date and terminal colors are off by default.
---
 pkg/log/log.go      | 139 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 pkg/log/log_test.go |  21 ++++++++
 2 files changed, 160 insertions(+)
 create mode 100644 pkg/log/log.go
 create mode 100644 pkg/log/log_test.go

diff --git a/pkg/log/log.go b/pkg/log/log.go
new file mode 100644
index 0000000..ad4a692
--- /dev/null
+++ b/pkg/log/log.go
@@ -0,0 +1,139 @@
+// package log provides a simple logger with leveled log messages.
+//
+//   - DebugLevel (highest verbosity)
+//   - InfoLevel
+//   - WarningLevel
+//   - ErrorLevel
+//   - FatalLevel (lowest verbosity)
+//
+// Output is by default written to STDERR.
+// A different output can be specified.
+// Dates and terminal colors can be turned on.
+package log
+
+import (
+	"io"
+	"log"
+	"os"
+	"time"
+)
+
+type level int
+
+const (
+	DebugLevel   level = iota // DebugLevel logs all messages
+	InfoLevel                 // InfoLevel logs info messages and and above
+	WarningLevel              // WarningLevel logs warning messages and above
+	ErrorLevel                // ErrorLevel logs error messages and above
+	FatalLevel                // FatalLevel only logs fatal messages
+)
+
+const (
+	colorDate    = "\033[37m"
+	colorDebug   = "\033[95m"
+	colorInfo    = "\033[94m"
+	colorWarning = "\033[93m"
+	colorError   = "\033[91m"
+	colorFatal   = "\033[31m"
+	colorReset   = "\033[0m"
+
+	tagDebug   = "DEBU"
+	tagInfo    = "INFO"
+	tagWarning = "WARN"
+	tagError   = "ERRO"
+	tagFatal   = "FATA"
+)
+
+type logger struct {
+	log.Logger
+
+	lv    level
+	date  bool
+	color bool
+}
+
+var l logger
+
+func init() {
+	l = newLogger(InfoLevel, os.Stderr, false, false)
+}
+
+// SetLevel sets the logging level.  Available options: DebugLevel, InfoLevel,
+// WarningLevel, ErrorLevel, FatalLevel.  Default: InfoLevel.
+func SetLevel(lv level) {
+	l.lv = lv
+}
+
+// SetOutput sets the logging output to a particular writer. Default: os.Stderr.
+func SetOutput(writer io.Writer) {
+	l = newLogger(l.lv, writer, l.date, l.color)
+}
+
+// SetDate (un)sets date output.  Default: off.
+func SetDate(ok bool) {
+	l.date = ok
+}
+
+// SetColor (un)sets terminal colors.  Default: off.
+func SetColor(ok bool) {
+	l.color = ok
+}
+
+func Debug(format string, v ...interface{}) {
+	if l.lv > DebugLevel {
+		return
+	}
+
+	l.Printf(l.fmt(tagDebug, colorDebug)+format, v...)
+}
+
+func Info(format string, v ...interface{}) {
+	if l.lv > InfoLevel {
+		return
+	}
+
+	l.Printf(l.fmt(tagInfo, colorInfo)+format, v...)
+}
+
+func Warning(format string, v ...interface{}) {
+	if l.lv > WarningLevel {
+		return
+	}
+
+	l.Printf(l.fmt(tagWarning, colorWarning)+format, v...)
+}
+
+func Error(format string, v ...interface{}) {
+	if l.lv > ErrorLevel {
+		return
+	}
+
+	l.Printf(l.fmt(tagError, colorError)+format, v...)
+}
+
+func Fatal(format string, v ...interface{}) {
+	l.Printf(l.fmt(tagFatal, colorFatal)+format, v...)
+	os.Exit(1)
+}
+
+func newLogger(lv level, writer io.Writer, date, color bool) logger {
+	return logger{
+		Logger: *log.New(writer, "", 0),
+		lv:     lv,
+		date:   date,
+		color:  color,
+	}
+}
+
+func (l *logger) fmt(tag, colorTag string) string {
+	date := ""
+	if l.date {
+		date = time.Now().Format(time.RFC1123) + " "
+	}
+	if l.color {
+		date = colorDate + date + colorReset
+		tag = colorTag + tag + colorReset
+	}
+	tag = "[" + tag + "] "
+	return date + tag
+}
diff --git a/pkg/log/log_test.go b/pkg/log/log_test.go
new file mode 100644
index 0000000..9f4076d
--- /dev/null
+++ b/pkg/log/log_test.go
@@ -0,0 +1,21 @@
+package log
+
+import (
+	"os"
+)
+
+func Example() {
+	SetOutput(os.Stdout)
+	SetLevel(WarningLevel)
+	SetDate(false)
+	SetColor(false)
+
+	Debug("some debug number: %d\n", 10)
+	Info("some info number: %d\n", 20)
+	Warning("some warning number: %d\n", 30)
+	Error("some error number: %d\n", 40)
+
+	// Output:
+	// [WARN] some warning number: 30
+	// [ERRO] some error number: 40
+}
-- 
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