From 09e88f31d1b4308bf82c7f4eb0dd83855ad67ffc Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Wed, 15 Jun 2016 23:17:51 +0200
Subject: toggledlog: assume command of color handling

We want to use colored error messages also outside of main,
so let's handle it in the logging package.

The fatal logger now automatically prints red.
---
 internal/toggledlog/log.go | 45 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 38 insertions(+), 7 deletions(-)

(limited to 'internal/toggledlog')

diff --git a/internal/toggledlog/log.go b/internal/toggledlog/log.go
index 23d7347..30fab18 100644
--- a/internal/toggledlog/log.go
+++ b/internal/toggledlog/log.go
@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"log"
 	"os"
+
+	"golang.org/x/crypto/ssh/terminal"
 )
 
 const (
@@ -12,6 +14,10 @@ const (
 	wpanicMsg   = "-wpanic turns this warning into a panic: "
 )
 
+// Escape sequences for terminal colors. These will be empty strings if stdout
+// is not a terminal.
+var ColorReset, ColorGrey, ColorRed, ColorGreen, ColorYellow string
+
 func JSONDump(obj interface{}) string {
 	b, err := json.MarshalIndent(obj, "", "\t")
 	if err != nil {
@@ -27,6 +33,10 @@ type toggledLogger struct {
 	Enabled bool
 	// Panic after logging a message, useful in regression tests
 	Wpanic bool
+	// Private prefix and postfix are used for coloring
+	prefix  string
+	postfix string
+
 	*log.Logger
 }
 
@@ -34,7 +44,7 @@ func (l *toggledLogger) Printf(format string, v ...interface{}) {
 	if !l.Enabled {
 		return
 	}
-	l.Logger.Printf(format, v...)
+	l.Logger.Printf(l.prefix + fmt.Sprintf(format, v...) + l.postfix)
 	if l.Wpanic {
 		l.Logger.Panic(wpanicMsg + fmt.Sprintf(format, v...))
 	}
@@ -43,9 +53,9 @@ func (l *toggledLogger) Println(v ...interface{}) {
 	if !l.Enabled {
 		return
 	}
-	l.Logger.Println(v...)
+	l.Logger.Println(l.prefix + fmt.Sprint(v...) + l.postfix)
 	if l.Wpanic {
-		l.Logger.Panic(wpanicMsg + fmt.Sprintln(v...))
+		l.Logger.Panic(wpanicMsg + fmt.Sprint(v...))
 	}
 }
 
@@ -65,8 +75,29 @@ var Warn *toggledLogger
 var Fatal *toggledLogger
 
 func init() {
-	Debug = &toggledLogger{false, false, log.New(os.Stdout, "", 0)}
-	Info = &toggledLogger{true, false, log.New(os.Stdout, "", 0)}
-	Warn = &toggledLogger{true, false, log.New(os.Stderr, "", 0)}
-	Fatal = &toggledLogger{true, false, log.New(os.Stderr, "", 0)}
+	if terminal.IsTerminal(int(os.Stdout.Fd())) {
+		ColorReset = "\033[0m"
+		ColorGrey = "\033[2m"
+		ColorRed = "\033[31m"
+		ColorGreen = "\033[32m"
+		ColorYellow = "\033[33m"
+	}
+
+	Debug = &toggledLogger{
+		Logger: log.New(os.Stdout, "", 0),
+	}
+	Info = &toggledLogger{
+		Enabled: true,
+		Logger:  log.New(os.Stdout, "", 0),
+	}
+	Warn = &toggledLogger{
+		Enabled: true,
+		Logger:  log.New(os.Stderr, "", 0),
+	}
+	Fatal = &toggledLogger{
+		Enabled: true,
+		Logger:  log.New(os.Stderr, "", 0),
+		prefix:  ColorRed,
+		postfix: ColorReset,
+	}
 }
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