Use colors for some output messages

internal/logger/logger.go

@@ -1,38 +1,58 @@
 package logger
 
 import (
-	"fmt"
 	"io"
+
+	"github.com/fatih/color"
 )
 
+type PrintFunc func(io.Writer, string, ...interface{})
+
+var (
+	Default PrintFunc = color.New(color.Reset).FprintfFunc()
+	Bold    PrintFunc = color.New(color.Bold).FprintfFunc()
+	Blue    PrintFunc = color.New(color.FgBlue, color.Bold).FprintfFunc()
+	Green   PrintFunc = color.New(color.FgGreen, color.Bold).FprintfFunc()
+	Cyan    PrintFunc = color.New(color.FgCyan, color.Bold).FprintfFunc()
+	Yellow  PrintFunc = color.New(color.FgYellow, color.Bold).FprintfFunc()
+	Magenta PrintFunc = color.New(color.FgMagenta, color.Bold).FprintfFunc()
+	Red     PrintFunc = color.New(color.FgRed, color.Bold).FprintfFunc()
+)
+
+// Logger is just a wrapper that prints stuff to STDOUT or STDERR,
+// with optional color.
 type Logger struct {
 	Stdout  io.Writer
 	Stderr  io.Writer
 	Verbose bool
 }
 
-func (l *Logger) Outf(s string, args ...interface{}) {
+// Outf prints stuff to STDOUT.
+func (l *Logger) Outf(print PrintFunc, s string, args ...interface{}) {
 	if len(args) == 0 {
 		s, args = "%s", []interface{}{s}
 	}
-	fmt.Fprintf(l.Stdout, s+"\n", args...)
+	print(l.Stdout, s+"\n", args...)
 }
 
-func (l *Logger) VerboseOutf(s string, args ...interface{}) {
+// VerboseOutf prints stuff to STDOUT if verbose mode is enabled.
+func (l *Logger) VerboseOutf(print PrintFunc, s string, args ...interface{}) {
 	if l.Verbose {
-		l.Outf(s, args...)
+		l.Outf(print, s, args...)
 	}
 }
 
-func (l *Logger) Errf(s string, args ...interface{}) {
+// Errf prints stuff to STDERR.
+func (l *Logger) Errf(print PrintFunc, s string, args ...interface{}) {
 	if len(args) == 0 {
 		s, args = "%s", []interface{}{s}
 	}
-	fmt.Fprintf(l.Stderr, s+"\n", args...)
+	print(l.Stderr, s+"\n", args...)
 }
 
-func (l *Logger) VerboseErrf(s string, args ...interface{}) {
+// VerboseErrf prints stuff to STDERR if verbose mode is enabled.
+func (l *Logger) VerboseErrf(print PrintFunc, s string, args ...interface{}) {
 	if l.Verbose {
-		l.Errf(s, args...)
+		l.Errf(print, s, args...)
 	}
 }