feat(log): add a log package

this package should be extracted into deis/pkg. PR forthcoming for that

cc/ @technosophos

Author: arschles

pkg/log/log.go

@@ -0,0 +1,72 @@
+// Package log is a convenience wrapper for logging messages of various levels (associated colors to come)
+// to the terminal. Much of this code has been shamelessly stolen from https://github.com/helm/helm/blob/master/log/log.go
+package log
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/labstack/gommon/color"
+)
+
+// Stdout is the logging destination for normal messages.
+var Stdout io.Writer = os.Stdout
+
+// Stderr is the logging destination for error messages.
+var Stderr io.Writer = os.Stderr
+
+// IsDebugging toggles whether or not to enable debug output and behavior.
+var IsDebugging = false
+
+// Msg passes through the formatter, but otherwise prints exactly as-is.
+//
+// No prettification.
+func Msg(format string, v ...interface{}) {
+	fmt.Fprintf(Stdout, appendNewLine(format), v...)
+}
+
+// Die prints an error and then call os.Exit(1).
+func Die(format string, v ...interface{}) {
+	Err(format, v...)
+	if IsDebugging {
+		panic(fmt.Sprintf(format, v...))
+	}
+	os.Exit(1)
+}
+
+// CleanExit prints a message and then exits with 0.
+func CleanExit(format string, v ...interface{}) {
+	Info(format, v...)
+	os.Exit(0)
+}
+
+// Err prints an error message. It does not cause an exit.
+func Err(format string, v ...interface{}) {
+	fmt.Fprint(Stderr, color.Red("[ERROR] "))
+	fmt.Fprintf(Stderr, appendNewLine(format), v...)
+}
+
+// Info prints a green-tinted message.
+func Info(format string, v ...interface{}) {
+	fmt.Fprint(Stderr, "---> ")
+	fmt.Fprintf(Stderr, appendNewLine(format), v...)
+}
+
+// Debug prints a cyan-tinted message if IsDebugging is true.
+func Debug(msg string, v ...interface{}) {
+	if IsDebugging {
+		fmt.Fprint(Stderr, color.Cyan("[DEBUG] "))
+		Msg(msg, v...)
+	}
+}
+
+// Warn prints a yellow-tinted warning message.
+func Warn(format string, v ...interface{}) {
+	fmt.Fprint(Stderr, color.Yellow("[WARN] "))
+	Msg(format, v...)
+}
+
+func appendNewLine(format string) string {
+	return format + "\n"
+}