logger with helper methods (#1216)

* support unix daemon socket

* refactor(logger): logger fields changed to map[string]interface{}

* improvement(logger): adding string to Level Parser

* improvement(logger): rename ParseLevel to GetLevel

* refactor(logger): adding basic logger

adding micro default logger, and refactor logger interface

* refactor(logger): moved basic logger to top level package

* refactor(logger): adding default logger

logger/default.go

@@ -0,0 +1,96 @@
+package logger
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"os"
+)
+
+type defaultLogger struct {
+	opts Options
+	err  error
+}
+
+// Init(opts...) should only overwrite provided options
+func (l *defaultLogger) Init(opts ...Option) error {
+	for _, o := range opts {
+		o(&l.opts)
+	}
+	return nil
+}
+
+func (l *defaultLogger) String() string {
+	return "default"
+}
+
+func (l *defaultLogger) Fields(fields map[string]interface{}) Logger {
+	l.opts.Fields = fields
+	return l
+}
+
+func (l *defaultLogger) Error(err error) Logger {
+	l.err = err
+	return l
+}
+
+func (l *defaultLogger) Log(level Level, v ...interface{}) {
+	if !l.opts.Level.Enabled(level) {
+		return
+	}
+	msg := fmt.Sprint(v...)
+
+	fields := l.opts.Fields
+	fields["level"] = level.String()
+	fields["message"] = msg
+	if l.err != nil {
+		fields["error"] = l.err.Error()
+	}
+
+	enc := json.NewEncoder(l.opts.Out)
+
+	if err := enc.Encode(fields); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func (l *defaultLogger) Logf(level Level, format string, v ...interface{}) {
+	if level < l.opts.Level {
+		return
+	}
+	msg := fmt.Sprintf(format, v...)
+
+	fields := l.opts.Fields
+	fields["level"] = level.String()
+	fields["message"] = msg
+	if l.err != nil {
+		fields["error"] = l.err.Error()
+	}
+
+	enc := json.NewEncoder(l.opts.Out)
+
+	if err := enc.Encode(fields); err != nil {
+		log.Fatal(err)
+	}
+
+}
+
+func (n *defaultLogger) Options() Options {
+	return n.opts
+}
+
+// NewLogger builds a new logger based on options
+func NewLogger(opts ...Option) Logger {
+	// Default options
+	options := Options{
+		Level:   InfoLevel,
+		Fields:  make(map[string]interface{}),
+		Out:     os.Stderr,
+		Context: context.Background(),
+	}
+
+	l := &defaultLogger{opts: options}
+	_ = l.Init(opts...)
+	return l
+}