// this forks the logrus json formatter to rename msg -> message as that's the
// expected field. Ideally the logger should make it easier for us.
package log

import (
	"encoding/json"
	"fmt"
	"runtime"
	"time"

	"github.com/mattn/go-colorable"
	"github.com/sirupsen/logrus"
)

var (
	DefaultTimestampFormat = time.RFC3339Nano
)

type JSONFormatter struct {
	// TimestampFormat sets the format used for marshaling timestamps.
	TimestampFormat string
}

func CreateLogger() *logrus.Logger {
	logger := logrus.New()
	logger.Out = colorable.NewColorableStderr()
	logger.Formatter = &logrus.TextFormatter{ForceColors: runtime.GOOS == "windows"}
	return logger
}

func (f *JSONFormatter) Format(entry *logrus.Entry) ([]byte, error) {
	data := make(logrus.Fields, len(entry.Data)+3)
	for k, v := range entry.Data {
		switch v := v.(type) {
		case error:
			// Otherwise errors are ignored by `encoding/json`
			// https://github.com/sirupsen/logrus/issues/137
			data[k] = v.Error()
		default:
			data[k] = v
		}
	}
	prefixFieldClashes(data)

	timestampFormat := f.TimestampFormat
	if timestampFormat == "" {
		timestampFormat = DefaultTimestampFormat
	}

	data["time"] = entry.Time.Format(timestampFormat)
	data["message"] = entry.Message
	data["level"] = entry.Level.String()

	serialized, err := json.Marshal(data)
	if err != nil {
		return nil, fmt.Errorf("Failed to marshal fields to JSON, %v", err)
	}
	return append(serialized, '\n'), nil
}

// This is to not silently overwrite `time`, `msg` and `level` fields when
// dumping it. If this code wasn't there doing:
//
//  logrus.WithField("level", 1).Info("hello")
//
// Would just silently drop the user provided level. Instead with this code
// it'll logged as:
//
//  {"level": "info", "fields.level": 1, "msg": "hello", "time": "..."}
//
// It's not exported because it's still using Data in an opinionated way. It's to
// avoid code duplication between the two default formatters.
func prefixFieldClashes(data logrus.Fields) {
	if t, ok := data["time"]; ok {
		data["fields.time"] = t
	}

	if m, ok := data["msg"]; ok {
		data["fields.msg"] = m
	}

	if l, ok := data["level"]; ok {
		data["fields.level"] = l
	}
}