package main

import (
	"fmt"

	"git.frostfs.info/TrueCloudLab/zapjournald"
	"github.com/spf13/viper"
	"github.com/ssgreg/journald"
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

const (
	destinationStdout   string = "stdout"
	destinationJournald string = "journald"
)

type Logger struct {
	logger *zap.Logger
	lvl    zap.AtomicLevel
}

func pickLogger(v *viper.Viper) *Logger {
	lvl, err := getLogLevel(v.GetString(cfgLoggerLevel))
	if err != nil {
		panic(err)
	}

	dest := v.GetString(cfgLoggerDestination)

	if dest == destinationStdout {
		return newStdoutLogger(lvl)
	}

	if dest == destinationJournald {
		return newJournaldLogger(lvl)
	}

	panic(fmt.Sprintf("wrong destination for logger: %s", dest))
}

func newStdoutLogger(lvl zapcore.Level) *Logger {
	c := zap.NewProductionConfig()
	c.Level = zap.NewAtomicLevelAt(lvl)
	c.Encoding = "console"
	c.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder

	l, err := c.Build(
		zap.AddStacktrace(zap.NewAtomicLevelAt(zap.FatalLevel)),
	)
	if err != nil {
		panic(fmt.Sprintf("build zap logger instance: %v", err))
	}

	return &Logger{logger: l, lvl: c.Level}
}

func newJournaldLogger(lvl zapcore.Level) *Logger {
	c := zap.NewProductionConfig()
	c.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder
	c.Level = zap.NewAtomicLevelAt(lvl)

	// We can use NewJSONEncoder instead if, say, frontend
	// would like to access journald logs and parse them easily.
	encoder := zapjournald.NewPartialEncoder(zapcore.NewConsoleEncoder(c.EncoderConfig), zapjournald.SyslogFields)

	core := zapjournald.NewCore(c.Level, encoder, &journald.Journal{}, zapjournald.SyslogFields)
	coreWithContext := core.With([]zapcore.Field{
		zapjournald.SyslogFacility(zapjournald.LogDaemon),
		zapjournald.SyslogIdentifier(),
		zapjournald.SyslogPid(),
	})
	l := zap.New(coreWithContext, zap.AddStacktrace(zap.NewAtomicLevelAt(zap.FatalLevel)))
	return &Logger{logger: l, lvl: c.Level}
}

func getLogLevel(lvlStr string) (zapcore.Level, error) {
	var lvl zapcore.Level
	err := lvl.UnmarshalText([]byte(lvlStr))
	if err != nil {
		return lvl, fmt.Errorf("incorrect logger level configuration %s (%v), "+
			"value should be one of %v", lvlStr, err, [...]zapcore.Level{
			zapcore.DebugLevel,
			zapcore.InfoLevel,
			zapcore.WarnLevel,
			zapcore.ErrorLevel,
			zapcore.DPanicLevel,
			zapcore.PanicLevel,
			zapcore.FatalLevel,
		})
	}
	return lvl, nil
}