/*
Copyright 2018 The Knative Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package logging

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"strings"

	"github.com/blendle/zapdriver"
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
	corev1 "k8s.io/api/core/v1"

	"knative.dev/pkg/changeset"
	"knative.dev/pkg/logging/logkey"
)

const (
	configMapNameEnv   = "CONFIG_LOGGING_NAME"
	loggerConfigKey    = "zap-logger-config"
	fallbackLoggerName = "fallback-logger"
)

var (
	errEmptyLoggerConfig     = errors.New("empty logger configuration")
	errEmptyJSONLogginString = errors.New("json logging string is empty")
)

// NewLogger creates a logger with the supplied configuration.
// In addition to the logger, it returns AtomicLevel that can
// be used to change the logging level at runtime.
// If configuration is empty, a fallback configuration is used.
// If configuration cannot be used to instantiate a logger,
// the same fallback configuration is used.
func NewLogger(configJSON string, levelOverride string, opts ...zap.Option) (*zap.SugaredLogger, zap.AtomicLevel) {
	logger, atomicLevel, err := newLoggerFromConfig(configJSON, levelOverride, opts)
	if err == nil {
		return enrichLoggerWithCommitID(logger), atomicLevel
	}

	loggingCfg := stackdriverConfig()

	if levelOverride != "" {
		if level, err := levelFromString(levelOverride); err == nil {
			loggingCfg.Level = zap.NewAtomicLevelAt(*level)
		}
	}

	logger, err = loggingCfg.Build(opts...)
	if err != nil {
		panic(err)
	}

	slogger := enrichLoggerWithCommitID(logger.Named(fallbackLoggerName))
	slogger.Warnw("Failed to parse logging config - using default zap production config", zap.Error(err))
	return slogger, loggingCfg.Level
}

func enrichLoggerWithCommitID(logger *zap.Logger) *zap.SugaredLogger {
	revision := changeset.Get()
	if revision == changeset.Unknown {
		logger.Info("Unable to read vcs.revision from binary")
		return logger.Sugar()
	}

	// Enrich logs with the components git revision.
	return logger.With(zap.String(logkey.Commit, revision)).Sugar()
}

// NewLoggerFromConfig creates a logger using the provided Config
func NewLoggerFromConfig(config *Config, name string, opts ...zap.Option) (*zap.SugaredLogger, zap.AtomicLevel) {
	var componentLvl string
	if lvl, defined := config.LoggingLevel[name]; defined {
		componentLvl = lvl.String()
	}

	logger, level := NewLogger(config.LoggingConfig, componentLvl, opts...)
	return logger.Named(name), level
}

func newLoggerFromConfig(configJSON, levelOverride string, opts []zap.Option) (*zap.Logger, zap.AtomicLevel, error) {
	loggingCfg, err := zapConfigFromJSON(configJSON)
	if err != nil {
		return nil, zap.AtomicLevel{}, err
	}

	if levelOverride != "" {
		if level, err := levelFromString(levelOverride); err == nil {
			loggingCfg.Level = zap.NewAtomicLevelAt(*level)
		}
	}

	logger, err := loggingCfg.Build(opts...)
	if err != nil {
		return nil, zap.AtomicLevel{}, err
	}

	logger.Debug("Successfully created the logger.")
	logger.Debug("Logging level set to: " + loggingCfg.Level.String())
	return logger, loggingCfg.Level, nil
}

func zapConfigFromJSON(configJSON string) (*zap.Config, error) {
	loggingCfg := stackdriverConfig()

	if configJSON != "" {
		if err := json.Unmarshal([]byte(configJSON), &loggingCfg); err != nil {
			return nil, err
		}
	}
	return &loggingCfg, nil
}

// Config contains the configuration defined in the logging ConfigMap.
// +k8s:deepcopy-gen=true
type Config struct {
	LoggingConfig string
	LoggingLevel  map[string]zapcore.Level
}

type lcfg struct{}

// WithConfig associates a logging configuration with the context.
func WithConfig(ctx context.Context, cfg *Config) context.Context {
	return context.WithValue(ctx, lcfg{}, cfg)
}

// GetConfig gets the logging config from the provided context.
func GetConfig(ctx context.Context) *Config {
	untyped := ctx.Value(lcfg{})
	if untyped == nil {
		return nil
	}
	return untyped.(*Config)
}

func defaultConfig() *Config {
	return &Config{
		LoggingLevel: make(map[string]zapcore.Level),
	}
}

// NewConfigFromMap creates a LoggingConfig from the supplied map,
// expecting the given list of components.
func NewConfigFromMap(data map[string]string) (*Config, error) {
	lc := defaultConfig()
	if zlc, ok := data[loggerConfigKey]; ok {
		lc.LoggingConfig = zlc
	}

	for k, v := range data {
		if component := strings.TrimPrefix(k, "loglevel."); component != k && component != "" {
			if len(v) > 0 {
				level, err := levelFromString(v)
				if err != nil {
					return nil, err
				}
				lc.LoggingLevel[component] = *level
			}
		}
	}
	return lc, nil
}

// NewConfigFromConfigMap creates a Config from the supplied ConfigMap,
// expecting the given list of components.
func NewConfigFromConfigMap(configMap *corev1.ConfigMap) (*Config, error) {
	return NewConfigFromMap(configMap.Data)
}

func levelFromString(level string) (*zapcore.Level, error) {
	var zapLevel zapcore.Level
	if err := zapLevel.UnmarshalText([]byte(level)); err != nil {
		return nil, fmt.Errorf("invalid logging level: %v", level)
	}
	return &zapLevel, nil
}

// UpdateLevelFromConfigMap returns a helper func that can be used to update the logging level
// when a config map is updated
func UpdateLevelFromConfigMap(logger *zap.SugaredLogger, atomicLevel zap.AtomicLevel,
	levelKey string) func(configMap *corev1.ConfigMap) {
	return func(configMap *corev1.ConfigMap) {
		config, err := NewConfigFromConfigMap(configMap)
		if err != nil {
			logger.Errorw("Failed to parse the logging configmap. Previous config map will be used.", zap.Error(err))
			return
		}

		level, defined := config.LoggingLevel[levelKey]
		if !defined {
			// reset to global level
			loggingCfg, err := zapConfigFromJSON(config.LoggingConfig)
			switch {
			case errors.Is(err, errEmptyLoggerConfig):
				level = zap.NewAtomicLevel().Level()
			case err != nil:
				logger.Errorw("Failed to parse logger configuration. Previous log level retained for "+levelKey,
					zap.Error(err))
				return
			default:
				level = loggingCfg.Level.Level()
			}
		}

		if atomicLevel.Level() != level {
			logger.Infof("Updating logging level for %v from %v to %v.", levelKey, atomicLevel.Level(), level)
			atomicLevel.SetLevel(level)
		}
	}
}

// ConfigMapName gets the name of the logging ConfigMap
func ConfigMapName() string {
	if cm := os.Getenv(configMapNameEnv); cm != "" {
		return cm
	}
	return "config-logging"
}

// JSONToConfig converts a JSON string of a Config.
// Always returns a non-nil Config.
func JSONToConfig(jsonCfg string) (*Config, error) {
	if jsonCfg == "" {
		return nil, errEmptyJSONLogginString
	}

	var configMap map[string]string
	if err := json.Unmarshal([]byte(jsonCfg), &configMap); err != nil {
		return nil, err
	}

	cfg, err := NewConfigFromMap(configMap)
	if err != nil {
		// Get the default config from logging package.
		return NewConfigFromConfigMap(nil)
	}
	return cfg, nil
}

// ConfigToJSON  converts a Config to a JSON string.
func ConfigToJSON(cfg *Config) (string, error) {
	if cfg == nil || cfg.LoggingConfig == "" {
		return "", nil
	}

	jsonCfg, err := json.Marshal(map[string]string{
		loggerConfigKey: cfg.LoggingConfig,
	})
	return string(jsonCfg), err
}

func stackdriverConfig() zap.Config {
	cfg := zapdriver.NewProductionConfig()
	cfg.EncoderConfig.EncodeDuration = zapcore.StringDurationEncoder
	return cfg
}
