package config

import (
	"bytes"
	"encoding/csv"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"reflect"
	"strings"
	"time"

	"github.com/fsnotify/fsnotify"
	"github.com/mitchellh/mapstructure"
	"github.com/spf13/afero"
	"github.com/spf13/cast"
	"github.com/spf13/pflag"
)

// SupportedExts are universally supported extensions.
var SupportedExts = []string{"json", "toml", "yaml", "yml", "properties", "props", "prop", "hcl"}

type UnsupportedConfigError string

// Error returns the formatted configuration error.
func (str UnsupportedConfigError) Error() string {
	return fmt.Sprintf("Unsupported Config Type %q", string(str))
}

// ConfigFileNotFoundError denotes failing to find configuration file.
type ConfigFileNotFoundError struct {
	name, locations string
}

// Error returns the formatted configuration error.
func (fnfe ConfigFileNotFoundError) Error() string {
	return fmt.Sprintf("Config File %q Not Found in %q", fnfe.name, fnfe.locations)
}

type CircularReferenceAliasError struct {
	alias, key, realKey string
}

// Error returns the formatted configuration error.
func (crae CircularReferenceAliasError) Error() string {
	return fmt.Sprintf("Creating circular reference alias[%q] for key[%q]:realKey[%q]", crae.alias, crae.key, crae.realKey)
}

type Configurator interface {
	OnConfigChange(run func(in fsnotify.Event))
	WatchConfig()
	SetConfigType(in string)
	SetConfigFile(in string)
	SetEnvPrefix(in string)
	SetConfigName(in string)
	AddConfigPath(in string) error
	ReadConfig(in io.Reader) error
	ReadInConfig() error
	AutomaticEnv()
	SetEnvKeyReplacer(r *strings.Replacer)
	RegisterAlias(alias string, key string) error
	SetDefault(key string, value interface{})
	Set(key string, value interface{})
	IsSet(key string) bool
	Get(key string) interface{}
	GetString(key string) string
	GetBool(key string) bool
	GetInt(key string) int
	GetInt64(key string) int64
	GetFloat64(key string) float64
	GetTime(key string) time.Time
	GetDuration(key string) time.Duration
	GetStringSlice(key string) []string
	GetStringMap(key string) map[string]interface{}
	GetStringMapString(key string) map[string]string
	GetStringMapStringSlice(key string) map[string][]string
	GetSizeInBytes(key string) uint
	Sub(key string) Configurator
	UnmarshalKey(key string, rawVal interface{}) error
	Unmarshal(rawVal interface{}) error
	UnmarshalExact(rawVal interface{}) error
	BindPFlags(flags *pflag.FlagSet) error
	BindPFlag(key string, flag *pflag.Flag) error
	BindFlagValues(flags FlagValueSet) (err error)
	BindFlagValue(key string, flag FlagValue) error
	BindEnv(input ...string) error
	AllSettings() map[string]interface{}
	AllKeys() []string
}

type configurator struct {
	keyDelim    string
	configPaths []string
	// The filesystem to read config from.
	fs afero.Fs
	// Name of file to look for inside the path
	configName string
	configFile string
	configType string
	envPrefix  string

	automaticEnvApplied bool
	envKeyReplacer      *strings.Replacer

	config         map[string]interface{}
	override       map[string]interface{}
	defaults       map[string]interface{}
	kvstore        map[string]interface{}
	pflags         map[string]FlagValue
	env            map[string]string
	aliases        map[string]string
	typeByDefValue bool

	onConfigChange func(fsnotify.Event)
}

var _c *configurator

func init() {
	_c = New().(*configurator)
}

func New() Configurator {
	c := new(configurator)
	c.keyDelim = "."
	c.configName = "config"
	c.fs = afero.NewOsFs()
	c.config = make(map[string]interface{})
	c.override = make(map[string]interface{})
	c.defaults = make(map[string]interface{})
	c.kvstore = make(map[string]interface{})
	c.pflags = make(map[string]FlagValue)
	c.env = make(map[string]string)
	c.aliases = make(map[string]string)
	c.typeByDefValue = false

	return c
}

func OnConfigChange(run func(in fsnotify.Event)) { _c.OnConfigChange(run) }
func (c *configurator) OnConfigChange(run func(in fsnotify.Event)) {
	c.onConfigChange = run
}

func WatchConfig() { _c.WatchConfig() }
func (c *configurator) WatchConfig() {
	go func() {
		watcher, err := fsnotify.NewWatcher()
		if err != nil {
			log.Fatal(err)
		}
		defer watcher.Close()

		// we have to watch the entire directory to pick up renames/atomic saves in a cross-platform way
		filename, err := c.getConfigFile()
		if err != nil {
			log.Println("error:", err)
			return
		}

		configFile := filepath.Clean(filename)
		configDir, _ := filepath.Split(configFile)

		done := make(chan bool)
		go func() {
			for {
				select {
				case event := <-watcher.Events:
					// we only care about the config file
					if filepath.Clean(event.Name) == configFile {
						if event.Op&fsnotify.Write == fsnotify.Write || event.Op&fsnotify.Create == fsnotify.Create {
							err := c.ReadInConfig()
							if err != nil {
								log.Println("error:", err)
							}
							c.onConfigChange(event)
						}
					}
				case err := <-watcher.Errors:
					log.Println("error:", err)
				}
			}
		}()

		watcher.Add(configDir)
		<-done
	}()
}

func SetConfigType(in string) { _c.SetConfigType(in) }
func (c *configurator) SetConfigType(in string) {
	if in != "" {
		c.configType = in
	}
}

func SetConfigFile(in string) { _c.SetConfigFile(in) }
func (c *configurator) SetConfigFile(in string) {
	if in != "" {
		c.configFile = in
	}
}

func SetEnvPrefix(in string) { _c.SetEnvPrefix(in) }
func (c *configurator) SetEnvPrefix(in string) {
	if in != "" {
		c.envPrefix = in
	}
}

// SetConfigName sets name for the config file.
// Does not include extension.
func SetConfigName(in string) { _c.SetConfigName(in) }
func (c *configurator) SetConfigName(in string) {
	if in != "" {
		c.configName = in
		c.configFile = ""
	}
}

// AddConfigPath adds a path for Viper to search for the config file in.
// Can be called multiple times to define multiple search paths.
func AddConfigPath(in string) error { return _c.AddConfigPath(in) }
func (c *configurator) AddConfigPath(in string) error {
	if in != "" {
		absin, err := absPathify(in)
		if nil != err {
			return err
		}

		if !stringInSlice(absin, c.configPaths) {
			c.configPaths = append(c.configPaths, absin)
		}
	}
	return nil
}

func ReadConfig(in io.Reader) error { return _c.ReadConfig(in) }
func (c *configurator) ReadConfig(in io.Reader) error {
	c.config = make(map[string]interface{})
	return c.unmarshalReader(in, c.config)
}

// ReadInConfig will discover and load the configuration file from disk
// and key/value stores, searching in one of the defined paths.
func ReadInConfig() error { return _c.ReadInConfig() }
func (c *configurator) ReadInConfig() error {
	filename, err := c.getConfigFile()
	if err != nil {
		return err
	}

	if !stringInSlice(c.getConfigType(), SupportedExts) {
		return UnsupportedConfigError(c.getConfigType())
	}

	file, err := afero.ReadFile(c.fs, filename)
	if err != nil {
		return err
	}

	config := make(map[string]interface{})

	err = c.unmarshalReader(bytes.NewReader(file), config)
	if err != nil {
		return err
	}

	c.config = config
	return nil
}

// AutomaticEnv has Viper check ENV variables for all.
// keys set in config, default & flags
func AutomaticEnv() { _c.AutomaticEnv() }
func (c *configurator) AutomaticEnv() {
	c.automaticEnvApplied = true
}

// SetEnvKeyReplacer sets the strings.Replacer on the viper object
// Useful for mapping an environmental variable to a key that does
// not match it.
func SetEnvKeyReplacer(r *strings.Replacer) { _c.SetEnvKeyReplacer(r) }
func (c *configurator) SetEnvKeyReplacer(r *strings.Replacer) {
	c.envKeyReplacer = r
}

func RegisterAlias(alias string, key string) error { return _c.RegisterAlias(alias, key) }
func (c *configurator) RegisterAlias(alias string, key string) error {
	return c.registerAlias(alias, strings.ToLower(key))
}

func (c *configurator) registerAlias(alias string, key string) error {
	alias = strings.ToLower(alias)
	if alias != key && alias != c.realKey(key) {
		_, exists := c.aliases[alias]

		if !exists {
			// if we alias something that exists in one of the maps to another
			// name, we'll never be able to get that value using the original
			// name, so move the config value to the new realkey.
			if val, ok := c.config[alias]; ok {
				delete(c.config, alias)
				c.config[key] = val
			}
			if val, ok := c.kvstore[alias]; ok {
				delete(c.kvstore, alias)
				c.kvstore[key] = val
			}
			if val, ok := c.defaults[alias]; ok {
				delete(c.defaults, alias)
				c.defaults[key] = val
			}
			if val, ok := c.override[alias]; ok {
				delete(c.override, alias)
				c.override[key] = val
			}
			c.aliases[alias] = key
		}
	} else {
		return CircularReferenceAliasError{alias: alias, key: key, realKey: c.realKey(key)}
	}
	return nil
}

func SetDefault(key string, value interface{}) { _c.SetDefault(key, value) }
func (c *configurator) SetDefault(key string, value interface{}) {
	// If alias passed in, then set the proper default
	key = c.realKey(strings.ToLower(key))
	value = toCaseInsensitiveValue(value)

	path := strings.Split(key, c.keyDelim)
	lastKey := strings.ToLower(path[len(path)-1])
	deepestMap := deepSearch(c.defaults, path[0:len(path)-1])

	// set innermost value
	deepestMap[lastKey] = value
}

func Set(key string, value interface{}) { _c.Set(key, value) }
func (c *configurator) Set(key string, value interface{}) {
	// If alias passed in, then set the proper override
	key = c.realKey(strings.ToLower(key))
	value = toCaseInsensitiveValue(value)

	path := strings.Split(key, c.keyDelim)
	lastKey := strings.ToLower(path[len(path)-1])
	deepestMap := deepSearch(c.override, path[0:len(path)-1])

	// set innermost value
	deepestMap[lastKey] = value
}

func IsSet(key string) bool { return _c.IsSet(key) }
func (c *configurator) IsSet(key string) bool {
	lcaseKey := strings.ToLower(key)
	val := c.find(lcaseKey)
	return val != nil
}

func Get(key string) interface{} { return _c.Get(key) }
func (c *configurator) Get(key string) interface{} {
	lcaseKey := strings.ToLower(key)
	val := c.find(lcaseKey)
	if val == nil {
		return nil
	}

	if c.typeByDefValue {
		// TODO(bep) this branch isn't covered by a single test.
		valType := val
		path := strings.Split(lcaseKey, c.keyDelim)
		defVal := c.searchMap(c.defaults, path)
		if defVal != nil {
			valType = defVal
		}

		switch valType.(type) {
		case bool:
			return cast.ToBool(val)
		case string:
			return cast.ToString(val)
		case int64, int32, int16, int8, int:
			return cast.ToInt(val)
		case float64, float32:
			return cast.ToFloat64(val)
		case time.Time:
			return cast.ToTime(val)
		case time.Duration:
			return cast.ToDuration(val)
		case []string:
			return cast.ToStringSlice(val)
		}
	}

	return val
}

// GetString returns the value associated with the key as a string.
func GetString(key string) string { return _c.GetString(key) }
func (c *configurator) GetString(key string) string {
	return cast.ToString(c.Get(key))
}

// GetBool returns the value associated with the key as a boolean.
func GetBool(key string) bool { return _c.GetBool(key) }
func (c *configurator) GetBool(key string) bool {
	return cast.ToBool(c.Get(key))
}

// GetInt returns the value associated with the key as an integer.
func GetInt(key string) int { return _c.GetInt(key) }
func (c *configurator) GetInt(key string) int {
	return cast.ToInt(c.Get(key))
}

// GetInt64 returns the value associated with the key as an integer.
func GetInt64(key string) int64 { return _c.GetInt64(key) }
func (c *configurator) GetInt64(key string) int64 {
	return cast.ToInt64(c.Get(key))
}

// GetFloat64 returns the value associated with the key as a float64.
func GetFloat64(key string) float64 { return _c.GetFloat64(key) }
func (c *configurator) GetFloat64(key string) float64 {
	return cast.ToFloat64(c.Get(key))
}

// GetTime returns the value associated with the key as time.
func GetTime(key string) time.Time { return _c.GetTime(key) }
func (c *configurator) GetTime(key string) time.Time {
	return cast.ToTime(c.Get(key))
}

// GetDuration returns the value associated with the key as a duration.
func GetDuration(key string) time.Duration { return _c.GetDuration(key) }
func (c *configurator) GetDuration(key string) time.Duration {
	return cast.ToDuration(c.Get(key))
}

// GetStringSlice returns the value associated with the key as a slice of strings.
func GetStringSlice(key string) []string { return _c.GetStringSlice(key) }
func (c *configurator) GetStringSlice(key string) []string {
	return cast.ToStringSlice(c.Get(key))
}

// GetStringMap returns the value associated with the key as a map of interfaces.
func GetStringMap(key string) map[string]interface{} { return _c.GetStringMap(key) }
func (c *configurator) GetStringMap(key string) map[string]interface{} {
	return cast.ToStringMap(c.Get(key))
}

// GetStringMapString returns the value associated with the key as a map of strings.
func GetStringMapString(key string) map[string]string { return _c.GetStringMapString(key) }
func (c *configurator) GetStringMapString(key string) map[string]string {
	return cast.ToStringMapString(c.Get(key))
}

// GetStringMapStringSlice returns the value associated with the key as a map to a slice of strings.
func GetStringMapStringSlice(key string) map[string][]string { return _c.GetStringMapStringSlice(key) }
func (c *configurator) GetStringMapStringSlice(key string) map[string][]string {
	return cast.ToStringMapStringSlice(c.Get(key))
}

// GetSizeInBytes returns the size of the value associated with the given key
// in bytes.
func GetSizeInBytes(key string) uint { return _c.GetSizeInBytes(key) }
func (c *configurator) GetSizeInBytes(key string) uint {
	sizeStr := cast.ToString(c.Get(key))
	return parseSizeInBytes(sizeStr)
}

// Sub returns new Viper instance representing a sub tree of this instance.
// Sub is case-insensitive for a key.
func Sub(key string) Configurator { return _c.Sub(key) }
func (c *configurator) Sub(key string) Configurator {
	subv := New()
	data := c.Get(key)
	if data == nil {
		return nil
	}

	if reflect.TypeOf(data).Kind() == reflect.Map {
		subv.(*configurator).config = cast.ToStringMap(data)
		return subv
	}
	return nil
}

func (c *configurator) getConfigFile() (string, error) {
	// if explicitly set, then use it
	if c.configFile != "" {
		return c.configFile, nil
	}

	cf, err := c.findConfigFile()
	if err != nil {
		return "", err
	}

	c.configFile = cf
	return c.getConfigFile()
}

func (c *configurator) getConfigType() string {
	if c.configType != "" {
		return c.configType
	}

	cf, err := c.getConfigFile()
	if err != nil {
		return ""
	}

	ext := filepath.Ext(cf)

	if len(ext) > 1 {
		return ext[1:]
	}

	return ""
}

func (c *configurator) findConfigFile() (string, error) {
	for _, cp := range c.configPaths {
		file := c.searchInPath(cp)
		if file != "" {
			return file, nil
		}
	}
	return "", ConfigFileNotFoundError{c.configName, fmt.Sprintf("%s", c.configPaths)}
}

func (c *configurator) searchInPath(in string) (filename string) {
	for _, ext := range SupportedExts {
		if b, _ := exists(filepath.Join(in, c.configName+"."+ext)); b {
			return filepath.Join(in, c.configName+"."+ext)
		}
	}

	return ""
}

func unmarshalReader(in io.Reader, config map[string]interface{}) error {
	return _c.unmarshalReader(in, config)
}

func (c *configurator) unmarshalReader(in io.Reader, config map[string]interface{}) error {
	return unmarshallConfigReader(in, config, c.getConfigType())
}

func (c *configurator) insensitiviseMaps() {
	insensitiviseMap(c.config)
	insensitiviseMap(c.defaults)
	insensitiviseMap(c.override)
	insensitiviseMap(c.kvstore)
}

func (c *configurator) realKey(key string) string {
	newkey, exists := c.aliases[key]
	if exists {
		return c.realKey(newkey)
	}
	return key
}

func (c *configurator) searchMap(source map[string]interface{}, path []string) interface{} {
	if len(path) == 0 {
		return source
	}

	next, ok := source[path[0]]
	if ok {
		// Fast path
		if len(path) == 1 {
			return next
		}

		// Nested case
		switch next.(type) {
		case map[interface{}]interface{}:
			return c.searchMap(cast.ToStringMap(next), path[1:])
		case map[string]interface{}:
			// Type assertion is safe here since it is only reached
			// if the type of `next` is the same as the type being asserted
			return c.searchMap(next.(map[string]interface{}), path[1:])
		default:
			// got a value but nested key expected, return "nil" for not found
			return nil
		}
	}
	return nil
}

// UnmarshalKey takes a single key and unmarshals it into a Struct.
func UnmarshalKey(key string, rawVal interface{}) error { return _c.UnmarshalKey(key, rawVal) }
func (c *configurator) UnmarshalKey(key string, rawVal interface{}) error {
	err := decode(c.Get(key), defaultDecoderConfig(rawVal))

	if err != nil {
		return err
	}

	c.insensitiviseMaps()

	return nil
}

// Unmarshal unmarshals the config into a Struct. Make sure that the tags
// on the fields of the structure are properly set.
func Unmarshal(rawVal interface{}) error { return _c.Unmarshal(rawVal) }
func (c *configurator) Unmarshal(rawVal interface{}) error {
	err := decode(c.AllSettings(), defaultDecoderConfig(rawVal))

	if err != nil {
		return err
	}

	c.insensitiviseMaps()

	return nil
}

// defaultDecoderConfig returns default mapsstructure.DecoderConfig with suppot
// of time.Duration values
func defaultDecoderConfig(output interface{}) *mapstructure.DecoderConfig {
	return &mapstructure.DecoderConfig{
		Metadata:         nil,
		Result:           output,
		WeaklyTypedInput: true,
		DecodeHook:       mapstructure.StringToTimeDurationHookFunc(),
	}
}

// A wrapper around mapstructure.Decode that mimics the WeakDecode functionality
func decode(input interface{}, config *mapstructure.DecoderConfig) error {
	decoder, err := mapstructure.NewDecoder(config)
	if err != nil {
		return err
	}
	return decoder.Decode(input)
}

// UnmarshalExact unmarshals the config into a Struct, erroring if a field is nonexistent
// in the destination struct.
func (c *configurator) UnmarshalExact(rawVal interface{}) error {
	config := defaultDecoderConfig(rawVal)
	config.ErrorUnused = true

	err := decode(c.AllSettings(), config)

	if err != nil {
		return err
	}

	c.insensitiviseMaps()

	return nil
}

// BindPFlags binds a full flag set to the configuration, using each flag's long
// name as the config key.
func BindPFlags(flags *pflag.FlagSet) error { return _c.BindPFlags(flags) }
func (c *configurator) BindPFlags(flags *pflag.FlagSet) error {
	return c.BindFlagValues(pflagValueSet{flags})
}

// BindPFlag binds a specific key to a pflag (as used by cobra).
// Example (where serverCmd is a Cobra instance):
//
//	 serverCmd.Flags().Int("port", 1138, "Port to run Application server on")
//	 Viper.BindPFlag("port", serverCmd.Flags().Lookup("port"))
//
func BindPFlag(key string, flag *pflag.Flag) error { return _c.BindPFlag(key, flag) }
func (c *configurator) BindPFlag(key string, flag *pflag.Flag) error {
	return c.BindFlagValue(key, pflagValue{flag})
}

// BindFlagValues binds a full FlagValue set to the configuration, using each flag's long
// name as the config key.
func BindFlagValues(flags FlagValueSet) error { return _c.BindFlagValues(flags) }
func (c *configurator) BindFlagValues(flags FlagValueSet) (err error) {
	flags.VisitAll(func(flag FlagValue) {
		if err = c.BindFlagValue(flag.Name(), flag); err != nil {
			return
		}
	})
	return nil
}

// BindFlagValue binds a specific key to a FlagValue.
// Example (where serverCmd is a Cobra instance):
//
//	 serverCmd.Flags().Int("port", 1138, "Port to run Application server on")
//	 Viper.BindFlagValue("port", serverCmd.Flags().Lookup("port"))
//
func BindFlagValue(key string, flag FlagValue) error { return _c.BindFlagValue(key, flag) }
func (c *configurator) BindFlagValue(key string, flag FlagValue) error {
	if flag == nil {
		return fmt.Errorf("flag for %q is nil", key)
	}
	c.pflags[strings.ToLower(key)] = flag
	return nil
}

// BindEnv binds a Viper key to a ENV variable.
// ENV variables are case sensitive.
// If only a key is provided, it will use the env key matching the key, uppercased.
// EnvPrefix will be used when set when env name is not provided.
func BindEnv(input ...string) error { return _c.BindEnv(input...) }
func (c *configurator) BindEnv(input ...string) error {
	var key, envkey string
	if len(input) == 0 {
		return fmt.Errorf("BindEnv missing key to bind to")
	}

	key = strings.ToLower(input[0])

	if len(input) == 1 {
		envkey = c.mergeWithEnvPrefix(key)
	} else {
		envkey = input[1]
	}

	c.env[key] = envkey

	return nil
}

func (c *configurator) find(lcaseKey string) interface{} {

	var (
		val    interface{}
		exists bool
		path   = strings.Split(lcaseKey, c.keyDelim)
		nested = len(path) > 1
	)

	// compute the path through the nested maps to the nested value
	if nested && c.isPathShadowedInDeepMap(path, castMapStringToMapInterface(c.aliases)) != "" {
		return nil
	}

	// if the requested key is an alias, then return the proper key
	lcaseKey = c.realKey(lcaseKey)
	path = strings.Split(lcaseKey, c.keyDelim)
	nested = len(path) > 1

	// Set() override first
	val = c.searchMap(c.override, path)
	if val != nil {
		return val
	}
	if nested && c.isPathShadowedInDeepMap(path, c.override) != "" {
		return nil
	}

	// PFlag override next
	flag, exists := c.pflags[lcaseKey]
	if exists && flag.HasChanged() {
		switch flag.ValueType() {
		case "int", "int8", "int16", "int32", "int64":
			return cast.ToInt(flag.ValueString())
		case "bool":
			return cast.ToBool(flag.ValueString())
		case "stringSlice":
			s := strings.TrimPrefix(flag.ValueString(), "[")
			s = strings.TrimSuffix(s, "]")
			res, _ := readAsCSV(s)
			return res
		default:
			return flag.ValueString()
		}
	}
	if nested && c.isPathShadowedInFlatMap(path, c.pflags) != "" {
		return nil
	}

	// Env override next
	if c.automaticEnvApplied {
		// even if it hasn't been registered, if automaticEnv is used,
		// check any Get request
		if val = c.getEnv(c.mergeWithEnvPrefix(lcaseKey)); val != "" {
			return val
		}
		if nested && c.isPathShadowedInAutoEnv(path) != "" {
			return nil
		}
	}
	envkey, exists := c.env[lcaseKey]
	if exists {
		if val = c.getEnv(envkey); val != "" {
			return val
		}
	}
	if nested && c.isPathShadowedInFlatMap(path, c.env) != "" {
		return nil
	}

	// Config file next
	val = c.searchMapWithPathPrefixes(c.config, path)
	if val != nil {
		return val
	}
	if nested && c.isPathShadowedInDeepMap(path, c.config) != "" {
		return nil
	}

	// K/V store next
	val = c.searchMap(c.kvstore, path)
	if val != nil {
		return val
	}
	if nested && c.isPathShadowedInDeepMap(path, c.kvstore) != "" {
		return nil
	}

	// Default next
	val = c.searchMap(c.defaults, path)
	if val != nil {
		return val
	}
	if nested && c.isPathShadowedInDeepMap(path, c.defaults) != "" {
		return nil
	}

	// last chance: if no other value is returned and a flag does exist for the value,
	// get the flag's value even if the flag's value has not changed
	if flag, exists := c.pflags[lcaseKey]; exists {
		switch flag.ValueType() {
		case "int", "int8", "int16", "int32", "int64":
			return cast.ToInt(flag.ValueString())
		case "bool":
			return cast.ToBool(flag.ValueString())
		case "stringSlice":
			s := strings.TrimPrefix(flag.ValueString(), "[")
			s = strings.TrimSuffix(s, "]")
			res, _ := readAsCSV(s)
			return res
		default:
			return flag.ValueString()
		}
	}
	// last item, no need to check shadowing

	return nil
}

func (c *configurator) searchMapWithPathPrefixes(source map[string]interface{}, path []string) interface{} {
	if len(path) == 0 {
		return source
	}

	// search for path prefixes, starting from the longest one
	for i := len(path); i > 0; i-- {
		prefixKey := strings.ToLower(strings.Join(path[0:i], c.keyDelim))

		next, ok := source[prefixKey]
		if ok {
			// Fast path
			if i == len(path) {
				return next
			}

			// Nested case
			var val interface{}
			switch next.(type) {
			case map[interface{}]interface{}:
				val = c.searchMapWithPathPrefixes(cast.ToStringMap(next), path[i:])
			case map[string]interface{}:
				// Type assertion is safe here since it is only reached
				// if the type of `next` is the same as the type being asserted
				val = c.searchMapWithPathPrefixes(next.(map[string]interface{}), path[i:])
			default:
				// got a value but nested key expected, do nothing and look for next prefix
			}
			if val != nil {
				return val
			}
		}
	}

	// not found
	return nil
}

func (c *configurator) isPathShadowedInDeepMap(path []string, m map[string]interface{}) string {
	var parentVal interface{}
	for i := 1; i < len(path); i++ {
		parentVal = c.searchMap(m, path[0:i])
		if parentVal == nil {
			// not found, no need to add more path elements
			return ""
		}
		switch parentVal.(type) {
		case map[interface{}]interface{}:
			continue
		case map[string]interface{}:
			continue
		default:
			// parentVal is a regular value which shadows "path"
			return strings.Join(path[0:i], c.keyDelim)
		}
	}
	return ""
}

func (c *configurator) isPathShadowedInFlatMap(path []string, mi interface{}) string {
	// unify input map
	var m map[string]interface{}
	switch mi.(type) {
	case map[string]string, map[string]FlagValue:
		m = cast.ToStringMap(mi)
	default:
		return ""
	}

	// scan paths
	var parentKey string
	for i := 1; i < len(path); i++ {
		parentKey = strings.Join(path[0:i], c.keyDelim)
		if _, ok := m[parentKey]; ok {
			return parentKey
		}
	}
	return ""
}

func (c *configurator) isPathShadowedInAutoEnv(path []string) string {
	var parentKey string
	var val string
	for i := 1; i < len(path); i++ {
		parentKey = strings.Join(path[0:i], c.keyDelim)
		if val = c.getEnv(c.mergeWithEnvPrefix(parentKey)); val != "" {
			return parentKey
		}
	}
	return ""
}

func (c *configurator) getEnv(key string) string {
	if c.envKeyReplacer != nil {
		key = c.envKeyReplacer.Replace(key)
	}
	return os.Getenv(key)
}

func (c *configurator) mergeWithEnvPrefix(in string) string {
	if c.envPrefix != "" {
		return strings.ToUpper(c.envPrefix + "_" + in)
	}

	return strings.ToUpper(in)
}

func castToMapStringInterface(
	src map[interface{}]interface{}) map[string]interface{} {
	tgt := map[string]interface{}{}
	for k, v := range src {
		tgt[fmt.Sprintf("%v", k)] = v
	}
	return tgt
}

func castMapStringToMapInterface(src map[string]string) map[string]interface{} {
	tgt := map[string]interface{}{}
	for k, v := range src {
		tgt[k] = v
	}
	return tgt
}

func castMapFlagToMapInterface(src map[string]FlagValue) map[string]interface{} {
	tgt := map[string]interface{}{}
	for k, v := range src {
		tgt[k] = v
	}
	return tgt
}

func readAsCSV(val string) ([]string, error) {
	if val == "" {
		return []string{}, nil
	}
	stringReader := strings.NewReader(val)
	csvReader := csv.NewReader(stringReader)
	return csvReader.Read()
}

// AllSettings merges all settings and returns them as a map[string]interface{}.
func AllSettings() map[string]interface{} { return _c.AllSettings() }
func (c *configurator) AllSettings() map[string]interface{} {
	m := map[string]interface{}{}
	// start from the list of keys, and construct the map one value at a time
	for _, k := range c.AllKeys() {
		value := c.Get(k)
		if value == nil {
			// should not happen, since AllKeys() returns only keys holding a value,
			// check just in case anything changes
			continue
		}
		path := strings.Split(k, c.keyDelim)
		lastKey := strings.ToLower(path[len(path)-1])
		deepestMap := deepSearch(m, path[0:len(path)-1])
		// set innermost value
		deepestMap[lastKey] = value
	}
	return m
}

// AllKeys returns all keys holding a value, regardless of where they are set.
// Nested keys are returned with a v.keyDelim (= ".") separator
func AllKeys() []string { return _c.AllKeys() }
func (c *configurator) AllKeys() []string {
	m := map[string]bool{}
	// add all paths, by order of descending priority to ensure correct shadowing
	m = c.flattenAndMergeMap(m, castMapStringToMapInterface(c.aliases), "")
	m = c.flattenAndMergeMap(m, c.override, "")
	m = c.mergeFlatMap(m, castMapFlagToMapInterface(c.pflags))
	m = c.mergeFlatMap(m, castMapStringToMapInterface(c.env))
	m = c.flattenAndMergeMap(m, c.config, "")
	m = c.flattenAndMergeMap(m, c.kvstore, "")
	m = c.flattenAndMergeMap(m, c.defaults, "")

	// convert set of paths to list
	a := []string{}
	for x := range m {
		a = append(a, x)
	}
	return a
}

// flattenAndMergeMap recursively flattens the given map into a map[string]bool
// of key paths (used as a set, easier to manipulate than a []string):
// - each path is merged into a single key string, delimited with v.keyDelim (= ".")
// - if a path is shadowed by an earlier value in the initial shadow map,
//   it is skipped.
// The resulting set of paths is merged to the given shadow set at the same time.
func (c *configurator) flattenAndMergeMap(shadow map[string]bool, m map[string]interface{}, prefix string) map[string]bool {
	if shadow != nil && prefix != "" && shadow[prefix] {
		// prefix is shadowed => nothing more to flatten
		return shadow
	}
	if shadow == nil {
		shadow = make(map[string]bool)
	}

	var m2 map[string]interface{}
	if prefix != "" {
		prefix += c.keyDelim
	}
	for k, val := range m {
		fullKey := prefix + k
		switch val.(type) {
		case map[string]interface{}:
			m2 = val.(map[string]interface{})
		case map[interface{}]interface{}:
			m2 = cast.ToStringMap(val)
		default:
			// immediate value
			shadow[strings.ToLower(fullKey)] = true
			continue
		}
		// recursively merge to shadow map
		shadow = c.flattenAndMergeMap(shadow, m2, fullKey)
	}
	return shadow
}

// mergeFlatMap merges the given maps, excluding values of the second map
// shadowed by values from the first map.
func (c *configurator) mergeFlatMap(shadow map[string]bool, m map[string]interface{}) map[string]bool {
	// scan keys
outer:
	for k, _ := range m {
		path := strings.Split(k, c.keyDelim)
		// scan intermediate paths
		var parentKey string
		for i := 1; i < len(path); i++ {
			parentKey = strings.Join(path[0:i], c.keyDelim)
			if shadow[parentKey] {
				// path is shadowed, continue
				continue outer
			}
		}
		// add key
		shadow[strings.ToLower(k)] = true
	}
	return shadow
}