package viper

import (
	"errors"
	"strings"
	"sync"

	"github.com/spf13/viper/internal/encoding/dotenv"
	"github.com/spf13/viper/internal/encoding/json"
	"github.com/spf13/viper/internal/encoding/toml"
	"github.com/spf13/viper/internal/encoding/yaml"
)

// Encoder encodes Viper's internal data structures into a byte representation.
// It's primarily used for encoding a map[string]any into a file format.
type Encoder interface {
	Encode(v map[string]any) ([]byte, error)
}

// Decoder decodes the contents of a byte slice into Viper's internal data structures.
// It's primarily used for decoding contents of a file into a map[string]any.
type Decoder interface {
	Decode(b []byte, v map[string]any) error
}

// Codec combines [Encoder] and [Decoder] interfaces.
type Codec interface {
	Encoder
	Decoder
}

// TODO: consider adding specific errors for not found scenarios

// EncoderRegistry returns an [Encoder] for a given format.
//
// Format is case-insensitive.
//
// [EncoderRegistry] returns an error if no [Encoder] is registered for the format.
type EncoderRegistry interface {
	Encoder(format string) (Encoder, error)
}

// DecoderRegistry returns an [Decoder] for a given format.
//
// Format is case-insensitive.
//
// [DecoderRegistry] returns an error if no [Decoder] is registered for the format.
type DecoderRegistry interface {
	Decoder(format string) (Decoder, error)
}

// [CodecRegistry] combines [EncoderRegistry] and [DecoderRegistry] interfaces.
type CodecRegistry interface {
	EncoderRegistry
	DecoderRegistry
}

// WithEncoderRegistry sets a custom [EncoderRegistry].
func WithEncoderRegistry(r EncoderRegistry) Option {
	return optionFunc(func(v *Viper) {
		v.encoderRegistry = r
	})
}

// WithDecoderRegistry sets a custom [DecoderRegistry].
func WithDecoderRegistry(r DecoderRegistry) Option {
	return optionFunc(func(v *Viper) {
		v.decoderRegistry = r
	})
}

// WithCodecRegistry sets a custom [EncoderRegistry] and [DecoderRegistry].
func WithCodecRegistry(r CodecRegistry) Option {
	return optionFunc(func(v *Viper) {
		v.encoderRegistry = r
		v.decoderRegistry = r
	})
}

type codecRegistry struct {
	v *Viper
}

func (r codecRegistry) Encoder(format string) (Encoder, error) {
	encoder, ok := r.codec(format)
	if !ok {
		return nil, errors.New("encoder not found for this format")
	}

	return encoder, nil
}

func (r codecRegistry) Decoder(format string) (Decoder, error) {
	decoder, ok := r.codec(format)
	if !ok {
		return nil, errors.New("decoder not found for this format")
	}

	return decoder, nil
}

func (r codecRegistry) codec(format string) (Codec, bool) {
	switch strings.ToLower(format) {
	case "yaml", "yml":
		return yaml.Codec{}, true

	case "json":
		return json.Codec{}, true

	case "toml":
		return toml.Codec{}, true

	case "dotenv", "env":
		return &dotenv.Codec{}, true
	}

	return nil, false
}

// DefaultCodecRegistry is a simple implementation of [CodecRegistry] that allows registering custom [Codec]s.
type DefaultCodecRegistry struct {
	codecs map[string]Codec

	mu   sync.RWMutex
	once sync.Once
}

// NewCodecRegistry returns a new [CodecRegistry], ready to accept custom [Codec]s.
func NewCodecRegistry() *DefaultCodecRegistry {
	r := &DefaultCodecRegistry{}

	r.init()

	return r
}

func (r *DefaultCodecRegistry) init() {
	r.once.Do(func() {
		r.codecs = map[string]Codec{}
	})
}

// RegisterCodec registers a custom [Codec].
//
// Format is case-insensitive.
func (r *DefaultCodecRegistry) RegisterCodec(format string, codec Codec) error {
	r.init()

	r.mu.Lock()
	defer r.mu.Unlock()

	r.codecs[strings.ToLower(format)] = codec

	return nil
}

// Encoder implements the [EncoderRegistry] interface.
//
// Format is case-insensitive.
func (r *DefaultCodecRegistry) Encoder(format string) (Encoder, error) {
	encoder, ok := r.codec(format)
	if !ok {
		return nil, errors.New("encoder not found for this format")
	}

	return encoder, nil
}

// Decoder implements the [DecoderRegistry] interface.
//
// Format is case-insensitive.
func (r *DefaultCodecRegistry) Decoder(format string) (Decoder, error) {
	decoder, ok := r.codec(format)
	if !ok {
		return nil, errors.New("decoder not found for this format")
	}

	return decoder, nil
}

func (r *DefaultCodecRegistry) codec(format string) (Codec, bool) {
	r.mu.Lock()
	defer r.mu.Unlock()

	format = strings.ToLower(format)

	if r.codecs != nil {
		codec, ok := r.codecs[format]
		if ok {
			return codec, true
		}
	}

	switch format {
	case "yaml", "yml":
		return yaml.Codec{}, true

	case "json":
		return json.Codec{}, true

	case "toml":
		return toml.Codec{}, true

	case "dotenv", "env":
		return &dotenv.Codec{}, true
	}

	return nil, false
}