package config

import (
	"bytes"
	"encoding/gob"
	"encoding/json"
	"fmt"
	"strings"

	"github.com/imdario/mergo"
	"google.golang.org/protobuf/encoding/protojson"
	"google.golang.org/protobuf/proto"
)

// Reader is config reader.
type Reader interface {
	Merge(...*KeyValue) error
	Value(string) (Value, bool)
	Source() ([]byte, error)
	Resolve() error
}

type reader struct {
	opts   options
	values map[string]interface{}
}

func newReader(opts options) Reader {
	return &reader{
		opts:   opts,
		values: make(map[string]interface{}),
	}
}

func (r *reader) Merge(kvs ...*KeyValue) error {
	merged, err := cloneMap(r.values)
	if err != nil {
		return err
	}
	for _, kv := range kvs {
		next := make(map[string]interface{})
		if err := r.opts.decoder(kv, next); err != nil {
			return err
		}
		if err := mergo.Map(&merged, convertMap(next), mergo.WithOverride); err != nil {
			return err
		}
	}
	r.values = merged
	return nil
}

func (r *reader) Value(path string) (Value, bool) {
	return readValue(r.values, path)
}

func (r *reader) Source() ([]byte, error) {
	return marshalJSON(convertMap(r.values))
}

func (r *reader) Resolve() error {
	return r.opts.resolver(r.values)
}

func cloneMap(src map[string]interface{}) (map[string]interface{}, error) {
	// https://gist.github.com/soroushjp/0ec92102641ddfc3ad5515ca76405f4d
	var buf bytes.Buffer
	gob.Register(map[string]interface{}{})
	gob.Register([]interface{}{})
	enc := gob.NewEncoder(&buf)
	dec := gob.NewDecoder(&buf)
	err := enc.Encode(src)
	if err != nil {
		return nil, err
	}
	var copy map[string]interface{}
	err = dec.Decode(&copy)
	if err != nil {
		return nil, err
	}
	return copy, nil
}

func convertMap(src interface{}) interface{} {
	switch m := src.(type) {
	case map[string]interface{}:
		dst := make(map[string]interface{}, len(m))
		for k, v := range m {
			dst[k] = convertMap(v)
		}
		return dst
	case map[interface{}]interface{}:
		dst := make(map[string]interface{}, len(m))
		for k, v := range m {
			dst[fmt.Sprint(k)] = convertMap(v)
		}
		return dst
	case []interface{}:
		dst := make([]interface{}, len(m))
		for k, v := range m {
			dst[k] = convertMap(v)
		}
		return dst
	default:
		return src
	}
}

// readValue read Value in given map[string]interface{}
// by the given path, will return false if not found.
func readValue(values map[string]interface{}, path string) (Value, bool) {
	var (
		next = values
		keys = strings.Split(path, ".")
		last = len(keys) - 1
	)
	for idx, key := range keys {
		value, ok := next[key]
		if !ok {
			return nil, false
		}
		if idx == last {
			av := &atomicValue{}
			av.Store(value)
			return av, true
		}
		switch vm := value.(type) {
		case map[string]interface{}:
			next = vm
		default:
			return nil, false
		}
	}
	return nil, false
}

func marshalJSON(v interface{}) ([]byte, error) {
	if m, ok := v.(proto.Message); ok {
		return protojson.MarshalOptions{EmitUnpopulated: true}.Marshal(m)
	}
	return json.Marshal(v)
}

func unmarshalJSON(data []byte, v interface{}) error {
	if m, ok := v.(proto.Message); ok {
		return protojson.UnmarshalOptions{DiscardUnknown: true}.Unmarshal(data, m)
	}
	return json.Unmarshal(data, v)
}