package ssob

import (
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"reflect"
	"sync"
)

type Decoder struct {
	mutex sync.Mutex
	r     io.Reader
}

func NewDecoder(r io.Reader) *Decoder {
	dec := new(Decoder)
	dec.r = r
	return dec
}

func (dec *Decoder) Decode(e interface{}) (err error) {
	return dec.DecodeValue(reflect.ValueOf(e))
}

func (dec *Decoder) DecodeValue(value reflect.Value) (err error) {
	if value.Type() == reflect.TypeOf(errors.New("")) || value.Type() == reflect.TypeOf((*error)(nil)) {
		var errstr string
		if err = dec.Decode(&errstr); err != nil {
			return err
		}
		if errstr != "" {
			*value.Interface().(*error) = errors.New(errstr)
		}
		return nil
	}

	if value.Kind() == reflect.Invalid {
		return fmt.Errorf("ssob: Cannot decode nil: %w", ErrValueInvalid)
	}

	if value.Kind() == reflect.Ptr && value.IsNil() {
		return fmt.Errorf("ssob: Cannot decode nil of type %s: %w", value.Type().String(), ErrValueInvalid)
	}

	dec.mutex.Lock()
	defer dec.mutex.Unlock()

	lb := make([]byte, 4)
	err = binary.Read(dec.r, binary.BigEndian, lb)
	if err != nil {
		return err
	}
	l, n, err := UnmarshalInt32(lb)
	if err != nil || n != 4 {
		return err
	}

	bb := make([]byte, l)
	err = binary.Read(dec.r, binary.BigEndian, bb)
	if err != nil {
		return err
	}

	_, err = unmarshal(value.Interface(), bb)
	return err
}