package ssob

import (
	"encoding/binary"
	"errors"
	"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.Kind() == reflect.Invalid {
		return errors.New("ssob: Cannot decode nil value")
	}

	if value.Kind() == reflect.Ptr && value.IsNil() {
		return errors.New("ssob: Cannot decode nil of type " + value.Type().String())
	}

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

	lb := make([]byte, 8)
	err = binary.Read(dec.r, binary.BigEndian, lb)
	if err != nil {
		return err
	}
	l, n, err := unmarshalInt64(lb)
	if err != nil || n != 8 {
		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
}