package nul

import (
	"encoding/json"

	"github.com/reiver/go-erorr"
)

const errNilReceiver = erorr.Error("nul: nil receiver")

var _ json.Unmarshaler = new(Nullable[bool])
var _ json.Unmarshaler = new(Nullable[string])

// UnmarshalJSON makes it so json.Unmarshaler is implemented.
func (receiver *Nullable[T]) UnmarshalJSON(data []byte) error {
	if nil == receiver {
		return errNilReceiver
	}

	switch interface{}(receiver.value).(type) {
	case bool,string,json.Unmarshaler:
		// these are OK.
	default:
		return erorr.Errorf("nul: cannot unmarshal into something of type %T from JSON because parameterized type is ‘%T’ rather than ‘bool’, ‘string’, or ‘json.Unmarshaler’", receiver, receiver.value)
	}

	if 4 == len(data) && 'n' == data[0] && 'u' == data[1] && 'l' == data[2] && 'l' == data[3] {
		*receiver = Null[T]()
		return nil

	}

	{
		var dst T

		err := json.Unmarshal(data, &dst)
		if nil != err {
			return err
		}

		*receiver = Something(dst)
	}

	return nil
}