package meta

import "bytes"

type ChangedFields struct {
	fieldNames map[string]struct{}
	fieldsKey  *bytes.Buffer
}

func NewChangedFields(fieldCount int) ChangedFields {
	keyBuffer := bytes.NewBuffer(make([]byte, 0, fieldCount*2))

	cf := ChangedFields{
		fieldNames: make(map[string]struct{}, fieldCount),
		fieldsKey:  keyBuffer,
	}
	return cf
}

func (cf *ChangedFields) Reset() {
	if cf.fieldNames == nil {
		cf.fieldNames = make(map[string]struct{})
	} else {
		for k := range cf.fieldNames {
			delete(cf.fieldNames, k)
		}
	}
}

func (cf ChangedFields) Changed(field string) bool {
	_, ok := cf.fieldNames[field]
	return ok
}

func (cf *ChangedFields) SetChanged(fields ...string) {
	if cf.fieldNames == nil {
		cf.fieldNames = make(map[string]struct{})
	}

	for _, field := range fields {
		if _, exists := cf.fieldNames[field]; exists {
			continue
		}

		cf.fieldNames[field] = struct{}{}
		cf.fieldsKey.WriteString(field)
	}
}

func (cf ChangedFields) Empty() bool {
	return len(cf.fieldNames) == 0
}

func (cf ChangedFields) IsNil() bool {
	return cf.fieldNames == nil
}

func (cf ChangedFields) GetFieldsKey() string {
	return cf.fieldsKey.String()
}