package placement

import (
	"errors"
	"strings"

	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap"
)

const (
	attrPrefix = "$attribute:"
)

type Metric interface {
	CalculateValue(*netmap.NodeInfo, *netmap.NodeInfo) []byte
}

func ValidateMetric(raw string) error {
	if strings.HasPrefix(raw, attrPrefix) {
		return nil
	}
	return errors.New("unsupported priority metric")
}

func ParseMetric(raw string) Metric {
	if attr, found := strings.CutPrefix(raw, attrPrefix); found {
		return NewAttributeMetric(attr)
	}
	return nil
}

// attributeMetric describes priority metric based on attribute.
type attributeMetric struct {
	attribute string
}

// CalculateValue return [0] if from and to contains attribute attributeMetric.attribute and
// the value of attribute is the same. In other case return [1].
func (am *attributeMetric) CalculateValue(from *netmap.NodeInfo, to *netmap.NodeInfo) []byte {
	fromAttr := from.Attribute(am.attribute)
	toAttr := to.Attribute(am.attribute)
	if len(fromAttr) > 0 && len(toAttr) > 0 && fromAttr == toAttr {
		return []byte{0}
	}
	return []byte{1}
}

func NewAttributeMetric(raw string) Metric {
	attr, _ := strings.CutPrefix(raw, attrPrefix)
	return &attributeMetric{attribute: attr}
}