package domain

import (
	"errors"

	rvboxv1 "github.com/rvbox/rvbox/gen/go/rvbox/v1"
)

var ErrNoCompatibleProtocol = errors.New("no compatible protocol version")

// SelectProtocol chooses the highest mutually supported minor version.
func SelectProtocol(server, client *rvboxv1.ProtocolRange) (*rvboxv1.ProtocolVersion, error) {
	if server == nil || client == nil || server.Major == 0 || client.Major == 0 || server.Major != client.Major || server.MinMinor > server.MaxMinor || client.MinMinor > client.MaxMinor {
		return nil, ErrNoCompatibleProtocol
	}
	minimum := server.MinMinor
	if client.MinMinor > minimum {
		minimum = client.MinMinor
	}
	maximum := server.MaxMinor
	if client.MaxMinor < maximum {
		maximum = client.MaxMinor
	}
	if minimum > maximum {
		return nil, ErrNoCompatibleProtocol
	}
	return &rvboxv1.ProtocolVersion{Major: server.Major, Minor: maximum}, nil
}