// Package planner builds offline previews. It does not inspect or change a host.
package planner

import (
	"errors"
	"net"
	"regexp"
	"strings"
)

const ProtocolVersion = 1

var (
	idPattern     = regexp.MustCompile(`^[a-z][a-z0-9-]{0,47}$`)
	digestPattern = regexp.MustCompile(`^sha256:[a-f0-9]{64}$`)
	labelPattern  = regexp.MustCompile(`^[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?$`)
)

// Intent contains no secrets. ObservedStateDigest is caller-supplied in offline
// mode; a future executor must obtain it independently from the target host.
type Intent struct {
	ProtocolVersion     int    `json:"protocolVersion"`
	HostID              string `json:"hostId"`
	InstanceID          string `json:"instanceId"`
	AppID               string `json:"appId"`
	PackageDigest       string `json:"packageDigest"`
	ImageDigest         string `json:"imageDigest"`
	Domain              string `json:"domain"`
	ObservedStateDigest string `json:"observedStateDigest"`
}

func (i Intent) Validate() error {
	if i.ProtocolVersion != ProtocolVersion {
		return errors.New("unsupported protocol version")
	}
	for _, id := range []string{i.HostID, i.InstanceID, i.AppID} {
		if !idPattern.MatchString(id) {
			return errors.New("invalid resource identifier")
		}
	}
	for _, digest := range []string{i.PackageDigest, i.ImageDigest, i.ObservedStateDigest} {
		if !digestPattern.MatchString(digest) {
			return errors.New("expected a SHA-256 digest")
		}
	}
	labels := strings.Split(i.Domain, ".")
	if len(i.Domain) > 253 || len(labels) < 2 || net.ParseIP(i.Domain) != nil {
		return errors.New("expected an ASCII DNS hostname")
	}
	for _, label := range labels {
		if !labelPattern.MatchString(label) {
			return errors.New("invalid DNS hostname label")
		}
	}
	return nil
}