// Package state persists task metadata. It never executes application actions.
package state

import (
	"errors"
	"regexp"
)

var (
	ErrBusy       = errors.New("host state is locked")
	ErrClosed     = errors.New("session is closed")
	ErrPoisoned   = errors.New("state write outcome uncertain; reopen and reconcile")
	ErrConflict   = errors.New("operation identity or revision conflict")
	ErrUnresolved = errors.New("another operation requires completion or reconciliation")
	ErrTransition = errors.New("invalid operation transition")
	ErrNotFound   = errors.New("operation not found")
	ErrCapacity   = errors.New("operation history capacity exhausted")
	idPattern     = regexp.MustCompile(`^[a-z][a-z0-9-]{0,47}$`)
	hashPattern   = regexp.MustCompile(`^sha256:[a-f0-9]{64}$`)
)

type Status string

const (
	Queued          Status = "queued"
	Running         Status = "running"
	Succeeded       Status = "succeeded"
	FailedRecovered Status = "failed_recovered"
	NeedsAttention  Status = "needs_attention"
	Unknown         Status = "unknown"
	Cancelled       Status = "cancelled"
)

type Operation struct {
	ID       string `json:"id"`
	PlanHash string `json:"planHash"`
	Status   Status `json:"status"`
	Revision uint64 `json:"revision"`
}

func (s Status) terminal() bool { return s == Succeeded || s == FailedRecovered || s == Cancelled }
func (s Status) valid() bool {
	return s.terminal() || s == Queued || s == Running || s == NeedsAttention || s == Unknown
}
func allowed(from, to Status) bool {
	switch from {
	case Queued:
		return to == Running || to == Cancelled
	case Running:
		return to == Succeeded || to == FailedRecovered || to == NeedsAttention || to == Unknown
	case NeedsAttention, Unknown:
		return to == Succeeded || to == FailedRecovered
	default:
		return false
	}
}