package model

import (
	"errors"
	"time"
)

var (
	ErrPollExhausted = errors.New("poll budget exhausted; reconciliation required")
	ErrPollInFlight  = errors.New("a poll round is still in flight")
	ErrPollResolved  = errors.New("poll already resolved")
	ErrPollNotDue    = errors.New("poll interval has not elapsed")
)

// NextRound 用数据库时间检查已锁定的查询快照。调用方还必须核验执行门控，
// 并在同一事务中写入计数、唯一轮次及对应的 Pulse 任务。
// 下一查询时间为空表示持久化暂挂，不能视为允许立即发起查询。
func (p PollState) NextRound(now time.Time) (uint32, error) {
	if p.ResolvedAt != nil {
		return 0, ErrPollResolved
	}
	if p.MaxRounds == 0 || p.UsedRounds >= p.MaxRounds || !now.Before(p.DeadlineAt) {
		return 0, ErrPollExhausted
	}
	if p.CurrentTaskID != nil {
		return 0, ErrPollInFlight
	}
	if p.NextPollAt == nil || now.Before(*p.NextPollAt) {
		return 0, ErrPollNotDue
	}
	return p.UsedRounds + 1, nil
}