// Package domain 定义采购服务的业务实体与不依赖外部系统的状态规则。
package domain

import (
	"errors"
	"time"
)

var ErrInvalidTaskTransition = errors.New("invalid task status transition")

type TaskStatus string

const (
	TaskStatusDraft                  TaskStatus = "DRAFT"
	TaskStatusPending                TaskStatus = "PENDING"
	TaskStatusClaimed                TaskStatus = "CLAIMED"
	TaskStatusOrdering               TaskStatus = "ORDERING"
	TaskStatusWaitingPayment         TaskStatus = "WAITING_PAYMENT"
	TaskStatusReconciliationRequired TaskStatus = "RECONCILIATION_REQUIRED"
	TaskStatusNeedsManual            TaskStatus = "NEEDS_MANUAL"
	TaskStatusSucceeded              TaskStatus = "SUCCEEDED"
	TaskStatusFailed                 TaskStatus = "FAILED"
	TaskStatusCanceled               TaskStatus = "CANCELED"
)

type Source string

const (
	SourceManual Source = "MANUAL"
	SourceExcel  Source = "EXCEL"
	SourceERP    Source = "ERP"
)

type Task struct {
	ID               string
	Source           Source
	SourceRef        *string
	Title            string
	GoodsID          string
	SKUColor         string
	SKUSize          string
	Quantity         int
	MaxTotalPrice    string
	ReferenceAssetID *string
	Status           TaskStatus
	Version          int
	CreatedAt        time.Time
	UpdatedAt        time.Time
}

// CanTransitionTo 只接受架构已定义的任务状态转移，未知状态或未列出的动作均拒绝。
func (status TaskStatus) CanTransitionTo(next TaskStatus) bool {
	_, allowed := taskTransitions[status][next]
	return allowed
}

// TransitionTask 返回下一状态；非法转移必须在写库前失败，不能由调用方猜测补救路径。
func TransitionTask(current, next TaskStatus) (TaskStatus, error) {
	if !current.CanTransitionTo(next) {
		return current, ErrInvalidTaskTransition
	}

	return next, nil
}

var taskTransitions = map[TaskStatus]map[TaskStatus]struct{}{
	TaskStatusDraft: {
		TaskStatusPending:  {},
		TaskStatusCanceled: {},
	},
	TaskStatusPending: {
		TaskStatusClaimed:  {},
		TaskStatusDraft:    {},
		TaskStatusCanceled: {},
	},
	TaskStatusClaimed: {
		TaskStatusOrdering: {},
		TaskStatusDraft:    {},
	},
	TaskStatusOrdering: {
		TaskStatusNeedsManual:            {},
		TaskStatusWaitingPayment:         {},
		TaskStatusReconciliationRequired: {},
	},
	TaskStatusNeedsManual: {
		TaskStatusDraft:    {},
		TaskStatusCanceled: {},
	},
	TaskStatusWaitingPayment: {
		TaskStatusSucceeded: {},
	},
	TaskStatusReconciliationRequired: {
		TaskStatusWaitingPayment: {},
		TaskStatusFailed:         {},
	},
}