package services

import (
	"context"
	"errors"
	"fmt"

	"tyapi-server/internal/domains/finance/entities"
	"tyapi-server/internal/domains/finance/value_objects"

	"github.com/shopspring/decimal"
)

// InvoiceDomainService 发票领域服务接口
// 职责：处理发票领域的业务规则和计算逻辑，不涉及外部依赖
type InvoiceDomainService interface {
	// 验证发票信息完整性
	ValidateInvoiceInfo(ctx context.Context, info *value_objects.InvoiceInfo, invoiceType value_objects.InvoiceType) error

	// 验证开票金额是否合法（基于业务规则）
	ValidateInvoiceAmount(ctx context.Context, amount decimal.Decimal, availableAmount decimal.Decimal) error

	// 计算可开票金额（纯计算逻辑）
	CalculateAvailableAmount(totalRecharged decimal.Decimal, totalGifted decimal.Decimal, totalInvoiced decimal.Decimal) decimal.Decimal

	// 验证发票申请状态转换
	ValidateStatusTransition(currentStatus entities.ApplicationStatus, targetStatus entities.ApplicationStatus) error

	// 验证发票申请业务规则
	ValidateInvoiceApplication(ctx context.Context, application *entities.InvoiceApplication) error
}

// InvoiceDomainServiceImpl 发票领域服务实现
type InvoiceDomainServiceImpl struct {
	// 领域服务不依赖仓储，只处理业务规则
}

// NewInvoiceDomainService 创建发票领域服务
func NewInvoiceDomainService() InvoiceDomainService {
	return &InvoiceDomainServiceImpl{}
}

// ValidateInvoiceInfo 验证发票信息完整性
func (s *InvoiceDomainServiceImpl) ValidateInvoiceInfo(ctx context.Context, info *value_objects.InvoiceInfo, invoiceType value_objects.InvoiceType) error {
	if info == nil {
		return errors.New("发票信息不能为空")
	}

	switch invoiceType {
	case value_objects.InvoiceTypeGeneral:
		return info.ValidateForGeneralInvoice()
	case value_objects.InvoiceTypeSpecial:
		return info.ValidateForSpecialInvoice()
	default:
		return errors.New("无效的发票类型")
	}
}

// ValidateInvoiceAmount 验证开票金额是否合法（基于业务规则）
func (s *InvoiceDomainServiceImpl) ValidateInvoiceAmount(ctx context.Context, amount decimal.Decimal, availableAmount decimal.Decimal) error {
	if amount.LessThanOrEqual(decimal.Zero) {
		return errors.New("开票金额必须大于0")
	}

	if amount.GreaterThan(availableAmount) {
		return fmt.Errorf("开票金额不能超过可开票金额，可开票金额：%s", availableAmount.String())
	}

	// 最小开票金额限制
	minAmount := decimal.NewFromFloat(0.01) // 最小0.01元
	if amount.LessThan(minAmount) {
		return fmt.Errorf("开票金额不能少于%s元", minAmount.String())
	}

	return nil
}

// CalculateAvailableAmount 计算可开票金额（纯计算逻辑）
func (s *InvoiceDomainServiceImpl) CalculateAvailableAmount(totalRecharged decimal.Decimal, totalGifted decimal.Decimal, totalInvoiced decimal.Decimal) decimal.Decimal {
	// 可开票金额 = 充值金额 - 已开票金额（不包含赠送金额）
	availableAmount := totalRecharged.Sub(totalInvoiced)
	if availableAmount.LessThan(decimal.Zero) {
		availableAmount = decimal.Zero
	}
	return availableAmount
}

// ValidateStatusTransition 验证发票申请状态转换
func (s *InvoiceDomainServiceImpl) ValidateStatusTransition(currentStatus entities.ApplicationStatus, targetStatus entities.ApplicationStatus) error {
	// 定义允许的状态转换
	allowedTransitions := map[entities.ApplicationStatus][]entities.ApplicationStatus{
		entities.ApplicationStatusPending: {
			entities.ApplicationStatusCompleted,
			entities.ApplicationStatusRejected,
		},
		entities.ApplicationStatusCompleted: {
			// 已完成状态不能再转换
		},
		entities.ApplicationStatusRejected: {
			// 已拒绝状态不能再转换
		},
	}

	allowedTargets, exists := allowedTransitions[currentStatus]
	if !exists {
		return fmt.Errorf("无效的当前状态：%s", currentStatus)
	}

	for _, allowed := range allowedTargets {
		if allowed == targetStatus {
			return nil
		}
	}

	return fmt.Errorf("不允许从状态 %s 转换到状态 %s", currentStatus, targetStatus)
}

// ValidateInvoiceApplication 验证发票申请业务规则
func (s *InvoiceDomainServiceImpl) ValidateInvoiceApplication(ctx context.Context, application *entities.InvoiceApplication) error {
	if application == nil {
		return errors.New("发票申请不能为空")
	}

	// 验证基础字段
	if application.UserID == "" {
		return errors.New("用户ID不能为空")
	}

	if application.Amount.LessThanOrEqual(decimal.Zero) {
		return errors.New("申请金额必须大于0")
	}

	// 验证发票类型
	if !application.InvoiceType.IsValid() {
		return errors.New("无效的发票类型")
	}

	// 验证开票信息
	if application.CompanyName == "" {
		return errors.New("公司名称不能为空")
	}

	if application.TaxpayerID == "" {
		return errors.New("纳税人识别号不能为空")
	}

	if application.ReceivingEmail == "" {
		return errors.New("发票接收邮箱不能为空")
	}

	return nil
}