package employeecollection

import (
	"context"
	"time"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"

	approvalapp "github.com/break/junhong_cmp_fiber/internal/application/approval"
	"github.com/break/junhong_cmp_fiber/internal/model"
	"github.com/break/junhong_cmp_fiber/pkg/auditcontext"
	"github.com/break/junhong_cmp_fiber/pkg/constants"
	"github.com/break/junhong_cmp_fiber/pkg/errors"
)

// ApprovalDecisionHandler 将渠道无关企业微信审批终态应用到员工代收款核销申请。
// 通过才增加账单已核销金额，驳回才释放预占；重复、乱序或延迟回调都不重复入账。
type ApprovalDecisionHandler struct {
	db    *gorm.DB
	audit ApplicationAuditWriter
}

// NewApprovalDecisionHandler 创建员工代收款核销审批终态消费者。
func NewApprovalDecisionHandler(db *gorm.DB, audit ApplicationAuditWriter) *ApprovalDecisionHandler {
	return &ApprovalDecisionHandler{db: db, audit: audit}
}

// Handle 幂等消费标准审批终态。
// 业务标识为审批尝试记录主键：先锁定尝试记录并校验审批实例一致，再按申请与账单 ID 升序加锁。
func (h *ApprovalDecisionHandler) Handle(ctx context.Context, event approvalapp.TerminalDecisionEvent) error {
	if h == nil || h.db == nil || h.audit == nil {
		return errors.New(errors.CodeInternalError, "员工代收款核销审批终态能力未配置")
	}
	if event.BusinessType != constants.ApprovalBusinessTypeEmployeeCollection || event.BusinessID == 0 || event.InstanceID == 0 {
		return errors.New(errors.CodeInvalidParam, "员工代收款核销审批终态参数无效")
	}
	ctx = auditcontext.With(ctx, auditcontext.Context{CorrelationID: event.CorrelationID, ParentEventID: event.EventID})
	return h.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		var attempt model.EmployeeCollectionApplicationAttempt
		if err := tx.WithContext(ctx).Clauses(clause.Locking{Strength: "UPDATE"}).
			First(&attempt, event.BusinessID).Error; err != nil {
			if err == gorm.ErrRecordNotFound {
				return errors.New(errors.CodeNotFound, "核销审批尝试记录不存在")
			}
			return errors.Wrap(errors.CodeDatabaseError, err, "锁定核销审批尝试记录失败")
		}
		if attempt.ApprovalInstanceID == nil || *attempt.ApprovalInstanceID != event.InstanceID {
			return errors.New(errors.CodeConflict, "核销审批尝试记录关联的审批实例不一致")
		}
		application, err := lockApplication(ctx, tx, attempt.ApplicationID)
		if err != nil {
			return err
		}
		if application.LatestAttemptID != attempt.ID {
			// 已被更新尝试取代的历史尝试终态不再改变申请事实。
			return nil
		}
		switch event.Decision {
		case constants.ApprovalDecisionApproved:
			return h.applyApproved(ctx, tx, application, &attempt, event)
		case constants.ApprovalDecisionRejected:
			return h.applyClosed(ctx, tx, application, &attempt, event,
				constants.EmployeeCollectionApplicationStatusRejected, "企业微信审批已驳回")
		case constants.ApprovalDecisionCancelled:
			return h.applyClosed(ctx, tx, application, &attempt, event,
				constants.EmployeeCollectionApplicationStatusRevoked, "企业微信审批已撤销")
		case constants.ApprovalDecisionDeleted:
			return h.applyClosed(ctx, tx, application, &attempt, event,
				constants.EmployeeCollectionApplicationStatusRevoked, "企业微信审批已删除")
		case constants.ApprovalDecisionRevokedAfterApproved:
			return h.applyRevoked(ctx, tx, application, &attempt, event)
		default:
			return errors.New(errors.CodeInvalidParam, "不支持的核销申请审批终态")
		}
	})
}

// applyApproved 将本次尝试的全部预占分摊转入已核销并重算账单状态。
// 仅当申请仍处于审批中时推进，重复或乱序回调不重复增加已核销金额。
func (h *ApprovalDecisionHandler) applyApproved(
	ctx context.Context,
	tx *gorm.DB,
	application *model.EmployeeCollectionApplication,
	attempt *model.EmployeeCollectionApplicationAttempt,
	event approvalapp.TerminalDecisionEvent,
) error {
	if application.Status != constants.EmployeeCollectionApplicationStatusPending {
		return nil
	}
	allocations, err := loadAttemptAllocations(ctx, tx, attempt.ID)
	if err != nil {
		return err
	}
	if _, err := lockBillsInAscendingOrder(ctx, tx, allocationCommandsOf(allocations)); err != nil {
		return err
	}
	now := time.Now().UTC()
	for _, allocation := range allocations {
		if err := approveAllocation(ctx, tx, allocation, now); err != nil {
			return err
		}
		if err := settleBillReservation(ctx, tx, allocation); err != nil {
			return err
		}
	}
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionApplication{}).
		Where("id = ? AND status = ?", application.ID, constants.EmployeeCollectionApplicationStatusPending).
		Updates(map[string]any{
			"status":     constants.EmployeeCollectionApplicationStatusApproved,
			"decided_at": now, "updater": 0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "标记核销申请已通过失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "核销申请状态已变化")
	}
	before := application.Status
	application.Status = constants.EmployeeCollectionApplicationStatusApproved
	application.DecidedAt = &now
	application.Updater = 0
	bills, err := reloadBills(ctx, tx, allocationCommandsOf(allocations))
	if err != nil {
		return err
	}
	approvedEventID, err := decisionEventID(application.ID, attempt.AttemptNo, "approved")
	if err != nil {
		return err
	}
	return h.audit.WriteEmployeeCollectionApplication(ctx, tx, ApplicationAudit{
		EventID:     approvedEventID,
		ActionCode:  constants.AuditActionEmployeeCollectionApplicationApproved,
		Summary:     "企业微信审批通过，核销分摊转入已核销",
		Application: application, Attempt: attempt, Allocations: allocations, Bills: bills,
		BeforeData: map[string]any{"status": before},
		AfterData:  applicationAuditSnapshot(application), CorrelationID: event.CorrelationID,
	})
}

// applyClosed 处理最终驳回与渠道撤销、删除：释放全部预占并把申请置为对应终态。
func (h *ApprovalDecisionHandler) applyClosed(
	ctx context.Context,
	tx *gorm.DB,
	application *model.EmployeeCollectionApplication,
	attempt *model.EmployeeCollectionApplicationAttempt,
	event approvalapp.TerminalDecisionEvent,
	targetStatus int,
	reason string,
) error {
	if application.Status != constants.EmployeeCollectionApplicationStatusPending {
		return nil
	}
	allocations, err := loadAttemptAllocations(ctx, tx, attempt.ID)
	if err != nil {
		return err
	}
	if _, err := lockBillsInAscendingOrder(ctx, tx, allocationCommandsOf(allocations)); err != nil {
		return err
	}
	now := time.Now().UTC()
	for _, allocation := range allocations {
		if err := releaseAllocation(ctx, tx, allocation, now); err != nil {
			return err
		}
		if err := releaseBillReservation(ctx, tx, allocation); err != nil {
			return err
		}
	}
	terminalReason := ""
	if targetStatus == constants.EmployeeCollectionApplicationStatusRevoked {
		terminalReason = reason
	}
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionApplication{}).
		Where("id = ? AND status = ?", application.ID, constants.EmployeeCollectionApplicationStatusPending).
		Updates(map[string]any{
			"status": targetStatus, "decided_at": now,
			"terminal_reason": terminalReason, "updater": 0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "更新核销申请终态失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "核销申请状态已变化")
	}
	before := application.Status
	application.Status = targetStatus
	application.DecidedAt = &now
	application.TerminalReason = terminalReason
	application.Updater = 0
	bills, err := reloadBills(ctx, tx, allocationCommandsOf(allocations))
	if err != nil {
		return err
	}
	closedEventID, err := decisionEventID(application.ID, attempt.AttemptNo, decisionEventSuffix(event.Decision))
	if err != nil {
		return err
	}
	return h.audit.WriteEmployeeCollectionApplication(ctx, tx, ApplicationAudit{
		EventID:     closedEventID,
		ActionCode:  constants.AuditActionEmployeeCollectionApplicationRejected,
		Summary:     "企业微信审批未通过，核销申请预占已释放",
		Application: application, Attempt: attempt, Allocations: allocations, Bills: bills,
		BeforeData: map[string]any{"status": before},
		AfterData:  applicationAuditSnapshot(application), CorrelationID: event.CorrelationID,
	})
}

// applyRevoked 处理通过后撤销。
// 申请已通过：不回滚已核销金额，只转异常终态并禁止自动重提。
// 申请仍在审批中（渠道乱序投递）：释放全部审批中预占并转异常终态，避免预占永久占用账单。
func (h *ApprovalDecisionHandler) applyRevoked(
	ctx context.Context,
	tx *gorm.DB,
	application *model.EmployeeCollectionApplication,
	attempt *model.EmployeeCollectionApplicationAttempt,
	event approvalapp.TerminalDecisionEvent,
) error {
	switch application.Status {
	case constants.EmployeeCollectionApplicationStatusApproved:
		return h.revokeApproved(ctx, tx, application, attempt, event)
	case constants.EmployeeCollectionApplicationStatusPending:
		return h.revokePending(ctx, tx, application, attempt, event)
	default:
		// 已驳回、已撤销等终态不再改变事实。
		return nil
	}
}

// revokeApproved 在已通过态撤销：保留已核销金额，仅转异常终态。
func (h *ApprovalDecisionHandler) revokeApproved(
	ctx context.Context,
	tx *gorm.DB,
	application *model.EmployeeCollectionApplication,
	attempt *model.EmployeeCollectionApplicationAttempt,
	event approvalapp.TerminalDecisionEvent,
) error {
	now := time.Now().UTC()
	terminalReason := "企业微信通过后撤销"
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionApplication{}).
		Where("id = ? AND status = ?", application.ID, constants.EmployeeCollectionApplicationStatusApproved).
		Updates(map[string]any{
			"status":     constants.EmployeeCollectionApplicationStatusRevoked,
			"decided_at": now, "terminal_reason": terminalReason, "updater": 0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "标记核销申请通过后撤销失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "核销申请状态已变化")
	}
	before := application.Status
	application.Status = constants.EmployeeCollectionApplicationStatusRevoked
	application.DecidedAt = &now
	application.TerminalReason = terminalReason
	application.Updater = 0
	allocations, err := loadAttemptAllocations(ctx, tx, attempt.ID)
	if err != nil {
		return err
	}
	bills, err := reloadBills(ctx, tx, allocationCommandsOf(allocations))
	if err != nil {
		return err
	}
	revokedEventID, err := decisionEventID(application.ID, attempt.AttemptNo, "revoked")
	if err != nil {
		return err
	}
	return h.audit.WriteEmployeeCollectionApplication(ctx, tx, ApplicationAudit{
		EventID:     revokedEventID,
		ActionCode:  constants.AuditActionEmployeeCollectionApplicationRevoked,
		Summary:     "企业微信通过后撤销，已核销金额不回滚",
		Application: application, Attempt: attempt, Allocations: allocations, Bills: bills,
		BeforeData: map[string]any{"status": before},
		AfterData:  applicationAuditSnapshot(application), CorrelationID: event.CorrelationID,
	})
}

// revokePending 在审批中态撤销：释放全部审批中预占并转异常终态。
func (h *ApprovalDecisionHandler) revokePending(
	ctx context.Context,
	tx *gorm.DB,
	application *model.EmployeeCollectionApplication,
	attempt *model.EmployeeCollectionApplicationAttempt,
	event approvalapp.TerminalDecisionEvent,
) error {
	allocations, err := loadAttemptAllocations(ctx, tx, attempt.ID)
	if err != nil {
		return err
	}
	if _, err := lockBillsInAscendingOrder(ctx, tx, allocationCommandsOf(allocations)); err != nil {
		return err
	}
	now := time.Now().UTC()
	for _, allocation := range allocations {
		if err := releaseAllocation(ctx, tx, allocation, now); err != nil {
			return err
		}
		if err := releaseBillReservation(ctx, tx, allocation); err != nil {
			return err
		}
	}
	terminalReason := "企业微信通过后在本地审批中状态被撤销"
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionApplication{}).
		Where("id = ? AND status = ?", application.ID, constants.EmployeeCollectionApplicationStatusPending).
		Updates(map[string]any{
			"status":     constants.EmployeeCollectionApplicationStatusRevoked,
			"decided_at": now, "terminal_reason": terminalReason, "updater": 0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "标记核销申请撤销失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "核销申请状态已变化")
	}
	before := application.Status
	application.Status = constants.EmployeeCollectionApplicationStatusRevoked
	application.DecidedAt = &now
	application.TerminalReason = terminalReason
	application.Updater = 0
	bills, err := reloadBills(ctx, tx, allocationCommandsOf(allocations))
	if err != nil {
		return err
	}
	revokedEventID, err := decisionEventID(application.ID, attempt.AttemptNo, "revoked")
	if err != nil {
		return err
	}
	return h.audit.WriteEmployeeCollectionApplication(ctx, tx, ApplicationAudit{
		EventID:     revokedEventID,
		ActionCode:  constants.AuditActionEmployeeCollectionApplicationRevoked,
		Summary:     "企业微信通过后撤销，申请仍在审批中，已释放预占",
		Application: application, Attempt: attempt, Allocations: allocations, Bills: bills,
		BeforeData: map[string]any{"status": before},
		AfterData:  applicationAuditSnapshot(application), CorrelationID: event.CorrelationID,
	})
}

// loadAttemptAllocations 按账单 ID 升序读取本次尝试的分摊，保证后续加锁与写入次序唯一。
func loadAttemptAllocations(ctx context.Context, tx *gorm.DB, attemptID uint) ([]*model.EmployeeCollectionApplicationAllocation, error) {
	var allocations []model.EmployeeCollectionApplicationAllocation
	if err := tx.WithContext(ctx).Clauses(clause.Locking{Strength: "UPDATE"}).
		Where("attempt_id = ?", attemptID).Order("bill_id ASC, id ASC").Find(&allocations).Error; err != nil {
		return nil, errors.Wrap(errors.CodeDatabaseError, err, "查询核销审批尝试分摊失败")
	}
	if len(allocations) == 0 {
		return nil, errors.New(errors.CodeConflict, "核销审批尝试记录缺少分摊事实")
	}
	result := make([]*model.EmployeeCollectionApplicationAllocation, 0, len(allocations))
	for index := range allocations {
		result = append(result, &allocations[index])
	}
	return result, nil
}

// allocationCommandsOf 提取分摊涉及的账单与金额，用于复用升序加锁函数。
func allocationCommandsOf(allocations []*model.EmployeeCollectionApplicationAllocation) []ApplicationAllocationCommand {
	items := make([]ApplicationAllocationCommand, 0, len(allocations))
	for _, allocation := range allocations {
		items = append(items, ApplicationAllocationCommand{BillID: allocation.BillID, Amount: allocation.Amount})
	}
	return items
}

// approveAllocation 把分摊从审批中预占条件更新为已通过；重复处理时返回冲突。
func approveAllocation(
	ctx context.Context,
	tx *gorm.DB,
	allocation *model.EmployeeCollectionApplicationAllocation,
	now time.Time,
) error {
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionApplicationAllocation{}).
		Where("id = ? AND status = ?", allocation.ID, constants.EmployeeCollectionAllocationStatusPending).
		Updates(map[string]any{
			"status": constants.EmployeeCollectionAllocationStatusApproved, "released_at": now, "updater": 0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "标记核销分摊已通过失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "核销分摊状态已变化")
	}
	allocation.Status = constants.EmployeeCollectionAllocationStatusApproved
	allocation.ReleasedAt = &now
	return nil
}

// releaseAllocation 把分摊从审批中预占条件更新为已释放；重复处理时返回冲突。
func releaseAllocation(
	ctx context.Context,
	tx *gorm.DB,
	allocation *model.EmployeeCollectionApplicationAllocation,
	now time.Time,
) error {
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionApplicationAllocation{}).
		Where("id = ? AND status = ?", allocation.ID, constants.EmployeeCollectionAllocationStatusPending).
		Updates(map[string]any{
			"status": constants.EmployeeCollectionAllocationStatusReleased, "released_at": now, "updater": 0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "释放核销分摊预占失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "核销分摊状态已变化")
	}
	allocation.Status = constants.EmployeeCollectionAllocationStatusReleased
	allocation.ReleasedAt = &now
	return nil
}

// settleBillReservation 将账单预占转为已核销并重算账单状态。
// 条件更新要求账单预占不小于分摊金额，并检查 RowsAffected，避免并发下重复入账。
func settleBillReservation(
	ctx context.Context,
	tx *gorm.DB,
	allocation *model.EmployeeCollectionApplicationAllocation,
) error {
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionBill{}).
		Where("id = ? AND reserved_amount >= ?", allocation.BillID, allocation.Amount).
		Updates(map[string]any{
			"received_amount": gorm.Expr("received_amount + ?", allocation.Amount),
			"reserved_amount": gorm.Expr("reserved_amount - ?", allocation.Amount),
			"status": gorm.Expr(
				"CASE WHEN received_amount + ? >= receivable_amount THEN ?::smallint WHEN received_amount + ? > 0 THEN ?::smallint ELSE ?::smallint END",
				allocation.Amount, constants.EmployeeCollectionBillStatusSettled,
				allocation.Amount, constants.EmployeeCollectionBillStatusPartial,
				constants.EmployeeCollectionBillStatusPending,
			),
			"updater": 0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "账单预占转入已核销失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "账单预占已变化，核销未入账")
	}
	return nil
}

// releaseBillReservation 释放账单预占金额，条件更新并检查 RowsAffected。
func releaseBillReservation(
	ctx context.Context,
	tx *gorm.DB,
	allocation *model.EmployeeCollectionApplicationAllocation,
) error {
	result := tx.WithContext(ctx).Model(&model.EmployeeCollectionBill{}).
		Where("id = ? AND reserved_amount >= ?", allocation.BillID, allocation.Amount).
		Updates(map[string]any{
			"reserved_amount": gorm.Expr("reserved_amount - ?", allocation.Amount),
			"updater":         0,
		})
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "释放账单预占失败")
	}
	if result.RowsAffected != 1 {
		return errors.New(errors.CodeConflict, "账单预占已变化")
	}
	return nil
}

// reloadBills 重新读取受影响账单，保证审计快照反映终态金额。
// 账单行已在同一事务内持有排他锁，这里只做一次按 ID 升序的普通读取。
func reloadBills(
	ctx context.Context,
	tx *gorm.DB,
	items []ApplicationAllocationCommand,
) ([]*model.EmployeeCollectionBill, error) {
	billIDs := make([]uint, 0, len(items))
	for _, item := range items {
		billIDs = append(billIDs, item.BillID)
	}
	var bills []model.EmployeeCollectionBill
	if err := tx.WithContext(ctx).Where("id IN ?", billIDs).Order("id ASC").Find(&bills).Error; err != nil {
		return nil, errors.Wrap(errors.CodeDatabaseError, err, "查询受影响员工代收款账单失败")
	}
	result := make([]*model.EmployeeCollectionBill, 0, len(bills))
	for index := range bills {
		result = append(result, &bills[index])
	}
	return result, nil
}

// decisionEventID 生成审批终态审计事件的稳定标识，并约束在审计列宽内。
func decisionEventID(applicationID uint, attemptNo int, suffix string) (string, error) {
	return composeAuditEventID(
		"employee_collection", "application", uintText(applicationID), "attempt", intText(attemptNo), suffix)
}

// decisionEventSuffix 把渠道决策映射为审计事件后缀。
func decisionEventSuffix(decision string) string {
	switch decision {
	case constants.ApprovalDecisionRejected:
		return "rejected"
	case constants.ApprovalDecisionCancelled:
		return "cancelled"
	case constants.ApprovalDecisionDeleted:
		return "deleted"
	default:
		return "closed"
	}
}