package usecase

import (
	"context"
	"errors"
	"strconv"
	"strings"
	"unicode/utf8"

	"cmroubao/backend-api/internal/domain"
)

var (
	ErrProcurementStateConflict = errors.New(
		"procurement request state conflict",
	)
	ErrProcurementSourceChanged = errors.New(
		"procurement request source changed",
	)
)

type ProcurementService struct {
	repository ProcurementRepository
	clock      Clock
	ids        IDGenerator
}

type CreateProcurementRequestCommand struct {
	CreatorSubject           string
	ActorUserID              string
	FreightOrderItemID       string
	ConfirmProcurementNeeded bool
}

type CreateProcurementRequestResult struct {
	Request  domain.ProcurementRequest
	Replayed bool
}

type BindProcurementReferenceCommand struct {
	CreatorSubject string
	ActorUserID    string
	RequestID      string
	ImageAssetID   string
}

type CreateProcurementTaskCommand struct {
	CreatorSubject string
	ActorUserID    string
	RequestID      string
	IdempotencyKey string
}

type CreateProcurementTaskResult struct {
	Task     domain.PurchaseTask
	Replayed bool
}

func NewProcurementService(
	repository ProcurementRepository,
	clock Clock,
	ids IDGenerator,
) (*ProcurementService, error) {
	if repository == nil || clock == nil || ids == nil {
		return nil, errors.New("procurement service dependencies are required")
	}
	return &ProcurementService{
		repository: repository,
		clock:      clock,
		ids:        ids,
	}, nil
}

func (service *ProcurementService) CreateRequest(
	ctx context.Context,
	command CreateProcurementRequestCommand,
) (CreateProcurementRequestResult, error) {
	command.CreatorSubject = strings.TrimSpace(command.CreatorSubject)
	command.ActorUserID = strings.TrimSpace(command.ActorUserID)
	command.FreightOrderItemID = strings.TrimSpace(
		command.FreightOrderItemID,
	)
	fields := map[string]string{}
	if command.CreatorSubject == "" {
		fields["creator_subject"] = "is required"
	}
	if !isUUID(command.ActorUserID) {
		fields["actor_user_id"] = "must be a UUID"
	}
	if !isUUID(command.FreightOrderItemID) {
		fields["freight_order_item_id"] = "must be a UUID"
	}
	if !command.ConfirmProcurementNeeded {
		fields["confirm_procurement_needed"] =
			"must be explicitly confirmed"
	}
	if len(fields) > 0 {
		return CreateProcurementRequestResult{}, invalidError(
			"PROCUREMENT_REQUEST_INVALID",
			"procurement request is invalid",
			fields,
		)
	}
	source, err := service.repository.GetProcurementSourceItem(
		ctx,
		command.CreatorSubject,
		command.FreightOrderItemID,
	)
	if err != nil {
		return CreateProcurementRequestResult{}, wrapRepositoryError(err)
	}
	requestID, err := service.ids.NewID()
	if err != nil {
		return CreateProcurementRequestResult{}, procurementInternal(err)
	}
	now := service.clock.Now().UTC()
	request := domain.ProcurementRequest{
		ID:                           requestID,
		CreatorSubject:               command.CreatorSubject,
		FreightOrderItemID:           source.Item.ID,
		SourceRevision:               source.Item.Revision,
		SourceSHA256:                 source.Item.CanonicalSHA256,
		Title:                        strings.TrimSpace(source.Item.Title),
		ProductSpec:                  strings.TrimSpace(source.Item.ProductSpec),
		SKU:                          strings.TrimSpace(source.Item.SKU),
		Quantity:                     source.Item.Quantity,
		SourcePurchaseStatus:         source.Item.PurchaseStatus,
		SourceIsCanceled:             source.IsCanceled,
		ProcurementConfirmedByUserID: command.ActorUserID,
		ProcurementConfirmedAt:       now,
		Status:                       domain.ProcurementNeedsImage,
		CreatedAt:                    now,
		UpdatedAt:                    now,
	}
	if code := procurementBlockingCode(request); code != "" {
		request.Status = domain.ProcurementBlocked
		request.BlockingCode = &code
	}
	stored, created, err := service.repository.CreateProcurementRequest(
		ctx,
		request,
	)
	if err != nil {
		return CreateProcurementRequestResult{}, wrapProcurementError(err)
	}
	return CreateProcurementRequestResult{
		Request:  stored,
		Replayed: !created,
	}, nil
}

func (service *ProcurementService) ListForOrder(
	ctx context.Context,
	creatorSubject, orderID string,
) ([]domain.ProcurementRequest, error) {
	requests, err := service.repository.ListProcurementRequestsForOrder(
		ctx,
		strings.TrimSpace(creatorSubject),
		strings.TrimSpace(orderID),
	)
	if err != nil {
		return nil, wrapProcurementError(err)
	}
	return requests, nil
}

func (service *ProcurementService) Get(
	ctx context.Context,
	creatorSubject, requestID string,
) (domain.ProcurementRequest, error) {
	request, err := service.repository.GetProcurementRequest(
		ctx,
		strings.TrimSpace(creatorSubject),
		strings.TrimSpace(requestID),
	)
	if err != nil {
		return domain.ProcurementRequest{}, wrapProcurementError(err)
	}
	return request, nil
}

func (service *ProcurementService) BindReference(
	ctx context.Context,
	command BindProcurementReferenceCommand,
) (domain.ProcurementRequest, error) {
	command.CreatorSubject = strings.TrimSpace(command.CreatorSubject)
	command.ActorUserID = strings.TrimSpace(command.ActorUserID)
	command.RequestID = strings.TrimSpace(command.RequestID)
	command.ImageAssetID = strings.TrimSpace(command.ImageAssetID)
	fields := map[string]string{}
	if command.CreatorSubject == "" {
		fields["creator_subject"] = "is required"
	}
	if !isUUID(command.ActorUserID) {
		fields["actor_user_id"] = "must be a UUID"
	}
	if !isUUID(command.RequestID) {
		fields["procurement_request_id"] = "must be a UUID"
	}
	if !isUUID(command.ImageAssetID) {
		fields["image_asset_id"] = "must be a UUID"
	}
	if len(fields) > 0 {
		return domain.ProcurementRequest{}, invalidError(
			"PROCUREMENT_REFERENCE_INVALID",
			"procurement reference is invalid",
			fields,
		)
	}
	request, err := service.repository.BindProcurementReference(
		ctx,
		command.CreatorSubject,
		command.RequestID,
		command.ImageAssetID,
		service.clock.Now().UTC(),
	)
	if err != nil {
		return domain.ProcurementRequest{}, wrapProcurementError(err)
	}
	return request, nil
}

func (service *ProcurementService) CreateTask(
	ctx context.Context,
	command CreateProcurementTaskCommand,
) (CreateProcurementTaskResult, error) {
	if err := validateWriteIdentity(
		command.CreatorSubject,
		command.IdempotencyKey,
	); err != nil {
		return CreateProcurementTaskResult{}, err
	}
	command.CreatorSubject = strings.TrimSpace(command.CreatorSubject)
	command.ActorUserID = strings.TrimSpace(command.ActorUserID)
	command.RequestID = strings.TrimSpace(command.RequestID)
	if !isUUID(command.ActorUserID) || !isUUID(command.RequestID) {
		return CreateProcurementTaskResult{}, invalidError(
			"PROCUREMENT_TASK_INVALID",
			"procurement task request is invalid",
			map[string]string{
				"request": "actor and procurement request must be UUIDs",
			},
		)
	}
	request, err := service.repository.GetProcurementRequest(
		ctx,
		command.CreatorSubject,
		command.RequestID,
	)
	if err != nil {
		return CreateProcurementTaskResult{}, wrapProcurementError(err)
	}
	if request.Status != domain.ProcurementTaskCreated &&
		request.SourceChanged {
		return CreateProcurementTaskResult{}, wrapProcurementError(
			ErrProcurementSourceChanged,
		)
	}
	if request.Status != domain.ProcurementReady &&
		request.Status != domain.ProcurementTaskCreated {
		return CreateProcurementTaskResult{}, wrapProcurementError(
			ErrProcurementStateConflict,
		)
	}
	if request.ReferenceAssetID == nil {
		return CreateProcurementTaskResult{}, wrapProcurementError(
			ErrProcurementStateConflict,
		)
	}
	taskID, err := service.ids.NewID()
	if err != nil {
		return CreateProcurementTaskResult{}, procurementInternal(err)
	}
	eventID, err := service.ids.NewID()
	if err != nil {
		return CreateProcurementTaskResult{}, procurementInternal(err)
	}
	now := service.clock.Now().UTC()
	sourceRefValue := "erp-procurement:" + request.ID +
		":r" + strconv.Itoa(request.SourceRevision)
	actorUserID := command.ActorUserID
	description := ""
	if request.ProductSpec != "" {
		description = "ERP 规格：" + request.ProductSpec
	}
	task := domain.PurchaseTask{
		ID:              taskID,
		CreatorSubject:  command.CreatorSubject,
		CreatedByUserID: &actorUserID,
		SourceRef:       &sourceRefValue,
		Title:           request.Title,
		Description:     description,
		SKU:             request.SKU,
		ImageAssetID:    *request.ReferenceAssetID,
		Quantity:        *request.Quantity,
		Currency:        domain.CurrencyCNY,
		Status:          domain.TaskStatusPending,
		Version:         1,
		CreatedAt:       now,
		UpdatedAt:       now,
	}
	if err := domain.ValidateTaskInput(
		task.CreatorSubject,
		task.SourceRef,
		task.Title,
		task.Description,
		task.SKU,
		task.ImageAssetID,
		task.Quantity,
	); err != nil {
		return CreateProcurementTaskResult{}, wrapProcurementError(
			ErrProcurementStateConflict,
		)
	}
	event := domain.TaskEvent{
		ID:          eventID,
		TaskID:      task.ID,
		ActorUserID: &actorUserID,
		Type:        "TASK_CREATED",
		Message:     "task created from procurement request",
		OccurredAt:  now,
	}
	source := domain.PurchaseTaskSource{
		TaskID:               task.ID,
		ProcurementRequestID: request.ID,
		FreightOrderItemID:   request.FreightOrderItemID,
		SourceRevision:       request.SourceRevision,
		SourceSHA256:         request.SourceSHA256,
		CreatedAt:            now,
	}
	requestHash := hashJSON(struct {
		RequestID    string `json:"request_id"`
		SourceSHA256 string `json:"source_sha256"`
	}{
		RequestID:    request.ID,
		SourceSHA256: request.SourceSHA256,
	})
	created, wasCreated, err := service.repository.CreateProcurementTask(
		ctx,
		request,
		task,
		event,
		source,
		strings.TrimSpace(command.IdempotencyKey),
		requestHash,
	)
	if err != nil {
		return CreateProcurementTaskResult{}, wrapProcurementError(err)
	}
	return CreateProcurementTaskResult{
		Task:     created,
		Replayed: !wasCreated,
	}, nil
}

func procurementBlockingCode(
	request domain.ProcurementRequest,
) string {
	if request.SourceIsCanceled != nil && *request.SourceIsCanceled {
		return domain.ProcurementBlockSourceCanceled
	}
	if request.Title == "" ||
		utf8.RuneCountInString(request.Title) > domain.MaxTitleRunes ||
		len([]byte(request.Title)) > domain.MaxTitleBytes {
		return domain.ProcurementBlockTitleRequired
	}
	if request.SKU == "" ||
		len([]byte(request.SKU)) > domain.MaxSKUBytes {
		return domain.ProcurementBlockSKURequired
	}
	if request.Quantity == nil || *request.Quantity <= 0 {
		return domain.ProcurementBlockQuantityRequired
	}
	return ""
}

func wrapProcurementError(err error) error {
	switch {
	case errors.Is(err, ErrProcurementSourceChanged):
		return newError(
			ErrorKindConflict,
			"PROCUREMENT_SOURCE_CHANGED",
			"freight source changed; create a request for the current revision",
			err,
		)
	case errors.Is(err, ErrProcurementStateConflict):
		return newError(
			ErrorKindConflict,
			"PROCUREMENT_STATE_CONFLICT",
			"procurement request state does not allow this operation",
			err,
		)
	case errors.Is(err, ErrAssetUnavailable):
		return newError(
			ErrorKindConflict,
			"PROCUREMENT_ASSET_UNAVAILABLE",
			"reference image is not available for this procurement request",
			err,
		)
	default:
		return wrapRepositoryError(err)
	}
}

func procurementInternal(err error) error {
	return newError(
		ErrorKindInternal,
		"INTERNAL_ERROR",
		"internal server error",
		err,
	)
}