cmroubao/backend-api/internal/usecase/execution_result_service.go

package usecase

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"io"
	"net/url"
	"regexp"
	"strconv"
	"strings"
	"time"
	"unicode/utf8"

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

const (
	executionResultEventsOperation     = "EVENTS"
	executionResultEvidenceOperation   = "EVIDENCE"
	executionResultCandidatesOperation = "CANDIDATES"
	executionResultCompleteOperation   = "COMPLETE"
	executionResultFailOperation       = "FAIL"

	manualFirstMode = "MANUAL_FIRST"
	aiAssistedMode  = "AI_ASSISTED"
)

type ExecutionResultService struct {
	repository ExecutionResultRepository
	store      ReferenceImageStore
	clock      Clock
	ids        IDGenerator
}

type ExecutionResultIdentity struct {
	UserID          string
	DeviceID        string
	TaskID          string
	ExecutionID     string
	ClaimGeneration int64
	ClaimToken      string
	IdempotencyKey  string
}

type ClientExecutionEvent struct {
	ID         string `json:"event_id"`
	Step       string `json:"step"`
	Type       string `json:"type"`
	Message    string `json:"message"`
	OccurredAt string `json:"occurred_at"`
}

type AppendExecutionEventsCommand struct {
	Identity ExecutionResultIdentity
	Events   []ClientExecutionEvent
}

type UploadExecutionEvidenceCommand struct {
	Identity          ExecutionResultIdentity
	DeclaredMediaType string
	Content           io.Reader
}

type ExecutionProvenance struct {
	ProviderID    string `json:"provider_id"`
	Model         string `json:"model"`
	PromptVersion string `json:"prompt_version"`
	SchemaVersion int    `json:"schema_version"`
}

type CandidateEvaluation struct {
	Decision           string                              `json:"decision"`
	Score              float64                             `json:"score"`
	Matched            []string                            `json:"matched"`
	MissingOrUncertain []string                            `json:"missing_or_uncertain"`
	RejectionReasons   []string                            `json:"rejection_reasons"`
	Confidence         float64                             `json:"confidence"`
	HardConstraints    []CandidateHardConstraintEvaluation `json:"hard_constraints"`
}

type CandidateHardConstraintEvaluation struct {
	Kind     string `json:"kind"`
	Expected string `json:"expected"`
	Status   string `json:"status"`
	Evidence string `json:"evidence"`
}

type ExecutionCandidate struct {
	Ordinal          int                  `json:"ordinal"`
	Title            string               `json:"title"`
	SKUText          string               `json:"sku_text"`
	Price            string               `json:"price"`
	ProductURL       string               `json:"product_url"`
	ImageURL         string               `json:"image_url"`
	EvidenceAssetIDs []string             `json:"evidence_asset_ids"`
	Evaluation       *CandidateEvaluation `json:"evaluation"`
}

type CandidateRecommendation struct {
	CandidateOrdinal int      `json:"candidate_ordinal"`
	PolicyVersion    string   `json:"policy_version"`
	Reasons          []string `json:"reasons"`
}

type StoreExecutionCandidatesCommand struct {
	Identity          ExecutionResultIdentity
	TaskContentSHA256 string
	ExecutionMode     string
	SearchQuery       string
	Provenance        *ExecutionProvenance
	Candidates        []ExecutionCandidate
	Recommendation    *CandidateRecommendation
}

type CompleteExecutionCommand struct {
	Identity          ExecutionResultIdentity
	TaskContentSHA256 string
	ExecutionMode     string
	Outcome           string
	OperatorReason    string
	Candidate         *ExecutionCandidate
	OrderSubmitted    bool
}

type FailExecutionCommand struct {
	Identity         ExecutionResultIdentity
	ErrorCode        string
	ErrorMessage     string
	ErrorStep        string
	Retryable        bool
	EvidenceAssetIDs []string
}

type UploadExecutionEvidenceResult struct {
	Evidence domain.ExecutionEvidenceAsset
	Replayed bool
}

type ExecutionEvidenceContent struct {
	Evidence domain.ExecutionEvidenceAsset
	Content  io.ReadCloser
}

func NewExecutionResultService(
	repository ExecutionResultRepository,
	store ReferenceImageStore,
	clock Clock,
	ids IDGenerator,
) (*ExecutionResultService, error) {
	if repository == nil || store == nil || clock == nil || ids == nil {
		return nil, errors.New("execution result service dependencies are required")
	}
	return &ExecutionResultService{
		repository: repository,
		store:      store,
		clock:      clock,
		ids:        ids,
	}, nil
}

func (service *ExecutionResultService) AppendEvents(
	ctx context.Context,
	command AppendExecutionEventsCommand,
) (bool, error) {
	identity, err := normalizeExecutionIdentity(command.Identity)
	if err != nil {
		return false, err
	}
	if len(command.Events) < 1 || len(command.Events) > 32 {
		return false, executionResultInvalid("events", "must contain 1 to 32 events")
	}
	now := service.clock.Now().UTC()
	events := make([]domain.ExecutionEvent, 0, len(command.Events))
	seen := make(map[string]struct{}, len(command.Events))
	for _, event := range command.Events {
		parsed, eventErr := normalizeClientEvent(event, identity.TaskID, identity.ExecutionID, now)
		if eventErr != nil {
			return false, eventErr
		}
		if _, found := seen[parsed.ID]; found {
			return false, executionResultInvalid("events", "event_id must be unique")
		}
		seen[parsed.ID] = struct{}{}
		events = append(events, parsed)
	}
	requestHash, err := executionResultHash(command.Events)
	if err != nil {
		return false, internalExecutionResultFailure(err)
	}
	replayed, err := service.repository.AppendExecutionEvents(
		ctx,
		service.write(identity, executionResultEventsOperation, requestHash, now),
		events,
	)
	if err != nil {
		return false, wrapLifecycleRepositoryError(err)
	}
	return replayed, nil
}

func (service *ExecutionResultService) UploadEvidence(
	ctx context.Context,
	command UploadExecutionEvidenceCommand,
) (UploadExecutionEvidenceResult, error) {
	identity, err := normalizeExecutionIdentity(command.Identity)
	if err != nil {
		return UploadExecutionEvidenceResult{}, err
	}
	if command.Content == nil {
		return UploadExecutionEvidenceResult{}, executionResultInvalid("file", "required")
	}
	evidenceID, err := service.ids.NewID()
	if err != nil {
		return UploadExecutionEvidenceResult{}, internalExecutionResultFailure(err)
	}
	normalized, err := service.store.Put(
		ctx,
		evidenceID,
		command.DeclaredMediaType,
		command.Content,
	)
	if err != nil {
		return UploadExecutionEvidenceResult{}, mapImageStoreError(err)
	}
	cleanup := func() {
		_ = service.store.Delete(context.Background(), normalized.StorageKey)
	}
	now := service.clock.Now().UTC()
	requestHash, err := executionResultHash(struct {
		InputSHA256 string `json:"input_sha256"`
	}{InputSHA256: normalized.InputSHA256})
	if err != nil {
		cleanup()
		return UploadExecutionEvidenceResult{}, internalExecutionResultFailure(err)
	}
	evidence, replayed, err := service.repository.CreateExecutionEvidence(
		ctx,
		service.write(identity, executionResultEvidenceOperation, requestHash, now),
		domain.ExecutionEvidenceAsset{
			ID:          evidenceID,
			TaskID:      identity.TaskID,
			ExecutionID: identity.ExecutionID,
			MediaType:   normalized.MediaType,
			SizeBytes:   normalized.SizeBytes,
			SHA256:      normalized.SHA256,
			StorageKey:  normalized.StorageKey,
			CreatedAt:   now,
		},
	)
	if err != nil {
		cleanup()
		return UploadExecutionEvidenceResult{}, wrapLifecycleRepositoryError(err)
	}
	if replayed {
		cleanup()
	}
	return UploadExecutionEvidenceResult{Evidence: evidence, Replayed: replayed}, nil
}

func (service *ExecutionResultService) StoreCandidates(
	ctx context.Context,
	command StoreExecutionCandidatesCommand,
) (bool, error) {
	identity, err := normalizeExecutionIdentity(command.Identity)
	if err != nil {
		return false, err
	}
	if err := validateCandidateCommand(command); err != nil {
		return false, err
	}
	provenanceJSON, candidatesJSON, recommendationJSON, err := candidateJSON(command)
	if err != nil {
		return false, internalExecutionResultFailure(err)
	}
	now := service.clock.Now().UTC()
	requestHash, err := executionResultHash(command)
	if err != nil {
		return false, internalExecutionResultFailure(err)
	}
	replayed, err := service.repository.StoreExecutionCandidates(
		ctx,
		service.write(identity, executionResultCandidatesOperation, requestHash, now),
		domain.ExecutionCandidateBatch{
			TaskID:             identity.TaskID,
			ExecutionID:        identity.ExecutionID,
			TaskContentSHA256:  command.TaskContentSHA256,
			ExecutionMode:      command.ExecutionMode,
			SearchQuery:        strings.TrimSpace(command.SearchQuery),
			ProvenanceJSON:     provenanceJSON,
			CandidatesJSON:     candidatesJSON,
			RecommendationJSON: recommendationJSON,
			ReceivedAt:         now,
		},
	)
	if err != nil {
		return false, wrapLifecycleRepositoryError(err)
	}
	return replayed, nil
}

func (service *ExecutionResultService) Complete(
	ctx context.Context,
	command CompleteExecutionCommand,
) (domain.PurchaseTask, bool, error) {
	identity, err := normalizeExecutionIdentity(command.Identity)
	if err != nil {
		return domain.PurchaseTask{}, false, err
	}
	if err := validateCompleteCommand(command); err != nil {
		return domain.PurchaseTask{}, false, err
	}
	selectedJSON, err := optionalJSON(command.Candidate)
	if err != nil {
		return domain.PurchaseTask{}, false, internalExecutionResultFailure(err)
	}
	now := service.clock.Now().UTC()
	requestHash, err := executionResultHash(command)
	if err != nil {
		return domain.PurchaseTask{}, false, internalExecutionResultFailure(err)
	}
	mode := command.ExecutionMode
	taskHash := command.TaskContentSHA256
	outcome := command.Outcome
	reason := strings.TrimSpace(command.OperatorReason)
	task, replayed, err := service.repository.CompleteExecution(
		ctx,
		service.write(identity, executionResultCompleteOperation, requestHash, now),
		domain.ExecutionOutcome{
			TaskID:                identity.TaskID,
			ExecutionID:           identity.ExecutionID,
			ResultType:            "COMPLETE",
			ExecutionMode:         &mode,
			TaskContentSHA256:     &taskHash,
			Outcome:               &outcome,
			OperatorReason:        &reason,
			SelectedCandidateJSON: selectedJSON,
			OrderSubmitted:        false,
			ReceivedAt:            now,
		},
	)
	if err != nil {
		return domain.PurchaseTask{}, false, wrapLifecycleRepositoryError(err)
	}
	return task, replayed, nil
}

func (service *ExecutionResultService) Fail(
	ctx context.Context,
	command FailExecutionCommand,
) (domain.PurchaseTask, bool, error) {
	identity, err := normalizeExecutionIdentity(command.Identity)
	if err != nil {
		return domain.PurchaseTask{}, false, err
	}
	if err := validateFailCommand(command); err != nil {
		return domain.PurchaseTask{}, false, err
	}
	evidenceJSON, err := optionalJSON(command.EvidenceAssetIDs)
	if err != nil {
		return domain.PurchaseTask{}, false, internalExecutionResultFailure(err)
	}
	now := service.clock.Now().UTC()
	requestHash, err := executionResultHash(command)
	if err != nil {
		return domain.PurchaseTask{}, false, internalExecutionResultFailure(err)
	}
	code := strings.TrimSpace(command.ErrorCode)
	message := strings.TrimSpace(command.ErrorMessage)
	step := strings.TrimSpace(command.ErrorStep)
	retryable := command.Retryable
	task, replayed, err := service.repository.FailExecution(
		ctx,
		service.write(identity, executionResultFailOperation, requestHash, now),
		domain.ExecutionOutcome{
			TaskID:               identity.TaskID,
			ExecutionID:          identity.ExecutionID,
			ResultType:           "FAIL",
			EvidenceAssetIDsJSON: evidenceJSON,
			ErrorCode:            &code,
			ErrorMessage:         &message,
			ErrorStep:            &step,
			Retryable:            &retryable,
			OrderSubmitted:       false,
			ReceivedAt:           now,
		},
	)
	if err != nil {
		return domain.PurchaseTask{}, false, wrapLifecycleRepositoryError(err)
	}
	return task, replayed, nil
}

func (service *ExecutionResultService) OpenEvidence(
	ctx context.Context,
	taskID string,
	evidenceID string,
) (ExecutionEvidenceContent, error) {
	evidence, err := service.repository.GetExecutionEvidence(ctx, taskID, evidenceID)
	if err != nil {
		return ExecutionEvidenceContent{}, wrapLifecycleRepositoryError(err)
	}
	content, err := service.store.Open(ctx, evidence.StorageKey)
	if err != nil {
		return ExecutionEvidenceContent{}, mapImageStoreError(err)
	}
	return ExecutionEvidenceContent{Evidence: evidence, Content: content}, nil
}

func (service *ExecutionResultService) write(
	identity ExecutionResultIdentity,
	operation string,
	requestHash string,
	now time.Time,
) ExecutionResultWrite {
	return ExecutionResultWrite{
		ExecutionResultAuthorization: ExecutionResultAuthorization{
			UserID:          identity.UserID,
			DeviceID:        identity.DeviceID,
			TaskID:          identity.TaskID,
			ExecutionID:     identity.ExecutionID,
			ClaimGeneration: identity.ClaimGeneration,
			ClaimTokenHash:  hashSecret(identity.ClaimToken),
		},
		Operation:      operation,
		IdempotencyKey: identity.IdempotencyKey,
		RequestHash:    requestHash,
		Now:            now,
	}
}

func normalizeExecutionIdentity(
	identity ExecutionResultIdentity,
) (ExecutionResultIdentity, error) {
	identity.UserID = strings.TrimSpace(identity.UserID)
	identity.DeviceID = strings.TrimSpace(identity.DeviceID)
	identity.TaskID = strings.TrimSpace(identity.TaskID)
	identity.ExecutionID = strings.TrimSpace(identity.ExecutionID)
	identity.IdempotencyKey = strings.TrimSpace(identity.IdempotencyKey)
	fields := map[string]string{}
	if !isUUID(identity.UserID) {
		fields["user_id"] = "must be a UUID"
	}
	if !isUUID(identity.DeviceID) {
		fields["device_id"] = "must be a UUID"
	}
	if !isUUID(identity.TaskID) {
		fields["task_id"] = "must be a UUID"
	}
	if !isUUID(identity.ExecutionID) {
		fields["execution_id"] = "must be a UUID"
	}
	if identity.ClaimGeneration < 1 {
		fields["claim_generation"] = "must be a positive integer"
	}
	if strings.TrimSpace(identity.ClaimToken) == "" {
		fields["claim_token"] = "required"
	}
	if len([]byte(identity.IdempotencyKey)) == 0 ||
		len([]byte(identity.IdempotencyKey)) > maxIdempotencyKeyBytes ||
		!isPrintableASCII(identity.IdempotencyKey) {
		fields["idempotency_key"] = "must be printable ASCII up to 128 bytes"
	}
	if len(fields) > 0 {
		return ExecutionResultIdentity{}, invalidError(
			"EXECUTION_RESULT_INVALID",
			"execution result request is invalid",
			fields,
		)
	}
	return identity, nil
}

func normalizeClientEvent(
	event ClientExecutionEvent,
	taskID string,
	executionID string,
	now time.Time,
) (domain.ExecutionEvent, error) {
	if !isUUID(strings.TrimSpace(event.ID)) {
		return domain.ExecutionEvent{}, executionResultInvalid("event_id", "must be a UUID")
	}
	step := strings.TrimSpace(event.Step)
	typeValue := strings.TrimSpace(event.Type)
	message := strings.TrimSpace(event.Message)
	if !validLifecycleStep(step) {
		return domain.ExecutionEvent{}, executionResultInvalid("step", "must be uppercase ASCII")
	}
	if !validLifecycleStep(typeValue) {
		return domain.ExecutionEvent{}, executionResultInvalid("type", "must be uppercase ASCII")
	}
	if !validAuditText(message, 1000) {
		return domain.ExecutionEvent{}, executionResultInvalid("message", "is invalid or contains sensitive material")
	}
	occurredAt, err := time.Parse(time.RFC3339Nano, strings.TrimSpace(event.OccurredAt))
	if err != nil || occurredAt.After(now.Add(5*time.Minute)) ||
		occurredAt.Before(now.Add(-7*24*time.Hour)) {
		return domain.ExecutionEvent{}, executionResultInvalid("occurred_at", "must be a recent RFC3339 timestamp")
	}
	return domain.ExecutionEvent{
		ID:          strings.TrimSpace(event.ID),
		TaskID:      taskID,
		ExecutionID: executionID,
		Step:        step,
		Type:        typeValue,
		Message:     message,
		OccurredAt:  occurredAt.UTC(),
		ReceivedAt:  now,
	}, nil
}

func validateCandidateCommand(command StoreExecutionCandidatesCommand) error {
	if !sha256Pattern.MatchString(command.TaskContentSHA256) {
		return executionResultInvalid("task_content_sha256", "must be lowercase SHA-256")
	}
	if !validExecutionMode(command.ExecutionMode) {
		return executionResultInvalid("execution_mode", "must be MANUAL_FIRST or AI_ASSISTED")
	}
	if !validAuditText(command.SearchQuery, 512) {
		return executionResultInvalid("search_query", "is invalid")
	}
	if len(command.Candidates) > 5 {
		return executionResultInvalid("candidates", "must contain at most 5 candidates")
	}
	if command.ExecutionMode == aiAssistedMode {
		if !validProvenance(command.Provenance) {
			return executionResultInvalid("provenance", "is required for AI_ASSISTED")
		}
	} else if command.Provenance != nil {
		return executionResultInvalid("provenance", "must be omitted for MANUAL_FIRST")
	}
	strictSKUMatching := command.ExecutionMode == aiAssistedMode &&
		command.Provenance.SchemaVersion >= 2
	for index, candidate := range command.Candidates {
		if candidate.Ordinal != index+1 ||
			!validCandidate(candidate, command.ExecutionMode) ||
			(strictSKUMatching && !validSKUMatchedCandidate(candidate)) {
			return executionResultInvalid("candidates", "must be continuous, bounded observations")
		}
	}
	if strictSKUMatching && len(command.Candidates) > 0 &&
		(command.Recommendation == nil ||
			command.Recommendation.CandidateOrdinal != 1) {
		return executionResultInvalid(
			"recommendation",
			"must select the first sorted SKU-matched candidate",
		)
	}
	if command.Recommendation != nil {
		recommendation := command.Recommendation
		if recommendation.CandidateOrdinal < 1 ||
			recommendation.CandidateOrdinal > len(command.Candidates) ||
			!validAuditText(recommendation.PolicyVersion, 128) ||
			!validStringList(recommendation.Reasons, 8, 160) {
			return executionResultInvalid("recommendation", "is invalid")
		}
	}
	return nil
}

func validateCompleteCommand(command CompleteExecutionCommand) error {
	if !sha256Pattern.MatchString(command.TaskContentSHA256) ||
		!validExecutionMode(command.ExecutionMode) ||
		!validOutcome(command.Outcome) ||
		!validAuditText(command.OperatorReason, 1000) ||
		command.OrderSubmitted {
		return executionResultInvalid("complete", "contains an invalid outcome or order state")
	}
	if command.Outcome == "CANDIDATE_ACCEPTED" {
		if command.Candidate == nil || !validCandidate(*command.Candidate, command.ExecutionMode) {
			return executionResultInvalid("candidate", "is required for CANDIDATE_ACCEPTED")
		}
	} else if command.Candidate != nil {
		return executionResultInvalid("candidate", "must be omitted for this outcome")
	}
	return nil
}

func validateFailCommand(command FailExecutionCommand) error {
	if !validLifecycleStep(strings.TrimSpace(command.ErrorCode)) ||
		!validLifecycleStep(strings.TrimSpace(command.ErrorStep)) ||
		!validAuditText(command.ErrorMessage, 1000) {
		return executionResultInvalid("error", "is invalid")
	}
	if len(command.EvidenceAssetIDs) > 5 {
		return executionResultInvalid("evidence_asset_ids", "must contain at most 5 items")
	}
	for _, id := range command.EvidenceAssetIDs {
		if !isUUID(strings.TrimSpace(id)) {
			return executionResultInvalid("evidence_asset_ids", "must contain UUIDs")
		}
	}
	return nil
}

func validCandidate(candidate ExecutionCandidate, mode string) bool {
	if candidate.Ordinal < 1 ||
		!validAuditText(candidate.Title, 512) ||
		!validOptionalAuditText(candidate.SKUText, 512) ||
		!validOptionalAuditText(candidate.Price, 64) ||
		!validObservationURL(candidate.ProductURL) ||
		!validObservationURL(candidate.ImageURL) ||
		len(candidate.EvidenceAssetIDs) > 5 {
		return false
	}
	for _, id := range candidate.EvidenceAssetIDs {
		if !isUUID(strings.TrimSpace(id)) {
			return false
		}
	}
	if mode == manualFirstMode {
		return candidate.Evaluation == nil
	}
	return validEvaluation(candidate.Evaluation)
}

func validEvaluation(value *CandidateEvaluation) bool {
	if value == nil || value.Score < 0 || value.Score > 1 ||
		value.Confidence < 0 || value.Confidence > 1 {
		return false
	}
	if value.Decision != "REVIEW" && value.Decision != "REJECT" &&
		value.Decision != "MANUAL_REQUIRED" {
		return false
	}
	return validStringList(value.Matched, 12, 160) &&
		validStringList(value.MissingOrUncertain, 12, 160) &&
		validStringList(value.RejectionReasons, 12, 160) &&
		validCandidateHardConstraints(value.HardConstraints)
}

func validSKUMatchedCandidate(candidate ExecutionCandidate) bool {
	value := candidate.Evaluation
	return value != nil &&
		value.Decision == "REVIEW" &&
		value.Score >= 0.75 &&
		value.Confidence >= 0.75 &&
		len(value.RejectionReasons) == 0 &&
		len(value.HardConstraints) == 2
}

func validCandidateHardConstraints(
	values []CandidateHardConstraintEvaluation,
) bool {
	if len(values) == 0 {
		return true
	}
	if len(values) != 2 {
		return false
	}
	seen := map[string]struct{}{}
	for _, value := range values {
		if (value.Kind != "COLOR" && value.Kind != "SIZE") ||
			value.Status != "MATCH" ||
			!validAuditText(value.Expected, 128) ||
			!validAuditText(value.Evidence, 160) {
			return false
		}
		if _, duplicate := seen[value.Kind]; duplicate {
			return false
		}
		seen[value.Kind] = struct{}{}
	}
	return len(seen) == 2
}

func validProvenance(value *ExecutionProvenance) bool {
	return value != nil &&
		validAuditText(value.ProviderID, 64) &&
		validAuditText(value.Model, 256) &&
		validAuditText(value.PromptVersion, 128) &&
		value.SchemaVersion >= 1 && value.SchemaVersion <= 32
}

func validExecutionMode(value string) bool {
	return value == manualFirstMode || value == aiAssistedMode
}

func validOutcome(value string) bool {
	switch value {
	case "CANDIDATE_ACCEPTED", "CANDIDATE_REJECTED", "NO_MATCH", "MANUAL_REQUIRED":
		return true
	default:
		return false
	}
}

func validObservationURL(value string) bool {
	if strings.TrimSpace(value) == "" {
		return true
	}
	parsed, err := url.Parse(strings.TrimSpace(value))
	return err == nil &&
		(parsed.Scheme == "https" || parsed.Scheme == "http") &&
		parsed.Host != "" &&
		parsed.User == nil &&
		len(value) <= 2048
}

func validAuditText(value string, maximum int) bool {
	value = strings.TrimSpace(value)
	if value == "" || !utf8.ValidString(value) || len([]byte(value)) > maximum {
		return false
	}
	lower := strings.ToLower(value)
	return !strings.Contains(lower, "authorization:") &&
		!strings.Contains(lower, "api_key") &&
		!strings.Contains(lower, "bearer ")
}

func validOptionalAuditText(value string, maximum int) bool {
	return strings.TrimSpace(value) == "" || validAuditText(value, maximum)
}

func validStringList(values []string, maximumItems int, maximumText int) bool {
	if len(values) > maximumItems {
		return false
	}
	seen := map[string]struct{}{}
	for _, value := range values {
		if !validAuditText(value, maximumText) {
			return false
		}
		key := strings.ToLower(strings.TrimSpace(value))
		if _, duplicate := seen[key]; duplicate {
			return false
		}
		seen[key] = struct{}{}
	}
	return true
}

func candidateJSON(command StoreExecutionCandidatesCommand) (*string, string, *string, error) {
	var provenance *string
	if command.Provenance != nil {
		encoded, err := json.Marshal(command.Provenance)
		if err != nil {
			return nil, "", nil, err
		}
		value := string(encoded)
		provenance = &value
	}
	candidates, err := json.Marshal(command.Candidates)
	if err != nil {
		return nil, "", nil, err
	}
	var recommendation *string
	if command.Recommendation != nil {
		encoded, err := json.Marshal(command.Recommendation)
		if err != nil {
			return nil, "", nil, err
		}
		value := string(encoded)
		recommendation = &value
	}
	return provenance, string(candidates), recommendation, nil
}

func optionalJSON(value any) (*string, error) {
	if value == nil {
		return nil, nil
	}
	encoded, err := json.Marshal(value)
	if err != nil {
		return nil, err
	}
	result := string(encoded)
	return &result, nil
}

func executionResultHash(value any) (string, error) {
	encoded, err := json.Marshal(value)
	if err != nil {
		return "", err
	}
	sum := sha256.Sum256(encoded)
	return hex.EncodeToString(sum[:]), nil
}

func TaskContentSHA256(task domain.PurchaseTask) string {
	budget := ""
	if task.MaxBudgetCents != nil {
		budget = strconv.FormatInt(*task.MaxBudgetCents, 10)
	}
	payload := strings.Join([]string{
		task.Title,
		task.Description,
		task.SKU,
		task.ImageAssetID,
		strconv.Itoa(task.Quantity),
		budget,
		task.Currency,
	}, "\x00")
	sum := sha256.Sum256([]byte(payload))
	return hex.EncodeToString(sum[:])
}

func executionResultInvalid(field string, message string) error {
	return invalidError(
		"EXECUTION_RESULT_INVALID",
		"execution result request is invalid",
		map[string]string{field: message},
	)
}

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

var sha256Pattern = regexp.MustCompile("^[0-9a-f]{64}$")