tercul-backend/internal/app/localization/service.go

package localization

import (
	"context"
	"errors"
	"tercul/internal/domain"
	"tercul/internal/platform/log"
)

// Service resolves localized attributes using translations
type Service interface {
	GetWorkContent(ctx context.Context, workID uint, preferredLanguage string) (string, error)
	GetAuthorBiography(ctx context.Context, authorID uint, preferredLanguage string) (string, error)
}

type service struct {
	translationRepo domain.TranslationRepository
}

func NewService(translationRepo domain.TranslationRepository) Service {
	return &service{translationRepo: translationRepo}
}

func (s *service) GetWorkContent(ctx context.Context, workID uint, preferredLanguage string) (string, error) {
	if workID == 0 {
		return "", errors.New("invalid work ID")
	}
	log.LogDebug("fetching translations for work", log.F("work_id", workID))
	translations, err := s.translationRepo.ListByWorkID(ctx, workID)
	if err != nil {
		log.LogError("failed to fetch translations for work", log.F("work_id", workID), log.F("error", err))
		return "", err
	}
	return pickContent(ctx, translations, preferredLanguage), nil
}

func (s *service) GetAuthorBiography(ctx context.Context, authorID uint, preferredLanguage string) (string, error) {
	if authorID == 0 {
		return "", errors.New("invalid author ID")
	}
	log.LogDebug("fetching translations for author", log.F("author_id", authorID))
	translations, err := s.translationRepo.ListByEntity(ctx, "Author", authorID)
	if err != nil {
		log.LogError("failed to fetch translations for author", log.F("author_id", authorID), log.F("error", err))
		return "", err
	}

	// Prefer Description from Translation as biography proxy
	var byLang *domain.Translation
	for i := range translations {
		tr := &translations[i]
		if tr.IsOriginalLanguage && tr.Description != "" {
			log.LogDebug("found original language biography for author", log.F("author_id", authorID), log.F("language", tr.Language))
			return tr.Description, nil
		}
		if tr.Language == preferredLanguage && byLang == nil && tr.Description != "" {
			byLang = tr
		}
	}
	if byLang != nil {
		log.LogDebug("found preferred language biography for author", log.F("author_id", authorID), log.F("language", byLang.Language))
		return byLang.Description, nil
	}

	// fallback to any non-empty description
	for i := range translations {
		if translations[i].Description != "" {
			log.LogDebug("found fallback biography for author", log.F("author_id", authorID), log.F("language", translations[i].Language))
			return translations[i].Description, nil
		}
	}

	log.LogDebug("no biography found for author", log.F("author_id", authorID))
	return "", nil
}

func pickContent(ctx context.Context, translations []domain.Translation, preferredLanguage string) string {
	var byLang *domain.Translation
	for i := range translations {
		tr := &translations[i]
		if tr.IsOriginalLanguage {
			log.LogDebug("found original language content", log.F("language", tr.Language))
			return tr.Content
		}
		if tr.Language == preferredLanguage && byLang == nil {
			byLang = tr
		}
	}
	if byLang != nil {
		log.LogDebug("found preferred language content", log.F("language", byLang.Language))
		return byLang.Content
	}
	if len(translations) > 0 {
		log.LogDebug("found fallback content", log.F("language", translations[0].Language))
		return translations[0].Content
	}

	log.LogDebug("no content found")
	return ""
}