CUB-113: implement core CRUD API endpoints

- Add dtos package with request/response structs
- Add repositories: Material, Filament, Printer, PrintJob, UsageLog
- Add services: FilamentService, PrinterService, PrintJobService
- Add handlers for all 5 resources with consistent error responses
- Wire all endpoints into Chi router under /api
- Validation on POST/PUT filament endpoints
- Filter/pagination support on list endpoints
- Soft-delete for filaments (DELETE /api/filaments/{id})
- go build ./... && go vet ./... → PASS

backend/internal/services/.gitkeep

@@ -1 +0,0 @@
-# Services

backend/internal/services/services.go

@@ -0,0 +1,82 @@
+// Package services contains business logic and application services.
+package services
+
+import (
+	"context"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/models"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/repositories"
+)
+
+// FilamentService wraps FilamentRepository with business logic and validation.
+type FilamentService struct {
+	repo *repositories.FilamentRepository
+}
+
+// NewFilamentService creates a FilamentService backed by the given repository.
+func NewFilamentService(repo *repositories.FilamentRepository) *FilamentService {
+	return &FilamentService{repo: repo}
+}
+
+// List returns paginated filament spools filtered by the given criteria.
+func (s *FilamentService) List(ctx context.Context, filter repositories.FilamentFilter) ([]models.FilamentSpool, int, error) {
+	return s.repo.GetAll(ctx, filter)
+}
+
+// GetByID returns a single filament spool by ID.
+func (s *FilamentService) GetByID(ctx context.Context, id int) (*models.FilamentSpool, error) {
+	return s.repo.GetByID(ctx, id)
+}
+
+// Create validates and creates a new filament spool.
+func (s *FilamentService) Create(ctx context.Context, spool *models.FilamentSpool) (*models.FilamentSpool, error) {
+	if err := validateFilamentSpool(spool); err != nil {
+		return nil, err
+	}
+	return s.repo.Create(ctx, spool)
+}
+
+// Update applies partial updates to a filament spool after validation.
+func (s *FilamentService) Update(ctx context.Context, id int, updates map[string]interface{}) (*models.FilamentSpool, error) {
+	return s.repo.Update(ctx, id, updates)
+}
+
+// SoftDelete marks a filament spool as deleted.
+func (s *FilamentService) SoftDelete(ctx context.Context, id int) (bool, error) {
+	return s.repo.SoftDelete(ctx, id)
+}
+
+// PrinterService wraps PrinterRepository.
+type PrinterService struct {
+	repo *repositories.PrinterRepository
+}
+
+// NewPrinterService creates a PrinterService backed by the given repository.
+func NewPrinterService(repo *repositories.PrinterRepository) *PrinterService {
+	return &PrinterService{repo: repo}
+}
+
+// List returns all printers.
+func (s *PrinterService) List(ctx context.Context) ([]models.Printer, error) {
+	return s.repo.GetAll(ctx)
+}
+
+// PrintJobService wraps PrintJobRepository.
+type PrintJobService struct {
+	repo *repositories.PrintJobRepository
+}
+
+// NewPrintJobService creates a PrintJobService backed by the given repository.
+func NewPrintJobService(repo *repositories.PrintJobRepository) *PrintJobService {
+	return &PrintJobService{repo: repo}
+}
+
+// List returns paginated print jobs filtered by the given criteria.
+func (s *PrintJobService) List(ctx context.Context, filter repositories.PrintJobFilter) ([]models.PrintJob, int, error) {
+	return s.repo.GetAll(ctx, filter)
+}
+
+// GetByID returns a single print job by ID.
+func (s *PrintJobService) GetByID(ctx context.Context, id int) (*models.PrintJob, error) {
+	return s.repo.GetByID(ctx, id)
+}

backend/internal/services/validation.go

@@ -0,0 +1,74 @@
+package services
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/dtos"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/models"
+)
+
+// colorHexPattern validates hex color strings like #FF0000 or #ff0000.
+var colorHexPattern = regexp.MustCompile(`^#[0-9A-Fa-f]{6}$`)
+
+// validateFilamentSpool performs validation on a FilamentSpool entity.
+// Returns a descriptive error on failure.
+func validateFilamentSpool(s *models.FilamentSpool) error {
+	if s.Name == "" {
+		return errors.New("name is required")
+	}
+	if s.MaterialBaseID <= 0 {
+		return errors.New("material_base_id is required")
+	}
+	if s.MaterialFinishID <= 0 {
+		return errors.New("material_finish_id is required")
+	}
+	if !colorHexPattern.MatchString(s.ColorHex) {
+		return fmt.Errorf("color_hex must be a valid hex color (e.g., #FF0000)")
+	}
+	if s.InitialGrams <= 0 {
+		return errors.New("initial_grams must be greater than 0")
+	}
+	if s.RemainingGrams < 0 {
+		return errors.New("remaining_grams must be >= 0")
+	}
+	return nil
+}
+
+// ValidateCreateFilamentRequest validates a creation DTO.
+func ValidateCreateFilamentRequest(req dtos.CreateFilamentRequest) error {
+	if req.Name == "" {
+		return errors.New("name is required")
+	}
+	if req.MaterialBaseID <= 0 {
+		return errors.New("material_base_id is required")
+	}
+	if req.MaterialFinishID <= 0 {
+		return errors.New("material_finish_id is required")
+	}
+	if !colorHexPattern.MatchString(req.ColorHex) {
+		return fmt.Errorf("color_hex must be a valid hex color (e.g., #FF0000)")
+	}
+	if req.InitialGrams <= 0 {
+		return errors.New("initial_grams must be greater than 0")
+	}
+	if req.RemainingGrams < 0 {
+		return errors.New("remaining_grams must be >= 0")
+	}
+	return nil
+}
+
+// ValidateUpdateFilamentRequest validates partial update fields.
+func ValidateUpdateFilamentRequest(req dtos.UpdateFilamentRequest) error {
+	if req.ColorHex != nil && !colorHexPattern.MatchString(*req.ColorHex) {
+		return fmt.Errorf("color_hex must be a valid hex color (e.g., #FF0000)")
+	}
+	if req.InitialGrams != nil && *req.InitialGrams <= 0 {
+		return errors.New("initial_grams must be greater than 0")
+	}
+	if req.RemainingGrams != nil && *req.RemainingGrams < 0 {
+		return errors.New("remaining_grams must be >= 0")
+	}
+	return nil
+}