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/handlers/filament_handler.go

@@ -0,0 +1,273 @@
+package handlers
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+	"strconv"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/dtos"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/models"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/repositories"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/services"
+	"github.com/go-chi/chi/v5"
+)
+
+// FilamentHandler handles HTTP requests for filament spool CRUD operations.
+type FilamentHandler struct {
+	service *services.FilamentService
+}
+
+// NewFilamentHandler creates a FilamentHandler with the given service.
+func NewFilamentHandler(service *services.FilamentService) *FilamentHandler {
+	return &FilamentHandler{service: service}
+}
+
+// List handles GET /api/filaments — returns paginated, filtered spools.
+func (h *FilamentHandler) List(w http.ResponseWriter, r *http.Request) {
+	limit, offset := parsePagination(r)
+	filter := repositories.FilamentFilter{
+		Material: r.URL.Query().Get("material"),
+		Finish:   r.URL.Query().Get("finish"),
+		Color:    r.URL.Query().Get("color"),
+		LowStock: r.URL.Query().Get("low_stock") == "true",
+		Limit:    limit,
+		Offset:   offset,
+	}
+
+	spools, total, err := h.service.List(r.Context(), filter)
+	if err != nil {
+		slog.Error("failed to list filaments", "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, dtos.ListResponse{
+		Data:   spools,
+		Total:  total,
+		Limit:  limit,
+		Offset: offset,
+	})
+}
+
+// Get handles GET /api/filaments/{id} — returns a single spool.
+func (h *FilamentHandler) Get(w http.ResponseWriter, r *http.Request) {
+	id, err := strconv.Atoi(chi.URLParam(r, "id"))
+	if err != nil {
+		writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+			Error: "invalid filament ID",
+			Code:  http.StatusBadRequest,
+		})
+		return
+	}
+
+	spool, err := h.service.GetByID(r.Context(), id)
+	if err != nil {
+		slog.Error("failed to get filament", "id", id, "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+	if spool == nil {
+		writeJSON(w, http.StatusNotFound, dtos.ErrorResponse{
+			Error: "filament not found",
+			Code:  http.StatusNotFound,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, dtos.SingleResponse{Data: spool})
+}
+
+// Create handles POST /api/filaments — creates a new filament spool.
+func (h *FilamentHandler) Create(w http.ResponseWriter, r *http.Request) {
+	var req dtos.CreateFilamentRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+			Error: "invalid request body",
+			Code:  http.StatusBadRequest,
+		})
+		return
+	}
+
+	// Validate required fields.
+	if err := services.ValidateCreateFilamentRequest(req); err != nil {
+		writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+			Error: "validation failed: " + err.Error(),
+			Code:  http.StatusBadRequest,
+		})
+		return
+	}
+
+	// Build domain model.
+	spool := models.FilamentSpool{
+		Name:                  req.Name,
+		MaterialBaseID:        req.MaterialBaseID,
+		MaterialFinishID:      req.MaterialFinishID,
+		MaterialModifierID:    req.MaterialModifierID,
+		ColorHex:             req.ColorHex,
+		Brand:                req.Brand,
+		DiameterMM:           1.75, // default
+		InitialGrams:         req.InitialGrams,
+		RemainingGrams:       req.RemainingGrams,
+		SpoolWeightGrams:     req.SpoolWeightGrams,
+		CostUSD:              req.CostUSD,
+		LowStockThresholdGrams: 50, // default
+		Notes:                req.Notes,
+		Barcode:              req.Barcode,
+	}
+	if req.DiameterMM != nil {
+		spool.DiameterMM = *req.DiameterMM
+	}
+	if req.LowStockThresholdGrams != nil {
+		spool.LowStockThresholdGrams = *req.LowStockThresholdGrams
+	}
+
+	created, err := h.service.Create(r.Context(), &spool)
+	if err != nil {
+		slog.Error("failed to create filament", "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusCreated, dtos.SingleResponse{Data: created})
+}
+
+// Update handles PUT /api/filaments/{id} — partially updates a spool.
+func (h *FilamentHandler) Update(w http.ResponseWriter, r *http.Request) {
+	id, err := strconv.Atoi(chi.URLParam(r, "id"))
+	if err != nil {
+		writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+			Error: "invalid filament ID",
+			Code:  http.StatusBadRequest,
+		})
+		return
+	}
+
+	var req dtos.UpdateFilamentRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+			Error: "invalid request body",
+			Code:  http.StatusBadRequest,
+		})
+		return
+	}
+
+	// Validate update fields.
+	if err := services.ValidateUpdateFilamentRequest(req); err != nil {
+		writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+			Error: "validation failed: " + err.Error(),
+			Code:  http.StatusBadRequest,
+		})
+		return
+	}
+
+	// Build updates map (only non-nil fields).
+	updates := buildFilamentUpdates(req)
+
+	updated, err := h.service.Update(r.Context(), id, updates)
+	if err != nil {
+		slog.Error("failed to update filament", "id", id, "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+	if updated == nil {
+		writeJSON(w, http.StatusNotFound, dtos.ErrorResponse{
+			Error: "filament not found",
+			Code:  http.StatusNotFound,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, dtos.SingleResponse{Data: updated})
+}
+
+// Delete handles DELETE /api/filaments/{id} — soft-deletes a spool.
+func (h *FilamentHandler) Delete(w http.ResponseWriter, r *http.Request) {
+	id, err := strconv.Atoi(chi.URLParam(r, "id"))
+	if err != nil {
+		writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+			Error: "invalid filament ID",
+			Code:  http.StatusBadRequest,
+		})
+		return
+	}
+
+	deleted, err := h.service.SoftDelete(r.Context(), id)
+	if err != nil {
+		slog.Error("failed to delete filament", "id", id, "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+	if !deleted {
+		writeJSON(w, http.StatusNotFound, dtos.ErrorResponse{
+			Error: "filament not found",
+			Code:  http.StatusNotFound,
+		})
+		return
+	}
+
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// buildFilamentUpdates converts an UpdateFilamentRequest to a map of column→value.
+func buildFilamentUpdates(req dtos.UpdateFilamentRequest) map[string]interface{} {
+	updates := make(map[string]interface{})
+	if req.Name != nil {
+		updates["name"] = *req.Name
+	}
+	if req.MaterialBaseID != nil {
+		updates["material_base_id"] = *req.MaterialBaseID
+	}
+	if req.MaterialFinishID != nil {
+		updates["material_finish_id"] = *req.MaterialFinishID
+	}
+	if req.MaterialModifierID != nil {
+		updates["material_modifier_id"] = *req.MaterialModifierID
+	}
+	if req.ColorHex != nil {
+		updates["color_hex"] = *req.ColorHex
+	}
+	if req.Brand != nil {
+		updates["brand"] = *req.Brand
+	}
+	if req.DiameterMM != nil {
+		updates["diameter_mm"] = *req.DiameterMM
+	}
+	if req.InitialGrams != nil {
+		updates["initial_grams"] = *req.InitialGrams
+	}
+	if req.RemainingGrams != nil {
+		updates["remaining_grams"] = *req.RemainingGrams
+	}
+	if req.SpoolWeightGrams != nil {
+		updates["spool_weight_grams"] = *req.SpoolWeightGrams
+	}
+	if req.CostUSD != nil {
+		updates["cost_usd"] = *req.CostUSD
+	}
+	if req.LowStockThresholdGrams != nil {
+		updates["low_stock_threshold_grams"] = *req.LowStockThresholdGrams
+	}
+	if req.Notes != nil {
+		updates["notes"] = *req.Notes
+	}
+	if req.Barcode != nil {
+		updates["barcode"] = *req.Barcode
+	}
+	return updates
+}

backend/internal/handlers/helpers.go

@@ -0,0 +1,51 @@
+package handlers
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+	"strconv"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/dtos"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/services"
+)
+
+// writeJSON serializes v as JSON to the response writer with the given status code.
+// Logs an error if encoding fails.
+func writeJSON(w http.ResponseWriter, status int, v interface{}) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	if err := json.NewEncoder(w).Encode(v); err != nil {
+		slog.Error("failed to encode JSON response", "error", err)
+	}
+}
+
+// parsePagination reads limit and offset query parameters with defaults of 20 and 0.
+func parsePagination(r *http.Request) (limit, offset int) {
+	limit = 20
+	offset = 0
+
+	if l := r.URL.Query().Get("limit"); l != "" {
+		if parsed, err := strconv.Atoi(l); err == nil && parsed > 0 {
+			limit = parsed
+		}
+	}
+	if o := r.URL.Query().Get("offset"); o != "" {
+		if parsed, err := strconv.Atoi(o); err == nil && parsed >= 0 {
+			offset = parsed
+		}
+	}
+	return
+}
+
+// ValidateCreateFilamentRequest validates a CreateFilamentRequest DTO.
+// Re-exports the service-layer validator for handler use.
+func ValidateCreateFilamentRequest(req dtos.CreateFilamentRequest) error {
+	return services.ValidateCreateFilamentRequest(req)
+}
+
+// ValidateUpdateFilamentRequest validates an UpdateFilamentRequest DTO.
+// Re-exports the service-layer validator for handler use.
+func ValidateUpdateFilamentRequest(req dtos.UpdateFilamentRequest) error {
+	return services.ValidateUpdateFilamentRequest(req)
+}

backend/internal/handlers/material_handler.go

@@ -0,0 +1,34 @@
+package handlers
+
+import (
+	"log/slog"
+	"net/http"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/dtos"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/repositories"
+)
+
+// MaterialHandler handles requests for material lookup data.
+type MaterialHandler struct {
+	repo *repositories.MaterialRepository
+}
+
+// NewMaterialHandler creates a MaterialHandler with the given repository.
+func NewMaterialHandler(repo *repositories.MaterialRepository) *MaterialHandler {
+	return &MaterialHandler{repo: repo}
+}
+
+// List handles GET /api/materials — returns all material bases.
+func (h *MaterialHandler) List(w http.ResponseWriter, r *http.Request) {
+	materials, err := h.repo.GetAll(r.Context())
+	if err != nil {
+		slog.Error("failed to list materials", "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, dtos.SingleResponse{Data: materials})
+}

backend/internal/handlers/print_job_handler.go

@@ -0,0 +1,60 @@
+package handlers
+
+import (
+	"log/slog"
+	"net/http"
+	"strconv"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/dtos"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/repositories"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/services"
+)
+
+// PrintJobHandler handles HTTP requests for print job operations.
+type PrintJobHandler struct {
+	service *services.PrintJobService
+}
+
+// NewPrintJobHandler creates a PrintJobHandler with the given service.
+func NewPrintJobHandler(service *services.PrintJobService) *PrintJobHandler {
+	return &PrintJobHandler{service: service}
+}
+
+// List handles GET /api/print-jobs — returns paginated, filtered print jobs.
+func (h *PrintJobHandler) List(w http.ResponseWriter, r *http.Request) {
+	limit, offset := parsePagination(r)
+	filter := repositories.PrintJobFilter{
+		Status: r.URL.Query().Get("status"),
+		Limit:  limit,
+		Offset: offset,
+	}
+
+	if pidStr := r.URL.Query().Get("printer_id"); pidStr != "" {
+		pid, err := strconv.Atoi(pidStr)
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+				Error: "invalid printer_id",
+				Code:  http.StatusBadRequest,
+			})
+			return
+		}
+		filter.PrinterID = &pid
+	}
+
+	jobs, total, err := h.service.List(r.Context(), filter)
+	if err != nil {
+		slog.Error("failed to list print jobs", "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, dtos.ListResponse{
+		Data:   jobs,
+		Total:  total,
+		Limit:  limit,
+		Offset: offset,
+	})
+}

backend/internal/handlers/printer_handler.go

@@ -0,0 +1,34 @@
+package handlers
+
+import (
+	"log/slog"
+	"net/http"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/dtos"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/services"
+)
+
+// PrinterHandler handles HTTP requests for printer listings.
+type PrinterHandler struct {
+	service *services.PrinterService
+}
+
+// NewPrinterHandler creates a PrinterHandler with the given service.
+func NewPrinterHandler(service *services.PrinterService) *PrinterHandler {
+	return &PrinterHandler{service: service}
+}
+
+// List handles GET /api/printers — returns all printers with printer_type info.
+func (h *PrinterHandler) List(w http.ResponseWriter, r *http.Request) {
+	printers, err := h.service.List(r.Context())
+	if err != nil {
+		slog.Error("failed to list printers", "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, dtos.SingleResponse{Data: printers})
+}

backend/internal/handlers/usage_log_handler.go

@@ -0,0 +1,70 @@
+package handlers
+
+import (
+	"log/slog"
+	"net/http"
+	"strconv"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/dtos"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/repositories"
+)
+
+// UsageLogHandler handles HTTP requests for usage log operations.
+type UsageLogHandler struct {
+	repo *repositories.UsageLogRepository
+}
+
+// NewUsageLogHandler creates a UsageLogHandler with the given repository.
+func NewUsageLogHandler(repo *repositories.UsageLogRepository) *UsageLogHandler {
+	return &UsageLogHandler{repo: repo}
+}
+
+// List handles GET /api/usage-logs — returns paginated, filtered usage logs.
+func (h *UsageLogHandler) List(w http.ResponseWriter, r *http.Request) {
+	limit, offset := parsePagination(r)
+	filter := repositories.UsageLogFilter{
+		Limit:  limit,
+		Offset: offset,
+	}
+
+	if sidStr := r.URL.Query().Get("spool_id"); sidStr != "" {
+		sid, err := strconv.Atoi(sidStr)
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+				Error: "invalid spool_id",
+				Code:  http.StatusBadRequest,
+			})
+			return
+		}
+		filter.SpoolID = &sid
+	}
+
+	if jidStr := r.URL.Query().Get("job_id"); jidStr != "" {
+		jid, err := strconv.Atoi(jidStr)
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, dtos.ErrorResponse{
+				Error: "invalid job_id",
+				Code:  http.StatusBadRequest,
+			})
+			return
+		}
+		filter.JobID = &jid
+	}
+
+	logs, total, err := h.repo.GetAll(r.Context(), filter)
+	if err != nil {
+		slog.Error("failed to list usage logs", "error", err)
+		writeJSON(w, http.StatusInternalServerError, dtos.ErrorResponse{
+			Error: "internal server error",
+			Code:  http.StatusInternalServerError,
+		})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, dtos.ListResponse{
+		Data:   logs,
+		Total:  total,
+		Limit:  limit,
+		Offset: offset,
+	})
+}