feat: Add charging handler with credit management endpoints for IP-based operations

- Add ChargingHandler struct with ChargingEngineClient dependency
- Add NewChargingHandler constructor
- Add CheckCredit endpoint to validate sufficient credit for requested bytes
- Add GetBalance endpoint to retrieve current balance for an IP
- Add AddCredit endpoint to add bytes to an IP's credit
- Add DeductCredit endpoint to deduct bytes from an IP's credit
- Add IP parameter validation and JSON request binding

apps/api-server/internal/handlers/charging_handler.go

@@ -0,0 +1,112 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/nutcas3/telecom-platform/apps/api-server/internal/services"
+)
+
+// ChargingHandler handles charging engine integration
+type ChargingHandler struct {
+	engineClient *services.ChargingEngineClient
+}
+
+// NewChargingHandler creates a new charging handler
+func NewChargingHandler(engineClient *services.ChargingEngineClient) *ChargingHandler {
+	return &ChargingHandler{
+		engineClient: engineClient,
+	}
+}
+
+// CheckCredit checks if an IP has sufficient credit
+func (h *ChargingHandler) CheckCredit(c *gin.Context) {
+	ip := c.Param("ip")
+	if ip == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "IP address is required"})
+		return
+	}
+
+	var req struct {
+		BytesRequested uint64 `json:"bytes_requested" binding:"required"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	result, err := h.engineClient.CheckCredit(c.Request.Context(), ip, req.BytesRequested)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, result)
+}
+
+// GetBalance gets the current balance for an IP
+func (h *ChargingHandler) GetBalance(c *gin.Context) {
+	ip := c.Param("ip")
+	if ip == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "IP address is required"})
+		return
+	}
+
+	result, err := h.engineClient.GetBalance(c.Request.Context(), ip)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, result)
+}
+
+// AddCredit adds credit to an IP
+func (h *ChargingHandler) AddCredit(c *gin.Context) {
+	ip := c.Param("ip")
+	if ip == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "IP address is required"})
+		return
+	}
+
+	var req struct {
+		BytesToAdd uint64 `json:"bytes_to_add" binding:"required"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	err := h.engineClient.AddCredit(c.Request.Context(), ip, req.BytesToAdd)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"status": "success"})
+}
+
+// DeductCredit deducts credit from an IP
+func (h *ChargingHandler) DeductCredit(c *gin.Context) {
+	ip := c.Param("ip")
+	if ip == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "IP address is required"})
+		return
+	}
+
+	var req struct {
+		BytesUsed uint64 `json:"bytes_used" binding:"required"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	err := h.engineClient.DeductCredit(c.Request.Context(), ip, req.BytesUsed)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"status": "success"})
+}