goplt/services/gateway/gateway.go

// Package gateway provides API Gateway implementation.
package gateway

import (
	"net/http"
	"strings"

	"git.dcentral.systems/toolz/goplt/internal/client"
	"git.dcentral.systems/toolz/goplt/pkg/config"
	"git.dcentral.systems/toolz/goplt/pkg/logger"
	"git.dcentral.systems/toolz/goplt/pkg/registry"
	"github.com/gin-gonic/gin"
)

// Gateway handles routing requests to backend services.
type Gateway struct {
	config        config.ConfigProvider
	log           logger.Logger
	clientFactory *client.ServiceClientFactory
	registry      registry.ServiceRegistry
	routes        []RouteConfig
}

// RouteConfig defines a route configuration.
type RouteConfig struct {
	Path         string
	Service      string
	AuthRequired bool
}

// NewGateway creates a new API Gateway instance.
func NewGateway(
	cfg config.ConfigProvider,
	log logger.Logger,
	clientFactory *client.ServiceClientFactory,
	reg registry.ServiceRegistry,
) (*Gateway, error) {
	// Load route configurations
	routes := loadRoutes(cfg)

	return &Gateway{
		config:        cfg,
		log:           log,
		clientFactory: clientFactory,
		registry:      reg,
		routes:        routes,
	}, nil
}

// SetupRoutes configures routes on the Gin router.
func (g *Gateway) SetupRoutes(router *gin.Engine) {
	// Register routes with wildcard support
	// Gin uses /*path for wildcards, so we convert /** to /*path
	for _, route := range g.routes {
		route := route // Capture for closure

		// Convert /** wildcard to Gin's /*path format
		ginPath := route.Path
		hasWildcard := strings.HasSuffix(ginPath, "/**")
		if hasWildcard {
			ginPath = strings.TrimSuffix(ginPath, "/**") + "/*path"
		}

		// Register all HTTP methods for this route
		router.Any(ginPath, func(c *gin.Context) {
			// Extract the remaining path
			var remainingPath string
			if hasWildcard {
				// Extract from Gin's path parameter
				pathParam := c.Param("path")
				if pathParam != "" {
					remainingPath = "/" + pathParam
				} else {
					remainingPath = "/"
				}
			} else {
				// Exact match - no remaining path
				remainingPath = "/"
			}

			// Route to appropriate service handler
			switch route.Service {
			case "auth-service":
				g.handleAuthService(c, route, remainingPath)
			case "identity-service":
				g.handleIdentityService(c, route, remainingPath)
			default:
				g.log.Warn("Unknown service",
					logger.String("service", route.Service),
				)
				c.JSON(http.StatusNotFound, gin.H{
					"error": "Service not found",
				})
			}
		})
	}

	// Default handler for unmatched routes
	router.NoRoute(func(c *gin.Context) {
		c.JSON(http.StatusNotFound, gin.H{
			"error": "Route not found",
			"path":  c.Request.URL.Path,
		})
	})
}

// matchRoute finds the matching route configuration for a given path.
func (g *Gateway) matchRoute(path string) *RouteConfig {
	for _, route := range g.routes {
		if g.pathMatches(path, route.Path) {
			return &route
		}
	}
	return nil
}

// pathMatches checks if a request path matches a route pattern.
// Supports wildcard matching: "/api/v1/auth/**" matches "/api/v1/auth/login", etc.
func (g *Gateway) pathMatches(requestPath, routePath string) bool {
	// Remove trailing slashes for comparison
	requestPath = strings.TrimSuffix(requestPath, "/")
	routePath = strings.TrimSuffix(routePath, "/")

	// Exact match
	if requestPath == routePath {
		return true
	}

	// Wildcard match: routePath ends with "/**"
	if strings.HasSuffix(routePath, "/**") {
		prefix := strings.TrimSuffix(routePath, "/**")
		return strings.HasPrefix(requestPath, prefix+"/") || requestPath == prefix
	}

	return false
}

// extractRemainingPath extracts the path segment after the route prefix.
// Example: path="/api/v1/auth/login", route="/api/v1/auth/**" -> returns "/login"
func (g *Gateway) extractRemainingPath(requestPath, routePath string) string {
	// Remove trailing slashes
	requestPath = strings.TrimSuffix(requestPath, "/")
	routePath = strings.TrimSuffix(routePath, "/")

	// Handle wildcard routes
	if strings.HasSuffix(routePath, "/**") {
		prefix := strings.TrimSuffix(routePath, "/**")
		if strings.HasPrefix(requestPath, prefix) {
			remaining := strings.TrimPrefix(requestPath, prefix)
			if remaining == "" {
				return "/"
			}
			return remaining
		}
	}

	// Exact match - no remaining path
	if requestPath == routePath {
		return "/"
	}

	return ""
}

// loadRoutes loads route configurations from config.
func loadRoutes(cfg config.ConfigProvider) []RouteConfig {
	if cfg == nil {
		return []RouteConfig{}
	}

	// Get routes from config
	routesInterface := cfg.Get("gateway.routes")
	if routesInterface == nil {
		return []RouteConfig{}
	}

	// Convert to slice of RouteConfig
	routesSlice, ok := routesInterface.([]interface{})
	if !ok {
		return []RouteConfig{}
	}

	routes := make([]RouteConfig, 0, len(routesSlice))
	for _, routeInterface := range routesSlice {
		routeMap, ok := routeInterface.(map[string]interface{})
		if !ok {
			continue
		}

		route := RouteConfig{}

		if path, ok := routeMap["path"].(string); ok {
			route.Path = path
		}

		if service, ok := routeMap["service"].(string); ok {
			route.Service = service
		}

		if authRequired, ok := routeMap["auth_required"].(bool); ok {
			route.AuthRequired = authRequired
		}

		// Only add route if it has required fields
		if route.Path != "" && route.Service != "" {
			routes = append(routes, route)
		}
	}

	return routes
}