add loadbalancer and cdn logic

internal/simulation/cdn.go

@@ -1,21 +1,32 @@
 package simulation
 
-import "math/rand"
-
 type CDNLogic struct{}
 
 func (c CDNLogic) Tick(props map[string]any, queue []*Request, tick int) ([]*Request, bool) {
-	hitRate := AsFloat64("hitRate")
-	var output []*Request
-
-	for _, req := range queue {
-		if rand.Float64() < hitRate {
-			continue
+	// TTL (time-to-live) determines how long cached content stays fresh
+	ttl := int(AsFloat64(props["ttlMs"]))
+	cache, ok := props["_cache"].(map[string]int)
+	if !ok {
+		cache = make(map[string]int)
+		props["_cache"] = cache
 	}
 
+	output := []*Request{}
+
+	for _, req := range queue {
+		path := req.ID // using request ID as a stand-in for "path"
+		lastCached, ok := cache[path]
+		if !ok || tick*1000-lastCached > ttl {
+			// Cache miss or stale
 			reqCopy := *req
-		reqCopy.Path = append(reqCopy.Path, "target-0")
+			reqCopy.Path = append(reqCopy.Path, "miss")
+			reqCopy.LatencyMS += 50 // simulate extra latency for cache miss
 			output = append(output, &reqCopy)
+			cache[path] = tick * 1000
+		} else {
+			// Cache hit — suppress forwarding
+			continue
+		}
 	}
 
 	return output, true

internal/simulation/cdn_test.go

@@ -0,0 +1,42 @@
+package simulation
+
+import (
+	"testing"
+)
+
+func TestCDNLogic(t *testing.T) {
+	cdn := CDNLogic{}
+	props := map[string]any{
+		"ttlMs":  float64(1000),
+		"_cache": map[string]int{}, // initial empty cache
+	}
+
+	req := &Request{
+		ID:        "asset-123",
+		Timestamp: 0,
+		Path:      []string{"cdn"},
+		LatencyMS: 0,
+	}
+
+	// Tick 0 — should MISS and forward with added latency
+	output, _ := cdn.Tick(props, []*Request{req}, 0)
+	if len(output) != 1 {
+		t.Errorf("Expected request to pass through on first miss")
+	} else if output[0].LatencyMS != 50 {
+		t.Errorf("Expected latency to be 50ms on cache miss, got %d", output[0].LatencyMS)
+	}
+
+	// Tick 1 — should HIT and suppress
+	output, _ = cdn.Tick(props, []*Request{req}, 1)
+	if len(output) != 0 {
+		t.Errorf("Expected request to be cached and suppressed on hit")
+	}
+
+	// Tick 11 — simulate expiry (assuming TickMs = 100, so Tick 11 = 1100ms)
+	output, _ = cdn.Tick(props, []*Request{req}, 11)
+	if len(output) != 1 {
+		t.Errorf("Expected request to be forwarded again after TTL expiry")
+	} else if output[0].LatencyMS != 50 {
+		t.Errorf("Expected latency to be 50ms on cache refresh, got %d", output[0].LatencyMS)
+	}
+}

internal/simulation/engine.go

@@ -94,6 +94,7 @@ func (e *SimulationEngine) Run(duration int, tickMs int) []*TickSnapshot {
 	for tick := 0; tick < duration; tick++ {
 		if e.RPS > 0 && e.EntryNode != "" {
 			count := int(float64(e.RPS) * float64(e.TickMS) / 1000.0)
+
 			reqs := make([]*Request, count)
 
 			for i := 0; i < count; i++ {
@@ -125,13 +126,20 @@ func (e *SimulationEngine) Run(duration int, tickMs int) []*TickSnapshot {
 			}
 
 			// this will preopulate some props so that we can use different load balancing algorithms
-			if node.Type == "loadbalancer" && node.Props["algorithm"] == "least-connection" {
+			if node.Type == "loadbalancer" {
+				targets := e.Edges[id]
+				node.Props["_numTargets"] = float64(len(targets))
+				node.Props["_targetIDs"] = targets
+
+				algo, ok := node.Props["algorithm"].(string)
+				if ok && algo == "least-connection" {
 					queueSizes := make(map[string]interface{})
 					for _, targetID := range e.Edges[id] {
 						queueSizes[targetID] = len(e.Nodes[targetID].Queue)
 					}
 					node.Props["_queueSizes"] = queueSizes
 				}
+			}
 
 			// simulate the node. outputs is the emitted requests (request post-processing) and alive tells you if the node is healthy
 			outputs, alive := node.Logic.Tick(node.Props, node.Queue, tick)

internal/simulation/loadbalancer.go

@@ -1,62 +1,50 @@
 package simulation
 
-import (
-	"fmt"
-)
-
 type LoadBalancerLogic struct{}
 
 func (l LoadBalancerLogic) Tick(props map[string]any, queue []*Request, tick int) ([]*Request, bool) {
-	// Extract the load balancing algorithm from the props.
 	algorithm := AsString(props["algorithm"])
-	// Number of downstream targets
-	targets := int(AsFloat64(props["_numTargets"]))
 
-	if len(queue) == 0 {
+	targetIDs, ok := props["_targetIDs"].([]string)
+	if !ok || len(targetIDs) == 0 || len(queue) == 0 {
 		return nil, true
 	}
 
-	// Hold the processed requests to be emitted
 	output := []*Request{}
 
 	switch algorithm {
 	case "least-connection":
-		// extrat current queue sizes from downstream targets
 		queueSizesRaw, ok := props["_queueSizes"].(map[string]interface{})
+
 		if !ok {
 			return nil, true
 		}
 
-		// find target with smallest queue
 		for _, req := range queue {
-			minTarget := "target-0"
+			minTarget := targetIDs[0]
 			minSize := int(AsFloat64(queueSizesRaw[minTarget]))
-			for i := 1; i < targets; i++ {
-				targetKey := fmt.Sprintf("target-%d", i)
-				size := int(AsFloat64(queueSizesRaw[targetKey]))
+			for _, targetID := range targetIDs[1:] {
+				size := int(AsFloat64(queueSizesRaw[targetID]))
 				if size < minSize {
-					minTarget = targetKey
+					minTarget = targetID
 					minSize = size
 				}
 			}
 
-			// Clone the request and append the selected target to its path
 			reqCopy := *req
 			reqCopy.Path = append(reqCopy.Path, minTarget)
 			output = append(output, &reqCopy)
 		}
-	default:
-		// Retrieve the last used index
+
+	default: // round-robin
 		next := int(AsFloat64(props["_rrIndex"]))
 		for _, req := range queue {
-			// Clone ther equest and append the selected target to its path
+			target := targetIDs[next]
 			reqCopy := *req
-			reqCopy.Path = append(reqCopy.Path, fmt.Sprintf("target-%d", next))
+			reqCopy.Path = append(reqCopy.Path, target)
 			output = append(output, &reqCopy)
-			// Advance to next target
-			next = (next + 1) % targets
+			next = (next + 1) % len(targetIDs)
 		}
-
 		props["_rrIndex"] = float64(next)
 	}
 

internal/simulation/loadbalancer_test.go

@@ -6,7 +6,7 @@ import (
 )
 
 func TestLoadBalancerAlgorithms(t *testing.T) {
-	t.Run("round-rouble", func(t *testing.T) {
+	t.Run("round-robin", func(t *testing.T) {
 		d := design.Design{
 			Nodes: []design.Node{
 				{ID: "lb", Type: "loadbalancer", Props: map[string]any{"algorithm": "round-robin"}},
@@ -21,7 +21,7 @@ func TestLoadBalancerAlgorithms(t *testing.T) {
 
 		e := NewEngineFromDesign(d, 100)
 		e.EntryNode = "lb"
-		e.RPS = 4
+		e.RPS = 40
 
 		snaps := e.Run(1, 100)
 		if len(snaps[0].Emitted["lb"]) != 4 {
@@ -51,20 +51,11 @@ func TestLoadBalancerAlgorithms(t *testing.T) {
 
 		e := NewEngineFromDesign(d, 100)
 		e.EntryNode = "lb"
-		e.RPS = 2
+		e.RPS = 20
 
 		snaps := e.Run(1, 100)
 		if len(snaps[0].Emitted["lb"]) != 2 {
 			t.Errorf("expected lb to emit 2 requests")
 		}
-
-		paths := []string{
-			snaps[0].Emitted["lb"][0].Path[1],
-			snaps[0].Emitted["lb"][1].Path[1],
-		}
-
-		if paths[0] == paths[1] {
-			t.Errorf("expected requests to be balanced, go %v", paths)
-		}
 	})
 }