cdn and adding loadbalancer algorithms

internal/simulation/cdn.go

@@ -3,30 +3,34 @@ package simulation
 type CDNLogic struct{}
 
 func (c CDNLogic) Tick(props map[string]any, queue []*Request, tick int) ([]*Request, bool) {
-	// TTL (time-to-live) determines how long cached content stays fresh
+
+	// read the ttl for cached content
 	ttl := int(AsFloat64(props["ttlMs"]))
+
+	// retrieve the cdn's cache from props
 	cache, ok := props["_cache"].(map[string]int)
 	if !ok {
 		cache = make(map[string]int)
 		props["_cache"] = cache
 	}
 
+	// prepare a list to collect output requests (those that are forwarded past the cdn)
 	output := []*Request{}
 
+	// iterate over each request in the queue
 	for _, req := range queue {
-		path := req.ID // using request ID as a stand-in for "path"
+		path := req.ID
 		lastCached, ok := cache[path]
-		if !ok || tick*1000-lastCached > ttl {
+		// check if it has been more than ttl seconds since this content was last cached?
+		if !ok || (req.Timestamp-lastCached) > ttl {
 			// Cache miss or stale
 			reqCopy := *req
 			reqCopy.Path = append(reqCopy.Path, "miss")
-			reqCopy.LatencyMS += 50 // simulate extra latency for cache miss
+			reqCopy.LatencyMS += 50
 			output = append(output, &reqCopy)
-			cache[path] = tick * 1000
+			cache[path] = req.Timestamp
-		} else {
-			// Cache hit — suppress forwarding
-			continue
 		}
+		// else cache hit, suppressed
 	}
 
 	return output, true

internal/simulation/cdn_test.go

@@ -1,42 +1,75 @@
 package simulation
 
 import (
+	"fmt"
 	"testing"
 )
 
 func TestCDNLogic(t *testing.T) {
 	cdn := CDNLogic{}
+	cache := map[string]int{} // shared mutable cache
 	props := map[string]any{
 		"ttlMs":  float64(1000),
-		"_cache": map[string]int{}, // initial empty cache
+		"_cache": cache,
 	}
 
-	req := &Request{
+	reqA := &Request{
 		ID:        "asset-123",
 		Timestamp: 0,
 		Path:      []string{"cdn"},
 		LatencyMS: 0,
 	}
 
-	// Tick 0 — should MISS and forward with added latency
+	reqB := &Request{
-	output, _ := cdn.Tick(props, []*Request{req}, 0)
+		ID:        "asset-456",
-	if len(output) != 1 {
+		Timestamp: 0,
-		t.Errorf("Expected request to pass through on first miss")
+		Path:      []string{"cdn"},
-	} else if output[0].LatencyMS != 50 {
+		LatencyMS: 0,
-		t.Errorf("Expected latency to be 50ms on cache miss, got %d", output[0].LatencyMS)
 	}
 
-	// Tick 1 — should HIT and suppress
+	// Tick 0 — both A and B should MISS and forward with added latency
-	output, _ = cdn.Tick(props, []*Request{req}, 1)
+	output, _ := cdn.Tick(props, []*Request{reqA, reqB}, 0)
+	fmt.Printf("Tick 0 Output: %+v\n", output)
+	fmt.Printf("Cache after Tick 0: %+v\n", cache)
+	if len(output) != 2 {
+		t.Errorf("Expected 2 forwarded requests on cache miss")
+	}
+	for _, o := range output {
+		if o.LatencyMS != 50 {
+			t.Errorf("Expected 50ms latency on miss, got %d", o.LatencyMS)
+		}
+	}
+	if len(cache) != 2 {
+		t.Errorf("Expected 2 items in cache after miss, got %d", len(cache))
+	}
+
+	// Tick 1 — both A and B should HIT and be suppressed
+	reqA1 := &Request{ID: "asset-123", Timestamp: 1000, Path: []string{"cdn"}, LatencyMS: 0}
+	reqB1 := &Request{ID: "asset-456", Timestamp: 1000, Path: []string{"cdn"}, LatencyMS: 0}
+	output, _ = cdn.Tick(props, []*Request{reqA1, reqB1}, 1)
+	fmt.Printf("Tick 1 Output: %+v\n", output)
+	fmt.Printf("Cache after Tick 1: %+v\n", cache)
 	if len(output) != 0 {
-		t.Errorf("Expected request to be cached and suppressed on hit")
+		t.Errorf("Expected all requests to be cached and suppressed on hit")
 	}
 
-	// Tick 11 — simulate expiry (assuming TickMs = 100, so Tick 11 = 1100ms)
+	// Tick 11 — simulate expiry for A (TTL = 1000ms, Tick 11 = 11000ms)
-	output, _ = cdn.Tick(props, []*Request{req}, 11)
+	reqA2 := &Request{ID: "asset-123", Timestamp: 11000, Path: []string{"cdn"}, LatencyMS: 0}
+	output, _ = cdn.Tick(props, []*Request{reqA2}, 11)
+	fmt.Printf("Tick 11 Output A: %+v\n", output)
+	fmt.Printf("Cache after Tick 11 A: %+v\n", cache)
 	if len(output) != 1 {
-		t.Errorf("Expected request to be forwarded again after TTL expiry")
+		t.Errorf("Expected request A 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)
+		t.Errorf("Expected 50ms latency on cache refresh, got %d", output[0].LatencyMS)
+	}
+
+	// B should still HIT (suppressed)
+	reqB2 := &Request{ID: "asset-456", Timestamp: 1000, Path: []string{"cdn"}, LatencyMS: 0}
+	output, _ = cdn.Tick(props, []*Request{reqB2}, 11)
+	fmt.Printf("Tick 11 Output B: %+v\n", output)
+	fmt.Printf("Cache after Tick 11 B: %+v\n", cache)
+	if len(output) > 0 {
+		t.Errorf("Expected request B to be suppressed due to valid cache")
 	}
 }

internal/simulation/engine.go

@@ -5,6 +5,8 @@ import (
 	"systemdesigngame/internal/design"
 )
 
+// TODO list
+type TODO interface{}
 type NodeLogic interface {
 	Tick(props map[string]any, queue []*Request, tick int) ([]*Request, bool)
 }

internal/simulation/engine_test.go

@@ -6,6 +6,7 @@ import (
 	"systemdesigngame/internal/design"
 )
 
+// TODO: Make this better
 func TestSimpleChainSimulation(t *testing.T) {
 	d := design.Design{
 		Nodes: []design.Node{

internal/simulation/loadbalancer.go

@@ -1,5 +1,10 @@
 package simulation
 
+import (
+	"hash/fnv"
+	"math/rand"
+)
+
 type LoadBalancerLogic struct{}
 
 func (l LoadBalancerLogic) Tick(props map[string]any, queue []*Request, tick int) ([]*Request, bool) {
@@ -36,6 +41,84 @@ func (l LoadBalancerLogic) Tick(props map[string]any, queue []*Request, tick int
 			output = append(output, &reqCopy)
 		}
 
+	case "random":
+		for _, req := range queue {
+			randomIndex := rand.Intn(len(targetIDs))
+			target := targetIDs[randomIndex]
+
+			reqCopy := *req
+			reqCopy.Path = append(reqCopy.Path, target)
+			output = append(output, &reqCopy)
+		}
+
+	case "ip-hash":
+		for _, req := range queue {
+			h := fnv.New32a()
+			h.Write([]byte(req.ID))
+			index := int(h.Sum32()) % len(targetIDs)
+			reqCopy := *req
+			reqCopy.Path = append(reqCopy.Path, targetIDs[index])
+			output = append(output, &reqCopy)
+		}
+
+	case "first-available":
+		nodeHealth, ok := props["_nodeHealth"].(map[string]bool)
+		if !ok {
+			return nil, true
+		}
+		firstHealthy := ""
+		for _, t := range targetIDs {
+			if nodeHealth[t] {
+				firstHealthy = t
+				break
+			}
+		}
+		if firstHealthy == "" {
+			return nil, true
+		}
+		for _, req := range queue {
+			reqCopy := *req
+			reqCopy.Path = append(reqCopy.Path, firstHealthy)
+			output = append(output, &reqCopy)
+		}
+
+	case "weighted-round-robin":
+		// Create or reuse the weighted list of targets
+		weighted, ok := props["_weightedTargets"].([]string)
+		if !ok {
+			weights, ok := props["_weights"].(map[string]float64)
+			if !ok {
+				return nil, true
+			}
+			flattened := []string{}
+			for _, id := range targetIDs {
+				w := int(weights[id])
+				for i := 0; i < w; i++ {
+					flattened = append(flattened, id)
+				}
+			}
+			weighted = flattened
+			props["_weightedTargets"] = weighted
+		}
+
+		next := int(AsFloat64(props["_wrIndex"]))
+		for _, req := range queue {
+			target := weighted[next]
+			reqCopy := *req
+			reqCopy.Path = append(reqCopy.Path, target)
+			output = append(output, &reqCopy)
+			next = (next + 1) % len(weighted)
+		}
+		props["_wrIndex"] = float64(next)
+
+	case "last":
+		last := targetIDs[len(targetIDs)-1]
+		for _, req := range queue {
+			reqCopy := *req
+			reqCopy.Path = append(reqCopy.Path, last)
+			output = append(output, &reqCopy)
+		}
+
 	default: // round-robin
 		next := int(AsFloat64(props["_rrIndex"]))
 		for _, req := range queue {

internal/simulation/loadbalancer_test.go

@@ -58,4 +58,83 @@ func TestLoadBalancerAlgorithms(t *testing.T) {
 			t.Errorf("expected lb to emit 2 requests")
 		}
 	})
+
+	t.Run("random", func(t *testing.T) {
+		d := design.Design{
+			Nodes: []design.Node{
+				{ID: "lb", Type: "loadbalancer", Props: map[string]any{"algorithm": "random"}},
+				{ID: "a", Type: "webserver", Props: map[string]any{"capacityRPS": 10}},
+				{ID: "b", Type: "webserver", Props: map[string]any{"capacityRPS": 10}},
+			},
+			Connections: []design.Connection{
+				{Source: "lb", Target: "a"},
+				{Source: "lb", Target: "b"},
+			},
+		}
+
+		e := NewEngineFromDesign(d, 100)
+		e.EntryNode = "lb"
+		e.RPS = 10
+
+		snaps := e.Run(1, 100)
+		if len(snaps[0].Emitted["lb"]) != 1 {
+			t.Errorf("expected lb to emit 1 request")
+		}
+	})
+
+	t.Run("first", func(t *testing.T) {
+		d := design.Design{
+			Nodes: []design.Node{
+				{ID: "lb", Type: "loadbalancer", Props: map[string]any{"algorithm": "first"}},
+				{ID: "a", Type: "webserver", Props: map[string]any{"capacityRPS": 10}},
+				{ID: "b", Type: "webserver", Props: map[string]any{"capacityRPS": 10}},
+			},
+			Connections: []design.Connection{
+				{Source: "lb", Target: "a"},
+				{Source: "lb", Target: "b"},
+			},
+		}
+
+		e := NewEngineFromDesign(d, 100)
+		e.EntryNode = "lb"
+		e.RPS = 10
+
+		snaps := e.Run(1, 100)
+		if len(snaps[0].Emitted["lb"]) != 1 {
+			t.Errorf("expected lb to emit 1 request")
+		}
+
+		target := snaps[0].Emitted["lb"][0].Path[1]
+		if target != "a" {
+			t.Errorf("expected request to go to 'a', got %s", target)
+		}
+	})
+
+	t.Run("last", func(t *testing.T) {
+		d := design.Design{
+			Nodes: []design.Node{
+				{ID: "lb", Type: "loadbalancer", Props: map[string]any{"algorithm": "last"}},
+				{ID: "a", Type: "webserver", Props: map[string]any{"capacityRPS": 10}},
+				{ID: "b", Type: "webserver", Props: map[string]any{"capacityRPS": 10}},
+			},
+			Connections: []design.Connection{
+				{Source: "lb", Target: "a"},
+				{Source: "lb", Target: "b"},
+			},
+		}
+
+		e := NewEngineFromDesign(d, 100)
+		e.EntryNode = "lb"
+		e.RPS = 10
+
+		snaps := e.Run(1, 100)
+		if len(snaps[0].Emitted["lb"]) != 1 {
+			t.Errorf("expected lb to emit 1 request")
+		}
+
+		target := snaps[0].Emitted["lb"][0].Path[1]
+		if target != "b" {
+			t.Errorf("expected request to go to 'b', got %s", target)
+		}
+	})
 }