refactor scheduler filters package (#797)

* refactor schdeuler filters package to simplify and improve readability and maintainability

Signed-off-by: Nir Rozenbaum <[email protected]>

* filter refactor finalizing

Signed-off-by: Nir Rozenbaum <[email protected]>

---------

Signed-off-by: Nir Rozenbaum <[email protected]>

Author: nirrozenbaum

pkg/epp/scheduling/config.go

@@ -18,8 +18,6 @@ package scheduling
 
 import (
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/plugins"
-	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/plugins/filter"
-	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/plugins/picker"
 )
 
 // NewSchedulerConfig creates a new SchedulerConfig object with the given plugins.
@@ -42,15 +40,3 @@ type SchedulerConfig struct {
 	picker              plugins.Picker
 	postSchedulePlugins []plugins.PostSchedule
 }
-
-// When the scheduler is initialized with NewScheduler function, this config will be used as default.
-// it's possible to call NewSchedulerWithConfig to pass a different argument.
-
-// For build time plugins changes, it's recommended to change the defaultConfig variable in this file.
-var defaultConfig = &SchedulerConfig{
-	preSchedulePlugins:  []plugins.PreSchedule{},
-	filters:             []plugins.Filter{&filter.SheddableRequestFilter{}, filter.LowLatencyFilter},
-	scorers:             map[plugins.Scorer]int{},
-	picker:              &picker.RandomPicker{},
-	postSchedulePlugins: []plugins.PostSchedule{},
-}

pkg/epp/scheduling/plugins/filter/decision_tree_filter.go

@@ -0,0 +1,81 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package filter
+
+import (
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/plugins"
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/types"
+	logutil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/logging"
+)
+
+// DecisionTreeFilter applies current fitler, and then recursively applies next filters
+// depending success or failure of the current filter.
+// It can be used to construct a flow chart algorithm.
+type DecisionTreeFilter struct {
+	Current plugins.Filter
+	// NextOnSuccess filter will be applied after successfully applying the current filter.
+	// The filtered results will be passed to the next filter.
+	NextOnSuccess plugins.Filter
+	// NextOnFailure filter will be applied if current filter results in no pods.
+	// The original input will be passed to the next filter.
+	NextOnFailure plugins.Filter
+	// NextOnSuccessOrFailure is a convenience field to configure the next filter regardless of the
+	// success or failure of the current filter.
+	// NOTE: When using NextOnSuccessOrFailure, both nextOnSuccess and nextOnFailure SHOULD be nil.
+	// However if that's not the case, nextOnSuccess and nextOnFailure will be used, instead of
+	// NextOnSuccessOrFailure, in the success and failure scenarios, respectively.
+	NextOnSuccessOrFailure plugins.Filter
+}
+
+// Name returns the name of the filter.
+func (f *DecisionTreeFilter) Name() string {
+	if f == nil {
+		return "nil"
+	}
+	return f.Current.Name()
+}
+
+// Filter filters out pods that doesn't meet the filter criteria.
+func (f *DecisionTreeFilter) Filter(ctx *types.SchedulingContext, pods []types.Pod) []types.Pod {
+	loggerTrace := ctx.Logger.V(logutil.TRACE)
+	filteredPod := f.Current.Filter(ctx, pods)
+
+	next := f.NextOnSuccessOrFailure
+	if len(filteredPod) > 0 {
+		if f.NextOnSuccess == nil && f.NextOnSuccessOrFailure == nil {
+			// No succeeding filters to run, return.
+			return filteredPod
+		}
+		if f.NextOnSuccess != nil {
+			next = f.NextOnSuccess
+		}
+		loggerTrace.Info("Filter succeeded", "filter", f.Name(), "next", next.Name(), "filteredPodCount", len(filteredPod))
+		// On success, pass the filtered result to the next filter.
+		return next.Filter(ctx, filteredPod)
+	} else {
+		if f.NextOnFailure == nil && f.NextOnSuccessOrFailure == nil {
+			// No succeeding filters to run, return.
+			return filteredPod
+		}
+		if f.NextOnFailure != nil {
+			next = f.NextOnFailure
+		}
+		loggerTrace.Info("Filter failed", "filter", f.Name(), "next", next.Name())
+		// On failure, pass the initial set of pods to the next filter.
+		return next.Filter(ctx, pods)
+	}
+}