From 55676a35757bcbf2fa40cc3fd144ba412c65b658 Mon Sep 17 00:00:00 2001
From: Runxi Yu
Date: Tue, 9 Jun 2026 05:15:58 +0000
Subject: internal/cache: add (and move clock to internal/cache/clock)

---
 internal/cache/clock/shard_test.go | 149 +++++++++++++++++++++++++++++++++++++
 1 file changed, 149 insertions(+)
 create mode 100644 internal/cache/clock/shard_test.go

(limited to 'internal/cache/clock/shard_test.go')

diff --git a/internal/cache/clock/shard_test.go b/internal/cache/clock/shard_test.go
new file mode 100644
index 00000000..d974a30e
--- /dev/null
+++ b/internal/cache/clock/shard_test.go
@@ -0,0 +1,149 @@
+package clock //nolint:testpackage
+
+import "testing"
+
+func TestShardEvictsOldest(t *testing.T) {
+	t.Parallel()
+
+	shard := newShard[string, string](8)
+	shard.add("a", "a", 4)
+	shard.add("b", "b", 4)
+	shard.add("c", "c", 4) // overflows, evicts
+
+	if _, ok := shard.peek("a"); ok {
+		t.Fatalf("a should have been evicted")
+	}
+
+	for _, key := range []string{"b", "c"} {
+		if _, ok := shard.peek(key); !ok {
+			t.Fatalf("%s should remain present", key)
+		}
+	}
+
+	if got := shard.loadWeight(); got != 8 {
+		t.Fatalf("weight = %d, want 8", got)
+	}
+
+	if got := shard.len(); got != 2 {
+		t.Fatalf("len = %d, want 2", got)
+	}
+}
+
+func TestShardGetGivesSecondChance(t *testing.T) {
+	t.Parallel()
+
+	shard := newShard[string, string](8)
+	shard.add("a", "a", 4)
+	shard.add("b", "b", 4)
+	shard.add("c", "c", 4) // a evicted; b and c survive
+
+	if _, ok := shard.get("b"); !ok {
+		t.Fatalf("get(b) should hit")
+	}
+
+	shard.add("d", "d", 4) // b was just touched, so c is evicted instead
+
+	if _, ok := shard.peek("c"); ok {
+		t.Fatalf("c should have been evicted after b was touched")
+	}
+
+	for _, key := range []string{"b", "d"} {
+		if _, ok := shard.peek(key); !ok {
+			t.Fatalf("%s should remain present", key)
+		}
+	}
+}
+
+func TestShardPeekGivesNoSecondChance(t *testing.T) {
+	t.Parallel()
+
+	shard := newShard[string, string](8)
+	shard.add("a", "a", 4)
+	shard.add("b", "b", 4)
+	shard.add("c", "c", 4) // a is evicted; b and c survive with cleared bits
+
+	if _, ok := shard.peek("b"); !ok {
+		t.Fatalf("peek(b) should hit")
+	}
+
+	shard.add("d", "d", 4) // peek did not refresh b, so b is evicted
+
+	if _, ok := shard.peek("b"); ok {
+		t.Fatalf("b should have been evicted; peek must not grant a second chance")
+	}
+
+	for _, key := range []string{"c", "d"} {
+		if _, ok := shard.peek(key); !ok {
+			t.Fatalf("%s should remain present", key)
+		}
+	}
+}
+
+func TestShardReplaceUpdatesWeight(t *testing.T) {
+	t.Parallel()
+
+	shard := newShard[string, string](100)
+	shard.add("a", "old", 4)
+	shard.add("a", "new", 6)
+
+	if got, ok := shard.peek("a"); !ok || got != "new" {
+		t.Fatalf("peek(a) = (%q, %v), want (new, true)", got, ok)
+	}
+
+	if got := shard.loadWeight(); got != 6 {
+		t.Fatalf("weight = %d, want 6", got)
+	}
+
+	if got := shard.len(); got != 1 {
+		t.Fatalf("len = %d, want 1", got)
+	}
+}
+
+func TestShardRejectsOversized(t *testing.T) {
+	t.Parallel()
+
+	shard := newShard[string, string](5)
+	shard.add("a", "x", 3)
+
+	if shard.add("b", "big", 6) {
+		t.Fatalf("oversized add should report false")
+	}
+
+	if shard.add("a", "huge", 6) {
+		t.Fatalf("oversized replace should report false")
+	}
+
+	if got, ok := shard.peek("a"); !ok || got != "x" {
+		t.Fatalf("peek(a) = (%q, %v), want (x, true); cache must be unchanged", got, ok)
+	}
+
+	if _, ok := shard.peek("b"); ok {
+		t.Fatalf("b must not have been admitted")
+	}
+
+	if got := shard.loadWeight(); got != 3 {
+		t.Fatalf("weight = %d, want 3", got)
+	}
+}
+
+func TestShardClear(t *testing.T) {
+	t.Parallel()
+
+	shard := newShard[string, string](100)
+	shard.add("a", "a", 4)
+	shard.add("b", "b", 4)
+
+	shard.clear()
+
+	if got := shard.loadWeight(); got != 0 {
+		t.Fatalf("weight = %d, want 0", got)
+	}
+
+	if got := shard.len(); got != 0 {
+		t.Fatalf("len = %d, want 0", got)
+	}
+
+	if _, ok := shard.peek("a"); ok {
+		t.Fatalf("a should be gone after clear")
+	}
+}
-- 
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