package locks

import (
	"sync"
	"testing"
)

func TestGetShardIndex_Distribution(t *testing.T) {
	t.Parallel()
	const N = 1000
	counts := make([]int, NumLockShards)
	for i := 0; i < N; i++ {
		key := "steam/depot/test/" + string(rune('a'+i%26)) + string(rune(i))
		idx := GetShardIndex(key)
		if idx < 0 || idx >= NumLockShards {
			t.Fatalf("shard %d out of range", idx)
		}
		counts[idx]++
	}
	// Very rough: no shard should get 0 if N large (probabilistic)
	zeros := 0
	for _, c := range counts {
		if c == 0 {
			zeros++
		}
	}
	if zeros > NumLockShards/2 {
		t.Logf("shard counts: %v", counts)
		t.Errorf("too many zero shards (%d); hash not distributing well?", zeros)
	}
}

func TestGetKeyLock_SameKeySameLock(t *testing.T) {
	t.Parallel()
	keyLocks := make([]sync.Map, NumLockShards)
	l1 := GetKeyLock(keyLocks, "foo/bar")
	l2 := GetKeyLock(keyLocks, "foo/bar")
	if l1 != l2 {
		t.Error("same key must return identical *RWMutex pointer for sharded locking")
	}
}

func TestGetKeyLock_DifferentKeysMayDiffer(t *testing.T) {
	t.Parallel()
	keyLocks := make([]sync.Map, NumLockShards)
	l1 := GetKeyLock(keyLocks, "a")
	l2 := GetKeyLock(keyLocks, "b")
	// May or may not be same shard; just ensure non-nil
	if l1 == nil || l2 == nil {
		t.Error("locks must be non-nil")
	}
}