fix(level-hash): allow configuring load factor threshold for auto expand

utilities/level-hash/src/main/java/com/itsaky/androidide/levelhash/LevelHash.kt

@@ -39,7 +39,7 @@ import androidx.annotation.FloatRange
  * as well. This results in decreased access performance and insertion failures.
  * It is **recommended** to enable [AbstractLevelHashBuilder.autoExpand] which
  * will automatically expand the level hash when the load factor reaches a certain
- * threshold (specifically, when the top level is full).
+ * threshold ([LevelHash.loadFactor]).
  *
  * @param K The key type.
  * @param V The value type.
@@ -164,6 +164,11 @@ interface LevelHash<K : Any, V : Any?> : AutoCloseable {
      */
     const val BUCKET_SIZE_DEFAULT = 4
 
+    /**
+     * Default load factor threshold for auto expand.
+     */
+    const val AUTO_EXPAND_LOAD_FACTOR_THRESHOLD: Float = 0.92f
+
     /**
      * Build an in-memory level hash.
      */

utilities/level-hash/src/main/java/com/itsaky/androidide/levelhash/builders.kt

@@ -33,6 +33,7 @@ abstract class AbstractLevelHashBuilder<K : Any, V : Any?> {
   protected var hashFn: LevelHashFn<K>? = null
   protected var uniqueKeys = false
   protected var autoExpand = true
+  protected var loadFactorForAutoExpand = LevelHash.AUTO_EXPAND_LOAD_FACTOR_THRESHOLD
   protected var seedGenerator: SeedGeneratorFn = ::levelHashDefaultSeeds
 
   /**
@@ -112,7 +113,8 @@ class InMemoryHashBuilder<K : Any, V : Any?> :
       levelHashFn = hashFn!!,
       seeds = seedGenerator(),
       uniqueKeys = uniqueKeys,
-      autoExpand = autoExpand
+      autoExpand = autoExpand,
+      loadFactorForAutoExpand = loadFactorForAutoExpand,
     )
   }
 }
@@ -170,6 +172,7 @@ class PersistentHashBuilder<K : Any, V : Any?> :
       bucketSize = bucketSize,
       uniqueKeys = uniqueKeys,
       autoExpand = autoExpand,
+      loadFactorForAutoExpand = loadFactorForAutoExpand,
       levelHashFn = hashFn!!,
       seeds = seeds,
       keyExternalizer = keyExternalizer,

utilities/level-hash/src/main/java/com/itsaky/androidide/levelhash/internal/AbstractLevelHash.kt

@@ -38,6 +38,7 @@ internal abstract class AbstractLevelHash<K : Any, V : Any?> internal constructo
   final override val bucketSize: Int,
   protected val uniqueKeys: Boolean,
   protected val autoExpand: Boolean,
+  protected val loadFactorForAutoExpand: Float,
   protected val levelHashFn: LevelHashFn<K>,
   protected val seeds: Pair<HashT, HashT>,
 ) : LevelHash<K, V> {
@@ -123,7 +124,7 @@ internal abstract class AbstractLevelHash<K : Any, V : Any?> internal constructo
 
   override fun insert(key: K, value: V): Boolean {
 
-    if (loadFactor() >= 0.92 && autoExpand) {
+    if (loadFactor() >= loadFactorForAutoExpand && autoExpand) {
       check(expand()) {
         "Failed to expand the level hash"
       }

utilities/level-hash/src/main/java/com/itsaky/androidide/levelhash/internal/InMemoryLevelHash.kt

@@ -34,10 +34,18 @@ internal class InMemoryLevelHash<K : Any, V : Any?>(
   bucketSize: Int,
   uniqueKeys: Boolean,
   autoExpand: Boolean,
+  loadFactorForAutoExpand: Float,
   levelHashFn: LevelHashFn<K>,
   seeds: Pair<HashT, HashT>,
-) : AbstractLevelHash<K, V>(levelSize, bucketSize, uniqueKeys, autoExpand,
-  levelHashFn, seeds) {
+) : AbstractLevelHash<K, V>(
+  levelSize,
+  bucketSize,
+  uniqueKeys,
+  autoExpand,
+  loadFactorForAutoExpand,
+  levelHashFn,
+  seeds
+) {
 
   private val levels = Array(LEVEL_COUNT) { levelIndex ->
     allocateLevel(levelSize, levelIndex, bucketSize)

utilities/level-hash/src/main/java/com/itsaky/androidide/levelhash/internal/PersistentLevelHash.kt

@@ -34,14 +34,21 @@ internal class PersistentLevelHash<K : Any, V : Any?>(
   bucketSize: Int,
   uniqueKeys: Boolean,
   autoExpand: Boolean,
+  loadFactorForAutoExpand: Float,
   levelHashFn: LevelHashFn<K>,
   seeds: Pair<HashT, HashT>,
   keyExternalizer: DataExternalizer<K>,
   valueExternalizer: DataExternalizer<V>,
   indexFile: File,
-) : AbstractLevelHash<K, V>(levelSize = levelSize, bucketSize = bucketSize,
-  uniqueKeys = uniqueKeys, autoExpand = autoExpand, levelHashFn = levelHashFn,
-  seeds = seeds) {
+) : AbstractLevelHash<K, V>(
+  levelSize = levelSize,
+  bucketSize = bucketSize,
+  uniqueKeys = uniqueKeys,
+  autoExpand = autoExpand,
+  loadFactorForAutoExpand = loadFactorForAutoExpand,
+  levelHashFn = levelHashFn,
+  seeds = seeds
+) {
 
   @VisibleForTesting
   internal val io = PersistentLevelHashIO(indexFile, levelSize, bucketSize, keyExternalizer,

utilities/level-hash/src/main/java/com/itsaky/androidide/levelhash/internal/PersistentLevelHashIO.kt

@@ -42,6 +42,7 @@ private val logger = LoggerFactory.getLogger(PersistentLevelHashIO::class.java)
 //    improved performance when seeking through the file.
 // TODO: The above is also applicable for the keymap file when the level hash is
 //    expanded and new regions for the levels are allocated.
+// TODO: Allow concurrent access to the level hash.
 
 /**
  * This class is responsible for performing the IO operations for the level hash