chore: various refactoring changes for iceberg [iceberg]

common/pom.xml

@@ -51,6 +51,10 @@ under the License.
       <groupId>org.apache.parquet</groupId>
       <artifactId>parquet-hadoop</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.apache.parquet</groupId>
+      <artifactId>parquet-format-structures</artifactId>
+    </dependency>
     <dependency>
       <groupId>org.apache.arrow</groupId>
       <artifactId>arrow-vector</artifactId>

common/src/main/java/org/apache/comet/parquet/AbstractColumnReader.java

@@ -89,6 +89,10 @@ ColumnDescriptor getDescriptor() {
     return descriptor;
   }
 
+  String getPath() {
+    return String.join(".", this.descriptor.getPath());
+  }
+
   /**
    * Set the batch size of this reader to be 'batchSize'. Also initializes the native column reader.
    */

common/src/main/java/org/apache/comet/parquet/IcebergCometNativeBatchReader.java

@@ -0,0 +1,79 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.comet.parquet;
+
+import java.util.Map;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.spark.sql.catalyst.InternalRow;
+import org.apache.spark.sql.execution.metric.SQLMetric;
+import org.apache.spark.sql.types.StructType;
+
+/**
+ * A specialized NativeBatchReader for Iceberg that accepts ParquetMetadata as a JSON string. This
+ * allows Iceberg to pass metadata in serialized form with a two-step initialization pattern.
+ */
+public class IcebergCometNativeBatchReader extends NativeBatchReader {
+
+  public IcebergCometNativeBatchReader(StructType requiredSchema) {
+    super();
+    this.sparkSchema = requiredSchema;
+  }
+
+  /** Initialize the reader using FileInfo instead of PartitionedFile. */
+  public void init(
+      Configuration conf,
+      FileInfo fileInfo,
+      byte[] parquetMetadataBytes,
+      byte[] nativeFilter,
+      int capacity,
+      StructType dataSchema,
+      boolean isCaseSensitive,
+      boolean useFieldId,
+      boolean ignoreMissingIds,
+      boolean useLegacyDateTimestamp,
+      StructType partitionSchema,
+      InternalRow partitionValues,
+      AbstractColumnReader[] preInitializedReaders,
+      Map<String, SQLMetric> metrics)
+      throws Throwable {
+
+    // Set parent fields
+    this.conf = conf;
+    this.fileInfo = fileInfo;
+    this.footer = new ParquetMetadataSerializer().deserialize(parquetMetadataBytes);
+    this.nativeFilter = nativeFilter;
+    this.capacity = capacity;
+    this.dataSchema = dataSchema;
+    this.isCaseSensitive = isCaseSensitive;
+    this.useFieldId = useFieldId;
+    this.ignoreMissingIds = ignoreMissingIds;
+    this.partitionSchema = partitionSchema;
+    this.partitionValues = partitionValues;
+    this.preInitializedReaders = preInitializedReaders;
+
+    // Call parent init method
+    super.init();
+  }
+
+  public StructType getSparkSchema() {
+    return this.sparkSchema;
+  }
+}