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H2O Avro Parser
There is a newer version: 3.46.0.6
package water.parser.avro;

import org.apache.avro.Schema;

import java.util.Arrays;
import java.util.List;

import water.fvec.Vec;

/**
 * Utilities to work with Avro schema.
 */
public final class AvroUtil {

  /** Return true if the given schema can be transformed
   * into h2o type.
   *
   * @param s  avro field schema
   * @return  true if the schema can be transformed into H2O type
   */
  public static boolean isSupportedSchema(Schema s) {
    Schema.Type typ =  s.getType();
    switch (typ) {
      case BOOLEAN:
      case INT:
      case LONG:
      case FLOAT:
      case DOUBLE:
      case ENUM:
      case STRING:
      case NULL:
      case BYTES:
        return true;
      case UNION: // Flattenize the union
        List unionSchemas = s.getTypes();
        if (unionSchemas.size() == 1) {
          return isSupportedSchema(unionSchemas.get(0));
        } else if (unionSchemas.size() == 2) {
          Schema s1 = unionSchemas.get(0);
          Schema s2 = unionSchemas.get(1);
          return s1.getType().equals(Schema.Type.NULL) && isSupportedSchema(s2)
                 || s2.getType().equals(Schema.Type.NULL) && isSupportedSchema(s1);
        }
      default:
        return false;
    }
  }

  /**
   * Transform Avro schema into H2O type.
   *
   * @param s  avro schema
   * @return  a byte representing H2O column type
   * @throws IllegalArgumentException  if schema is not supported
   */
  public static byte schemaToColumnType(Schema s) {
    Schema.Type typ =  s.getType();
    switch (typ) {
      case BOOLEAN:
      case INT:
      case LONG:
      case FLOAT:
      case DOUBLE:
        return Vec.T_NUM;
      case ENUM:
        return Vec.T_CAT;
      case STRING:
        return Vec.T_STR;
      case NULL:
        return Vec.T_BAD;
      case BYTES:
        return Vec.T_STR;
      case UNION: // Flattenize the union
        List unionSchemas = s.getTypes();
        if (unionSchemas.size() == 1) {
          return schemaToColumnType(unionSchemas.get(0));
        } else if (unionSchemas.size() == 2) {
          Schema s1 = unionSchemas.get(0);
          Schema s2 = unionSchemas.get(1);
          if (s1.getType().equals(Schema.Type.NULL)) return schemaToColumnType(s2);
          else if (s2.getType().equals(Schema.Type.NULL)) return schemaToColumnType(s1);
        }
      default:
        throw new IllegalArgumentException("Unsupported Avro schema type: " + s);
    }
  }

  static String[] getDomain(Schema fieldSchema) {
    if (fieldSchema.getType() == Schema.Type.ENUM) {
      return fieldSchema.getEnumSymbols().toArray(new String[] {});
    } else if (fieldSchema.getType() == Schema.Type.UNION) {
      List unionSchemas = fieldSchema.getTypes();
      if (unionSchemas.size() == 1) {
        return getDomain(unionSchemas.get(0));
      } else if (unionSchemas.size() == 2) {
        Schema s1 = unionSchemas.get(0);
        Schema s2 = unionSchemas.get(1);
        if (s1.getType() == Schema.Type.NULL) return getDomain(s2);
        else if (s2.getType() == Schema.Type.NULL) return getDomain(s1);
      }
    }
    throw new IllegalArgumentException("Cannot get domain from field: " + fieldSchema);
  }

  /**
   * Transform Avro schema into its primitive representation.
   *
   * @param s  avro schema
   * @return  primitive type as a result of transformation
   * @throws IllegalArgumentException if the schema has no primitive transformation
   */
  public static Schema.Type toPrimitiveType(Schema s) {
    Schema.Type typ = s.getType();
    switch(typ) {
      case BOOLEAN:
      case INT:
      case LONG:
      case FLOAT:
      case DOUBLE:
      case ENUM:
      case STRING:
      case NULL:
      case BYTES:
        return typ;
      case UNION:
        List unionSchemas = s.getTypes();
        if (unionSchemas.size() == 1) {
          return toPrimitiveType(unionSchemas.get(0));
        } else if (unionSchemas.size() == 2) {
          Schema s1 = unionSchemas.get(0);
          Schema s2 = unionSchemas.get(1);
          if (s1.getType().equals(Schema.Type.NULL)) return toPrimitiveType(s2);
          else if (s2.getType().equals(Schema.Type.NULL)) return toPrimitiveType(s1);
        }
      default:
        throw new IllegalArgumentException("Unsupported Avro schema type: " + s);
    }
  }

  /**
   * The method "flattenize" the given Avro schema.
   * @param s  Avro schema
   * @return  List of supported fields which were extracted from original Schema
   */
  public static Schema.Field[] flatSchema(Schema s) {
    List fields = s.getFields();
    Schema.Field[] flatSchema = new Schema.Field[fields.size()];
    int cnt = 0;
    for (Schema.Field f : fields) {
      if (isSupportedSchema(f.schema())) {
        flatSchema[cnt] = f;
        cnt++;
      }
    }
    // Return resized array
    return cnt != flatSchema.length ? Arrays.copyOf(flatSchema, cnt) : flatSchema;
  }
}