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package org.molgenis.data.support;

import com.google.gson.Gson;
import org.molgenis.data.DataConverter;
import org.molgenis.data.Entity;
import org.molgenis.data.meta.model.Attribute;
import org.molgenis.data.meta.model.EntityType;

public class StringExpressionEvaluator implements ExpressionEvaluator {
  private Attribute targetAttribute;
  private Attribute sourceAttribute;

  /**
   * Constructs a new expression evaluator for an attribute whose expression is a simple string.
   *
   * @param attribute attribute meta data
   * @param entityType entity meta data
   */
  StringExpressionEvaluator(Attribute attribute, EntityType entityType) {
    targetAttribute = attribute;
    String expression = attribute.getExpression();
    if (expression == null) {
      throw new NullPointerException("Attribute has no expression.");
    }
    Gson gson = new Gson();
    String attributeName = gson.fromJson(expression, String.class);
    sourceAttribute = entityType.getAttribute(attributeName);
    if (sourceAttribute == null) {
      throw new IllegalArgumentException(
          "Expression for attribute '"
              + attribute.getName()
              + "' references non-existant attribute '"
              + attributeName
              + "'.");
    }
  }

  @Override
  public Object evaluate(Entity entity) {
    Object o = entity.get(sourceAttribute.getName());
    return DataConverter.convert(o, targetAttribute);
  }
}