package edu.washington.escience.myria.expression;

import java.util.Objects;

import com.fasterxml.jackson.annotation.JsonProperty;

import edu.washington.escience.myria.Type;
import edu.washington.escience.myria.expression.evaluate.ExpressionOperatorParameter;
import edu.washington.escience.myria.operator.StatefulApply;

/**
 * Simple expression operator that allows access to fields of the state in {@link StatefulApply}.
 */
public class StateExpression extends ZeroaryExpression {
  /***/
  private static final long serialVersionUID = 1L;

  /** The index in the input that is referenced. */
  @JsonProperty private final int columnIdx;

  /**
   * This is not really unused, it's used automagically by Jackson deserialization.
   */
  @SuppressWarnings("unused")
  private StateExpression() {
    columnIdx = -1;
  }

  /**
   * Default constructor.
   *
   * @param columnIdx the index in the state.
   */
  public StateExpression(final int columnIdx) {
    this.columnIdx = columnIdx;
  }

  @Override
  public Type getOutputType(final ExpressionOperatorParameter parameters) {
    return parameters.getStateSchema().getColumnType(getColumnIdx());
  }

  @Override
  public String getJavaString(final ExpressionOperatorParameter parameters) {
    // We generate a variable access into the state tuple.
    return new StringBuilder(Expression.STATE)
        .append(".get")
        .append(getOutputType(parameters).getName())
        .append("(")
        .append(getColumnIdx() + "+" + Expression.STATECOLOFFSET)
        .append(",")
        .append(Expression.STATEROW)
        .append(")")
        .toString();
  }

  /**
   * @return the column index of this variable.
   */
  public int getColumnIdx() {
    return columnIdx;
  }

  @Override
  public int hashCode() {
    return Objects.hash(getClass().getCanonicalName(), getColumnIdx());
  }

  @Override
  public boolean equals(final Object other) {
    if (other == null || !(other instanceof StateExpression)) {
      return false;
    }
    StateExpression otherExp = (StateExpression) other;
    return Objects.equals(getColumnIdx(), otherExp.getColumnIdx());
  }
}