/*
 * Copyright (C) 2009-2021 Lightbend Inc. <https://www.lightbend.com>
 */

package akka.japi.pf;

import scala.PartialFunction;
import scala.runtime.BoxedUnit;
import scala.Tuple2;

/**
 * Builder used to create a partial function for {@link akka.actor.FSM#onTransition}.
 *
 * @param <S> the state type
 */
public class FSMTransitionHandlerBuilder<S> {

  private final UnitPFBuilder<Tuple2<S, S>> builder = new UnitPFBuilder<Tuple2<S, S>>();

  /**
   * Add a case statement that matches on a from state and a to state.
   *
   * @param fromState the from state to match on, or null for any
   * @param toState the to state to match on, or null for any
   * @param apply an action to apply when the states match
   * @return the builder with the case statement added
   */
  public FSMTransitionHandlerBuilder<S> state(
      final S fromState, final S toState, final FI.UnitApplyVoid apply) {
    builder.match(
        Tuple2.class,
        new FI.TypedPredicate<Tuple2>() {
          @Override
          public boolean defined(Tuple2 t) {
            return (fromState == null || fromState.equals(t._1()))
                && (toState == null || toState.equals(t._2()));
          }
        },
        new FI.UnitApply<Tuple2>() {
          @Override
          public void apply(Tuple2 t) throws Exception {
            apply.apply();
          }
        });
    return this;
  }

  /**
   * Add a case statement that matches on a from state and a to state.
   *
   * @param fromState the from state to match on, or null for any
   * @param toState the to state to match on, or null for any
   * @param apply an action to apply when the states match
   * @return the builder with the case statement added
   */
  public FSMTransitionHandlerBuilder<S> state(
      final S fromState, final S toState, final FI.UnitApply2<S, S> apply) {
    builder.match(
        Tuple2.class,
        new FI.TypedPredicate<Tuple2>() {
          @Override
          public boolean defined(Tuple2 t) {
            return (fromState == null || fromState.equals(t._1()))
                && (toState == null || toState.equals(t._2()));
          }
        },
        new FI.UnitApply<Tuple2>() {
          @Override
          public void apply(Tuple2 t) throws Exception {
            @SuppressWarnings("unchecked")
            S sf = (S) t._1();
            @SuppressWarnings("unchecked")
            S st = (S) t._2();
            apply.apply(sf, st);
          }
        });
    return this;
  }

  /**
   * Build a {@link scala.PartialFunction} from this builder. After this call the builder will be
   * reset.
   *
   * @return a PartialFunction for this builder.
   */
  public PartialFunction<Tuple2<S, S>, BoxedUnit> build() {
    return builder.build();
  }
}
