ConditionScopes.java

/*
 * Copyright 2022 The Android Open Source Project
 *
 * Licensed 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 androidx.wear.protolayout.expression;

import androidx.annotation.NonNull;
import androidx.wear.protolayout.expression.DynamicBuilders.DynamicType;
import java.util.function.Function;

/**
 * Intermediate scopes used inside of {@code onCondition} expressions. This is to enable
 * functionality such as {@code
 * DynamicString.onCondition(...).use(constant("Foo")).elseUse(constant("Bar"))}.
 */
public class ConditionScopes {
  private ConditionScopes() {}

  interface ConditionBuilder<T extends DynamicType> {
    T buildCondition(T trueValue, T falseValue);
  }

  /**
   * Condition scope to allow binding the true value in a onConditional expression. {@code RawT}
   * is the native Java type that can be used when constructing a constant T (e.g. String for
   * DynamicString).
   */
  public static class ConditionScope<T extends DynamicType, RawT> {
    private final ConditionBuilder<T> conditionBuilder;
    private final Function<RawT, T> rawTypeMapper;

    ConditionScope(ConditionBuilder<T> conditionBuilder, Function<RawT, T> rawTypeMapper) {
      this.conditionBuilder = conditionBuilder;
      this.rawTypeMapper = rawTypeMapper;
    }

    /** Sets the value to use as the value when true in a conditional expression. */
    public @NonNull IfTrueScope<T, RawT> use(T valueWhenTrue) {
      return new IfTrueScope<>(valueWhenTrue, conditionBuilder, rawTypeMapper);
    }

    /** Sets the value to use as the value when true in a conditional expression. */
    public @NonNull IfTrueScope<T, RawT> use(RawT valueWhenTrue) {
      return use(rawTypeMapper.apply(valueWhenTrue));
    }
  }

  /**
   * Condition scope to allow binding the true value in a onConditional expression, yielding a
   * resulting Dynamic value.{@code RawT} is the native Java type that can be used when
   * constructing a constant T (e.g. String for DynamicString).
   */
  public static class IfTrueScope<T extends DynamicType, RawT> {
    private final T ifTrueValue;
    private final ConditionBuilder<T> conditionBuilder;
    private final Function<RawT, T> rawTypeMapper;

    IfTrueScope(
        T ifTrueValue,
        ConditionBuilder<T> conditionBuilder,
        Function<RawT, T> rawTypeMapper) {
      this.ifTrueValue = ifTrueValue;
      this.conditionBuilder = conditionBuilder;
      this.rawTypeMapper = rawTypeMapper;
    }

    /** Sets the value to use as the value when false in a conditional expression. */
    public T elseUse(T valueWhenFalse) {
      return conditionBuilder.buildCondition(ifTrueValue, valueWhenFalse);
    }

    /** Sets the value to use as the value when false in a conditional expression. */
    public T elseUse(RawT valueWhenFalse) {
      return elseUse(rawTypeMapper.apply(valueWhenFalse));
    }
  }
}