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This project contains utility classes that are used by various products and projects inside Atlassian and may have some utility to the world at large.

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/**
 * Copyright 2009 Atlassian Pty Ltd
 *
 * 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 io.atlassian.util.concurrent;

import java.util.function.Function;
import java.util.function.Supplier;

import static java.util.Objects.requireNonNull;

public final class Functions {
  /**
   * Get a function that uses the Supplier as a factory for all inputs.
   *
   * @param  the key type, ignored
   * @param  the result type
   * @param supplier called for all inputs
   * @return the function
   */
  public static  Function fromSupplier(final @NotNull Supplier supplier) {
    requireNonNull(supplier, "supplier");
    return d -> supplier.get();
  }

  /**
   * Get the value from a supplier.
   *
   * @param  the type returned, note the Supplier can be covariant.
   * @return a function that extracts the value from a supplier
   */
  static  Function, T> fromSupplier() {
    return Supplier::get;
  }

  /**
   * Get a function that weakly memoizes the output – ie. subsequent calls for
   * the same input value will return the same reference if it has not been
   * garbage collected because there are no external strong referents to it.
   *
   * @param  the input or key type for the function. Must be a value
   * (immutable) and have a well behaved hashcode implementation.
   * @param  the output type of the for the function.
   * @param f the function to call if the value is not already cached.
   * @return the function that will .
   */
  public static  Function weakMemoize(Function f) {
    return WeakMemoizer.weakMemoizer(f);
  }

  /**
   * Function that can be used to ignore any RuntimeExceptions that a
   * {@link Supplier} may produce and return null instead.
   * 
   * @param  the result type
   * @return a Function that transforms an exception into a null
   */
  static  Function, Supplier> ignoreExceptions() {
    return new ExceptionIgnorer<>();
  }

  static class ExceptionIgnorer implements Function, Supplier> {
    public Supplier apply(final Supplier from) {
      return new IgnoreAndReturnNull<>(from);
    }
  }

  static class IgnoreAndReturnNull implements Supplier {
    private final Supplier delegate;

    IgnoreAndReturnNull(final Supplier delegate) {
      this.delegate = requireNonNull(delegate, "delegate");
    }

    public T get() {
      try {
        return delegate.get();
      } catch (final RuntimeException ignore) {
        return null;
      }
    }
  }

  // /CLOVER:OFF
  private Functions() {}
  // /CLOVER:ON
}