// Copyright (C) 2014 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 com.google.gerrit.testutil;

import static com.google.common.base.Preconditions.checkArgument;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.common.base.Objects;
import com.google.common.collect.Lists;

import org.junit.runner.Runner;
import org.junit.runners.BlockJUnit4ClassRunner;
import org.junit.runners.Suite;
import org.junit.runners.model.FrameworkMethod;
import org.junit.runners.model.InitializationError;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.List;

/**
 * Suite to run tests with different {@code gerrit.config} values.
 * <p>
 * For each {@link Config} method in the class and base classes, a new group of
 * tests is created with the {@link Parameter} field set to the config.
 *
 * <pre>
 * @RunWith(ConfigSuite.class)
 * public abstract class MyAbstractTest {
 *   @ConfigSuite.Parameter
 *   protected Config cfg;
 *
 *   @ConfigSuite.Config
 *   public static Config firstConfig() {
 *     Config cfg = new Config();
 *     cfg.setString("gerrit", null, "testValue", "a");
 *   }
 * }
 *
 * public class MyTest {
 *   @ConfigSuite.Config
 *   public static Config secondConfig() {
 *     Config cfg = new Config();
 *     cfg.setString("gerrit", null, "testValue", "b");
 *   }
 *
 *   @Test
 *   public void myTest() {
 *     // Test using cfg.
 *   }
 * }
 * </pre>
 *
 * This creates a suite of tests with three groups:
 * <ul>
 *   <li><strong>default</strong>: {@code MyTest.myTest}</li>
 *   <li><strong>firstConfig</strong>: {@code MyTest.myTest[firstConfig]}</li>
 *   <li><strong>secondConfig</strong>: {@code MyTest.myTest[secondConfig]}</li>
 * </ul>
 */
public class ConfigSuite extends Suite {
  private static final String DEFAULT = "default";

  @Target({METHOD})
  @Retention(RUNTIME)
  public static @interface Config {
  }

  @Target({FIELD})
  @Retention(RUNTIME)
  public static @interface Parameter {
  }

  private static class ConfigRunner extends BlockJUnit4ClassRunner {
    private final Method configMethod;
    private final Field parameterField;
    private final String name;

    private ConfigRunner(Class<?> clazz, Field parameterField, String name,
        Method configMethod) throws InitializationError {
      super(clazz);
      this.parameterField = parameterField;
      this.name = name;
      this.configMethod = configMethod;
    }

    @Override
    public Object createTest() throws Exception {
      Object test = getTestClass().getJavaClass().newInstance();
      parameterField.set(test, callConfigMethod(configMethod));
      return test;
    }

    @Override
    protected String getName() {
      return Objects.firstNonNull(name, DEFAULT);
    }

    @Override
    protected String testName(FrameworkMethod method) {
      String n = method.getName();
      return name == null ? n : n + "[" + name + "]";
    }
  }

  private static List<Runner> runnersFor(Class<?> clazz) {
    List<Method> configs = getConfigs(clazz);
    Field field = getParameterField(clazz);
    List<Runner> result = Lists.newArrayListWithCapacity(configs.size() + 1);
    try {
      result.add(new ConfigRunner(clazz, field, null, null));
      for (Method m : configs) {
        result.add(new ConfigRunner(clazz, field, m.getName(), m));
      }
      return result;
    } catch (InitializationError e) {
      throw new RuntimeException(e);
    }
  }

  private static List<Method> getConfigs(Class<?> clazz) {
    List<Method> result = Lists.newArrayListWithExpectedSize(3);
    for (Method m : clazz.getMethods()) {
      Config ann = m.getAnnotation(Config.class);
      if (ann != null) {
        checkArgument(!m.getName().equals(DEFAULT),
            "@ConfigSuite.Config cannot be named %s", DEFAULT);
        result.add(m);
      }
    }
    return result;
  }

  private static org.eclipse.jgit.lib.Config callConfigMethod(Method m) {
    if (m == null) {
      return new org.eclipse.jgit.lib.Config();
    }
    checkArgument(
        org.eclipse.jgit.lib.Config.class.isAssignableFrom(m.getReturnType()),
        "%s must return Config", m);
    checkArgument((m.getModifiers() & Modifier.STATIC) != 0,
        "%s must be static", m);
    checkArgument(m.getParameterTypes().length == 0,
        "%s must take no parameters", m);
    try {
      return (org.eclipse.jgit.lib.Config) m.invoke(null);
    } catch (IllegalAccessException | IllegalArgumentException
        | InvocationTargetException e) {
      throw new IllegalArgumentException(e);
    }
  }

  private static Field getParameterField(Class<?> clazz) {
    List<Field> fields = Lists.newArrayListWithExpectedSize(1);
    for (Field f : clazz.getFields()) {
      if (f.getAnnotation(Parameter.class) != null) {
        fields.add(f);
      }
    }
    checkArgument(fields.size() == 1,
        "expected 1 @ConfigSuite.Parameter field, found: %s", fields);
    return fields.get(0);
  }

  public ConfigSuite(Class<?> clazz) throws InitializationError {
    super(clazz, runnersFor(clazz));
  }
}