/**
    * Copyright 2004-2014 The Kuali Foundation
    *
    * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
    *
   * 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 org.kuali.common.aws.auth;
  
  import java.util.List;
  
  import org.kuali.common.aws.model.ImmutableAWSCredentials;
  import org.kuali.common.util.Assert;
  import org.kuali.common.util.spring.SpringUtils;
  import org.kuali.common.util.spring.env.EnvironmentService;
  
  import com.amazonaws.auth.AWSCredentials;
  import com.amazonaws.auth.AWSCredentialsProvider;
  import com.google.common.collect.ImmutableList;
  
  public final class EnvCredentialsProvider implements AWSCredentialsProvider {
  
  	private final EnvironmentService env;
  	private final List<String> accessKeyProperties;
  	private final List<String> secretKeyProperties;
  
  	public static class Builder {
  
  		// Required
  		private final EnvironmentService env;
  
  		// Optional (default values are usually good enough)
  		private List<String> accessKeyProperties = ImmutableList.of("aws.accessKey", "aws.accessKeyId");
  		private List<String> secretKeyProperties = ImmutableList.of("aws.secretKey", "aws.secretAccessKey");
  
  		// Allow them to override which system properties / environment variables get examined
  		private static final String ACCESS_KEY_PROPERTIES = "aws.accessKeyProperties";
  		private static final String SECRET_KEY_PROPERTIES = "aws.secretKeyProperties";
  
  		public Builder(EnvironmentService env) {
  			this.env = env;
  		}
  
  		public Builder accessKeyProperties(List<String> accessKeyProperties) {
  			this.accessKeyProperties = accessKeyProperties;
  			return this;
  		}
  
  		public Builder secretKeyProperties(List<String> secretKeyProperties) {
  			this.secretKeyProperties = secretKeyProperties;
  			return this;
  		}
  
  		private void validate(EnvCredentialsProvider provider) {
  			Assert.noNulls(provider.getEnv(), provider.getAccessKeyProperties(), provider.getSecretKeyProperties());
  			Assert.isTrue(provider.getAccessKeyProperties().size() > 0, "Must provide at least one property to examine for AWS Access Key ID");
  			Assert.isTrue(provider.getSecretKeyProperties().size() > 0, "Must provide at least one property to examine for AWS Secret Key");
  		}
  
  		private void override() {
  			accessKeyProperties(SpringUtils.getStrings(env, ACCESS_KEY_PROPERTIES, accessKeyProperties));
  			secretKeyProperties(SpringUtils.getStrings(env, SECRET_KEY_PROPERTIES, secretKeyProperties));
  		}
  
  		private void finish() {
  			override();
  			this.accessKeyProperties = ImmutableList.copyOf(accessKeyProperties);
  			this.secretKeyProperties = ImmutableList.copyOf(secretKeyProperties);
  		}
  
  		public EnvCredentialsProvider build() {
  			finish();
  			EnvCredentialsProvider provider = new EnvCredentialsProvider(this);
  			validate(provider);
  			return provider;
  		}
  
  	}
  
  	private EnvCredentialsProvider(Builder builder) {
  		this.env = builder.env;
  		this.accessKeyProperties = builder.accessKeyProperties;
  		this.secretKeyProperties = builder.secretKeyProperties;
  	}
  
  	@Override
  	public AWSCredentials getCredentials() {
  		String accessKey = SpringUtils.getString(env, accessKeyProperties);
  		String secretKey = SpringUtils.getString(env, accessKeyProperties);
  		return new ImmutableAWSCredentials(accessKey, secretKey);
  	}
 
 	@Override
 	public void refresh() {
 		// noop
 	}
 
 	public EnvironmentService getEnv() {
 		return env;
 	}
 
 	public List<String> getAccessKeyProperties() {
 		return accessKeyProperties;
 	}
 
 	public List<String> getSecretKeyProperties() {
 		return secretKeyProperties;
 	}
 
 }