/*
    * #%L
    * wcm.io
    * %%
    * Copyright (C) 2014 wcm.io
    * %%
    * 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.
   * #L%
   */
  package io.wcm.caravan.pipeline.extensions.hal.client.action;
  
  import static io.wcm.caravan.io.http.request.CaravanHttpRequest.CORRELATION_ID_HEADER_NAME;
  
  import java.util.Collection;
  import java.util.Map;
  
  import org.apache.commons.lang3.StringUtils;
  import org.apache.http.client.methods.HttpGet;
  import org.osgi.annotation.versioning.ProviderType;
  
  import com.google.common.collect.Multimap;
  
  import io.wcm.caravan.hal.resource.Link;
  import io.wcm.caravan.io.http.request.CaravanHttpRequest;
  import io.wcm.caravan.io.http.request.CaravanHttpRequestBuilder;
  import io.wcm.caravan.pipeline.JsonPipeline;
  import io.wcm.caravan.pipeline.JsonPipelineContext;
  import io.wcm.caravan.pipeline.JsonPipelineExceptionHandler;
  import io.wcm.caravan.pipeline.JsonPipelineOutput;
  import io.wcm.caravan.pipeline.cache.CacheControlUtils;
  import io.wcm.caravan.pipeline.cache.CacheStrategy;
  import io.wcm.caravan.pipeline.extensions.hal.client.ServiceIdExtractor;
  import rx.Observable;
  
  /**
   * Action to load a HAL link.
   */
  @ProviderType
  public final class LoadLink extends AbstractHalClientAction {
  
    private final ServiceIdExtractor serviceId;
    private final Link link;
    private final Map<String, Object> parameters;
    private String httpMethod = HttpGet.METHOD_NAME;
  
    /**
     * @param serviceId Service ID
     * @param link Link to load
     * @param parameters URI parameters
     */
    public LoadLink(String serviceId, Link link, Map<String, Object> parameters) {
      this.serviceId = (path) -> serviceId;
      this.link = link;
      this.parameters = parameters;
    }
  
    /**
     * @param serviceId a function to extract the serviceid from a path
     * @param link Link to load
     * @param parameters URI parameters
     */
    public LoadLink(ServiceIdExtractor serviceId, Link link, Map<String, Object> parameters) {
      this.serviceId = serviceId;
      this.link = link;
      this.parameters = parameters;
    }
  
    @Override
    public String getId() {
      return "LOAD-LINK(" + httpMethod + "-" + serviceId.getServiceId(link.getHref()) + '-' + StringUtils.defaultIfBlank(link.getName(), "") + '-'
          + parameters.hashCode() + ")";
    }
  
    @Override
    public Observable<JsonPipelineOutput> execute(JsonPipelineOutput previousStepOutput, JsonPipelineContext pipelineContext) {
  
      CaravanHttpRequest request = createRequest(previousStepOutput);
      JsonPipeline pipeline = createPipeline(pipelineContext, request);
      return pipeline.getOutput().map(jsonPipelineOutput -> {
  
        int maxAge = CacheControlUtils.getLowestMaxAge(jsonPipelineOutput, previousStepOutput);
        return jsonPipelineOutput.withMaxAge(maxAge);
  
      });
  
    }
  
    /**
     * @param httpMethodToUse the HTTP method to use when loading the link
    * @return this
    */
   public HalClientAction withHttpMethod(String httpMethodToUse) {
     this.httpMethod = httpMethodToUse;
     return this;
   }
 
   private CaravanHttpRequest createRequest(JsonPipelineOutput previousStepOutput) {
 
     CaravanHttpRequestBuilder builder = getRequestBuilder();
     builder = setCacheControlHeaderIfExists(builder, previousStepOutput);
     builder = setCorrelationIdIfExists(builder, previousStepOutput);
     builder = setAdditionalHttpHeadersIfExists(builder);
     builder = builder.method(httpMethod);
     return builder.build(parameters);
 
   }
 
   private JsonPipeline createPipeline(JsonPipelineContext context, CaravanHttpRequest request) {
 
     if (hasLogger()) {
       getLogger().debug("Execute request: " + request);
     }
     JsonPipeline pipeline = context.getFactory().create(request, context.getProperties());
     pipeline = setCacheStrategyIfExists(pipeline);
     pipeline = addExceptionHandlers(pipeline);
     return pipeline;
 
   }
 
   /**
    * @return URL of the current link and parameters.
    */
   public String getUrl() {
     return getRequestBuilder().build(parameters).getUrl();
   }
 
   private CaravanHttpRequestBuilder getRequestBuilder() {
     return new CaravanHttpRequestBuilder(serviceId.getServiceId(link.getHref())).append(link.getHref());
   }
 
   /**
    * Adds a cache point to the given JSON pipeline if provided and the http request method is GET.
    * @param pipeline JSON pipeline
    * @return JSON pipeline with or without cache point
    */
   private JsonPipeline setCacheStrategyIfExists(JsonPipeline pipeline) {
     if (!HttpGet.METHOD_NAME.equals(httpMethod)) {
       return pipeline;
     }
     else {
       CacheStrategy cacheStrategy = getCacheStrategy();
       return cacheStrategy == null ? pipeline : pipeline.addCachePoint(cacheStrategy);
     }
   }
 
   /**
    * Sets the HTTP Cache-Control header to the given request builder if provided by the previous JSON pipeline output.
    * @param builder HTTP request builder
    * @param previousStepOutput Previous JSON output
    * @return HTTP request builder with or without HTTP Cache-Control header
    */
   private CaravanHttpRequestBuilder setCacheControlHeaderIfExists(CaravanHttpRequestBuilder builder, JsonPipelineOutput previousStepOutput) {
 
     if (previousStepOutput.getRequests().isEmpty()) {
       return builder;
     }
     CaravanHttpRequest previousRequest = previousStepOutput.getRequests().get(0);
     Collection<String> cacheControlHeader = previousRequest.getHeaders().get("Cache-Control");
     if (cacheControlHeader == null || cacheControlHeader.isEmpty()) {
       return builder;
     }
     return builder.header("Cache-Control", cacheControlHeader);
 
   }
 
   /**
    * Sets the {@code correlation-id} HTTP header to the given request builder if provided by the previous JSON pipeline
    * output.
    * @param builder HTTP request builder
    * @param previousStepOutput Previous JSON output
    * @return HTTP request builder with or without {@code correlation-id} HTTP header
    */
   private CaravanHttpRequestBuilder setCorrelationIdIfExists(CaravanHttpRequestBuilder builder, JsonPipelineOutput previousStepOutput) {
     return previousStepOutput.getCorrelationId() == null ? builder : builder.header(CORRELATION_ID_HEADER_NAME, previousStepOutput.getCorrelationId());
   }
 
   /**
    * Adds exception handler(s) to the given JSON pipeline if provided.
    * @param pipeline JSON pipeline
    * @return JSON pipeline with or without exception handler(s)
    */
   private JsonPipeline addExceptionHandlers(JsonPipeline pipeline) {
 
     JsonPipeline newPipeline = pipeline;
     for (JsonPipelineExceptionHandler handler : getExceptionHandlers()) {
       newPipeline = newPipeline.handleException(handler);
     }
     return newPipeline;
 
   }
 
   /**
    * Sets additional HTTP headers to the given request builder if provided.
    * @param builder HTTP request builder
    * @return HTTP request builder with or without headers
    */
   private CaravanHttpRequestBuilder setAdditionalHttpHeadersIfExists(CaravanHttpRequestBuilder builder) {
     getHttpHeaders().keySet().forEach(name -> builder.header(name, getHttpHeaders().get(name)));
     return builder;
   }
 
 }