/*
 * Copyright 2011-2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * 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://aws.amazon.com/apache2.0
 *
 * This file 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.amazonaws.internal;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.HttpURLConnection;
import java.net.URI;
import java.util.HashMap;
import java.util.Map;

import com.google.common.base.Charsets;
import com.google.common.io.CharStreams;
import com.google.common.io.Closeables;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.amazonaws.SdkClientException;
import com.amazonaws.AmazonServiceException;
import com.amazonaws.annotation.SdkInternalApi;
import com.amazonaws.retry.internal.CredentialsEndpointRetryParameters;
import com.amazonaws.retry.internal.CredentialsEndpointRetryPolicy;

@SdkInternalApi
public final class EC2CredentialsUtils {

    private static final Log LOG = LogFactory.getLog(EC2CredentialsUtils.class);

    private static EC2CredentialsUtils instance;

    private final ConnectionUtils connectionUtils;

    private EC2CredentialsUtils() {
        this(ConnectionUtils.getInstance());
    }

    EC2CredentialsUtils(ConnectionUtils connectionUtils) {
        this.connectionUtils = connectionUtils;
    }

    public static EC2CredentialsUtils getInstance() {
        if (instance == null) {
            instance = new EC2CredentialsUtils();
        }
        return instance;
    }

    /**
     * Connects to the given endpoint to read the resource
     * and returns the text contents.
     *
     * If the connection fails, the request will not be retried.
     *
     * @param endpoint
     *            The service endpoint to connect to.
     *
     * @return The text payload returned from the Amazon EC2 endpoint
     *         service for the specified resource path.
     *
     * @throws IOException
     *             If any problems were encountered while connecting to the
     *             service for the requested resource path.
     * @throws SdkClientException
     *             If the requested service is not found.
     */
    public String readResource(URI endpoint) throws IOException {
        return readResource(endpoint, CredentialsEndpointRetryPolicy.NO_RETRY, new HashMap<String, String>());
    }

    /**
     * Connects to the given endpoint to read the resource
     * and returns the text contents.
     *
     * @param endpoint
     *            The service endpoint to connect to.
     *
     * @param retryPolicy
     *            The custom retry policy that determines whether a
     *            failed request should be retried or not.
     *
     * @return The text payload returned from the Amazon EC2 endpoint
     *         service for the specified resource path.
     *
     * @throws IOException
     *             If any problems were encountered while connecting to the
     *             service for the requested resource path.
     * @throws SdkClientException
     *             If the requested service is not found.
     */
    public String readResource(URI endpoint, CredentialsEndpointRetryPolicy retryPolicy, Map<String, String> headers) throws IOException {
        int retriesAttempted = 0;
        InputStream inputStream = null;

        while (true) {
            try {
                HttpURLConnection connection = connectionUtils.connectToEndpoint(endpoint, headers);

                int statusCode = connection.getResponseCode();

                if (statusCode == HttpURLConnection.HTTP_OK) {
                    inputStream = connection.getInputStream();
                    try (Reader successReader = new InputStreamReader(inputStream, Charsets.UTF_8)) {
                      return CharStreams.toString(successReader);
                    }
                } else if (statusCode == HttpURLConnection.HTTP_NOT_FOUND) {
                    // This is to preserve existing behavior of EC2 Instance metadata service.
                    throw new SdkClientException("The requested metadata is not found at " + connection.getURL());
                } else {
                    if (!retryPolicy.shouldRetry(retriesAttempted++, CredentialsEndpointRetryParameters.builder().withStatusCode(statusCode).build())) {
                        inputStream = connection.getErrorStream();
                        handleErrorResponse(inputStream, statusCode, connection.getResponseMessage());
                    }
                }
            } catch (IOException ioException) {
                if (!retryPolicy.shouldRetry(retriesAttempted++, CredentialsEndpointRetryParameters.builder().withException(ioException).build())) {
                    throw ioException;
                }
                LOG.debug("An IOException occured when connecting to service endpoint: " + endpoint  + "\n Retrying to connect again.");
            } finally {
                Closeables.closeQuietly(inputStream);
            }
        }

    }

    private void handleErrorResponse(InputStream errorStream, int statusCode, String responseMessage) throws IOException {
        String errorCode = null;

        // Parse the error stream returned from the service.
        if(errorStream != null) {
            try (Reader errorReader = new InputStreamReader(errorStream, Charsets.UTF_8)) {
                String errorResponse = CharStreams.toString(errorReader);
                JsonParser parser = new JsonParser();

                JsonObject node = parser.parse(errorResponse).getAsJsonObject();
                JsonElement code = node.get("code");
                JsonElement message = node.get("message");
                if (code != null && message != null) {
                    errorCode = code.getAsString();
                    responseMessage = message.getAsString();
                }
            } catch (Exception exception) {
                LOG.debug("Unable to parse error stream");
            }
        }

        AmazonServiceException ase = new AmazonServiceException(responseMessage);
        ase.setStatusCode(statusCode);
        ase.setErrorCode(errorCode);
        throw ase;
    }
}