// vi: ts=4 sw=4 noet:
/*
==================================================================================
    Copyright (c) 2022 Alexandre Huff

   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.
==================================================================================
*/

/*
    Mnemonic:	restclient.cpp
    Abstract:	Implements a tiny wrapper on top of libcurl to handle with rest requests.

    Date:       8 Apr 2022
    Author:     Alexandre Huff
*/


#include "restclient.hpp"
#include <mutex>
#include <string.h>
#include <memory>
#include <sstream>

namespace restclient {

// callback to handle http responses
static size_t http_response_callback( const char *in, size_t size, size_t num, std::string *out ) {
    if( out == NULL ) {
        return 0;
    }
    const size_t totalBytes( size * num );
    out->append( in, totalBytes );
    return totalBytes;
}

/*
    Create a RestClient instance to exchange messages with
    a given rest api available on baseUrl, which consists of
    scheme://domain[:port]
*/
RestClient::RestClient( std::string baseUrl ) {
    this->baseUrl = baseUrl;

    init();
}

RestClient::~RestClient( ) {
    curl_slist_free_all( headers );
    curl_easy_cleanup( curl );
}

std::string RestClient::getBaseUrl( ) {
    return baseUrl;
}

void RestClient::init( ) {
    static std::mutex curl_mutex;

    {   // scoped mutex to make curl_global_init thread-safe
        const std::lock_guard<std::mutex> lock( curl_mutex );
        CURLcode code = curl_global_init( CURL_GLOBAL_DEFAULT );
        if( code != 0 ) {
            std::stringstream ss;
            ss << "curl_global_init returned error code " << code << ", unable to proceed";
            std::string s = std::to_string(code);
            throw RestClientException( ss.str() );
        }
    }

    try {
        curl = curl_easy_init();
        if( curl == NULL ) {
            throw RestClientException( "CURL did not return a handler, unable to proceed" );
        }

        // curl_easy_setopt( curl, CURLOPT_VERBOSE, 1L );
        if( curl_easy_setopt( curl, CURLOPT_TIMEOUT, 5 ) != CURLE_OK ) {
            throw RestClientException( "unable to set CURLOPT_TIMEOUT" );
        }

        /* provide a buffer to store errors in */
        if( curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errbuf) != CURLE_OK ) {
            throw RestClientException( "unable to set CURLOPT_ERRORBUFFER" );
        }
        errbuf[0] = 0;

        if( curl_easy_setopt( curl, CURLOPT_WRITEFUNCTION, http_response_callback ) != CURLE_OK ) {
            throw RestClientException( "unable to set CURLOPT_WRITEFUNCTION" );
        }

        headers = curl_slist_append( headers, "Accept: application/json" );
        headers = curl_slist_append( headers, "Content-Type: application/json" );
        if( curl_easy_setopt( curl, CURLOPT_HTTPHEADER, headers ) != CURLE_OK ) {
            throw RestClientException( "unable to set CURLOPT_HTTPHEADER" );
        }

    } catch( const RestClientException &e ) {   // avoid memory leakage
        if( headers != NULL ) {
            curl_slist_free_all( headers );
        }
        if( curl != NULL ) {
            curl_easy_cleanup( curl );
        }

        std::stringstream ss;
        ss << "Failed to initialize RestClient: " << e.what();
        throw RestClientException( ss.str() );
    }

}

/*
    Executes a GET request at the path of this RestClient instance.
    Returns the HTTP status code and the correspoding message body.
*/
response_t RestClient::do_get( std::string path ) {
    response_t response = { 0, "" };

    const std::string endpoint = baseUrl + path;

    if( curl_easy_setopt( curl, CURLOPT_WRITEDATA, &response.body ) != CURLE_OK ) {
        throw RestClientException( "unable to set CURLOPT_WRITEDATA" );
    }

    if( curl_easy_setopt( curl, CURLOPT_URL, endpoint.c_str() ) != CURLE_OK ) {
        throw RestClientException( "unable to set CURLOPT_URL" );
    }
    if( curl_easy_setopt( curl, CURLOPT_HTTPGET, 1L ) != CURLE_OK ) {
        throw RestClientException( "unable to set CURLOPT_HTTPGET" );
    }

    CURLcode res = curl_easy_perform( curl );
    if( res == CURLE_OK ) {
        if( curl_easy_getinfo( curl, CURLINFO_RESPONSE_CODE, &response.status_code ) != CURLE_OK ) {
            throw RestClientException( std::string("unable to get CURLINFO_RESPONSE_CODE. ") + errbuf );
        }
    } else {
        size_t len = strlen( errbuf );
        std::stringstream ss;
        ss << "unable to complete the request at " << endpoint.c_str();
        if(len)
            ss << ". " << errbuf;
        else
            ss << ". " << curl_easy_strerror( res );

        throw RestClientException( ss.str() );
    }

    return response;
}

/*
    Executes a POST request of a json message at the path of this RestClient instance.
    Returns the HTTP status code and the correspoding message body.
*/
response_t RestClient::do_post( std::string path, std::string json ) {
    response_t response = { 0, "" };

    const std::string endpoint = baseUrl + path;

    if( curl_easy_setopt( curl, CURLOPT_WRITEDATA, &response.body ) != CURLE_OK ) {
        throw RestClientException( "unable to set CURLOPT_WRITEDATA" );
    }

    if( curl_easy_setopt( curl, CURLOPT_URL, endpoint.c_str() ) != CURLE_OK ) {
        throw RestClientException( "unable to set CURLOPT_URL" );
    }
    if( curl_easy_setopt( curl, CURLOPT_POST, 1L ) != CURLE_OK ) {
        throw RestClientException( "unable to set CURLOPT_POST" );
    }
    if( curl_easy_setopt( curl, CURLOPT_POSTFIELDS, json.c_str() ) != CURLE_OK ) {
        throw RestClientException( "unable to set CURLOPT_POSTFIELDS" );
    }

    CURLcode res = curl_easy_perform( curl );
    if( res == CURLE_OK ) {
        if( curl_easy_getinfo( curl, CURLINFO_RESPONSE_CODE, &response.status_code ) != CURLE_OK ) {
            throw RestClientException( std::string("unable to get CURLINFO_RESPONSE_CODE. ") + errbuf );
        }
    } else {
        size_t len = strlen( errbuf );
        std::stringstream ss;
        ss << "unable to complete the request at " << endpoint.c_str();
        if(len)
            ss << ". " << errbuf;
        else
            ss << ". " << curl_easy_strerror( res );

        throw RestClientException( ss.str() );
    }

    return response;
}

} // namespace