var AwsEC2 = {
    params: {},

    setParams: function (params) {
        ['access_key', 'region', 'secret_key'].forEach(function (field) {
            if (typeof params !== 'object' || typeof params[field] === 'undefined' || params[field] === '') {
                throw 'Required param is not set: "' + field + '".';
            }
        });

        AwsEC2.params = params;
    },

    sign: function (key, message) {
        var hex = hmac('sha256', key, message);

        if ((hex.length % 2) === 1) {
            throw 'Invalid length of a hex string!';
        }

        var result = new Int8Array(hex.length / 2);
        for (var i = 0, b = 0; i < hex.length; i += 2, b++) {
            result[b] = parseInt(hex.substring(i, i + 2), 16);
        }

        return result;
    },

    prepareParams: function (params) {
        var result = [];

        Object.keys(params).sort().forEach(function (key) {
            if (typeof params[key] !== 'object') {
                result.push(key + '=' + encodeURIComponent(params[key]));
            }
            else {
                result.push(prepareObject(key, params[key]));
            }
        });

        return result.join('&');
    },

    request: function (method, region, service, host, params, data, uri) {
        if (typeof data === 'undefined' || data === null) {
            data = '';
        }

        var amzdate = (new Date()).toISOString().replace(/\.\d+Z/, 'Z').replace(/[-:]/g, ''),
            date = amzdate.replace(/T\d+Z/, ''),

            canonical_uri = '/' + uri,
            canonical_headers = 'content-encoding:amz-1.0\n' + 'host:' + host + '\n' + 'x-amz-date:' + amzdate + '\n',
            signed_headers = 'content-encoding;host;x-amz-date',
            canonical_request = method + '\n' + canonical_uri + '\n' + params + '\n' + canonical_headers + '\n' + signed_headers + '\n' + sha256(data),
            credential_scope = date + '/' + region + '/' + service + '/' + 'aws4_request',
            request_string = 'AWS4-HMAC-SHA256' + '\n' + amzdate + '\n' + credential_scope + '\n' + sha256(canonical_request),
            key = AwsEC2.sign('AWS4' + AwsEC2.params.secret_key, date);

        key = AwsEC2.sign(key, region);
        key = AwsEC2.sign(key, service);
        key = AwsEC2.sign(key, 'aws4_request');

        var request = new HttpRequest(),
            url = 'https://' + host + canonical_uri + '?' + params;

        if (typeof AwsEC2.params.proxy !== 'undefined' && AwsEC2.params.proxy !== '') {
            request.setProxy(AwsEC2.params.proxy);
        }
        request.addHeader('x-amz-date: ' + amzdate);
        request.addHeader('x-amz-content-sha256:' + sha256(data));
        request.addHeader('Accept: application/json');
        request.addHeader('Content-Type: application/json');
        request.addHeader('Content-Encoding: amz-1.0');
        request.addHeader('Authorization: ' + 'AWS4-HMAC-SHA256 Credential=' + AwsEC2.params.access_key + '/' + credential_scope + ', ' + 'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + hmac('sha256', key, request_string));

        Zabbix.log(4, '[ AWS EC2 ] Sending request: ' + url);

        response = request.post(url, data);

        Zabbix.log(4, '[ AWS EC2 ] Received response with status code ' + request.getStatus() + ': ' + response);

        if (request.getStatus() !== 200) {
            throw 'Request failed with status code ' + request.getStatus() + ': ' + response;
        }
        if (response !== null) {
            try {
                response = XML.toJson(response);
            }
            catch (error) {
                throw 'Failed to parse response received from AWS CloudWatch API. Check debug log for more information.';
            }
        }

        return JSON.parse(response);
    },

    tagToNameInstances: function (instance) {
        if (!Array.isArray(instance))
            instance = [instance];
        instance.forEach(function (item, index, instance_array) {
            if (typeof item !== 'object'
                || typeof item.instancesSet !== 'object'
                || typeof item.instancesSet.item !== 'object'
                || item.instancesSet.item.hasOwnProperty('instanceId') === false)
                throw 'Failed response parse. Check debug log for more information.';
            var instanceName = item.instancesSet.item.instanceId
            if (typeof item.instancesSet.item.tagSet === 'object'
                && typeof item.instancesSet.item.tagSet.item === 'object') {
                if (!Array.isArray(item.instancesSet.item.tagSet.item))
                  item.instancesSet.item.tagSet.item = [item.instancesSet.item.tagSet.item];
                item.instancesSet.item.tagSet.item.forEach(
                    function (tag) {
                        if (tag.hasOwnProperty('key') && tag.key === 'Name') {
                            instanceName = tag.value;
                        }
                    }
                );
            }
            instance_array[index]['instanceName'] = instanceName;
        });

        return instance;
    },

    listInstances: function () {
        var payload = {};

        payload['Action'] = 'DescribeInstances',
            payload['Version'] = '2016-11-15'

        result = AwsEC2.request('POST', AwsEC2.params.region, 'ec2', 'ec2.' + AwsEC2.params.region + '.amazonaws.com', AwsEC2.prepareParams(payload), '', '');

        if (typeof result !== 'object'
            || typeof result.DescribeInstancesResponse !== 'object'
            || typeof result.DescribeInstancesResponse.reservationSet !== 'object') {
            throw 'Cannot get EC2 instance list from AWS API. Check debug log for more information.';
        }

        if (result.DescribeInstancesResponse.reservationSet === null)
            return [];

        if (typeof result.DescribeInstancesResponse.reservationSet.item !== 'object')
            throw 'Cannot get EC2 instance list from AWS API. Check debug log for more information.';

        return AwsEC2.tagToNameInstances(result.DescribeInstancesResponse.reservationSet.item);
    }
};

try {
    AwsEC2.setParams(JSON.parse(value));

    return JSON.stringify(AwsEC2.listInstances());
}
catch (error) {
    error += (String(error).endsWith('.')) ? '' : '.';
    Zabbix.log(3, '[ AWS EC2 ] ERROR: ' + error);
    return JSON.stringify({ 'error': error });
}