var AwsEbs = {
    params: {},
    request_period: 600,

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

        AwsEbs.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;
    },

    prepareRecursive: function (prefix, param) {
        var result = {};

        if (typeof param === 'object') {
            if (Array.isArray(param)) {
                param.forEach(function (value, index) {
                    var nested = AwsEbs.prepareRecursive(prefix + '.member.' + (index + 1), value);
                    Object.keys(nested).forEach(function (key) {
                        result[key] = nested[key];
                    });
                });
            }
            else {
                Object.keys(param).forEach(function (k) {
                    var nested = AwsEbs.prepareRecursive(prefix + '.' + k, param[k]);
                    Object.keys(nested).forEach(function (key) {
                        result[key] = nested[key];
                    });
                });
            }
        }
        else {
            result[prefix] = param;
        }

        return result;
    },

    renderPayload: function (period, volume_id) {
        var metrics_list = [
            'VolumeReadBytes:Bytes',
            'VolumeWriteBytes:Bytes',
            'VolumeReadOps:Count',
            'VolumeWriteOps:Count',
            'VolumeTotalReadTime:Seconds',
            'VolumeTotalWriteTime:Seconds',
            'VolumeIdleTime:Seconds',
            'VolumeQueueLength:Count',
            'VolumeThroughputPercentage:Percent',
            'VolumeConsumedReadWriteOps:Count',
            'BurstBalance:Percent'
        ];

        var metric_payload = [];
        metrics_list.forEach(function (metric) {
            var parts = metric.split(':', 2);
            var name = parts[0].replace(/[^a-zA-Z0-9]/g, '');
            metric_payload.push({
                'Id': name.charAt(0).toLowerCase() + name.slice(1),
                'MetricStat': {
                    'Metric': {
                        'MetricName': parts[0],
                        'Namespace': 'AWS/EBS',
                        'Dimensions': [
                            {
                                'Name': 'VolumeId',
                                'Value': volume_id
                            }
                        ]
                    },
                    'Period': period,
                    'Stat': 'Average',
                    'Unit': parts[1]
                }
            });
        });

        return metric_payload;
    },

    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, params, data) {
        if (typeof data === 'undefined' || data === null) {
            data = '';
        }

        var amzdate = (new Date()).toISOString().replace(/\.\d+Z/, 'Z').replace(/[-:]/g, ''),
            date = amzdate.replace(/T\d+Z/, ''),
            host = service + '.' + region + '.amazonaws.com',
            canonical_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 = AwsEbs.sign('AWS4' + AwsEbs.params.secret_key, date);

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

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

        if (typeof AwsEbs.params.proxy !== 'undefined' && AwsEbs.params.proxy !== '') {
            request.setProxy(AwsEbs.params.proxy);
        }
        request.addHeader('x-amz-date: ' + amzdate);
        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=' + AwsEbs.params.access_key + '/' + credential_scope + ', ' + 'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + hmac('sha256', key, request_string));

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

        response = request.get(url);

        Zabbix.log(4, '[ AWS EBS ] 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 = JSON.parse(response);
            }
            catch (error) {
                throw 'Failed to parse response received from AWS CloudWatch API. Check debug log for more information.';
            }
        }

        return response;
    },

    getMetricsData: function () {
        var timestamp = new Date().getTime(),
            end_time = new Date(timestamp).toISOString().replace(/\.\d+Z/, 'Z'),
            start_time = new Date(timestamp - AwsEbs.request_period * 1000).toISOString().replace(/\.\d+Z/, 'Z'),
            payload = AwsEbs.prepareRecursive('MetricDataQueries', AwsEbs.renderPayload(AwsEbs.request_period, AwsEbs.params.volume_id));

        payload['Action'] = 'GetMetricData';
        payload['Version'] = '2010-08-01';
        payload['StartTime'] = start_time;
        payload['EndTime'] = end_time;
        payload['ScanBy'] = 'TimestampDescending';

        result = AwsEbs.request('GET', AwsEbs.params.region, 'monitoring', AwsEbs.prepareParams(payload));

        if (typeof result !== 'object'
                || typeof result.GetMetricDataResponse !== 'object'
                || typeof result.GetMetricDataResponse.GetMetricDataResult !== 'object'
                || typeof result.GetMetricDataResponse.GetMetricDataResult.MetricDataResults !== 'object') {
            throw 'Cannot get metrics data from AWS CloudWatch API. Check debug log for more information.';
        }

        return result.GetMetricDataResponse.GetMetricDataResult.MetricDataResults;
    }
};

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

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

    return JSON.stringify({'error': error});
}