var request = require('request');
var copy = require('copy-to');
var crypto = require('crypto');

var defaultOptions = {
  // API版本: https://help.aliyun.com/document_detail/29741.html
  apiVerison: '2015-01-09',
  region: 'cn-hangzhou',
  timeout: 120000
}

var config = {
  // DNS API的服务接入地址为：https://help.aliyun.com/document_detail/29744.html
  endpoint: 'http://alidns.aliyuncs.com/'
}

var ALIDNS = function(options) {
  if (!(this instanceof ALIDNS)) {
    return new ALIDNS(options);
  }
  this.options = defaultOptions;
  options && copy(options)
    .toCover(this.options);
  // 创建AccessKey
  // https://help.aliyun.com/document_detail/53045.html
  if (!this.options.accesskeyId ||
    !this.options.accesskeySecret) {
    throw new Error('accesskeyId, accesskeySecret is required');
  }
}

module.exports = ALIDNS;

var proto = ALIDNS.prototype;

proto.queryData = function(conditions = {}, fn) {
  // API概览 :
  // https://help.aliyun.com/document_detail/29740.html
  this._request('GET', conditions, fn);
}

// GET参数生成
proto._generateUrl = function(customParams) {
  var params = this._getBasicParams();
  for (var i in customParams) {
    var value = customParams[i];
    if (typeof value != 'string') {
      value = JSON.stringify(value);
    }
    params[i] = value;
  }
  params['Signature'] = this._computeSignature(params, 'GET');
  var url = '';
  for (var i in params) {
    url += '&' + this._percentEncode(i) + '=' + this._percentEncode(params[i]);
  }
  url = url.substring(1);

  return config.endpoint + '?' + url;
}

// POST参数生成
proto._generateBody = function(customParams) {
  var params = this._getBasicParams();
  for (var i in customParams) {
    var value = customParams[i];
    if (typeof value != 'string') {
      value = JSON.stringify(value);
    }
    params[i] = value;
  }
  params['Signature'] = this._computeSignature(params, 'POST');
  var fields_string = '';
  for (var i in params) {
    fields_string += '&' + this._percentEncode(i) + '=' + this._percentEncode(params[i]);
  }
  fields_string = fields_string.substring(1);
  return fields_string;
}

// 签名机制: https://help.aliyun.com/document_detail/29747.html
proto._computeSignature = function(params, method) {
  var keys = Object.keys(params);
  keys = keys.sort();
  var canonicalizedQueryString = '';
  for (var i = 0; i < keys.length; i++) {
    canonicalizedQueryString += '&' + this._percentEncode(keys[i]) +
      '=' + this._percentEncode(params[keys[i]]);
  }

  canonicalizedQueryString = this._percentEncode(canonicalizedQueryString.substring(1));
  var stringToSign = method + '&%2F&' + canonicalizedQueryString;
  var signature = crypto.createHmac('sha1', this.options.accesskeySecret + '&')
    .update(stringToSign)
    .digest()
    .toString('base64');
  return signature;
}

// 生成公共请求参数
// 公共请求参数说明: https://help.aliyun.com/document_detail/29745.html
proto._getBasicParams = function() {
  var now = new Date();
  var nonce = now.getTime() + '' + parseInt((Math.random() * 1000000000));
  return {
    RegionId: this.options.region,
    AccessKeyId: this.options.accesskeyId,
    Format: 'JSON',
    SignatureMethod: 'HMAC-SHA1',
    SignatureVersion: '1.0',
    SignatureNonce: nonce,
    Timestamp: now.toISOString(),
    Version: this.options.apiVerison
  }
}

// 规范化字符串,URL编码
proto._percentEncode = function(str) {
  var str = encodeURIComponent(str);
  str = str.replace(/\*/g, '%20');
  str = str.replace(/\'/g, '%27');
  str = str.replace(/\(/g, '%28');
  str = str.replace(/\)/g, '%29');
  return str;
}

// 调用请求
proto._request = function(method, body, fn) {
  var reqOptions = {
    timeout: this.options.timeout,
    method: method
  };

  if (method.toUpperCase() == 'GET') {
    reqOptions.url = this._generateUrl(body);
  } else {
    reqOptions.url = config.endpoint;
    reqOptions.body = this._generateBody(body);
    reqOptions.headers = { 'Content-Type': 'application/x-www-form-urlencoded' };
  }
  var that = this;
  request(reqOptions, function(err, response, body) {
    that._onRequestResponse(err, response, fn)
  });
}

// request请求回调
proto._onRequestResponse = function(err, response, fn) {
  if (err) {
    return fn(err, null)
  } else {
    try {
      var result = JSON.parse(response.body);
      if (result.Message) {
        return fn(new Error(result.Message), null);
      }
      return fn(null, result);
    } catch (e) {
      console.error(e);
      return fn(new Error('Request MetricStore failed: ' + response.body), null);
    }
  }
}