lib.js

const qs = require('querystring');
const crypto = require('crypto');
const fs = require('fs');
const request = require('requestretry');
const packageJson = require('./package.json')

/*
 * Image-Charts URL builder
 * @typedef ImageCharts
 */
function ImageCharts({secret, protocol, host, port, timeout, userAgent} = {}, previous = {}) {
  if (!(this instanceof ImageCharts)) {
    return new ImageCharts({secret, protocol, host, port, timeout, userAgent}, previous);
  }
  this._protocol = protocol || 'https';
  this._host = host || 'image-charts.com';
  this._port = port || 443;
  this._pathname = '/chart';
  this._timeout = typeof timeout !== 'undefined' ? timeout : 5000;
  this._query = {};
  this._secret = secret;
  this._userAgent = userAgent;
  Object.assign(this, previous);
}

ImageCharts.prototype._clone = function (param, value) {
  return new this.constructor({}, {
    ...this,
    _query:{
      ...this._query,
      [param]: value
    }
  });
};


/**
  * bvg= grouped bar chart, bvs= stacked bar chart, lc=line chart, ls=sparklines, p=pie chart. gv=graph viz
	*         Three-dimensional pie chart (p3) will be rendered in 2D, concentric pie chart are not supported.
	*         [Optional, line charts only] You can add :nda after the chart type in line charts to hide the default axes.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-type/}
  * @example
  * const chart = ImageCharts().cht("bvg");
  * const chart = ImageCharts().cht("p");
  * 
  * @param {string} value - Chart type
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.cht = function(value) {
  return this._clone('cht', value);
};

/**
  * chart data. At most 1,000 series, chm line markers included, and 10,080 points in total.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/data-format/}
  * @example
  * const chart = ImageCharts().chd("a:-100,200.5,75.55,110");
  * const chart = ImageCharts().chd("t:10,20,30|15,25,35");
  * const chart = ImageCharts().chd("s:BTb19_,Mn5tzb");
  * const chart = ImageCharts().chd("e:BaPoqM2s,-A__RMD6");
  * 
  * @param {string} value - chart data. At most 1,000 series, chm line markers included, and 10,080 points in total.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chd = function(value) {
  return this._clone('chd', value);
};

/**
  * You can configure some charts to scale automatically to fit their data with chds=a. The chart will be scaled so that the largest value is at the top of the chart and the smallest (or zero, if all values are greater than zero) will be at the bottom. Otherwise the "≶series_1_min>,≶series_1_max>,...,≶series_n_min>,≶series_n_max>" format set one or more minimum and maximum permitted values for each data series, separated by commas. You must supply both a max and a min. If you supply fewer pairs than there are data series, the last pair is applied to all remaining data series. Note that this does not change the axis range; to change the axis range, you must set the chxr parameter. Valid values range from (+/-)9.999e(+/-)199. You can specify values in either standard or E notation.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/data-format/#text-format-with-custom-scaling}
  * @example
  * const chart = ImageCharts().chds("-80,140");
  * 
  * @param {string} value - data format with custom scaling
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chds = function(value) {
  return this._clone('chds', value);
};

/**
  * How to encode the data in the QR code. 'UTF-8' is the default and only supported value. Contact our team if you wish to have support for Shift_JIS and/or ISO-8859-1.
  * [Reference documentation]{@link https://documentation.image-charts.com/qr-codes/#data-encoding}
  * @example
  * const chart = ImageCharts().choe("UTF-8");
  * 
  * @param {string} value - QRCode data encoding
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.choe = function(value) {
  return this._clone('choe', value);
};

/**
  * QRCode error correction level and optional margin
  * [Reference documentation]{@link https://documentation.image-charts.com/qr-codes/#error-correction-level-and-margin}
  * @example
  * const chart = ImageCharts().chld("L|4");
  * const chart = ImageCharts().chld("M|10");
  * const chart = ImageCharts().chld("Q|5");
  * const chart = ImageCharts().chld("H|18");
  * @default "L|4"
  * @param {string} value - QRCode error correction level and optional margin
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chld = function(value) {
  return this._clone('chld', value);
};

/**
  * You can specify the range of values that appear on each axis independently, using the chxr parameter. Note that this does not change the scale of the chart elements (use chds for that), only the scale of the axis labels.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-axis/#axis-range}
  * @example
  * const chart = ImageCharts().chxr("0,0,200");
  * const chart = ImageCharts().chxr("0,10,50,5");
  * const chart = ImageCharts().chxr("0,0,500|1,0,200");
  * 
  * @param {string} value - Axis data-range
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chxr = function(value) {
  return this._clone('chxr', value);
};

/**
  * Some clients like Flowdock/Facebook messenger and so on, needs an URL to ends with a valid image extension file to display the image, use this parameter at the end your URL to support them. Valid values are ".png", ".svg" and ".gif".
	*           Only QRCodes and GraphViz support svg output.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/output-format/}
  * @example
  * const chart = ImageCharts().chof(".png");
  * const chart = ImageCharts().chof(".svg");
  * const chart = ImageCharts().chof(".gif");
  * @default ".png"
  * @param {string} value - Image output format
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chof = function(value) {
  return this._clone('chof', value);
};

/**
  * Maximum chart size for all charts except maps is 998,001 pixels total (Google Image Charts was limited to 300,000), and maximum width or length is 999 pixels.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-size/}
  * @example
  * const chart = ImageCharts().chs("400x400");
  * 
  * @param {string} value - Chart size (<width>x<height>)
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chs = function(value) {
  return this._clone('chs', value);
};

/**
  * Format: <data_series_1_label>|...|<data_series_n_label>. The text for the legend entries. Each label applies to the corresponding series in the chd array. Use a + mark for a space. If you do not specify this parameter, the chart will not get a legend. There is no way to specify a line break in a label. The legend will typically expand to hold your legend text, and the chart area will shrink to accommodate the legend.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/legend-text-and-style/}
  * @example
  * const chart = ImageCharts().chdl("NASDAQ|FTSE100|DOW");
  * 
  * @param {string} value - Text for each series, to display in the legend. Each text between pipes holds at most 10,000 characters. The texts of chtt, chdl, chl and chxl hold at most 10,000 characters together that are not printable ASCII: accented letters, other scripts, emoji and line breaks.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chdl = function(value) {
  return this._clone('chdl', value);
};

/**
  * Specifies the color and font size of the legend text. <color>,<size>
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/legend-text-and-style/}
  * @example
  * const chart = ImageCharts().chdls("9e9e9e,17");
  * @default "000000"
  * @param {string} value - Chart legend text and style
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chdls = function(value) {
  return this._clone('chdls', value);
};

/**
  * Solid or dotted grid lines. A dashed grid needs at least 1 pixel per dash or space on average.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/grid-lines/}
  * @example
  * const chart = ImageCharts().chg("1,1");
  * const chart = ImageCharts().chg("0,1,1,5");
  * const chart = ImageCharts().chg("1,1,FF00FF");
  * const chart = ImageCharts().chg("1,1,1,1,CECECE");
  * 
  * @param {string} value - Solid or dotted grid lines. A dashed grid needs at least 1 pixel per dash or space on average.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chg = function(value) {
  return this._clone('chg', value);
};

/**
  * You can specify the colors of a specific series using the chco parameter.
	*       Format should be <series_2>,...,<series_m>, with each color in RRGGBB format hexadecimal number.
	*       The exact syntax and meaning can vary by chart type; see your specific chart type for details.
	*       Each entry in this string is an RRGGBB[AA] format hexadecimal number.
	*       If there are more series or elements in the chart than colors specified in your string, the API typically cycles through element colors from the start of that series (for elements) or for series colors from the start of the series list.
	*       Again, see individual chart documentation for details.
  * [Reference documentation]{@link https://documentation.image-charts.com/bar-charts/#examples}
  * @example
  * const chart = ImageCharts().chco("FFC48C");
  * const chart = ImageCharts().chco("FF0000,00FF00,0000FF");
  * @default "F56991,FF9F80,FFC48C,D1F2A5,EFFAB4"
  * @param {string} value - series colors
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chco = function(value) {
  return this._clone('chco', value);
};

/**
  * chart title. Each text between pipes holds at most 10,000 characters. The texts of chtt, chdl, chl and chxl hold at most 10,000 characters together that are not printable ASCII: accented letters, other scripts, emoji and line breaks.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-title/}
  * @example
  * const chart = ImageCharts().chtt("My beautiful chart");
  * 
  * @param {string} value - chart title. Each text between pipes holds at most 10,000 characters. The texts of chtt, chdl, chl and chxl hold at most 10,000 characters together that are not printable ASCII: accented letters, other scripts, emoji and line breaks.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chtt = function(value) {
  return this._clone('chtt', value);
};

/**
  * Format should be "<color>,<font_size>[,<opt_alignment>,<opt_font_family>,<opt_font_style>]", opt_alignement is not supported
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-title/}
  * @example
  * const chart = ImageCharts().chts("00FF00,17");
  * 
  * @param {string} value - chart title colors and font size
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chts = function(value) {
  return this._clone('chts', value);
};

/**
  * Specify which axes you want (from: "x", "y", "t" and "r"). You can use several of them, separated by a coma; for example: "x,x,y,r". Order is important.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-axis/#visible-axes}
  * @example
  * const chart = ImageCharts().chxt("y");
  * const chart = ImageCharts().chxt("x,y");
  * const chart = ImageCharts().chxt("x,x,y");
  * const chart = ImageCharts().chxt("x,y,t,r,t");
  * 
  * @param {string} value - Display values on your axis lines or change which axes are shown. At most 100 axes.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chxt = function(value) {
  return this._clone('chxt', value);
};

/**
  * Specify one parameter set for each axis that you want to label. Format "<axis_index>:|<label_1>|...|<label_n>|...|<axis_index>:|<label_1>|...|<label_n>". Separate multiple sets of labels using the pipe character ( | ).
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-axis/#custom-axis-labels}
  * @example
  * const chart = ImageCharts().chxl("0:|Jan|July|Jan");
  * const chart = ImageCharts().chxl("0:|Jan|July|Jan|1|10|20|30");
  * 
  * @param {string} value - Custom string axis labels on any axis. Each text between pipes holds at most 10,000 characters. The texts of chtt, chdl, chl and chxl hold at most 10,000 characters together that are not printable ASCII: accented letters, other scripts, emoji and line breaks. A radar draws a ring per label, completed with blanks up to the longest chd series minus its last value: at most 1,000 rings, and 100,000 ring corners with its spokes.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chxl = function(value) {
  return this._clone('chxl', value);
};

/**
  * You can specify the range of values that appear on each axis independently, using the chxr parameter. Note that this does not change the scale of the chart elements (use chds for that), only the scale of the axis labels.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-axis/#axis-label-styles}
  * @example
  * const chart = ImageCharts().chxs("1,0000DD");
  * const chart = ImageCharts().chxs("1N*cUSD*Mil,FF0000");
  * const chart = ImageCharts().chxs("1N*cEUR*,FF0000");
  * const chart = ImageCharts().chxs("2,0000DD,13,0,t");
  * const chart = ImageCharts().chxs("0N*p*per-month,0000FF");
  * const chart = ImageCharts().chxs("0N*e*,000000|1N*cUSD*Mil,FF0000|2N*2sz*,0000FF");
  * 
  * @param {string} value - Font size, color for axis labels, both custom labels and default label values. At most 100 styles, one per axis. Each number format after N holds at most 10,000 characters. An axis draws its format at each tick: at most 60,000 characters over all axes. A character in a font larger than 14 pixels counts once per 14 pixels of font size.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chxs = function(value) {
  return this._clone('chxs', value);
};

/**
  * 
	* format should be either:
	*   - line fills (fill the area below a data line with a solid color): chm=<b_or_B>,<color>,<start_line_index>,<end_line_index>,<0> |...| <b_or_B>,<color>,<start_line_index>,<end_line_index>,<0>
	*   - line marker (add a line that traces data in your chart): chm=D,<color>,<series_index>,<which_points>,<width>,<opt_z_order>
	*   - Text and Data Value Markers: chm=N<formatting_string>,<color>,<series_index>,<which_points>,<width>,<opt_z_order>,<font_family>,<font_style>
	*     
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/compound-charts/}
  * @example

  * 
  * @param {string} value - compound charts and line fills. Each marker text holds at most 10,000 characters. The last N marker of a series draws its type and text at each point of the series: at most 60,000 characters over all series. Each label counts 20 characters on top of its text. A character in a font larger than 14 pixels counts once per 14 pixels of font size.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chm = function(value) {
  return this._clone('chm', value);
};

/**
  * line thickness and solid/dashed style. A dashed line needs at least 1 pixel per dash or space on average, and a line width at most 2 times its dash period. Dashed lines run through at most 1,000 points in total.
  * [Reference documentation]{@link https://documentation.image-charts.com/line-charts/#line-styles}
  * @example
  * const chart = ImageCharts().chls("10");
  * const chart = ImageCharts().chls("3,6,3|5");
  * 
  * @param {string} value - line thickness and solid/dashed style. A dashed line needs at least 1 pixel per dash or space on average, and a line width at most 2 times its dash period. Dashed lines run through at most 1,000 points in total.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chls = function(value) {
  return this._clone('chls', value);
};

/**
  * If specified it will override "chdl" values
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-label/}
  * @example
  * const chart = ImageCharts().chl("label1|label2");
  * const chart = ImageCharts().chl("multi
	* line
	* label1|label2");
  * 
  * @param {string} value - bar, pie slice, doughnut slice and polar slice chart labels. Each text between pipes holds at most 10,000 characters. The texts of chtt, chdl, chl and chxl hold at most 10,000 characters together that are not printable ASCII: accented letters, other scripts, emoji and line breaks. A QR code or a Graphviz chart reads chl as its data, without these limits. A Graphviz chart has its own limits on the DOT source: at most 50,000 characters and 6 levels of braces, 200 nodes and 400 edges. These engines take fewer: neato 70 nodes and 200 edges, twopi 70 nodes and 200 edges, osage 75 nodes and 200 edges, fdp 60 nodes and 200 edges, circo 55 nodes and 110 edges. These graph attributes take a plain decimal number: mclimit from 0 to 5; maxiter from 0 to 1,000; normalize from -100,000,000,000 to 100,000,000,000 (or true, false, yes, no); esep at least 0; dpi at least 0; resolution at least 0. A PNG of more than 16,000,000 pixels, a graph that draws more than 20,000 characters of text, or a line of more than 500 characters is refused: request the SVG output with `chof=.svg` to lift these three.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chl = function(value) {
  return this._clone('chl', value);
};

/**
  * Position and style of labels on data
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-label/#positionning-and-formatting}
  * @example
  * const chart = ImageCharts().chlps("align,top|offset,10|color,FF00FF");
  * const chart = ImageCharts().chlps("align,top|offset,10|color,FF00FF");
  * 
  * @param {string} value - Position and style of labels on data
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chlps = function(value) {
  return this._clone('chlps', value);
};

/**
  * chart margins
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-margin/}
  * @example
  * const chart = ImageCharts().chma("30,30,30,30");
  * const chart = ImageCharts().chma("40,20");
  * 
  * @param {string} value - chart margins
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chma = function(value) {
  return this._clone('chma', value);
};

/**
  * Position of the legend and order of the legend entries
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/legend-text-and-style/}
  * @example

  * @default "r"
  * @param {string} value - Position of the legend and order of the legend entries
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chdlp = function(value) {
  return this._clone('chdlp', value);
};

/**
  * Background Fills. At most 100 gradient stops over all fills.
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/background-fill/}
  * @example
  * const chart = ImageCharts().chf("b0,lg,0,f44336,0.3,03a9f4,0.8");
  * @default "bg,s,FFFFFF"
  * @param {string} value - Background Fills. At most 100 gradient stops over all fills.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chf = function(value) {
  return this._clone('chf', value);
};

/**
  * Bar corner radius. Display bars with rounded corner.
  * [Reference documentation]{@link https://documentation.image-charts.com/bar-charts/#rounded-bar}
  * @example
  * const chart = ImageCharts().chbr("5");
  * const chart = ImageCharts().chbr("10");
  * 
  * @param {string} value - Bar corner radius. Display bars with rounded corner.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chbr = function(value) {
  return this._clone('chbr', value);
};

/**
  * gif configuration
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/animation/}
  * @example
  * const chart = ImageCharts().chan("1200");
  * const chart = ImageCharts().chan("1300|easeInOutSine");
  * 
  * @param {string} value - gif configuration
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chan = function(value) {
  return this._clone('chan', value);
};

/**
  * doughnut chart inside label. The inside label holds at most 3,000 characters.
  * [Reference documentation]{@link https://documentation.image-charts.com/pie-charts/#inside-label}
  * @example
  * const chart = ImageCharts().chli("95K€");
  * const chart = ImageCharts().chli("45%");
  * 
  * @param {string} value - doughnut chart inside label. The inside label holds at most 3,000 characters.
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.chli = function(value) {
  return this._clone('chli', value);
};

/**
  * image-charts enterprise `account_id`
  * [Reference documentation]{@link https://documentation.image-charts.com/enterprise/}
  * @example
  * const chart = ImageCharts().icac("accountId");
  * 
  * @param {string} value - image-charts enterprise `account_id`
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.icac = function(value) {
  return this._clone('icac', value);
};

/**
  * HMAC-SHA256 signature required to activate paid features
  * [Reference documentation]{@link https://documentation.image-charts.com/enterprise/}
  * @example
  * const chart = ImageCharts().ichm("0785cf22a0381c2e0239e27c126de4181f501d117c2c81745611e9db928b0376");
  * 
  * @param {string} value - HMAC-SHA256 signature required to activate paid features
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.ichm = function(value) {
  return this._clone('ichm', value);
};

/**
  * How to use icff to define font family as Google Font : https://developers.google.com/fonts/docs/css2
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-font/}
  * @example
  * const chart = ImageCharts().icff("Abel");
  * const chart = ImageCharts().icff("Akronim");
  * const chart = ImageCharts().icff("Alfa Slab One");
  * 
  * @param {string} value - Default font family for all text from Google Fonts. Use same syntax as Google Font CSS API
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.icff = function(value) {
  return this._clone('icff', value);
};

/**
  * Default font style for all text
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/chart-font/}
  * @example
  * const chart = ImageCharts().icfs("normal");
  * const chart = ImageCharts().icfs("italic");
  * 
  * @param {string} value - Default font style for all text
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.icfs = function(value) {
  return this._clone('icfs', value);
};

/**
  * localization (ISO 639-1)
  * [Reference documentation]{@link }
  * @example
  * const chart = ImageCharts().iclocale("en");
  * 
  * @param {string} value - localization (ISO 639-1)
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.iclocale = function(value) {
  return this._clone('iclocale', value);
};

/**
  * Retina is a marketing term coined by Apple that refers to devices and monitors that have a resolution and pixel density so high — roughly 300 or more pixels per inch – that a person is unable to discern the individual pixels at a normal viewing distance.
	*           In order to generate beautiful charts for these Retina displays, Image-Charts supports a retina mode that can be activated through the icretina=1 parameter
  * [Reference documentation]{@link https://documentation.image-charts.com/reference/retina/}
  * @example
  * const chart = ImageCharts().icretina("1");
  * 
  * @param {string} value - retina mode
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.icretina = function(value) {
  return this._clone('icretina', value);
};

/**
  * Background color for QR Codes
  * [Reference documentation]{@link https://documentation.image-charts.com/qr-codes/#background-color}
  * @example
  * const chart = ImageCharts().icqrb("FFFFFF");
  * @default "FFFFFF"
  * @param {string} value - Background color for QR Codes
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.icqrb = function(value) {
  return this._clone('icqrb', value);
};

/**
  * Foreground color for QR Codes
  * [Reference documentation]{@link https://documentation.image-charts.com/qr-codes/#foreground-color}
  * @example
  * const chart = ImageCharts().icqrf("000000");
  * @default "000000"
  * @param {string} value - Foreground color for QR Codes
  * @return {ImageCharts.constructor}
  */
ImageCharts.prototype.icqrf = function(value) {
  return this._clone('icqrf', value);
};


/**
  * Get the full Image-Charts API url (signed and encoded if necessary)
  * @return {string} full generated url
  */
ImageCharts.prototype.toURL = function () {
  const url = new URL(`${this._protocol}://${this._host}`);

  /* istanbul ignore else */
  if(this._port) {url.port = this._port}

  url.pathname = this._pathname;

  const searchParams = new URLSearchParams(this._query);

  if (this._query.icac && this._secret && this._secret.length) {
    searchParams.append('ichm', crypto.createHmac('sha256', this._secret).update(searchParams.toString()).digest('hex'));
  }

  url.search = searchParams.toString();

  return url.toString();
};

/**
 * Do a request to Image-Charts API with current configuration and yield a promise of a NodeJS buffer
 * @param {Object} options - override default retry behavior
 * @return {Promise<Buffer>} binary image represented as a NodeJS Buffer wrapped inside a promise
 */
ImageCharts.prototype.toBuffer = function (options) {
  const _options = Object.assign({}, {
    // request retry
    maxAttempts: 3,   // retry 3 times
    retryDelay: 2000,  // wait 2s before trying again
    retryStrategy: request.RetryStrategies.HTTPOrNetworkError // retry on 5xx or network errors
  }, options || {}, {
    timeout: this._timeout,
    url: this.toURL(),
    headers: { 'User-Agent': this._userAgent || (`javascript-image-charts/${packageJson.version}` + (this._query.icac ? ' ' + `(${this._query.icac})` : '')) },
    encoding: null, // make response body to Buffer.
  });

  return request(_options).then(res => {
    if(res.statusCode >= 200 && res.statusCode < 300){
        res.body._response = res;
        res.body._request = _options;
        return res.body;
    }

    const validation_message = res.headers['x-ic-error-validation']; // undefined || string
    const validation_code = res.headers['x-ic-error-code']; // undefined || string
    let message = validation_message ? JSON.parse(validation_message).map(x => x.message).join('\n').trim() : '';
    /* istanbul ignore next */
    message = message.length > 0 ? message : validation_code ? validation_code : res.statusMessage;
    const err = new Error(message);
    /* istanbul ignore next */
    err.code = validation_code || res.statusMessage;
    err.statusCode = res.statusCode;
    err._response = res;
    err._request = _options;
    return Promise.reject(err);
  })
};

/**
 * Do a request to Image-Charts API with current configuration and writes the content inside a file
 * @return {Promise}
 */
ImageCharts.prototype.toFile = function (file) {
  return this.toBuffer().then(buffer =>
    new Promise((resolve, reject) =>
      fs.writeFile(file, buffer, (err) => err ? reject(err) : resolve())))
};

/**
 * Do a request to Image-Charts API with current configuration and yield a promise of a base64 encoded data URI
 * @return {Promise<String>} base64 data URI wrapped inside a promise
 */
ImageCharts.prototype.toDataURI = function () {
  const encoding = 'base64';
  const mimetype = this._query.chan ? 'image/gif' : 'image/png';
  return this.toBuffer().then(buffer => `data:${mimetype};${encoding},${buffer.toString(encoding)}`);
};

module.exports = ImageCharts;