'use strict';

/* eslint-disable consistent-return */

function isWhiteSpace(chr) {
  return chr === 0x20 || chr === 0x09 || chr === 0x0D || chr === 0x0A;
}

// Filter NaN, Infinity, < 0
function isFinitePositive(val) {
  return typeof val === 'number' && isFinite(val) && val > 0;
}

function canBeSvg(buf) {
  var i = 0, max = buf.length;

  // byte order mark, https://github.com/nodeca/probe-image-size/issues/57
  if (buf[0] === 0xEF && buf[1] === 0xBB && buf[2] === 0xBF) i = 3;

  while (i < max && isWhiteSpace(buf[i])) i++;

  if (i === max) return false;
  return buf[i] === 0x3c; /* < */
}


// skip `<?` (comments), `<!` (directives, cdata, doctype),
// looking for `<svg>` or `<NAMESPACE:svg>`
var SVG_HEADER_RE  = /<[-_.:a-zA-Z0-9][^>]*>/;

// test if the top level element is svg + optional namespace,
// used to skip svg embedded in html
var SVG_TAG_RE     = /^<([-_.:a-zA-Z0-9]+:)?svg\s/;

var SVG_WIDTH_RE   = /[^-]\bwidth="([^%]+?)"|[^-]\bwidth='([^%]+?)'/;
var SVG_HEIGHT_RE  = /\bheight="([^%]+?)"|\bheight='([^%]+?)'/;
var SVG_VIEWBOX_RE = /\bview[bB]ox="(.+?)"|\bview[bB]ox='(.+?)'/;
var SVG_UNITS_RE   = /in$|mm$|cm$|pt$|pc$|px$|em$|ex$/;

function svgAttrs(str) {
  var width   = str.match(SVG_WIDTH_RE);
  var height  = str.match(SVG_HEIGHT_RE);
  var viewbox = str.match(SVG_VIEWBOX_RE);

  return {
    width:   width && (width[1] || width[2]),
    height:  height && (height[1] || height[2]),
    viewbox: viewbox && (viewbox[1] || viewbox[2])
  };
}


function units(str) {
  if (!SVG_UNITS_RE.test(str)) return 'px';

  return str.match(SVG_UNITS_RE)[0];
}


module.exports = function (data) {
  if (!canBeSvg(data)) return;

  var str = '';

  for (var i = 0; i < data.length; i++) {
    // 1. We can't rely on buffer features
    // 2. Don't care about UTF16 because ascii is enougth for our goals
    str += String.fromCharCode(data[i]);
  }

  // get top level element
  var svgTag = (str.match(SVG_HEADER_RE) || [ '' ])[0];

  // test if top level element is <svg>
  if (!SVG_TAG_RE.test(svgTag)) return;

  var attrs  = svgAttrs(svgTag);
  var width  = parseFloat(attrs.width);
  var height = parseFloat(attrs.height);

  // Extract from direct values

  if (attrs.width && attrs.height) {
    if (!isFinitePositive(width) || !isFinitePositive(height)) return;

    return {
      width:  width,
      height: height,
      type:   'svg',
      mime:   'image/svg+xml',
      wUnits: units(attrs.width),
      hUnits: units(attrs.height)
    };
  }

  // Extract from viewbox

  var parts = (attrs.viewbox || '').split(' ');
  var viewbox = {
    width:  parts[2],
    height: parts[3]
  };
  var vbWidth  = parseFloat(viewbox.width);
  var vbHeight = parseFloat(viewbox.height);

  if (!isFinitePositive(vbWidth) || !isFinitePositive(vbHeight)) return;
  if (units(viewbox.width) !== units(viewbox.height)) return;

  var ratio = vbWidth / vbHeight;

  if (attrs.width) {
    if (!isFinitePositive(width)) return;

    return {
      width:  width,
      height: width / ratio,
      type:   'svg',
      mime:   'image/svg+xml',
      wUnits: units(attrs.width),
      hUnits: units(attrs.width)
    };
  }

  if (attrs.height) {
    if (!isFinitePositive(height)) return;

    return {
      width:  height * ratio,
      height: height,
      type:   'svg',
      mime:   'image/svg+xml',
      wUnits: units(attrs.height),
      hUnits: units(attrs.height)
    };
  }

  return {
    width:  vbWidth,
    height: vbHeight,
    type:   'svg',
    mime:   'image/svg+xml',
    wUnits: units(viewbox.width),
    hUnits: units(viewbox.height)
  };
};