/* eslint-disable no-var, prefer-template */
var uppercasePattern = /[A-Z]/g;
var msPattern = /^ms-/;
var cache = {};

function toHyphenLower(match) {
  return '-' + match.toLowerCase()
}

function hyphenateStyleName(name) {
  if (cache.hasOwnProperty(name)) {
    return cache[name]
  }

  var hName = name.replace(uppercasePattern, toHyphenLower);
  return (cache[name] = msPattern.test(hName) ? '-' + hName : hName)
}

/**
 * Convert camel cased property names to dash separated.
 *
 * @param {Object} style
 * @return {Object}
 */

function convertCase(style) {
  var converted = {};

  for (var prop in style) {
    var key = prop.indexOf('--') === 0 ? prop : hyphenateStyleName(prop);
    converted[key] = style[prop];
  }

  if (style.fallbacks) {
    if (Array.isArray(style.fallbacks)) converted.fallbacks = style.fallbacks.map(convertCase);else converted.fallbacks = convertCase(style.fallbacks);
  }

  return converted;
}
/**
 * Allow camel cased property names by converting them back to dasherized.
 *
 * @param {Rule} rule
 */


function camelCase() {
  function onProcessStyle(style) {
    if (Array.isArray(style)) {
      // Handle rules like @font-face, which can have multiple styles in an array
      for (var index = 0; index < style.length; index++) {
        style[index] = convertCase(style[index]);
      }

      return style;
    }

    return convertCase(style);
  }

  function onChangeValue(value, prop, rule) {
    if (prop.indexOf('--') === 0) {
      return value;
    }

    var hyphenatedProp = hyphenateStyleName(prop); // There was no camel case in place

    if (prop === hyphenatedProp) return value;
    rule.prop(hyphenatedProp, value); // Core will ignore that property value we set the proper one above.

    return null;
  }

  return {
    onProcessStyle: onProcessStyle,
    onChangeValue: onChangeValue
  };
}

export default camelCase;
