index.js

const pxRegex = require("./lib/pixel-unit-regex");
const filterPropList = require("./lib/filter-prop-list");
const type = require("./lib/type");
const defaults = {
  rootValue: 16,
  unitPrecision: 5,
  selectorBlackList: [],
  propList: ["font", "font-size", "line-height", "letter-spacing"],
  replace: true,
  mediaQuery: false,
  minPixelValue: 0,
  exclude: /node_modules/i
};

const legacyOptions = {
  root_value: "rootValue",
  unit_precision: "unitPrecision",
  selector_black_list: "selectorBlackList",
  prop_white_list: "propList",
  media_query: "mediaQuery",
  propWhiteList: "propList"
};

function convertLegacyOptions(options) {
  if (typeof options !== "object") return;
  if (
    ((typeof options["prop_white_list"] !== "undefined" &&
      options["prop_white_list"].length === 0) ||
      (typeof options.propWhiteList !== "undefined" &&
        options.propWhiteList.length === 0)) &&
    typeof options.propList === "undefined"
  ) {
    options.propList = ["*"];
    delete options["prop_white_list"];
    delete options.propWhiteList;
  }
  Object.keys(legacyOptions).forEach(key => {
    if (Reflect.has(options, key)) {
      options[legacyOptions[key]] = options[key];
      delete options[key];
    }
  });
}

function createPropListMatcher(propList) {
  const hasWild = propList.indexOf("*") > -1;
  const matchAll = hasWild && propList.length === 1;
  const lists = {
    exact: filterPropList.exact(propList),
    contain: filterPropList.contain(propList),
    startWith: filterPropList.startWith(propList),
    endWith: filterPropList.endWith(propList),
    notExact: filterPropList.notExact(propList),
    notContain: filterPropList.notContain(propList),
    notStartWith: filterPropList.notStartWith(propList),
    notEndWith: filterPropList.notEndWith(propList)
  };
  return prop => {
    if (matchAll) return true;
    return (
      (hasWild ||
        lists.exact.indexOf(prop) > -1 ||
        lists.contain.some(function(m) {
          return prop.indexOf(m) > -1;
        }) ||
        lists.startWith.some(function(m) {
          return prop.indexOf(m) === 0;
        }) ||
        lists.endWith.some(function(m) {
          return prop.indexOf(m) === prop.length - m.length;
        })) &&
      !(
        lists.notExact.indexOf(prop) > -1 ||
        lists.notContain.some(function(m) {
          return prop.indexOf(m) > -1;
        }) ||
        lists.notStartWith.some(function(m) {
          return prop.indexOf(m) === 0;
        }) ||
        lists.notEndWith.some(function(m) {
          return prop.indexOf(m) === prop.length - m.length;
        })
      )
    );
  };
}

function createPxReplace(rootValue, unitPrecision, minPixelValue) {
  return (m, $1) => {
    if (!$1) return m;
    const pixels = parseFloat($1);
    if (pixels < minPixelValue) return m;
    const fixedVal = toFixed(pixels / rootValue, unitPrecision);
    return fixedVal === 0 ? "0" : fixedVal + "rem";
  };
}

function blacklistedSelector(blacklist, selector) {
  //  TODO: how to type selector non-string
  // if (typeof selector !== "string") return;
  return blacklist.some(regex => {
    if (typeof regex === "string") {
      return selector.indexOf(regex) !== -1;
    }
    return selector.match(regex);
  });
}

function toFixed(number, precision) {
  const multiplier = Math.pow(10, precision + 1),
    wholeNumber = Math.floor(number * multiplier);
  return (Math.round(wholeNumber / 10) * 10) / multiplier;
}

function declarationExists(decls, prop, value) {
  return decls.some(decl => decl.prop === prop && decl.value === value);
}


module.exports = (opts = { }) => {
    convertLegacyOptions(opts);
    opts = Object.assign({}, defaults, opts);
    const satisfyPropList = createPropListMatcher(opts.propList);
    const exclude = opts.exclude;


    let rootValue, pxReplace

    // Work with options here
    return {
        postcssPlugin: 'postcss-px2rem-media',
        Once (root) {
          // Calls once per file, since every file has single Root
          rootValue =
      typeof opts.rootValue === "function"
        ? opts.rootValue(root.source.input)
        : opts.rootValue;
    pxReplace = createPxReplace(
      rootValue,
      opts.unitPrecision,
      opts.minPixelValue
    );
        },
        AtRule: {
          media: atRule => {
            // All @media at-rules
            if (opts.mediaQuery) {
                if (atRule.params.indexOf("px") === -1) return;
                atRule.params = atRule.params.replace(pxRegex, pxReplace);
            }
            const filePath = atRule.source.input.file;
            if (
              exclude &&
              ((type.isFunction(exclude) && exclude(filePath)) ||
                (type.isString(exclude) && filePath.indexOf(exclude) !== -1) ||
                filePath.match(exclude) !== null)
            ) {
              return
            }
            atRule.walkDecls((decl, i) => {
              if (
                decl.value.indexOf("px") === -1 ||
                !satisfyPropList(decl.prop) ||
                blacklistedSelector(opts.selectorBlackList, decl.parent.selector)
              )
                return;

              const value = decl.value.replace(pxRegex, pxReplace);
              // if rem unit already exists, do not add or replace
              if (declarationExists(decl.parent, decl.prop, value)) return;

              if (opts.replace) {
                decl.value = value;
              } else {
                decl.parent.insertAfter(i, decl.clone({ value: value }));
              }
            });
          }
        }
      }
  }
  module.exports.postcss = true