/* @flow */
"use strict";

const _ = require("lodash");
const balancedMatch = require("balanced-match");

/**
 * Replace all of the characters that are arguments to a certain
 * CSS function with some innocuous character.
 *
 * This is useful if you need to use a RegExp to find a string
 * but want to ignore matches in certain functions (e.g. `url()`,
 * which might contain all kinds of false positives).
 *
 * For example:
 * blurFunctionArguments("abc url(abc) abc", "url") === "abc url(```) abc"
 *
 * @param {string} source
 * @param {string} functionName
 * @param {[string]} blurChar="`"
 * @return {string} - The result string, with the function arguments "blurred"
 */
module.exports = function(
  source /*: string*/,
  functionName /*: string*/
) /*: string*/ {
  const blurChar /*: string*/ =
    arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : "`";

  const nameWithParen = `${functionName.toLowerCase()}(`;
  const lowerCaseSource = source.toLowerCase();

  if (!_.includes(lowerCaseSource, nameWithParen)) {
    return source;
  }

  const functionNameLength /*: number*/ = functionName.length;

  let result = source;
  let searchStartIndex = 0;

  while (lowerCaseSource.indexOf(nameWithParen, searchStartIndex) !== -1) {
    const openingParenIndex =
      lowerCaseSource.indexOf(nameWithParen, searchStartIndex) +
      functionNameLength;
    const closingParenIndex =
      balancedMatch("(", ")", lowerCaseSource.slice(openingParenIndex)).end +
      openingParenIndex;
    const argumentsLength = closingParenIndex - openingParenIndex - 1;

    result =
      result.slice(0, openingParenIndex + 1) +
      _.repeat(blurChar, argumentsLength) +
      result.slice(closingParenIndex);
    searchStartIndex = closingParenIndex;
  }

  return result;
};