/* @flow */

/**
 * Compares a string to a second value that, if it fits a certain convention,
 * is converted to a regular expression before the comparison.
 * If it doesn't fit the convention, then two strings are compared.
 *
 * Any strings starting and ending with `/` are interpreted
 * as regular expressions.
 */
module.exports = function matchesStringOrRegExp(
  input /*: string | Array<string>*/,
  comparison /*: string | Array<string>*/
) /*: false | { match: string, pattern: string}*/ {
  if (!Array.isArray(input)) {
    return testAgainstStringOrArray(input, comparison);
  }

  for (const inputItem of input) {
    const testResult = testAgainstStringOrArray(inputItem, comparison);
    if (testResult) {
      return testResult;
    }
  }

  return false;
};

function testAgainstStringOrArray(value, comparison) {
  if (!Array.isArray(comparison)) {
    return testAgainstString(value, comparison);
  }

  for (const comparisonItem of comparison) {
    const testResult = testAgainstString(value, comparisonItem);
    if (testResult) {
      return testResult;
    }
  }
  return false;
}

function testAgainstString(value, comparison) {
  const firstComparisonChar = comparison[0];
  const lastComparisonChar = comparison[comparison.length - 1];
  const secondToLastComparisonChar = comparison[comparison.length - 2];

  const comparisonIsRegex =
    firstComparisonChar === "/" &&
    (lastComparisonChar === "/" ||
      (secondToLastComparisonChar === "/" && lastComparisonChar === "i"));

  const hasCaseInsensitiveFlag =
    comparisonIsRegex && lastComparisonChar === "i";

  if (comparisonIsRegex) {
    const valueMatches = hasCaseInsensitiveFlag
      ? new RegExp(comparison.slice(1, -2), "i").test(value)
      : new RegExp(comparison.slice(1, -1)).test(value);
    return valueMatches ? { match: value, pattern: comparison } : false;
  }

  return value === comparison ? { match: value, pattern: comparison } : false;
}