'use strict'

const { posix: path } = require('path')

/**
 * Computes the shortest relative path between two URLs.
 *
 * This function takes into account directory index URLs and extensionless
 * URLs. It assumes it's working with root-relative URLs, not absolute URLs.
 *
 * @memberof asciidoc-loader
 *
 * @param {String} from - The root-relative start URL.
 * @param {String} to - The root-relative target URL.
 * @param {String} [hash=''] - The URL hash to append to the URL (not #).
 *
 * @returns {String} The shortest relative path to travel from the start URL to the target URL.
 */
function computeRelativeUrlPath (from, to, hash = '') {
  if (to.charAt() !== '/') return to + hash
  if (to === from) return hash || (isDir(to) ? './' : path.basename(to))
  const rel = path.relative(path.dirname(from + '.'), to)
  return rel ? (isDir(to) ? rel + '/' : rel) + hash : (isDir(to) ? './' : '../' + path.basename(to)) + hash
}

function isDir (str) {
  return str.charAt(str.length - 1) === '/'
}

module.exports = computeRelativeUrlPath