url-relative

r.ts

import { resolve } from 'https://deno.land/std@0.105.0/path/posix.ts';

const CHAR_FORWARD_SLASH = 47;

/**
 * Return the relative path from `from` to `to` based on current working directory.
 * @param from path in current working directory
 * @param to path in current working directory
 */
export function relative(origFrom: string, origTo: string): string {
  if (origFrom === origTo) return "";

  let from = resolve(origFrom);
  let to = resolve(origTo);

  if (from === to) return "";

  // Trim any leading backslashes
  let fromStart = 1;
  const fromEnd = from.length;
  for (; fromStart < fromEnd; ++fromStart) {
    if (from.charCodeAt(fromStart) !== CHAR_FORWARD_SLASH) break;
  }
  const fromLen = fromEnd - fromStart;

  // Trim any leading backslashes
  let toStart = 1;
  const toEnd = to.length;
  for (; toStart < toEnd; ++toStart) {
    if (to.charCodeAt(toStart) !== CHAR_FORWARD_SLASH) break;
  }
  const toLen = toEnd - toStart;

  // Compare paths to find the longest common path from root
  const length = fromLen < toLen ? fromLen : toLen;
  let lastCommonSep = -1;
  let i = 0;
  for (; i <= length; ++i) {
    if (i === length) {
      if (toLen > length) {
        if (to.charCodeAt(toStart + i) === CHAR_FORWARD_SLASH) {
          // We get here if `from` is the exact base path for `to`.
          // For example: from='/foo/bar'; to='/foo/bar/baz'
          if(origFrom.charCodeAt(fromStart + i) === CHAR_FORWARD_SLASH) {
            return to.slice(toStart + i + 1);
          } else {
            return to.slice(toStart + lastCommonSep + 1);
          }
        } else if (i === 0) {
          // We get here if `from` is the root
          // For example: from='/'; to='/foo'
          return to.slice(toStart + i);
        }
      } else if (fromLen > length) {
        if (from.charCodeAt(fromStart + i) === CHAR_FORWARD_SLASH) {
          // We get here if `to` is the exact base path for `from`.
          // For example: from='/foo/bar/baz'; to='/foo/bar'
          lastCommonSep = i;
        } else if (i === 0) {
          // We get here if `to` is the root.
          // For example: from='/foo'; to='/'
          lastCommonSep = 0;
        }
      }
      break;
    }
    const fromCode = from.charCodeAt(fromStart + i);
    const toCode = to.charCodeAt(toStart + i);
    if (fromCode !== toCode) break;
    else if (fromCode === CHAR_FORWARD_SLASH) lastCommonSep = i;
  }

  let out = "";
  // Generate the relative path based on the path difference between `to`
  // and `from`
  for (i = fromStart + lastCommonSep + 1; i <= fromEnd; ++i) {
    if (i === fromEnd || from.charCodeAt(i) === CHAR_FORWARD_SLASH) {
      if (out.length === 0) out += "..";
      else out += "/..";
    }
  }

  // Lastly, append the rest of the destination (`to`) path that comes after
  // the common path parts
  if (out.length > 0) return out + to.slice(toStart + lastCommonSep);
  else {
    toStart += lastCommonSep;
    if (to.charCodeAt(toStart) === CHAR_FORWARD_SLASH) ++toStart;
    return to.slice(toStart);
  }
}