// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
import { CHAR_BACKWARD_SLASH } from "../_common/constants.ts";
import { resolve } from "./resolve.ts";
import { assertArgs } from "../_common/relative.ts";
/**
 * Return the relative path from `from` to `to` based on current working directory.
 *
 * An example in windws, for instance:
 *  from = 'C:\\orandea\\test\\aaa'
 *  to = 'C:\\orandea\\impl\\bbb'
 * The output of the function should be: '..\\..\\impl\\bbb'
 *
 * @param from path in current working directory
 * @param to path in current working directory
 */ export function relative(from, to) {
  assertArgs(from, to);
  const fromOrig = resolve(from);
  const toOrig = resolve(to);
  if (fromOrig === toOrig) return "";
  from = fromOrig.toLowerCase();
  to = toOrig.toLowerCase();
  if (from === to) return "";
  // Trim any leading backslashes
  let fromStart = 0;
  let fromEnd = from.length;
  for(; fromStart < fromEnd; ++fromStart){
    if (from.charCodeAt(fromStart) !== CHAR_BACKWARD_SLASH) break;
  }
  // Trim trailing backslashes (applicable to UNC paths only)
  for(; fromEnd - 1 > fromStart; --fromEnd){
    if (from.charCodeAt(fromEnd - 1) !== CHAR_BACKWARD_SLASH) break;
  }
  const fromLen = fromEnd - fromStart;
  // Trim any leading backslashes
  let toStart = 0;
  let toEnd = to.length;
  for(; toStart < toEnd; ++toStart){
    if (to.charCodeAt(toStart) !== CHAR_BACKWARD_SLASH) break;
  }
  // Trim trailing backslashes (applicable to UNC paths only)
  for(; toEnd - 1 > toStart; --toEnd){
    if (to.charCodeAt(toEnd - 1) !== CHAR_BACKWARD_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_BACKWARD_SLASH) {
          // We get here if `from` is the exact base path for `to`.
          // For example: from='C:\\foo\\bar'; to='C:\\foo\\bar\\baz'
          return toOrig.slice(toStart + i + 1);
        } else if (i === 2) {
          // We get here if `from` is the device root.
          // For example: from='C:\\'; to='C:\\foo'
          return toOrig.slice(toStart + i);
        }
      }
      if (fromLen > length) {
        if (from.charCodeAt(fromStart + i) === CHAR_BACKWARD_SLASH) {
          // We get here if `to` is the exact base path for `from`.
          // For example: from='C:\\foo\\bar'; to='C:\\foo'
          lastCommonSep = i;
        } else if (i === 2) {
          // We get here if `to` is the device root.
          // For example: from='C:\\foo\\bar'; to='C:\\'
          lastCommonSep = 3;
        }
      }
      break;
    }
    const fromCode = from.charCodeAt(fromStart + i);
    const toCode = to.charCodeAt(toStart + i);
    if (fromCode !== toCode) break;
    else if (fromCode === CHAR_BACKWARD_SLASH) lastCommonSep = i;
  }
  // We found a mismatch before the first common path separator was seen, so
  // return the original `to`.
  if (i !== length && lastCommonSep === -1) {
    return toOrig;
  }
  let out = "";
  if (lastCommonSep === -1) lastCommonSep = 0;
  // 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_BACKWARD_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 + toOrig.slice(toStart + lastCommonSep, toEnd);
  } else {
    toStart += lastCommonSep;
    if (toOrig.charCodeAt(toStart) === CHAR_BACKWARD_SLASH) ++toStart;
    return toOrig.slice(toStart, toEnd);
  }
}
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