// Copyright the Browserify authors. MIT License.
// Ported from https://github.com/browserify/path-browserify/

const { cwd, env } = Deno;
import { FormatInputPathObject, ParsedPath } from "./interface.ts";
import {
  CHAR_DOT,
  CHAR_BACKWARD_SLASH,
  CHAR_COLON,
  CHAR_QUESTION_MARK
} from "./constants.ts";

import {
  assertPath,
  isPathSeparator,
  isWindowsDeviceRoot,
  normalizeString,
  _format
} from "./utils.ts";
import { assert } from "../testing/asserts.ts";

export const sep = "\\";
export const delimiter = ";";

export function resolve(...pathSegments: string[]): string {
  let resolvedDevice = "";
  let resolvedTail = "";
  let resolvedAbsolute = false;

  for (let i = pathSegments.length - 1; i >= -1; i--) {
    let path: string;
    if (i >= 0) {
      path = pathSegments[i];
    } else if (!resolvedDevice) {
      path = cwd();
    } else {
      // Windows has the concept of drive-specific current working
      // directories. If we've resolved a drive letter but not yet an
      // absolute path, get cwd for that drive, or the process cwd if
      // the drive cwd is not available. We're sure the device is not
      // a UNC path at this points, because UNC paths are always absolute.
      path = env()[`=${resolvedDevice}`] || cwd();

      // Verify that a cwd was found and that it actually points
      // to our drive. If not, default to the drive's root.
      if (
        path === undefined ||
        path.slice(0, 3).toLowerCase() !== `${resolvedDevice.toLowerCase()}\\`
      ) {
        path = `${resolvedDevice}\\`;
      }
    }

    assertPath(path);

    const len = path.length;

    // Skip empty entries
    if (len === 0) continue;

    let rootEnd = 0;
    let device = "";
    let isAbsolute = false;
    const code = path.charCodeAt(0);

    // Try to match a root
    if (len > 1) {
      if (isPathSeparator(code)) {
        // Possible UNC root

        // If we started with a separator, we know we at least have an
        // absolute path of some kind (UNC or otherwise)
        isAbsolute = true;

        if (isPathSeparator(path.charCodeAt(1))) {
          // Matched double path separator at beginning
          let j = 2;
          let last = j;
          // Match 1 or more non-path separators
          for (; j < len; ++j) {
            if (isPathSeparator(path.charCodeAt(j))) break;
          }
          if (j < len && j !== last) {
            const firstPart = path.slice(last, j);
            // Matched!
            last = j;
            // Match 1 or more path separators
            for (; j < len; ++j) {
              if (!isPathSeparator(path.charCodeAt(j))) break;
            }
            if (j < len && j !== last) {
              // Matched!
              last = j;
              // Match 1 or more non-path separators
              for (; j < len; ++j) {
                if (isPathSeparator(path.charCodeAt(j))) break;
              }
              if (j === len) {
                // We matched a UNC root only
                device = `\\\\${firstPart}\\${path.slice(last)}`;
                rootEnd = j;
              } else if (j !== last) {
                // We matched a UNC root with leftovers

                device = `\\\\${firstPart}\\${path.slice(last, j)}`;
                rootEnd = j;
              }
            }
          }
        } else {
          rootEnd = 1;
        }
      } else if (isWindowsDeviceRoot(code)) {
        // Possible device root

        if (path.charCodeAt(1) === CHAR_COLON) {
          device = path.slice(0, 2);
          rootEnd = 2;
          if (len > 2) {
            if (isPathSeparator(path.charCodeAt(2))) {
              // Treat separator following drive name as an absolute path
              // indicator
              isAbsolute = true;
              rootEnd = 3;
            }
          }
        }
      }
    } else if (isPathSeparator(code)) {
      // `path` contains just a path separator
      rootEnd = 1;
      isAbsolute = true;
    }

    if (
      device.length > 0 &&
      resolvedDevice.length > 0 &&
      device.toLowerCase() !== resolvedDevice.toLowerCase()
    ) {
      // This path points to another device so it is not applicable
      continue;
    }

    if (resolvedDevice.length === 0 && device.length > 0) {
      resolvedDevice = device;
    }
    if (!resolvedAbsolute) {
      resolvedTail = `${path.slice(rootEnd)}\\${resolvedTail}`;
      resolvedAbsolute = isAbsolute;
    }

    if (resolvedAbsolute && resolvedDevice.length > 0) break;
  }

  // At this point the path should be resolved to a full absolute path,
  // but handle relative paths to be safe (might happen when process.cwd()
  // fails)

  // Normalize the tail path
  resolvedTail = normalizeString(
    resolvedTail,
    !resolvedAbsolute,
    "\\",
    isPathSeparator
  );

  return resolvedDevice + (resolvedAbsolute ? "\\" : "") + resolvedTail || ".";
}

export function normalize(path: string): string {
  assertPath(path);
  const len = path.length;
  if (len === 0) return ".";
  let rootEnd = 0;
  let device: string | undefined;
  let isAbsolute = false;
  const code = path.charCodeAt(0);

  // Try to match a root
  if (len > 1) {
    if (isPathSeparator(code)) {
      // Possible UNC root

      // If we started with a separator, we know we at least have an absolute
      // path of some kind (UNC or otherwise)
      isAbsolute = true;

      if (isPathSeparator(path.charCodeAt(1))) {
        // Matched double path separator at beginning
        let j = 2;
        let last = j;
        // Match 1 or more non-path separators
        for (; j < len; ++j) {
          if (isPathSeparator(path.charCodeAt(j))) break;
        }
        if (j < len && j !== last) {
          const firstPart = path.slice(last, j);
          // Matched!
          last = j;
          // Match 1 or more path separators
          for (; j < len; ++j) {
            if (!isPathSeparator(path.charCodeAt(j))) break;
          }
          if (j < len && j !== last) {
            // Matched!
            last = j;
            // Match 1 or more non-path separators
            for (; j < len; ++j) {
              if (isPathSeparator(path.charCodeAt(j))) break;
            }
            if (j === len) {
              // We matched a UNC root only
              // Return the normalized version of the UNC root since there
              // is nothing left to process

              return `\\\\${firstPart}\\${path.slice(last)}\\`;
            } else if (j !== last) {
              // We matched a UNC root with leftovers

              device = `\\\\${firstPart}\\${path.slice(last, j)}`;
              rootEnd = j;
            }
          }
        }
      } else {
        rootEnd = 1;
      }
    } else if (isWindowsDeviceRoot(code)) {
      // Possible device root

      if (path.charCodeAt(1) === CHAR_COLON) {
        device = path.slice(0, 2);
        rootEnd = 2;
        if (len > 2) {
          if (isPathSeparator(path.charCodeAt(2))) {
            // Treat separator following drive name as an absolute path
            // indicator
            isAbsolute = true;
            rootEnd = 3;
          }
        }
      }
    }
  } else if (isPathSeparator(code)) {
    // `path` contains just a path separator, exit early to avoid unnecessary
    // work
    return "\\";
  }

  let tail: string;
  if (rootEnd < len) {
    tail = normalizeString(
      path.slice(rootEnd),
      !isAbsolute,
      "\\",
      isPathSeparator
    );
  } else {
    tail = "";
  }
  if (tail.length === 0 && !isAbsolute) tail = ".";
  if (tail.length > 0 && isPathSeparator(path.charCodeAt(len - 1)))
    tail += "\\";
  if (device === undefined) {
    if (isAbsolute) {
      if (tail.length > 0) return `\\${tail}`;
      else return "\\";
    } else if (tail.length > 0) {
      return tail;
    } else {
      return "";
    }
  } else if (isAbsolute) {
    if (tail.length > 0) return `${device}\\${tail}`;
    else return `${device}\\`;
  } else if (tail.length > 0) {
    return device + tail;
  } else {
    return device;
  }
}

export function isAbsolute(path: string): boolean {
  assertPath(path);
  const len = path.length;
  if (len === 0) return false;

  const code = path.charCodeAt(0);
  if (isPathSeparator(code)) {
    return true;
  } else if (isWindowsDeviceRoot(code)) {
    // Possible device root

    if (len > 2 && path.charCodeAt(1) === CHAR_COLON) {
      if (isPathSeparator(path.charCodeAt(2))) return true;
    }
  }
  return false;
}

export function join(...paths: string[]): string {
  const pathsCount = paths.length;
  if (pathsCount === 0) return ".";

  let joined: string | undefined;
  let firstPart: string;
  for (let i = 0; i < pathsCount; ++i) {
    const path = paths[i];
    assertPath(path);
    if (path.length > 0) {
      if (joined === undefined) joined = firstPart = path;
      else joined += `\\${path}`;
    }
  }

  if (joined === undefined) return ".";

  // Make sure that the joined path doesn't start with two slashes, because
  // normalize() will mistake it for an UNC path then.
  //
  // This step is skipped when it is very clear that the user actually
  // intended to point at an UNC path. This is assumed when the first
  // non-empty string arguments starts with exactly two slashes followed by
  // at least one more non-slash character.
  //
  // Note that for normalize() to treat a path as an UNC path it needs to
  // have at least 2 components, so we don't filter for that here.
  // This means that the user can use join to construct UNC paths from
  // a server name and a share name; for example:
  //   path.join('//server', 'share') -> '\\\\server\\share\\')
  let needsReplace = true;
  let slashCount = 0;
  assert(firstPart != null);
  if (isPathSeparator(firstPart.charCodeAt(0))) {
    ++slashCount;
    const firstLen = firstPart.length;
    if (firstLen > 1) {
      if (isPathSeparator(firstPart.charCodeAt(1))) {
        ++slashCount;
        if (firstLen > 2) {
          if (isPathSeparator(firstPart.charCodeAt(2))) ++slashCount;
          else {
            // We matched a UNC path in the first part
            needsReplace = false;
          }
        }
      }
    }
  }
  if (needsReplace) {
    // Find any more consecutive slashes we need to replace
    for (; slashCount < joined.length; ++slashCount) {
      if (!isPathSeparator(joined.charCodeAt(slashCount))) break;
    }

    // Replace the slashes if needed
    if (slashCount >= 2) joined = `\\${joined.slice(slashCount)}`;
  }

  return normalize(joined);
}

// It will solve the relative path from `from` to `to`, for instance:
//  from = 'C:\\orandea\\test\\aaa'
//  to = 'C:\\orandea\\impl\\bbb'
// The output of the function should be: '..\\..\\impl\\bbb'
export function relative(from: string, to: string): string {
  assertPath(from);
  assertPath(to);

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

  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);
  }
}

export function toNamespacedPath(path: string): string {
  // Note: this will *probably* throw somewhere.
  if (typeof path !== "string") return path;
  if (path.length === 0) return "";

  const resolvedPath = resolve(path);

  if (resolvedPath.length >= 3) {
    if (resolvedPath.charCodeAt(0) === CHAR_BACKWARD_SLASH) {
      // Possible UNC root

      if (resolvedPath.charCodeAt(1) === CHAR_BACKWARD_SLASH) {
        const code = resolvedPath.charCodeAt(2);
        if (code !== CHAR_QUESTION_MARK && code !== CHAR_DOT) {
          // Matched non-long UNC root, convert the path to a long UNC path
          return `\\\\?\\UNC\\${resolvedPath.slice(2)}`;
        }
      }
    } else if (isWindowsDeviceRoot(resolvedPath.charCodeAt(0))) {
      // Possible device root

      if (
        resolvedPath.charCodeAt(1) === CHAR_COLON &&
        resolvedPath.charCodeAt(2) === CHAR_BACKWARD_SLASH
      ) {
        // Matched device root, convert the path to a long UNC path
        return `\\\\?\\${resolvedPath}`;
      }
    }
  }

  return path;
}

export function dirname(path: string): string {
  assertPath(path);
  const len = path.length;
  if (len === 0) return ".";
  let rootEnd = -1;
  let end = -1;
  let matchedSlash = true;
  let offset = 0;
  const code = path.charCodeAt(0);

  // Try to match a root
  if (len > 1) {
    if (isPathSeparator(code)) {
      // Possible UNC root

      rootEnd = offset = 1;

      if (isPathSeparator(path.charCodeAt(1))) {
        // Matched double path separator at beginning
        let j = 2;
        let last = j;
        // Match 1 or more non-path separators
        for (; j < len; ++j) {
          if (isPathSeparator(path.charCodeAt(j))) break;
        }
        if (j < len && j !== last) {
          // Matched!
          last = j;
          // Match 1 or more path separators
          for (; j < len; ++j) {
            if (!isPathSeparator(path.charCodeAt(j))) break;
          }
          if (j < len && j !== last) {
            // Matched!
            last = j;
            // Match 1 or more non-path separators
            for (; j < len; ++j) {
              if (isPathSeparator(path.charCodeAt(j))) break;
            }
            if (j === len) {
              // We matched a UNC root only
              return path;
            }
            if (j !== last) {
              // We matched a UNC root with leftovers

              // Offset by 1 to include the separator after the UNC root to
              // treat it as a "normal root" on top of a (UNC) root
              rootEnd = offset = j + 1;
            }
          }
        }
      }
    } else if (isWindowsDeviceRoot(code)) {
      // Possible device root

      if (path.charCodeAt(1) === CHAR_COLON) {
        rootEnd = offset = 2;
        if (len > 2) {
          if (isPathSeparator(path.charCodeAt(2))) rootEnd = offset = 3;
        }
      }
    }
  } else if (isPathSeparator(code)) {
    // `path` contains just a path separator, exit early to avoid
    // unnecessary work
    return path;
  }

  for (let i = len - 1; i >= offset; --i) {
    if (isPathSeparator(path.charCodeAt(i))) {
      if (!matchedSlash) {
        end = i;
        break;
      }
    } else {
      // We saw the first non-path separator
      matchedSlash = false;
    }
  }

  if (end === -1) {
    if (rootEnd === -1) return ".";
    else end = rootEnd;
  }
  return path.slice(0, end);
}

export function basename(path: string, ext = ""): string {
  if (ext !== undefined && typeof ext !== "string")
    throw new TypeError('"ext" argument must be a string');

  assertPath(path);

  let start = 0;
  let end = -1;
  let matchedSlash = true;
  let i: number;

  // Check for a drive letter prefix so as not to mistake the following
  // path separator as an extra separator at the end of the path that can be
  // disregarded
  if (path.length >= 2) {
    const drive = path.charCodeAt(0);
    if (isWindowsDeviceRoot(drive)) {
      if (path.charCodeAt(1) === CHAR_COLON) start = 2;
    }
  }

  if (ext !== undefined && ext.length > 0 && ext.length <= path.length) {
    if (ext.length === path.length && ext === path) return "";
    let extIdx = ext.length - 1;
    let firstNonSlashEnd = -1;
    for (i = path.length - 1; i >= start; --i) {
      const code = path.charCodeAt(i);
      if (isPathSeparator(code)) {
        // If we reached a path separator that was not part of a set of path
        // separators at the end of the string, stop now
        if (!matchedSlash) {
          start = i + 1;
          break;
        }
      } else {
        if (firstNonSlashEnd === -1) {
          // We saw the first non-path separator, remember this index in case
          // we need it if the extension ends up not matching
          matchedSlash = false;
          firstNonSlashEnd = i + 1;
        }
        if (extIdx >= 0) {
          // Try to match the explicit extension
          if (code === ext.charCodeAt(extIdx)) {
            if (--extIdx === -1) {
              // We matched the extension, so mark this as the end of our path
              // component
              end = i;
            }
          } else {
            // Extension does not match, so our result is the entire path
            // component
            extIdx = -1;
            end = firstNonSlashEnd;
          }
        }
      }
    }

    if (start === end) end = firstNonSlashEnd;
    else if (end === -1) end = path.length;
    return path.slice(start, end);
  } else {
    for (i = path.length - 1; i >= start; --i) {
      if (isPathSeparator(path.charCodeAt(i))) {
        // If we reached a path separator that was not part of a set of path
        // separators at the end of the string, stop now
        if (!matchedSlash) {
          start = i + 1;
          break;
        }
      } else if (end === -1) {
        // We saw the first non-path separator, mark this as the end of our
        // path component
        matchedSlash = false;
        end = i + 1;
      }
    }

    if (end === -1) return "";
    return path.slice(start, end);
  }
}

export function extname(path: string): string {
  assertPath(path);
  let start = 0;
  let startDot = -1;
  let startPart = 0;
  let end = -1;
  let matchedSlash = true;
  // Track the state of characters (if any) we see before our first dot and
  // after any path separator we find
  let preDotState = 0;

  // Check for a drive letter prefix so as not to mistake the following
  // path separator as an extra separator at the end of the path that can be
  // disregarded

  if (
    path.length >= 2 &&
    path.charCodeAt(1) === CHAR_COLON &&
    isWindowsDeviceRoot(path.charCodeAt(0))
  ) {
    start = startPart = 2;
  }

  for (let i = path.length - 1; i >= start; --i) {
    const code = path.charCodeAt(i);
    if (isPathSeparator(code)) {
      // If we reached a path separator that was not part of a set of path
      // separators at the end of the string, stop now
      if (!matchedSlash) {
        startPart = i + 1;
        break;
      }
      continue;
    }
    if (end === -1) {
      // We saw the first non-path separator, mark this as the end of our
      // extension
      matchedSlash = false;
      end = i + 1;
    }
    if (code === CHAR_DOT) {
      // If this is our first dot, mark it as the start of our extension
      if (startDot === -1) startDot = i;
      else if (preDotState !== 1) preDotState = 1;
    } else if (startDot !== -1) {
      // We saw a non-dot and non-path separator before our dot, so we should
      // have a good chance at having a non-empty extension
      preDotState = -1;
    }
  }

  if (
    startDot === -1 ||
    end === -1 ||
    // We saw a non-dot character immediately before the dot
    preDotState === 0 ||
    // The (right-most) trimmed path component is exactly '..'
    (preDotState === 1 && startDot === end - 1 && startDot === startPart + 1)
  ) {
    return "";
  }
  return path.slice(startDot, end);
}

export function format(pathObject: FormatInputPathObject): string {
  /* eslint-disable max-len */
  if (pathObject === null || typeof pathObject !== "object") {
    throw new TypeError(
      `The "pathObject" argument must be of type Object. Received type ${typeof pathObject}`
    );
  }
  return _format("\\", pathObject);
}

export function parse(path: string): ParsedPath {
  assertPath(path);

  const ret: ParsedPath = { root: "", dir: "", base: "", ext: "", name: "" };

  const len = path.length;
  if (len === 0) return ret;

  let rootEnd = 0;
  let code = path.charCodeAt(0);

  // Try to match a root
  if (len > 1) {
    if (isPathSeparator(code)) {
      // Possible UNC root

      rootEnd = 1;
      if (isPathSeparator(path.charCodeAt(1))) {
        // Matched double path separator at beginning
        let j = 2;
        let last = j;
        // Match 1 or more non-path separators
        for (; j < len; ++j) {
          if (isPathSeparator(path.charCodeAt(j))) break;
        }
        if (j < len && j !== last) {
          // Matched!
          last = j;
          // Match 1 or more path separators
          for (; j < len; ++j) {
            if (!isPathSeparator(path.charCodeAt(j))) break;
          }
          if (j < len && j !== last) {
            // Matched!
            last = j;
            // Match 1 or more non-path separators
            for (; j < len; ++j) {
              if (isPathSeparator(path.charCodeAt(j))) break;
            }
            if (j === len) {
              // We matched a UNC root only

              rootEnd = j;
            } else if (j !== last) {
              // We matched a UNC root with leftovers

              rootEnd = j + 1;
            }
          }
        }
      }
    } else if (isWindowsDeviceRoot(code)) {
      // Possible device root

      if (path.charCodeAt(1) === CHAR_COLON) {
        rootEnd = 2;
        if (len > 2) {
          if (isPathSeparator(path.charCodeAt(2))) {
            if (len === 3) {
              // `path` contains just a drive root, exit early to avoid
              // unnecessary work
              ret.root = ret.dir = path;
              return ret;
            }
            rootEnd = 3;
          }
        } else {
          // `path` contains just a drive root, exit early to avoid
          // unnecessary work
          ret.root = ret.dir = path;
          return ret;
        }
      }
    }
  } else if (isPathSeparator(code)) {
    // `path` contains just a path separator, exit early to avoid
    // unnecessary work
    ret.root = ret.dir = path;
    return ret;
  }

  if (rootEnd > 0) ret.root = path.slice(0, rootEnd);

  let startDot = -1;
  let startPart = rootEnd;
  let end = -1;
  let matchedSlash = true;
  let i = path.length - 1;

  // Track the state of characters (if any) we see before our first dot and
  // after any path separator we find
  let preDotState = 0;

  // Get non-dir info
  for (; i >= rootEnd; --i) {
    code = path.charCodeAt(i);
    if (isPathSeparator(code)) {
      // If we reached a path separator that was not part of a set of path
      // separators at the end of the string, stop now
      if (!matchedSlash) {
        startPart = i + 1;
        break;
      }
      continue;
    }
    if (end === -1) {
      // We saw the first non-path separator, mark this as the end of our
      // extension
      matchedSlash = false;
      end = i + 1;
    }
    if (code === CHAR_DOT) {
      // If this is our first dot, mark it as the start of our extension
      if (startDot === -1) startDot = i;
      else if (preDotState !== 1) preDotState = 1;
    } else if (startDot !== -1) {
      // We saw a non-dot and non-path separator before our dot, so we should
      // have a good chance at having a non-empty extension
      preDotState = -1;
    }
  }

  if (
    startDot === -1 ||
    end === -1 ||
    // We saw a non-dot character immediately before the dot
    preDotState === 0 ||
    // The (right-most) trimmed path component is exactly '..'
    (preDotState === 1 && startDot === end - 1 && startDot === startPart + 1)
  ) {
    if (end !== -1) {
      ret.base = ret.name = path.slice(startPart, end);
    }
  } else {
    ret.name = path.slice(startPart, startDot);
    ret.base = path.slice(startPart, end);
    ret.ext = path.slice(startDot, end);
  }

  // If the directory is the root, use the entire root as the `dir` including
  // the trailing slash if any (`C:\abc` -> `C:\`). Otherwise, strip out the
  // trailing slash (`C:\abc\def` -> `C:\abc`).
  if (startPart > 0 && startPart !== rootEnd) {
    ret.dir = path.slice(0, startPart - 1);
  } else ret.dir = ret.root;

  return ret;
}