// 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 {
  isWindows,
  CHAR_UPPERCASE_A,
  CHAR_LOWERCASE_A,
  CHAR_UPPERCASE_Z,
  CHAR_LOWERCASE_Z,
  CHAR_DOT,
  CHAR_FORWARD_SLASH,
  CHAR_BACKWARD_SLASH,
  CHAR_COLON,
  CHAR_QUESTION_MARK
} from "./constants.ts";

function assertPath(path: string): void {
  if (typeof path !== "string") {
    throw new TypeError(
      `Path must be a string. Received ${JSON.stringify(path)}`
    );
  }
}

function isPosixPathSeparator(code: number): boolean {
  return code === CHAR_FORWARD_SLASH;
}

function isPathSeparator(code: number): boolean {
  return isPosixPathSeparator(code) || code === CHAR_BACKWARD_SLASH;
}

function isWindowsDeviceRoot(code: number): boolean {
  return (
    (code >= CHAR_LOWERCASE_A && code <= CHAR_LOWERCASE_Z) ||
    (code >= CHAR_UPPERCASE_A && code <= CHAR_UPPERCASE_Z)
  );
}

// Resolves . and .. elements in a path with directory names
function normalizeString(
  path: string,
  allowAboveRoot: boolean,
  separator: string,
  isPathSeparator: (code: number) => boolean
): string {
  let res = "";
  let lastSegmentLength = 0;
  let lastSlash = -1;
  let dots = 0;
  let code: number;
  for (let i = 0, len = path.length; i <= len; ++i) {
    if (i < len) code = path.charCodeAt(i);
    else if (isPathSeparator(code)) break;
    else code = CHAR_FORWARD_SLASH;

    if (isPathSeparator(code)) {
      if (lastSlash === i - 1 || dots === 1) {
        // NOOP
      } else if (lastSlash !== i - 1 && dots === 2) {
        if (
          res.length < 2 ||
          lastSegmentLength !== 2 ||
          res.charCodeAt(res.length - 1) !== CHAR_DOT ||
          res.charCodeAt(res.length - 2) !== CHAR_DOT
        ) {
          if (res.length > 2) {
            const lastSlashIndex = res.lastIndexOf(separator);
            if (lastSlashIndex === -1) {
              res = "";
              lastSegmentLength = 0;
            } else {
              res = res.slice(0, lastSlashIndex);
              lastSegmentLength = res.length - 1 - res.lastIndexOf(separator);
            }
            lastSlash = i;
            dots = 0;
            continue;
          } else if (res.length === 2 || res.length === 1) {
            res = "";
            lastSegmentLength = 0;
            lastSlash = i;
            dots = 0;
            continue;
          }
        }
        if (allowAboveRoot) {
          if (res.length > 0) res += `${separator}..`;
          else res = "..";
          lastSegmentLength = 2;
        }
      } else {
        if (res.length > 0) res += separator + path.slice(lastSlash + 1, i);
        else res = path.slice(lastSlash + 1, i);
        lastSegmentLength = i - lastSlash - 1;
      }
      lastSlash = i;
      dots = 0;
    } else if (code === CHAR_DOT && dots !== -1) {
      ++dots;
    } else {
      dots = -1;
    }
  }
  return res;
}

function _format(sep: string, pathObject: FormatInputPathObject): string {
  const dir: string | null = pathObject.dir || pathObject.root;
  const base: string =
    pathObject.base || (pathObject.name || "") + (pathObject.ext || "");
  if (!dir) return base;
  if (dir === pathObject.root) return dir + base;
  return dir + sep + base;
}

export const win32 = {
  // path.resolve([from ...], to)
  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 || "."
    );
  },

  normalize(path: string): string {
    assertPath(path);
    const len = path.length;
    if (len === 0) return ".";
    let rootEnd = 0;
    let device: string;
    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;
    }
  },

  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;
  },

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

    let joined: string;
    let firstPart: string;
    for (let i = 0; i < pathsCount; ++i) {
      let 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;
    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 win32.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'
  relative(from: string, to: string): string {
    assertPath(from);
    assertPath(to);

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

    let fromOrig = win32.resolve(from);
    let toOrig = win32.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;
    }
    let 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;
    }
    let toLen = toEnd - toStart;

    // Compare paths to find the longest common path from root
    let 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;
      }
      let fromCode = from.charCodeAt(fromStart + i);
      let 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);
    }
  },

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

    const resolvedPath = win32.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;
  },

  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);
  },

  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);
    }
  },

  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);
  },

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

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

    let 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;
  },

  sep: "\\",
  delimiter: ";",
  win32: null,
  posix: null
};

export const posix = {
  // path.resolve([from ...], to)
  resolve(...pathSegments: string[]): string {
    let resolvedPath = "";
    let resolvedAbsolute = false;

    for (let i = pathSegments.length - 1; i >= -1 && !resolvedAbsolute; i--) {
      let path: string;

      if (i >= 0) path = pathSegments[i];
      else path = cwd();

      assertPath(path);

      // Skip empty entries
      if (path.length === 0) {
        continue;
      }

      resolvedPath = `${path}/${resolvedPath}`;
      resolvedAbsolute = path.charCodeAt(0) === CHAR_FORWARD_SLASH;
    }

    // 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 path
    resolvedPath = normalizeString(
      resolvedPath,
      !resolvedAbsolute,
      "/",
      isPosixPathSeparator
    );

    if (resolvedAbsolute) {
      if (resolvedPath.length > 0) return `/${resolvedPath}`;
      else return "/";
    } else if (resolvedPath.length > 0) return resolvedPath;
    else return ".";
  },

  normalize(path: string): string {
    assertPath(path);

    if (path.length === 0) return ".";

    const isAbsolute = path.charCodeAt(0) === CHAR_FORWARD_SLASH;
    const trailingSeparator =
      path.charCodeAt(path.length - 1) === CHAR_FORWARD_SLASH;

    // Normalize the path
    path = normalizeString(path, !isAbsolute, "/", isPosixPathSeparator);

    if (path.length === 0 && !isAbsolute) path = ".";
    if (path.length > 0 && trailingSeparator) path += "/";

    if (isAbsolute) return `/${path}`;
    return path;
  },

  isAbsolute(path: string): boolean {
    assertPath(path);
    return path.length > 0 && path.charCodeAt(0) === CHAR_FORWARD_SLASH;
  },

  join(...paths: string[]): string {
    if (paths.length === 0) return ".";
    let joined: string | undefined;
    for (let i = 0, len = paths.length; i < len; ++i) {
      let path = paths[i];
      assertPath(path);
      if (path.length > 0) {
        if (!joined) joined = path;
        else joined += `/${path}`;
      }
    }
    if (!joined) return ".";
    return posix.normalize(joined);
  },

  relative(from: string, to: string): string {
    assertPath(from);
    assertPath(to);

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

    from = posix.resolve(from);
    to = posix.resolve(to);

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

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

    // Compare paths to find the longest common path from root
    let 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'
            return to.slice(toStart + i + 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;
      }
      let fromCode = from.charCodeAt(fromStart + i);
      let 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);
    }
  },

  toNamespacedPath(path: string): string {
    // Non-op on posix systems
    return path;
  },

  dirname(path: string): string {
    assertPath(path);
    if (path.length === 0) return ".";
    const hasRoot = path.charCodeAt(0) === CHAR_FORWARD_SLASH;
    let end = -1;
    let matchedSlash = true;
    for (let i = path.length - 1; i >= 1; --i) {
      if (path.charCodeAt(i) === CHAR_FORWARD_SLASH) {
        if (!matchedSlash) {
          end = i;
          break;
        }
      } else {
        // We saw the first non-path separator
        matchedSlash = false;
      }
    }

    if (end === -1) return hasRoot ? "/" : ".";
    if (hasRoot && end === 1) return "//";
    return path.slice(0, end);
  },

  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;

    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 >= 0; --i) {
        const code = path.charCodeAt(i);
        if (code === CHAR_FORWARD_SLASH) {
          // 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 >= 0; --i) {
        if (path.charCodeAt(i) === CHAR_FORWARD_SLASH) {
          // 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);
    }
  },

  extname(path: string): string {
    assertPath(path);
    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;
    for (let i = path.length - 1; i >= 0; --i) {
      const code = path.charCodeAt(i);
      if (code === CHAR_FORWARD_SLASH) {
        // 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);
  },

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

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

    let ret: ParsedPath = { root: "", dir: "", base: "", ext: "", name: "" };
    if (path.length === 0) return ret;
    let isAbsolute = path.charCodeAt(0) === CHAR_FORWARD_SLASH;
    let start: number;
    if (isAbsolute) {
      ret.root = "/";
      start = 1;
    } else {
      start = 0;
    }
    let startDot = -1;
    let startPart = 0;
    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 >= start; --i) {
      const code = path.charCodeAt(i);
      if (code === CHAR_FORWARD_SLASH) {
        // 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) {
        if (startPart === 0 && isAbsolute) {
          ret.base = ret.name = path.slice(1, end);
        } else {
          ret.base = ret.name = path.slice(startPart, end);
        }
      }
    } else {
      if (startPart === 0 && isAbsolute) {
        ret.name = path.slice(1, startDot);
        ret.base = path.slice(1, end);
      } else {
        ret.name = path.slice(startPart, startDot);
        ret.base = path.slice(startPart, end);
      }
      ret.ext = path.slice(startDot, end);
    }

    if (startPart > 0) ret.dir = path.slice(0, startPart - 1);
    else if (isAbsolute) ret.dir = "/";

    return ret;
  },

  sep: "/",
  delimiter: ":",
  win32: null,
  posix: null
};

posix.win32 = win32.win32 = win32;
posix.posix = win32.posix = posix;

const module = isWindows ? win32 : posix;

export const resolve = module.resolve;
export const normalize = module.normalize;
export const isAbsolute = module.isAbsolute;
export const join = module.join;
export const relative = module.relative;
export const toNamespacedPath = module.toNamespacedPath;
export const dirname = module.dirname;
export const basename = module.basename;
export const extname = module.extname;
export const format = module.format;
export const parse = module.parse;
export const sep = module.sep;
export const delimiter = module.delimiter;