(*  Title:      Pure/General/url.ML

     ID:         $Id$

     Author:     Markus Wenzel, TU Muenchen

 Basic URLs, see RFC 1738 and RFC 2396.

 *)

 signature URL =

 sig

   datatype T =

     File of Path.T |

     RemoteFile of string * Path.T |

     Http of string * Path.T |

     Ftp of string * Path.T

   val append: T -> T -> T

   val implode: T -> string

   val explode: string -> T

 end;

 structure Url: URL =

 struct

 (* type url *)

 datatype T =

   File of Path.T |

   RemoteFile of string * Path.T |

   Http of string * Path.T |

   Ftp of string * Path.T;

 (* append *)

 fun append (File p)            (File p') = File (Path.append p p')

   | append (RemoteFile (h, p)) (File p') = RemoteFile (h, Path.append p p')

   | append (Http (h, p))       (File p') = Http (h, Path.append p p')

   | append (Ftp (h, p))        (File p') = Ftp (h, Path.append p p')

   | append _ url = url;

 (* implode *)

 fun implode_path p = if Path.is_current p then "" else Path.implode p;

 fun implode_url (File p) = implode_path p

   | implode_url (RemoteFile (h, p)) = "file://" ^ h ^ implode_path p

   | implode_url (Http (h, p)) = "http://" ^ h ^ implode_path p

   | implode_url (Ftp (h, p)) = "ftp://" ^ h ^ implode_path p;

 (* explode *)

 local

 val scan_host =

   (Scan.many1 (fn s => s <> "/" andalso Symbol.is_regular s) >> implode) --|

   Scan.ahead ($$ "/" || Scan.one Symbol.is_eof);

 val scan_path = Scan.many Symbol.is_regular >> (Path.explode o implode);

 val scan_path_root = Scan.many Symbol.is_regular >> (Path.explode o implode o cons "/");

 val scan_url =

   Scan.unless (Scan.this_string "file:" ||

     Scan.this_string "http:" || Scan.this_string "ftp:") scan_path >> File ||

   Scan.this_string "file:///" |-- scan_path_root >> File ||

   Scan.this_string "file://localhost/" |-- scan_path_root >> File ||

   Scan.this_string "file://" |-- scan_host -- scan_path >> RemoteFile ||

   Scan.this_string "file:/" |-- scan_path_root >> File ||

   Scan.this_string "http://" |-- scan_host -- scan_path >> Http ||

   Scan.this_string "ftp://" |-- scan_host -- scan_path >> Ftp;

 in

 fun explode_url s = Symbol.scanner "Malformed URL" scan_url (Symbol.explode s);

 end;

 (*final declarations of this structure!*)

 val implode = implode_url;

 val explode = explode_url;

 end;