(**************************************************************************)
(*                                                                        *)
(*                                 OCaml                                  *)
(*                                                                        *)
(*                   Jeremie Dimino, Jane Street Europe                   *)
(*                                                                        *)
(*   Copyright 2018 Jane Street Group LLC                                 *)
(*                                                                        *)
(*   All rights reserved.  This file is distributed under the terms of    *)
(*   the GNU Lesser General Public License version 2.1, with the          *)
(*   special exception on linking described in the file LICENSE.          *)
(*                                                                        *)
(**************************************************************************)

open Local_store

module STbl = Misc.Stdlib.String.Tbl

(* Mapping from basenames to full filenames *)
type registry = string STbl.t

let files : registry ref = s_table STbl.create 42
let files_uncap : registry ref = s_table STbl.create 42

module Dir = struct
  type t = {
    path : string;
    files : string list;
  }

  let path t = t.path
  let files t = t.files

  let find t fn =
    if List.mem fn t.files then
      Some (Filename.concat t.path fn)
    else
      None

  let find_uncap t fn =
    let fn = String.uncapitalize_ascii fn in
    let search base =
      if String.uncapitalize_ascii base = fn then
        Some (Filename.concat t.path base)
      else
        None
    in
    List.find_map search t.files

  (* For backward compatibility reason, simulate the behavior of
     [Misc.find_in_path]: silently ignore directories that don't exist
     + treat [""] as the current directory. *)
  let readdir_compat dir =
    try
      Sys.readdir (if dir = "" then Filename.current_dir_name else dir)
    with Sys_error _ ->
      [||]

  let create path =
    { path; files = Array.to_list (readdir_compat path) }
end

type auto_include_callback =
  (Dir.t -> string -> string option) -> string -> string

let dirs = s_ref []
let no_auto_include _ _ = raise Not_found
let auto_include_callback = ref no_auto_include

let reset () =
  assert (not Config.merlin || Local_store.is_bound ());
  STbl.clear !files;
  STbl.clear !files_uncap;
  dirs := [];
  auto_include_callback := no_auto_include

let get () = List.rev !dirs
let get_paths () = List.rev_map Dir.path !dirs

(* Optimized version of [add] below, for use in [init] and [remove_dir]: since
   we are starting from an empty cache, we can avoid checking whether a unit
   name already exists in the cache simply by adding entries in reverse
   order. *)
let prepend_add dir =
  List.iter (fun base ->
      let fn = Filename.concat dir.Dir.path base in
      STbl.replace !files base fn;
      STbl.replace !files_uncap (String.uncapitalize_ascii base) fn
    ) dir.Dir.files

let init ~auto_include l =
  reset ();
  dirs := List.rev_map Dir.create l;
  List.iter prepend_add !dirs;
  auto_include_callback := auto_include

let remove_dir dir =
  assert (not Config.merlin || Local_store.is_bound ());
  let new_dirs = List.filter (fun d -> Dir.path d <> dir) !dirs in
  if List.compare_lengths new_dirs !dirs <> 0 then begin
    reset ();
    List.iter prepend_add new_dirs;
    dirs := new_dirs
  end

(* General purpose version of function to add a new entry to load path: We only
   add a basename to the cache if it is not already present in the cache, in
   order to enforce left-to-right precedence. *)
let add dir =
  assert (not Config.merlin || Local_store.is_bound ());
  List.iter
    (fun base ->
       let fn = Filename.concat dir.Dir.path base in
       if not (STbl.mem !files base) then
         STbl.replace !files base fn;
       let ubase = String.uncapitalize_ascii base in
       if not (STbl.mem !files_uncap ubase) then
         STbl.replace !files_uncap ubase fn)
    dir.Dir.files;
  dirs := dir :: !dirs

let append_dir = add

let add_dir dir = add (Dir.create dir)

(* Add the directory at the start of load path - so basenames are
   unconditionally added. *)
let prepend_dir dir =
  assert (not Config.merlin || Local_store.is_bound ());
  prepend_add dir;
  dirs := !dirs @ [dir]

let is_basename fn = Filename.basename fn = fn

let auto_include_libs libs alert find_in_dir fn =
  let scan (lib, lazy dir) =
    let file = find_in_dir dir fn in
    let alert_and_add_dir _ =
      alert lib;
      append_dir dir
    in
    Option.iter alert_and_add_dir file;
    file
  in
  match List.find_map scan libs with
  | Some base -> base
  | None -> raise Not_found

let auto_include_otherlibs =
  (* Ensure directories are only ever scanned once *)
  let expand = Misc.expand_directory Config.standard_library in
  let otherlibs =
    let read_lib lib = lazy (Dir.create (expand ("+" ^ lib))) in
    List.map (fun lib -> (lib, read_lib lib)) ["dynlink"; "str"; "unix"] in
  auto_include_libs otherlibs

let find fn =
  assert (not Config.merlin || Local_store.is_bound ());
  try
    if is_basename fn && not !Sys.interactive then
      STbl.find !files fn
    else
      Misc.find_in_path (get_paths ()) fn
  with Not_found ->
    !auto_include_callback Dir.find fn

let find_uncap fn =
  assert (not Config.merlin || Local_store.is_bound ());
  try
    if is_basename fn && not !Sys.interactive then
      STbl.find !files_uncap (String.uncapitalize_ascii fn)
    else
      Misc.find_in_path_uncap (get_paths ()) fn
  with Not_found ->
    let fn_uncap = String.uncapitalize_ascii fn in
    !auto_include_callback Dir.find_uncap fn_uncap