(* Copyright (c) 2015 Daniel C. Bünzli
   Copyright (c) 2020-2024 Romain Calascibetta <romain.calascibetta@gmail.com>
   Copyright (c) 2024-2026 Thomas Gazagnaire <thomas@gazagnaire.org>

   Permission to use, copy, modify, and distribute this software for any
   purpose with or without fee is hereby granted, provided that the above
   copyright notice and this permission notice appear in all copies.

   THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. *)

(** Git references (branches, tags, HEAD). *)

type t = string

let head = "HEAD"
let master = "refs/heads/master"
let main = "refs/heads/main"

let of_string s =
  if String.length s = 0 then Error (`Msg "Empty reference")
  else if String.contains s '\x00' then
    Error (`Msg "Reference contains null byte")
  else if s.[0] = '/' then Error (`Msg "Absolute reference not allowed")
  else
    (* Collapse consecutive slashes *)
    let buf = Buffer.create (String.length s) in
    let last_was_slash = ref false in
    String.iter
      (fun c ->
        if c = '/' then (
          if not !last_was_slash then Buffer.add_char buf c;
          last_was_slash := true)
        else (
          Buffer.add_char buf c;
          last_was_slash := false))
      s;
    Ok (Buffer.contents buf)

let of_string_exn s =
  match of_string s with Ok r -> r | Error (`Msg m) -> invalid_arg m

let v = of_string_exn
let to_string t = t
let pp ppf t = Fmt.string ppf t
let equal = String.equal
let compare = String.compare
let hash = Hashtbl.hash

let segs t =
  String.split_on_char '/' t |> List.filter (fun s -> String.length s > 0)

let ( / ) t seg =
  if String.contains seg '\x00' || String.contains seg '/' then
    invalid_arg "Invalid segment";
  if t.[String.length t - 1] = '/' then t ^ seg else t ^ "/" ^ seg

let ( // ) t1 t2 =
  if t2.[0] = '/' then t2
  else if t1.[String.length t1 - 1] = '/' then t1 ^ t2
  else t1 ^ "/" ^ t2

(** Reference contents: either a direct hash or a symbolic reference. *)
type contents = Hash of Hash.t | Ref of t

let contents_equal a b =
  match (a, b) with
  | Hash a, Hash b -> Hash.equal a b
  | Ref a, Ref b -> equal a b
  | _ -> false

let contents_compare a b =
  match (a, b) with
  | Hash a, Hash b -> Hash.compare a b
  | Ref a, Ref b -> compare a b
  | Hash _, Ref _ -> -1
  | Ref _, Hash _ -> 1

let pp_contents ppf = function
  | Hash h -> Hash.pp ppf h
  | Ref r -> Fmt.pf ppf "ref: %s" r

(** Parse reference file contents. *)
let contents_of_string s =
  let s = String.trim s in
  if String.length s = 0 then Error (`Msg "Empty reference contents")
  else if String.length s >= 5 && String.sub s 0 5 = "ref: " then
    let ref_path = String.sub s 5 (String.length s - 5) in
    Result.map (fun r -> Ref r) (of_string ref_path)
  else
    (* Try to parse as a hex hash *)
    try Ok (Hash (Hash.of_hex s))
    with Invalid_argument _ ->
      Error (`Msg ("Invalid reference contents: " ^ s))

let contents_of_string_exn s =
  match contents_of_string s with Ok c -> c | Error (`Msg m) -> failwith m

(** Encode reference contents. *)
let contents_to_string = function
  | Hash h -> Hash.to_hex h ^ "\n"
  | Ref r -> "ref: " ^ r ^ "\n"

module Set = Set.Make (String)
module Map = Map.Make (String)