(* Copyright (c) 2013-2017 Thomas Gazagnaire <thomas@gazagnaire.org>
   Copyright (c) 2017-2024 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 object hashes (SHA-1 or SHA-256). *)

type t = Digestif.SHA1.t

let digest_size = Digestif.SHA1.digest_size
let pp = Digestif.SHA1.pp
let equal = Digestif.SHA1.equal
let compare = Digestif.SHA1.unsafe_compare

let of_raw_string s =
  if String.length s <> digest_size then
    invalid_arg "Hash.of_raw_string: invalid length";
  Digestif.SHA1.of_raw_string s

let to_raw_string = Digestif.SHA1.to_raw_string
let of_hex s = Digestif.SHA1.of_hex s
let to_hex t = Digestif.SHA1.to_hex t

let null =
  let s = String.make digest_size '\x00' in
  of_raw_string s

let v t = Hashtbl.hash (to_raw_string t)

module Set = Set.Make (struct
  type nonrec t = t

  let compare = compare
end)

module Map = Map.Make (struct
  type nonrec t = t

  let compare = compare
end)

(** Compute the hash of a git object. *)
let digest ~kind ~length contents =
  let kind_str =
    match kind with
    | `Blob -> "blob"
    | `Tree -> "tree"
    | `Commit -> "commit"
    | `Tag -> "tag"
  in
  let header = Fmt.str "%s %d\x00" kind_str length in
  let ctx = Digestif.SHA1.empty in
  let ctx = Digestif.SHA1.feed_string ctx header in
  let ctx = Digestif.SHA1.feed_string ctx contents in
  Digestif.SHA1.get ctx

let digest_string ~kind s = digest ~kind ~length:(String.length s) s