module String_map = struct
  include Map.Make(String)

  let add_or_create key v t=
    update key (function None -> Some [ v ] | Some xs -> Some (v :: xs)) t
end

let diff_map a b =
  let diff a b =
    String_map.fold (fun k v acc ->
      if not (String_map.mem k b) then (k, v) :: acc else acc)
      a [] |> List.rev
  in
  let added = diff b a
  and removed = diff a b
  and changed =
    String_map.fold (fun k v acc ->
      match String_map.find_opt k b with
      | None -> acc
      | Some v' -> if String.equal v v' then acc else (k, v, v') :: acc)
    a [] |> List.rev
  in
  (added, removed, changed)

let compare_env env1 env2 =
  let parse_env e =
    List.fold_left (fun m s ->
      match Astring.String.cut ~sep:"=" s with
      | Some (key, value) -> String_map.add key value m
      | None -> String_map.add s "" m)
    String_map.empty (Astring.String.cuts ~sep:"\n" e)
  in
  diff_map (parse_env env1) (parse_env env2)

let compare_pkgs p1 p2 =
  let parse_pkgs p =
    List.fold_left (fun m s ->
      match Astring.String.cut ~sep:"=" s with
      | Some (name, version) -> String_map.add name version m
      | None -> match Astring.String.cut ~sep:"-" s with
        | Some (name, version) -> String_map.add name version m
        | None -> String_map.add s "" m)
    String_map.empty (Astring.String.cuts ~sep:"\n" p)
  in
  diff_map (parse_pkgs p1) (parse_pkgs p2)