module L = Dimacs_lexer

type t = { buf: Lexing.lexbuf; mutable header: (int * int) option }

let create (ic : in_channel) : t =
  let buf = Lexing.from_channel ic in
  { buf; header = None }

let parse_header self =
  match self.header with
  | Some tup -> tup
  | None ->
    let i, j =
      try
        match L.token self.buf with
        | L.P ->
          (match L.token self.buf with
          | L.CNF ->
            (match L.token self.buf with
            | L.LIT i ->
              (match L.token self.buf with
              | L.LIT j -> i, j
              | _ -> raise Exit)
            | _ -> raise Exit)
          | _ -> raise Exit)
        | _ -> raise Exit
      with Exit -> Error.errorf "expected file to start with header"
    in
    self.header <- Some (i, j);
    i, j

let next_clause self : _ option =
  let rec loop acc =
    match L.token self.buf with
    | L.EOF when acc = [] -> None
    | L.EOF -> Error.errorf "unexpected EOF in a clause"
    | L.ZERO -> Some (List.rev acc)
    | L.LIT i -> loop (i :: acc)
    | _ -> Error.errorf "expected clause"
  in
  loop []

let iter self k =
  ignore (parse_header self : _ * _);
  let rec loop () =
    match next_clause self with
    | None -> ()
    | Some c ->
      k c;
      loop ()
  in
  loop ()