(* parse config file
   https://docs.taler.net/manpages/taler-exchange.conf.5.html

   do not support "$"-path expansion*)

(* TODO
   - integer
   - duration
   - YES|NO
   - alt_unit_names json pair

type duration_element = {
  number: int;
  unit_: [ `Year | `Week | `Day | `Hour | `Minute | `Second ];
}

let integer =
  take_while1 (function '0' .. '9' -> true | _ -> false) >>= fun s ->
  match int_of_string_opt s with
  | None -> fail "not an integer"
  | Some i -> return i

let duration_value =
  let number = whitespace *> integer in
  let unit =
    whitespace *> take_while1 (fun c -> not (is_whitespace c || is_eol c))
    >>= function
    | "year" | "years" -> return `Year
    | "week" | "weeks" -> return `Week
    | "day" | "days" -> return `Day
    | "hour" | "hours" -> return `Hour
    | "minute" | "minutes" -> return `Minute
    | "s" -> return `Second
    | _ -> fail "not a valid duration unit"
  in
  many1 (lift2 (fun number unit_ -> { number; unit_ }) number unit)
*)

let read_file file = In_channel.with_open_bin file In_channel.input_all

type item = {
  key: string;
  value: string;
}

type line =
  | Blank
  | Comment of string
  | Header of string
  | Item of item

open Angstrom

let is_eol = function '\n' | '\r' -> true | _ -> false
let is_whitespace = function ' ' | '\t' -> true | _ -> false
let whitespace = skip_while is_whitespace

let id =
  let ident_char = function
    | 'a' .. 'z' | 'A' .. 'Z' | '0' .. '9' | '_' | '-' -> true
    | _ -> false
  in
  take_while1 ident_char >>| String.lowercase_ascii

let take_till_end_of_line =
  take_till is_eol >>= fun s -> return s <* end_of_line

let blank = whitespace <* end_of_line >>| fun () -> Blank

let comment =
  whitespace *> (char '#' <|> char '%') *> take_till_end_of_line >>| fun s ->
  Comment s

let header = char '[' *> id <* char ']' <* end_of_line >>| fun s -> Header s

let item_value =
  let unquoted_value =
    take_while1 (fun c -> not (is_whitespace c || is_eol c))
  in
  let quoted_value =
    char '"' *> take_till is_eol >>= fun s ->
    match String.ends_with ~suffix:"\"" s with
    | false -> fail "invalid quoted value"
    | true ->
        let value = String.sub s 0 (String.length s - 1) in
        return value
  in
  quoted_value <|> unquoted_value

let item =
  lift2
    (fun key value -> Item { key; value })
    id
    (whitespace *> char '=' *> whitespace *> item_value)
  <* end_of_line

let config = many (choice [ blank; comment; header; item ]) <* end_of_input

let pp_line ppf line =
  let open Fmt in
  match line with
  | Blank -> Fmt.nop ppf ()
  | Comment s -> pf ppf "#%s" s
  | Header s -> pf ppf "[%s]" s
  | Item { key; value } -> (
      match String.contains value '"' || String.contains value ' ' with
      | false -> pf ppf "%s = %s" key value
      | true -> pf ppf "%s = \"%s\"" key value)

let pp ppf raw_line_l =
  let open Fmt in
  pf ppf "%a" (list ~sep:(any "\n") pp_line) raw_line_l

let parse s =
  match parse_string ~consume:All config s with
  | Error msg -> Fmt.failwith "config parse error: %s" msg
  | Ok v -> v

let () =
  let content = read_file "default.config" in
  (*Fmt.pr "%s" content;*)

  let config = parse content in

  Fmt.pr "%a@." pp config;

  ()