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(** Helpers to read JSON values.

    Contains functions to parse JSON values, show them for debugging, and
    extract information from them.

    Functions which extract information are rather strict: they don't try
    to be smart and automatically convert. For instance, [as_record] makes sure
    that all fields are taken into account. This is suited to write a tool that
    must be updated when the format of JSON values being manipulated changes.
    In our case, if the JSON schemas we read start to get more fields, we want
    to know; otherwise the resulting OpenAPI specification could be inaccurate. *)

include Tezt.JSON

let as_variant json =
  match as_object json with
  | [(name, value)] -> (name, value)
  | _ -> error json "expected an object with a single field"

let as_variant_named json name =
  match as_variant json with
  | name', value when name' = name -> value
  | _ -> error json "expected a variant named %s" name

let ( |~> ) json name = as_variant_named json name

(* Convert an [`O] into a record.
   Ensure no field is left.
   [make] takes an argument to get field from their names,
   and if at the end it did not consume all fields,
   an exception is raised. *)
let as_record json make =
  let fields = ref (as_object json) in
  let get (field : string) =
    let rec find previous = function
      | [] -> None
      | ((head_name, head_value) as head) :: tail ->
          if head_name = field then (
            fields := List.rev_append previous tail ;
            Some head_value)
          else find (head :: previous) tail
    in
    find [] !fields
  in
  let result = make get in
  if !fields <> [] then
    error
      json
      "unexpected fields in object: %s"
      (String.concat ", " (List.map fst !fields)) ;
  result

let output json =
  Ezjsonm.value_to_channel ~minify:false stdout json ;
  print_newline ()