(*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *)

(**
 * Hh_json parsing and pretty printing library.
 *)

(*
   <value> ::=
     | <object>
     | <array>
     | <string>
     | <number>
     | 'true'
     | 'false'
     | 'null'

   <object>   ::= '{' <members>* '}'
   <members>  ::= <pair> { ',' <pair> }* [',']
   <pair>     ::= <string> ':' <value>

   <array>    ::= '{' <elements>* '}'
   <elements> ::= <value> { ',' <value> }* [',']

   <number>   ::=

   Caveats:
    (+) No handling of Unicode yet
    (+) Numbers are just stored as strings
*)

module List = Base.List

type json =
  | JSON_Object of (string * json) list
  | JSON_Array of json list
  | JSON_String of string
  | JSON_Number of string
  | JSON_Bool of bool
  | JSON_Null

let is_digit = function
  | '0' .. '9' -> true
  | _ -> false

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

type env = {
  allow_trailing_comma: bool;
  data: string;
  mutable pos: int;
}

exception Syntax_error of string

(* Ignore whitespace in peek/eat/next/has_more to make code that uses them
   cleaner
*)

let peek env = env.data.[env.pos]

let has_more env = String.length env.data > env.pos

let syntax_error env msg =
  let err_msg =
    if has_more env then
      Printf.sprintf "%s at char[%d]=%c" msg env.pos env.data.[env.pos]
    else
      Printf.sprintf "%s after the last character" msg
  in
  raise (Syntax_error err_msg)

(* skip all blank and new line characters *)
let skip_blank_chars env =
  while has_more env && is_whitespace (peek env) do
    env.pos <- env.pos + 1
  done

let create_env strict s =
  let env = { allow_trailing_comma = not strict; data = s; pos = 0 } in
  skip_blank_chars env;
  env

let eat_ws env c =
  let c' = peek env in
  if c' = c then
    env.pos <- env.pos + 1
  else
    let err_msg = Printf.sprintf "eat_ws: expected %c, saw %c" c c' in
    syntax_error env err_msg

let eat env c =
  skip_blank_chars env;
  let c' = peek env in
  if c' = c then (
    env.pos <- env.pos + 1;
    skip_blank_chars env
  ) else
    let err_msg = Printf.sprintf "eat: expected %c, saw %c" c c' in
    syntax_error env err_msg

let match_substring_at s offset ss =
  let ss_len = String.length ss in
  if String.length s - offset >= ss_len then
    try
      for i = 0 to ss_len - 1 do
        if s.[i + offset] <> ss.[i] then raise Exit
      done;
      true
    with
    | Exit -> false
  else
    false

let js_literal env s js =
  skip_blank_chars env;
  if match_substring_at env.data env.pos s then (
    env.pos <- env.pos + String.length s;
    js
  ) else
    let err_msg = Printf.sprintf "expected '%s'" s in
    syntax_error env err_msg

let js_true env = js_literal env "true" (JSON_Bool true)

let js_false env = js_literal env "false" (JSON_Bool false)

let js_null env = js_literal env "null" JSON_Null

let buf_eat buf env c =
  eat env c;
  Buffer.add_char buf c

let buf_eat_all buf env c =
  eat_ws env c;
  Buffer.add_char buf c

let char_code env =
  let rec char_code_ (acc : int) env len =
    if len = 0 then
      acc
    else (
      env.pos <- env.pos + 1;
      let c = Char.lowercase_ascii (peek env) in
      let i =
        if '0' <= c && c <= '9' then
          Char.code c - Char.code '0'
        else if 'a' <= c && c <= 'f' then
          10 + Char.code c - Char.code 'a'
        else
          syntax_error env "expected hexadecimal digit"
      in
      char_code_ ((16 * acc) + i) env (len - 1)
    )
  in
  char_code_ 0 env 4

let js_string env =
  let buf = Buffer.create 128 in
  let rec loop env =
    let c = peek env in
    match c with
    | '"' -> JSON_String (Buffer.contents buf)
    | '\\' ->
      env.pos <- env.pos + 1;
      let c' = peek env in
      let c' =
        match c' with
        | 'n' -> '\n'
        | 'r' -> '\r'
        | 't' -> '\t'
        | 'u' ->
          let code = char_code env in
          Char.chr code
        | x -> x
      in
      env.pos <- env.pos + 1;
      Buffer.add_char buf c';
      loop env
    | _ ->
      buf_eat_all buf env c;
      loop env
  in
  (match peek env with
  | '"' -> env.pos <- env.pos + 1
  | _ -> syntax_error env "expected '\"' character");
  if peek env = '"' then (
    eat env '"';
    JSON_String ""
  ) else
    let res = loop env in
    eat env '"';
    res

let rec buf_eat_digits buf env =
  if has_more env then
    let c = peek env in
    if is_digit c then (
      buf_eat buf env c;
      buf_eat_digits buf env
    ) else
      ()
  (* encountered a non-digit char, stop *)
  else
    (* end of string, stop *)
    ()

let buf_eat_exp buf env =
  let c = peek env in
  if c = 'e' || c = 'E' then (
    buf_eat buf env c;
    let sign = peek env in
    if sign = '+' || sign = '-' then buf_eat buf env sign;
    buf_eat_digits buf env
  )

let js_number env =
  let buf = Buffer.create 32 in
  let c = peek env in
  if c = '-' then buf_eat buf env '-';
  buf_eat_digits buf env;

  (* ['-'] digits *)
  let c = peek env in
  if c = '.' then (
    (* ['.' digits ] *)
    buf_eat buf env '.';
    buf_eat_digits buf env
  );
  buf_eat_exp buf env;

  (* [exp digits] *)
  JSON_Number (Buffer.contents buf)

(* The recursive rules *)
let rec js_value env =
  let js_value_syntax_error () =
    let err_msg = "expected '{[\"0123456789' or {t,f,n}" in
    syntax_error env err_msg
  in
  if not (has_more env) then
    js_value_syntax_error ()
  else
    match peek env with
    | '{' -> js_object env
    | '[' -> js_array env
    | '"' -> js_string env
    | c when is_digit c || c = '-' -> js_number env
    | 't' -> js_true env
    | 'f' -> js_false env
    | 'n' -> js_null env
    | _ -> js_value_syntax_error ()

and js_object env =
  let rec loop members =
    let p = js_pair env in
    if peek env <> ',' then
      JSON_Object (List.rev (p :: members))
    else (
      eat env ',';
      if peek env = '}' then
        if env.allow_trailing_comma then
          JSON_Object (List.rev (p :: members))
        else
          syntax_error env "Hh_json.object: trailing comma"
      else
        loop (p :: members)
    )
  in
  eat env '{';
  if peek env = '}' then (
    eat env '}';
    JSON_Object []
  ) else
    let res = loop [] in
    eat env '}';
    res

and js_array env =
  let rec elements accum =
    let v = js_value env in
    if peek env <> ',' then
      JSON_Array (List.rev (v :: accum))
    else (
      eat env ',';
      if peek env = ']' then
        if env.allow_trailing_comma then
          JSON_Array (List.rev (v :: accum))
        else
          syntax_error env "Hh_json.array: trailing comma"
      else
        elements (v :: accum)
    )
  in
  eat env '[';
  if peek env = ']' then (
    eat env ']';
    JSON_Array []
  ) else
    let res = elements [] in
    eat env ']';
    res

and js_pair env =
  skip_blank_chars env;
  let k = js_string env in
  skip_blank_chars env;
  eat env ':';
  let v = js_value env in
  match k with
  | JSON_String s -> (s, v)
  | _ -> syntax_error env "Hh_json.js_pair: expected a JSON String"

let string_of_file filename =
  let ic = open_in filename in
  let buf = Buffer.create 5096 in
  let rec loop () =
    match
      try Some (input_line ic) with
      | _ -> None
    with
    | None -> Buffer.contents buf
    | Some l ->
      Buffer.add_string buf l;
      Buffer.add_char buf '\n';
      loop ()
  in
  loop ()

(* Writing JSON *)

let sort_object obj_entries =
  List.sort ~compare:(fun (k1, _) (k2, _) -> Stdlib.compare k1 k2) obj_entries

module type Output_stream_intf = sig
  type t

  val add_char : t -> char -> unit

  val add_string : t -> string -> unit

  val add_substring : t -> string -> int -> int -> unit
end

module Buffer_stream : Output_stream_intf with type t = Buffer.t = struct
  type t = Buffer.t

  let add_char b c = Buffer.add_char b c

  let add_string b s = Buffer.add_string b s

  let add_substring b s ofs len = Buffer.add_substring b s ofs len
end

module Channel_stream : Output_stream_intf with type t = Stdlib.out_channel = struct
  type t = Stdlib.out_channel

  let add_char b c = Stdlib.output_char b c

  let add_string b s = Stdlib.output_string b s

  let add_substring b s ofs len = Stdlib.output_substring b s ofs len
end

module Make_streamer (Out : Output_stream_intf) = struct
  (* Designed as a substitute for String.concat that passes a buffer
   * into which intermediate strings are added, and also includes left
   * and right bracket (lb and rb) in addition to sep. They are strings,
   * despite common case of (), [],{}, or even <>, to handle missing brackets,
   * brackets with spacing and multichar brackets like OCaml's arrays
   * ([| and |]). The conc_elt function parameter performs the operation of
   * transforming the list element to a string and adding it to the buffer, the
   * simplest example would be fun x -> Buffer.add_string (to_string x)
   *)
  let concat ~lb ~rb ~sep ~concat_elt buf l =
    Out.add_string buf lb;
    (match l with
    | [] -> ()
    | elt :: elts ->
      concat_elt buf elt;
      List.iter elts (fun e ->
          Out.add_string buf sep;
          concat_elt buf e
      ));
    Out.add_string buf rb

  let escape b s =
    Out.add_char b '"';
    let pos = ref 0 in
    let add_escaped i chr =
      Out.add_substring b s !pos (i - !pos);
      Out.add_string b chr;
      pos := i + 1
    in
    for i = 0 to String.length s - 1 do
      match s.[i] with
      | '\\' -> add_escaped i "\\\\"
      | '"' -> add_escaped i "\\\""
      | '\n' -> add_escaped i "\\n"
      | '\r' -> add_escaped i "\\r"
      | '\t' -> add_escaped i "\\t"
      | '\x00' .. '\x1f' as c ->
        let code = Char.code c in
        add_escaped i (Printf.sprintf "\\u%04x" code)
      | _ -> ()
    done;
    Out.add_substring b s !pos (String.length s - !pos);
    Out.add_char b '"'

  let rec add_json ~sort_keys (buf : Out.t) (json : json) : unit =
    match json with
    | JSON_Object l ->
      (* Make the pretty output deterministic by sorting the keys *)
      let l =
        if sort_keys then
          sort_object l
        else
          l
      in
      concat ~lb:"{" ~rb:"}" ~sep:"," ~concat_elt:(add_assoc ~sort_keys) buf l
    | JSON_Array l -> concat ~lb:"[" ~rb:"]" ~sep:"," ~concat_elt:(add_json ~sort_keys) buf l
    | JSON_String s -> escape buf s
    | JSON_Number n -> Out.add_string buf n
    | JSON_Bool b ->
      Out.add_string
        buf
        ( if b then
          "true"
        else
          "false"
        )
    | JSON_Null -> Out.add_string buf "null"

  and add_assoc ~sort_keys (buf : Out.t) (k, v) =
    escape buf k;
    Out.add_char buf ':';
    add_json ~sort_keys buf v
end

module Out_buffer = Make_streamer (Buffer_stream)
module Out_channel = Make_streamer (Channel_stream)

let rec json_to_string ?(sort_keys = false) ?(pretty = false) (json : json) : string =
  if pretty then
    json_to_multiline ~sort_keys json
  else
    let buf = Buffer.create 1024 in
    (* need a better estimate! *)
    Out_buffer.add_json ~sort_keys buf json;
    Buffer.contents buf

and json_to_multiline ?(sort_keys = false) json =
  let rec loop indent json =
    let single = json_to_string ~sort_keys json in
    if String.length single < 80 then
      single
    else
      match json with
      | JSON_Array l ->
        let nl = List.map l (loop (indent ^ "  ")) in
        "[\n" ^ indent ^ "  " ^ String.concat (",\n" ^ indent ^ "  ") nl ^ "\n" ^ indent ^ "]"
      | JSON_Object l ->
        (* Make the pretty output deterministic by sorting the keys *)
        let l =
          if sort_keys then
            sort_object l
          else
            l
        in
        let nl =
          List.map l (fun (k, v) ->
              indent
              ^ "  "
              ^ json_to_string ~sort_keys (JSON_String k)
              ^ ":"
              ^ loop (indent ^ "  ") v
          )
        in
        "{\n" ^ String.concat ",\n" nl ^ "\n" ^ indent ^ "}"
      | _ -> single
  in
  loop "" json

let json_to_output oc (json : json) : unit = Out_channel.add_json ~sort_keys:false oc json

let rec json_to_multiline_output oc (json : json) : unit =
  let json_assoc_to_output oc (k, v) : unit =
    Out_channel.escape oc k;
    output_string oc ":";
    json_to_multiline_output oc v
  in
  match json with
  | JSON_Object l ->
    Out_channel.concat ~lb:"{" ~rb:"}" ~sep:",\n" ~concat_elt:json_assoc_to_output oc l
  | JSON_Array l ->
    Out_channel.concat ~lb:"[" ~rb:"]" ~sep:",\n" ~concat_elt:json_to_multiline_output oc l
  | JSON_String s -> Out_channel.escape oc s
  | JSON_Number n -> output_string oc n
  | JSON_Bool b ->
    output_string
      oc
      ( if b then
        "true"
      else
        "false"
      )
  | JSON_Null -> output_string oc "null"

let output_json_endline ~pretty (oc : out_channel) (json : json) =
  if pretty then
    output_string oc (json_to_multiline json)
  else
    json_to_output oc json;
  output_char oc '\n';
  flush oc

let print_json_endline ?(pretty = false) (json : json) = output_json_endline ~pretty stdout json

let prerr_json_endline ?(pretty = false) (json : json) = output_json_endline ~pretty stderr json

let json_of_string ?(strict = true) s =
  let lb = create_env strict s in
  js_value lb

let json_of_file ?strict filename = json_of_string ?strict (string_of_file filename)

let int_ n = JSON_Number (string_of_int n)

let float_ n =
  let s = string_of_float n in
  (* ocaml strings can end in '.', which isn't allowed in json *)
  let len = String.length s in
  let s =
    if s.[len - 1] = '.' then
      String.sub s 0 (len - 1)
    else
      s
  in
  JSON_Number s

let string_ s = JSON_String s

let get_object_exn = function
  | JSON_Object o -> o
  | _ -> assert false

let get_array_exn = function
  | JSON_Array a -> a
  | _ -> assert false

let get_string_exn = function
  | JSON_String s -> s
  | _ -> assert false

let get_number_exn = function
  | JSON_Number s -> s
  | _ -> assert false

let get_number_int_exn = function
  | JSON_Number s -> int_of_string s
  | _ -> assert false

let get_bool_exn = function
  | JSON_Bool b -> b
  | _ -> assert false

let opt_string_to_json = function
  | Some x -> JSON_String x
  | None -> JSON_Null

let opt_int_to_json = function
  | Some x -> JSON_Number (string_of_int x)
  | None -> JSON_Null

type json_type =
  | Object_t
  | Array_t
  | String_t
  | Number_t
  | Integer_t
  | Bool_t

let json_type_to_string = function
  | Object_t -> "Object"
  | Array_t -> "Array"
  | String_t -> "String"
  | Number_t -> "Number"
  | Integer_t -> "Integer"
  | Bool_t -> "Bool"

module type Access = sig
  type keytrace = string list

  type access_failure =
    | Not_an_object of keytrace
    | Missing_key_error of string * keytrace
    | Wrong_type_error of keytrace * json_type

  type 'a m = ('a * keytrace, access_failure) result

  val keytrace_to_string : keytrace -> string

  val access_failure_to_string : access_failure -> string

  val return : 'a -> 'a m

  val ( >>= ) : 'a m -> ('a * keytrace -> 'b m) -> 'b m

  val counit_with : (access_failure -> 'a) -> 'a m -> 'a

  val to_option : 'a m -> 'a option

  val get_obj : string -> json * keytrace -> json m

  val get_bool : string -> json * keytrace -> bool m

  val get_string : string -> json * keytrace -> string m

  val get_number : string -> json * keytrace -> string m

  val get_number_int : string -> json * keytrace -> int m

  val get_array : string -> json * keytrace -> json list m

  val get_val : string -> json * keytrace -> json m
end

module Access = struct
  type keytrace = string list

  type access_failure =
    | Not_an_object of keytrace
    | Missing_key_error of string * keytrace
    | Wrong_type_error of keytrace * json_type

  type 'a m = ('a * keytrace, access_failure) result

  let keytrace_to_string x =
    if x = [] then
      ""
    else
      let res = List.rev x |> String.concat "." in
      " (at field `" ^ res ^ "`)"

  let access_failure_to_string = function
    | Not_an_object x -> Printf.sprintf "Value is not an object %s" (keytrace_to_string x)
    | Missing_key_error (x, y) -> Printf.sprintf "Missing key: %s%s" x (keytrace_to_string y)
    | Wrong_type_error (x, y) ->
      Printf.sprintf "Value expected to be %s%s" (json_type_to_string y) (keytrace_to_string x)

  let return v = Ok (v, [])

  let ( >>= ) m f =
    match m with
    | Error _ as x -> x
    | Ok x -> f x

  let counit_with f m =
    match m with
    | Ok (v, _) -> v
    | Error e -> f e

  let to_option = function
    | Ok (v, _) -> Some v
    | Error _ -> None

  let catch_type_error exp f (v, keytrace) =
    try Ok (f v, keytrace) with
    | Failure msg when String.equal "int_of_string" msg -> Error (Wrong_type_error (keytrace, exp))
    | Assert_failure _ -> Error (Wrong_type_error (keytrace, exp))

  let get_val k (v, keytrace) =
    try
      let obj = get_object_exn v in
      let candidate =
        List.fold_left obj ~init:None ~f:(fun opt (key, json) ->
            if opt <> None then
              opt
            else if key = k then
              Some json
            else
              None
        )
      in
      match candidate with
      | None -> Error (Missing_key_error (k, keytrace))
      | Some obj -> Ok (obj, k :: keytrace)
    with
    | Assert_failure _ -> Error (Not_an_object keytrace)

  let make_object_json v = JSON_Object (get_object_exn v)

  let get_obj k (v, keytrace) =
    get_val k (v, keytrace) >>= catch_type_error Object_t make_object_json

  let get_bool k (v, keytrace) = get_val k (v, keytrace) >>= catch_type_error Bool_t get_bool_exn

  let get_string k (v, keytrace) =
    get_val k (v, keytrace) >>= catch_type_error String_t get_string_exn

  let get_number k (v, keytrace) =
    get_val k (v, keytrace) >>= catch_type_error Number_t get_number_exn

  let get_number_int k (v, keytrace) =
    get_val k (v, keytrace) >>= catch_type_error Integer_t get_number_int_exn

  let get_array k (v, keytrace) = get_val k (v, keytrace) >>= catch_type_error Array_t get_array_exn
end

let ( >=@ ) : int -> int option -> bool =
 fun lhs rhs ->
  match rhs with
  | None -> false
  | Some rhs -> lhs >= rhs

let ( <=@ ) : int -> int option -> bool =
 fun lhs rhs ->
  match rhs with
  | None -> false
  | Some rhs -> lhs <= rhs

let json_truncate
    ?(max_string_length : int option)
    ?(max_child_count : int option)
    ?(max_depth : int option)
    ?(max_total_count : int option)
    ?(has_changed : bool ref option)
    (json : json) : json =
  let total_count = ref 0 in
  let mark_changed () =
    match has_changed with
    | None -> ()
    | Some r -> r := true
  in
  let rec truncate_children ~child_count children ~f =
    match children with
    | [] -> []
    | _ when !total_count >=@ max_total_count ->
      mark_changed ();
      []
    | _ when child_count >=@ max_child_count ->
      mark_changed ();
      []
    | c :: rest ->
      incr total_count;
      let c' = f c in
      (* because of mutable variable, it's important to do this first *)
      c' :: truncate_children (child_count + 1) rest f
  in
  let rec truncate ~(depth : int) (json : json) : json =
    match json with
    | JSON_Object []
    | JSON_Array []
    | JSON_Number _
    | JSON_Bool _
    | JSON_Null ->
      json
    | JSON_Object props ->
      let f (k, v) = (k, truncate (depth + 1) v) in
      if depth >=@ max_depth then (
        mark_changed ();
        JSON_Object []
      ) else
        JSON_Object (truncate_children ~child_count:0 props ~f)
    | JSON_Array values ->
      let f v = truncate (depth + 1) v in
      if depth >=@ max_depth then (
        mark_changed ();
        JSON_Array []
      ) else
        JSON_Array (truncate_children ~child_count:0 values ~f)
    | JSON_String s ->
      begin
        match max_string_length with
        | None -> json
        | Some max_string_length ->
          if String.length s <= max_string_length then
            JSON_String s
          else (
            mark_changed ();
            JSON_String (String.sub s 0 max_string_length ^ "...")
          )
      end
  in
  truncate ~depth:0 json

let json_truncate_string
    ?(max_string_length : int option)
    ?(max_child_count : int option)
    ?(max_depth : int option)
    ?(max_total_count : int option)
    ?(allowed_total_length : int option)
    ?(if_reformat_multiline = true)
    (s : string) : string =
  if String.length s <=@ allowed_total_length then
    s
  (* fast zero-allocation path for the commonest case *)
  else
    let has_changed = ref false in
    let json = json_of_string s in
    let truncated_json =
      json_truncate
        ?max_string_length
        ?max_child_count
        ?max_depth
        ?max_total_count
        ~has_changed
        json
    in
    if not !has_changed then
      s
    (* moderately fast fewer-string-allocating for another common case *)
    else if if_reformat_multiline then
      json_to_multiline truncated_json
    else
      json_to_string truncated_json

let get_field accessor on_failure json =
  Access.(
    let on_failure af = on_failure (access_failure_to_string af) in
    counit_with on_failure (return json >>= accessor)
  )

let get_field_opt accessor json = Access.(to_option (return json >>= accessor))

module JsonKey = struct
  type t = json

  (* Object comparison is SENSITIVE to the order of keys.                   *)
  (* Numbers are compared by string value, so "1" and "1.0" and "1.00" are  *)
  (* all different; this way we don't worry about different floating point  *)
  (* semantics between ocaml and json.                                      *)
  let rec compare (x : t) (y : t) =
    match (x, y) with
    | (JSON_Null, JSON_Null) -> 0
    | (JSON_Null, _) -> -1
    | (_, JSON_Null) -> 1
    | (JSON_Bool false, JSON_Bool false) -> 0
    | (JSON_Bool false, JSON_Bool true) -> -1
    | (JSON_Bool true, JSON_Bool false) -> 1
    | (JSON_Bool true, JSON_Bool true) -> 0
    | (JSON_Bool _, _) -> -1
    | (_, JSON_Bool _) -> 1
    | (JSON_Number x, JSON_Number y) -> String.compare x y
    | (JSON_Number _, _) -> -1
    | (_, JSON_Number _) -> 1
    | (JSON_String x, JSON_String y) -> String.compare x y
    | (JSON_String _, _) -> -1
    | (_, JSON_String _) -> 1
    | (JSON_Array (x :: xs), JSON_Array (y :: ys)) ->
      let r = compare x y in
      if r <> 0 then
        r
      else
        compare (JSON_Array xs) (JSON_Array ys)
    | (JSON_Array [], JSON_Array []) -> 0
    | (JSON_Array [], JSON_Array _) -> -1
    | (JSON_Array _, JSON_Array []) -> 1
    | (JSON_Array _, _) -> -1
    | (_, JSON_Array _) -> 1
    | (JSON_Object ((kx, vx) :: xs), JSON_Object ((ky, vy) :: ys)) ->
      let r = String.compare kx ky in
      if r <> 0 then
        r
      else
        let r = compare vx vy in
        if r <> 0 then
          r
        else
          compare (JSON_Object xs) (JSON_Object ys)
    | (JSON_Object [], JSON_Object []) -> 0
    | (JSON_Object [], JSON_Object _) -> -1
    | (JSON_Object _, JSON_Object []) -> 1
end

module JSet = Flow_set.Make (JsonKey)
module JMap = WrappedMap.Make (JsonKey)
