{
  (* START HEADER *)

type lexeme = string

let sprintf = Printf.sprintf

module Region = Simple_utils.Region
module Pos    = Simple_utils.Pos
module SMap   = Utils.String.Map
module SSet   = Utils.String.Set

(* TOKENS *)

type t =
  (* Symbols *)

  ARROW of Region.t  (* "->" *)
| CONS  of Region.t  (* "::" *)
| CAT   of Region.t  (* "^"  *)
(*| APPEND   (* "@"  *)*)

  (* Arithmetics *)

| MINUS of Region.t    (* "-" *)
| PLUS  of Region.t    (* "+" *)
| SLASH of Region.t    (* "/" *)
| TIMES of Region.t    (* "*" *)

  (* Compounds *)

| LPAR     of Region.t  (* "(" *)
| RPAR     of Region.t  (* ")" *)
| LBRACKET of Region.t  (* "[" *)
| RBRACKET of Region.t  (* "]" *)
| LBRACE   of Region.t  (* "{" *)
| RBRACE   of Region.t  (* "}" *)

  (* Separators *)

| COMMA of Region.t  (* "," *)
| SEMI  of Region.t  (* ";" *)
| VBAR  of Region.t  (* "|" *)
| COLON of Region.t  (* ":" *)
| DOT   of Region.t  (* "." *)

  (* Wildcard *)

| WILD of Region.t  (* "_" *)

  (* Comparisons *)

| EQ of Region.t      (* "="  *)
| NE of Region.t      (* "<>" *)
| LT of Region.t      (* "<"  *)
| GT of Region.t      (* ">"  *)
| LE of Region.t      (* "<=" *)
| GE of Region.t      (* ">=" *)

| BOOL_OR  of Region.t (* "||" *)
| BOOL_AND of Region.t (* "&&" *)

  (* Identifiers, labels, numbers and strings *)

| Ident  of string Region.reg
| Constr of string Region.reg
| Int    of (string * Z.t) Region.reg
| Nat    of (string * Z.t) Region.reg
| Mutez  of (string * Z.t) Region.reg
| String of string Region.reg
| Bytes  of (string * Hex.t) Region.reg
| Attr   of string Region.reg

  (* Keywords *)

(*| And*)
| Begin of Region.t
| Else  of Region.t
| End   of Region.t
| False of Region.t
| Fun   of Region.t
| Rec   of Region.t
| If    of Region.t
| In    of Region.t
| Let   of Region.t
| Match of Region.t
| Mod   of Region.t
| Not   of Region.t
| Of    of Region.t
| Or    of Region.t
| Then  of Region.t
| True  of Region.t
| Type  of Region.t
| With  of Region.t

  (* Data constructors *)

| C_None  of Region.t  (* "None"  *)
| C_Some  of Region.t  (* "Some"  *)

  (* Virtual tokens *)

| EOF of Region.t (* End of file *)


(* Projections *)

type token = t

let proj_token = function
  (* Literals *)

  String Region.{region; value} ->
    region, sprintf "Str %s" value
| Bytes Region.{region; value = s,b} ->
    region,
    sprintf "Bytes (\"%s\", \"0x%s\")" s (Hex.show b)
| Int Region.{region; value = s,n} ->
    region, sprintf "Int (\"%s\", %s)" s (Z.to_string n)
| Nat Region.{region; value = s,n} ->
    region, sprintf "Nat (\"%s\", %s)" s (Z.to_string n)
| Mutez Region.{region; value = s,n} ->
    region, sprintf "Mutez (\"%s\", %s)" s (Z.to_string n)
| Ident Region.{region; value} ->
    region, sprintf "Ident %s" value
| Constr Region.{region; value} ->
    region, sprintf "Constr %s" value
| Attr Region.{region; value} ->
   region, sprintf "Attr \"%s\"" value

  (* Symbols *)

| ARROW    region -> region, "ARROW"
| CONS     region -> region, "CONS"
| CAT      region -> region, "CAT"
| MINUS    region -> region, "MINUS"
| PLUS     region -> region, "PLUS"
| SLASH    region -> region, "SLASH"
| TIMES    region -> region, "TIMES"
| LPAR     region -> region, "LPAR"
| RPAR     region -> region, "RPAR"
| LBRACKET region -> region, "LBRACKET"
| RBRACKET region -> region, "RBRACKET"
| LBRACE   region -> region, "LBRACE"
| RBRACE   region -> region, "RBRACE"
| COMMA    region -> region, "COMMA"
| SEMI     region -> region, "SEMI"
| VBAR     region -> region, "VBAR"
| COLON    region -> region, "COLON"
| DOT      region -> region, "DOT"
| WILD     region -> region, "WILD"
| EQ       region -> region, "EQ"
| NE       region -> region, "NE"
| LT       region -> region, "LT"
| GT       region -> region, "GT"
| LE       region -> region, "LE"
| GE       region -> region, "GE"
| BOOL_OR  region -> region, "BOOL_OR"
| BOOL_AND region -> region, "BOOL_AND"

  (* Keywords *)

| Begin region -> region, "Begin"
| Else  region -> region, "Else"
| End   region -> region, "End"
| False region -> region, "False"
| Fun   region -> region, "Fun"
| Rec   region -> region, "Rec"
| If    region -> region, "If"
| In    region -> region, "In"
| Let   region -> region, "Let"
| Match region -> region, "Match"
| Mod   region -> region, "Mod"
| Not   region -> region, "Not"
| Of    region -> region, "Of"
| Or    region -> region, "Or"
| Then  region -> region, "Then"
| True  region -> region, "True"
| Type  region -> region, "Type"
| With  region -> region, "With"

  (* Data *)

| C_None region -> region, "C_None"
| C_Some region -> region, "C_Some"

  (* Virtual tokens *)

| EOF region -> region, "EOF"


let to_lexeme = function
  (* Literals *)

  String s   -> String.escaped s.Region.value
| Bytes b    -> fst b.Region.value
| Int i
| Nat i
| Mutez i    -> fst i.Region.value
| Ident id   -> id.Region.value
| Constr id  -> id.Region.value
| Attr a     -> a.Region.value

  (* Symbols *)

| ARROW    _ -> "->"
| CONS     _ -> "::"
| CAT      _ -> "^"
| MINUS    _ -> "-"
| PLUS     _ -> "+"
| SLASH    _ -> "/"
| TIMES    _ -> "*"
| LPAR     _ -> "("
| RPAR     _ -> ")"
| LBRACKET _ -> "["
| RBRACKET _ -> "]"
| LBRACE   _ -> "{"
| RBRACE   _ -> "}"
| COMMA    _ -> ","
| SEMI     _ -> ";"
| VBAR     _ -> "|"
| COLON    _ -> ":"
| DOT      _ -> "."
| WILD     _ -> "_"
| EQ       _ -> "="
| NE       _ -> "<>"
| LT       _ -> "<"
| GT       _ -> ">"
| LE       _ -> "<="
| GE       _ -> ">="
| BOOL_OR  _ -> "||"
| BOOL_AND _ -> "&&"

  (* Keywords *)

| Begin _ -> "begin"
| Else  _ -> "else"
| End   _ -> "end"
| False _ -> "false"
| Fun   _ -> "fun"
| Rec   _ -> "rec"
| If    _ -> "if"
| In    _ -> "in"
| Let   _ -> "let"
| Match _ -> "match"
| Mod   _ -> "mod"
| Not   _ -> "not"
| Of    _ -> "of"
| Or    _ -> "or"
| True  _ -> "true"
| Type  _ -> "type"
| Then  _ -> "then"
| With  _ -> "with"

(* Data constructors *)

| C_None  _ -> "None"
| C_Some  _ -> "Some"

(* Virtual tokens *)

| EOF _ -> ""

(* CONVERSIONS *)

let to_string token ?(offsets=true) mode =
  let region, val_str = proj_token token in
  let reg_str = region#compact ~offsets mode
  in sprintf "%s: %s" reg_str val_str

let to_region token = proj_token token |> fst

(* LEXIS *)

let keywords = [
  (fun reg -> Begin reg);
  (fun reg -> Else  reg);
  (fun reg -> End   reg);
  (fun reg -> False reg);
  (fun reg -> Fun   reg);
  (fun reg -> Rec   reg);
  (fun reg -> If    reg);
  (fun reg -> In    reg);
  (fun reg -> Let   reg);
  (fun reg -> Match reg);
  (fun reg -> Mod   reg);
  (fun reg -> Not   reg);
  (fun reg -> Of    reg);
  (fun reg -> Or    reg);
  (fun reg -> Then  reg);
  (fun reg -> True  reg);
  (fun reg -> Type  reg);
  (fun reg -> With  reg)]

let reserved =
  let open SSet in
  empty
    |> add "as"
    |> add "asr"
    |> add "class"
    |> add "constraint"
    |> add "do"
    |> add "done"
    |> add "downto"
    |> add "exception"
    |> add "external"
    |> add "for"
    |> add "function"
    |> add "functor"
    |> add "inherit"
    |> add "initializer"
    |> add "lazy"
    |> add "lsl"
    |> add "lsr"
    |> add "method"
    |> add "module"
    |> add "mutable"
    |> add "new"
    |> add "nonrec"
    |> add "object"
    |> add "open"
    |> add "private"
    |> add "sig"
    |> add "struct"
    |> add "to"
    |> add "try"
    |> add "val"
    |> add "virtual"
    |> add "when"
    |> add "while"

let constructors = [
  (fun reg -> C_None  reg);
  (fun reg -> C_Some  reg)
]

let add map (key, value) = SMap.add key value map

let mk_map mk_key list =
  let apply map value = add map (mk_key value, value)
  in List.fold_left apply SMap.empty list

type lexis = {
  kwd  : (Region.t -> token) SMap.t;
  cstr : (Region.t -> token) SMap.t;
  res  : SSet.t
}

let lexicon : lexis =
  let build list = mk_map (fun f -> to_lexeme (f Region.ghost)) list
  in {kwd  = build keywords;
      cstr = build constructors;
      res  = reserved}

(* Keywords *)

type kwd_err = Invalid_keyword

let mk_kwd ident region =
  match SMap.find_opt ident lexicon.kwd with
    Some mk_kwd -> Ok (mk_kwd region)
  |        None -> Error Invalid_keyword

(* Identifiers *)

type ident_err = Reserved_name

(* END OF HEADER *)
}

(* START LEXER DEFINITION *)

(* Named regular expressions *)

let small   = ['a'-'z']
let capital = ['A'-'Z']
let letter  = small | capital
let digit   = ['0'-'9']
let ident   = small (letter | '_' | digit)*
let constr  = capital (letter | '_' | digit)*

(* Rules *)

rule scan_ident region lexicon = parse
  (ident as value) eof {
    if   SSet.mem value lexicon.res
    then Error Reserved_name
    else Ok (match SMap.find_opt value lexicon.kwd with
               Some mk_kwd -> mk_kwd region
             |        None -> Ident Region.{region; value}) }

and scan_constr region lexicon = parse
  (constr as value) eof {
    match SMap.find_opt value lexicon.cstr with
      Some mk_cstr -> mk_cstr region
    |         None -> Constr Region.{region; value} }

(* END LEXER DEFINITION *)

{
(* START TRAILER *)

(* Smart constructors (injections) *)

let mk_string lexeme region =
  String Region.{region; value=lexeme}

let mk_bytes lexeme region =
  let norm = Str.(global_replace (regexp "_") "" lexeme) in
  let value = lexeme, `Hex norm
  in Bytes Region.{region; value}

type int_err = Non_canonical_zero

let mk_int lexeme region =
  let z =
    Str.(global_replace (regexp "_") "" lexeme) |> Z.of_string
  in if   Z.equal z Z.zero && lexeme <> "0"
     then Error Non_canonical_zero
     else Ok (Int Region.{region; value = lexeme,z})

type nat_err =
  Invalid_natural
| Non_canonical_zero_nat

let mk_nat lexeme region =
  match (String.index_opt lexeme 'n') with
      None -> Error Invalid_natural
  | Some _ -> let z =
               Str.(global_replace (regexp "_") "" lexeme) |>
                 Str.(global_replace (regexp "n") "") |>
                 Z.of_string in
             if   Z.equal z Z.zero && lexeme <> "0n"
             then Error Non_canonical_zero_nat
             else Ok (Nat Region.{region; value = lexeme,z})

let mk_mutez lexeme region =
  let z =
    Str.(global_replace (regexp "_") "" lexeme) |>
    Str.(global_replace (regexp "mutez") "") |>
    Z.of_string in
  if   Z.equal z Z.zero && lexeme <> "0mutez"
  then Error Non_canonical_zero
  else Ok (Mutez Region.{region; value = lexeme, z})

let eof region = EOF region

type sym_err = Invalid_symbol

let mk_sym lexeme region =
  match lexeme with
  (* Lexemes in common with all concrete syntaxes *)
    ";"   -> Ok (SEMI     region)
  | ","   -> Ok (COMMA    region)
  | "("   -> Ok (LPAR     region)
  | ")"   -> Ok (RPAR     region)
  | "["   -> Ok (LBRACKET region)
  | "]"   -> Ok (RBRACKET region)
  | "{"   -> Ok (LBRACE   region)
  | "}"   -> Ok (RBRACE   region)
  | "="   -> Ok (EQ       region)
  | ":"   -> Ok (COLON    region)
  | "|"   -> Ok (VBAR     region)
  | "->"  -> Ok (ARROW    region)
  | "."   -> Ok (DOT      region)
  | "_"   -> Ok (WILD     region)
  | "^"   -> Ok (CAT      region)
  | "+"   -> Ok (PLUS     region)
  | "-"   -> Ok (MINUS    region)
  | "*"   -> Ok (TIMES    region)
  | "/"   -> Ok (SLASH    region)
  | "<"   -> Ok (LT       region)
  | "<="  -> Ok (LE       region)
  | ">"   -> Ok (GT       region)
  | ">="  -> Ok (GE       region)

  (* Lexemes specific to CameLIGO *)
  | "<>"  -> Ok (NE        region)
  | "::"  -> Ok (CONS      region)
  | "||"  -> Ok (BOOL_OR   region)
  | "&&"  -> Ok (BOOL_AND  region)

  (* Invalid lexemes *)
  |     _ -> Error Invalid_symbol


(* Identifiers *)

let mk_ident lexeme region =
  Lexing.from_string lexeme |> scan_ident region lexicon

(* Constructors *)

let mk_constr lexeme region =
  Lexing.from_string lexeme |> scan_constr region lexicon

(* Attributes *)

type attr_err = Invalid_attribute

let mk_attr header lexeme region =
  if header = "[@" then Error Invalid_attribute
  else Ok (Attr Region.{value=lexeme; region})

(* Predicates *)

let is_string = function String _ -> true | _ -> false
let is_bytes  = function Bytes  _ -> true | _ -> false
let is_int    = function Int    _ -> true | _ -> false
let is_ident  = function Ident  _ -> true | _ -> false
let is_eof    = function EOF    _ -> true | _ -> false
let is_minus  = function MINUS  _ -> true | _ -> false

(* Errors *)

type error =
  Odd_lengthed_bytes
| Missing_break
| Negative_byte_sequence

let error_to_string = function
  Odd_lengthed_bytes ->
    "The length of the byte sequence is an odd number.\n\
     Hint: Add or remove a digit."
| Missing_break ->
    "Missing break.\n\
     Hint: Insert some space."
| Negative_byte_sequence ->
   "Negative byte sequence.\n\
    Hint: Remove the leading minus sign."

exception Error of error Region.reg

let format_error ?(offsets=true) mode Region.{region; value} ~file =
  let msg = error_to_string value
  and reg = region#to_string ~file ~offsets mode in
  let value = sprintf "Lexical error %s:\n%s\n" reg msg
  in Region.{value; region}

let fail region value = raise (Error Region.{region; value})

let check_right_context token next_token buffer : unit =
  let pos    = (to_region token)#stop in
  let region = Region.make ~start:pos ~stop:pos in
  match next_token buffer with
    None -> ()
  | Some (markup, next) ->
      if   is_minus token && is_bytes next
      then let region =
             Region.cover (to_region token) (to_region next)
           in fail region Negative_byte_sequence
      else
        match markup with
          [] ->
            if   is_int token
            then if   is_string next || is_ident next
                 then fail region Missing_break
                 else ()
            else
              if   is_string token
              then if   is_int next || is_bytes next || is_ident next
                   then fail region Missing_break
                   else ()
              else
                if   is_bytes token
                then if is_string next || is_ident next
                     then fail region Missing_break
                     else if   is_int next
                          then fail region Odd_lengthed_bytes
                          else ()
                else ()
        | _::_ -> ()

(* END TRAILER *)
}