module Quox.Parser.Lexer

import Quox.CharExtra
import Quox.Name
import Data.String.Extra
import Data.SortedMap
import public Data.String -- for singleton to reduce in IsReserved
import public Data.List.Elem
import public Text.Lexer
import public Text.Lexer.Tokenizer
import Derive.Prelude
%hide TT.Name


%default total
%language ElabReflection


||| @ Reserved reserved token
||| @ Name name, possibly qualified
||| @ Nat nat literal
||| @ Str string literal
||| @ Tag tag literal
||| @ TYPE "Type" or "★" with ascii nat directly after
||| @ Sup superscript or ^ number (displacement, or universe for ★)
public export
data Token =
    Reserved String
  | Name PName
  | Nat Nat
  | Str String
  | Tag String
  | TYPE Nat
  | Sup Nat
%runElab derive "Token" [Eq, Ord, Show]

||| token or whitespace
||| @ Skip whitespace, comments, etc
||| @ Invalid a token which failed a post-lexer check
|||           (e.g. a qualified name containing a keyword)
||| @ T a well formed token
public export
data ExtToken = Skip | Invalid String String | T Token
%runElab derive "ExtToken" [Eq, Ord, Show]


public export
data ErrorReason =
    NoRuleApply
  | ComposeNotClosing (Int, Int) (Int, Int)
  | Other String
%runElab derive "ErrorReason" [Eq, Ord, Show]

public export
record Error where
  constructor Err
  reason    : ErrorReason
  line, col : Int
  ||| `Nothing` if the error is at the end of the input
  char      : Maybe Char
%runElab derive "StopReason" [Eq, Ord, Show]
%runElab derive "Error"      [Eq, Ord, Show]


private
skip : Lexer -> Tokenizer ExtToken
skip t = match t $ const Skip

private
tmatch : Lexer -> (String -> Token) -> Tokenizer ExtToken
tmatch t f = match t (T . f)


||| [todo] escapes other than `\"` and (accidentally) `\\`
export
fromStringLit : String -> String
fromStringLit = pack . go . unpack . drop 1 . dropLast 1 where
  go : List Char -> List Char
  go []                = []
  go ['\\']            = ['\\'] -- i guess???
  go ('\\' :: c :: cs) = c :: go cs
  go (c :: cs)         = c :: go cs

private
string : Tokenizer ExtToken
string = tmatch stringLit (Str . fromStringLit)

private
nat : Tokenizer ExtToken
nat = tmatch (some (range '0' '9')) (Nat . cast)

private
tag : Tokenizer ExtToken
tag = tmatch (is '\'' <+> name)      (Tag . drop 1)
  <|> tmatch (is '\'' <+> stringLit) (Tag . fromStringLit . drop 1)



private %inline
fromSub : Char -> Char
fromSub c = case c of
  '₀' => '0'; '₁' => '1'; '₂' => '2'; '₃' => '3'; '₄' => '4'
  '₅' => '5'; '₆' => '6'; '₇' => '7'; '₈' => '8'; '₉' => '9'; _ => c

private %inline
fromSup : Char -> Char
fromSup c = case c of
  '⁰' => '0'; '¹' => '1'; '²' => '2'; '³' => '3'; '⁴' => '4'
  '⁵' => '5'; '⁶' => '6'; '⁷' => '7'; '⁸' => '8'; '⁹' => '9'; _ => c

private %inline
subToNat : String -> Nat
subToNat = cast . pack . map fromSub . unpack

private %inline
supToNat : String -> Nat
supToNat = cast . pack . map fromSup . unpack

-- ★0, Type0. base ★/Type is a Reserved
private
universe : Tokenizer ExtToken
universe = universeWith "★" <|> universeWith "Type" where
  universeWith : String -> Tokenizer ExtToken
  universeWith pfx =
    let len = length pfx in
    tmatch (exact pfx <+> digits) (TYPE . cast . drop len)

private
sup : Tokenizer ExtToken
sup = tmatch (some $ pred isSupDigit) (Sup . supToNat)
  <|> tmatch (is '^' <+> digits)      (Sup . cast . drop 1)


private %inline
choice : (xs : List (Tokenizer a)) -> (0 _ : NonEmpty xs) => Tokenizer a
choice (t :: ts) = foldl (\a, b => a <|> b) t ts


namespace Reserved
  ||| description of a reserved symbol
  ||| @ Word a reserved word (must not be followed by letters, digits, etc)
  ||| @ Sym a reserved symbol (must not be followed by symbolic chars)
  ||| @ Punc a character that doesn't show up in names (brackets, etc);
  |||        also a sequence ending in one of those, like `#[`, since the
  |||        difference relates to lookahead
  public export
  data Reserved1 = Word String | Sym String | Punc String
  %runElab derive "Reserved1" [Eq, Ord, Show]

  ||| description of a token that might have unicode & ascii-only aliases
  public export
  data Reserved = Only Reserved1 | Or Reserved1 Reserved1
  %runElab derive "Reserved" [Eq, Ord, Show]

  public export
  Sym1, Word1, Punc1 : String -> Reserved
  Sym1  = Only . Sym
  Word1 = Only . Word
  Punc1 = Only . Punc

public export
resString1 : Reserved1 -> String
resString1 (Punc x) = x
resString1 (Word w) = w
resString1 (Sym  s) = s

||| return the representative string for a token description. if there are
||| two, then it's the first one, which should be the full-unicode one
public export
resString : Reserved -> String
resString (Only r)   = resString1 r
resString (r `Or` _) = resString1 r

||| return both representative strings for a token description
public export
resString2 : Reserved -> List String
resString2 (Only r)   = [resString1 r]
resString2 (r `Or` s) = [resString1 r, resString1 s]

private
resTokenizer1 : Reserved1 -> String -> Tokenizer ExtToken
resTokenizer1 r str =
  let res : String -> Token := const $ Reserved str in
  case r of Word w => tmatch (exact w <+> reject idContEnd) res
            Sym  s => tmatch (exact s <+> reject symCont)   res
            Punc x => tmatch (exact x)                      res

||| match a reserved token
export
resTokenizer : Reserved -> Tokenizer ExtToken
resTokenizer (Only r)   = resTokenizer1 r (resString1 r)
resTokenizer (r `Or` s) =
  resTokenizer1 r (resString1 r) <|> resTokenizer1 s (resString1 r)

||| reserved words & symbols.
||| the tokens recognised by ``a `Or` b`` will be `Reserved a`.
||| e.g. `=>` in the input (if not part of a longer name)
||| will be returned as `Reserved "⇒"`.
public export
reserved : List Reserved
reserved =
  [Punc1 "(", Punc1 ")", Punc1 "[", Punc1 "]", Punc1 "{", Punc1 "}",
   Punc1 ",", Punc1 ";", Punc1 "#[",
   Sym1 "@",
   Sym1 ":",
   Sym "⇒" `Or` Sym "=>",
   Sym "→" `Or` Sym "->",
   Sym "×" `Or` Sym "**",
   Sym "≡" `Or` Sym "==",
   Sym "∷" `Or` Sym "::",
   Punc1 ".",
   Word1 "case",
   Word1 "case0", Word1 "case1",
   Word "caseω" `Or` Word "case#",
   Word1 "return",
   Word1 "of",
   Word1 "fst", Word1 "snd",
   Word1 "_",
   Word1 "Eq",
   Word "λ" `Or` Word "fun",
   Word "δ" `Or` Word "dfun",
   Word "ω" `Or` Sym "#",
   Sym "★" `Or` Word "Type",
   Word "ℕ" `Or` Word "Nat",
   Word1 "zero", Word1 "succ",
   Word1 "coe", Word1 "comp",
   Word1 "def",
   Word1 "def0",
   Word "defω" `Or` Word "def#",
   Sym1 "=",
   Word1 "load",
   Word1 "namespace"]

public export
reservedStrings : List String
reservedStrings = map resString reserved

public export
allReservedStrings : List String
allReservedStrings = foldMap resString2 reserved

||| `IsReserved str` is true if `Reserved str` might actually show up in
||| the token stream
public export
IsReserved : String -> Type
IsReserved str = So (str `elem` allReservedStrings)

private
name : Tokenizer ExtToken
name =
  match name $ \str =>
    let parts = split (== '.') $ normalizeNfc str in
    case find (`elem` allReservedStrings) (toList parts) of
      Nothing => T $ Name $ fromListP parts
      Just w  => Invalid "reserved word '\{w}' inside name \{str}" str

export
tokens : Tokenizer ExtToken
tokens = choice $
  map skip [pred isWhitespace,
            lineComment (exact "--" <+> reject symCont),
            blockComment (exact "{-") (exact "-}")] <+>
  [universe] <+>  -- ★ᵢ takes precedence over bare ★
  map resTokenizer reserved <+>
  [sup, nat, string, tag, name]

export
check : Alternative f =>
        WithBounds ExtToken -> Either Error (f (WithBounds Token))
check (MkBounded val irr bounds@(MkBounds line col _ _)) = case val of
  Skip            => Right empty
  T tok           => Right $ pure $ MkBounded tok irr bounds
  Invalid msg tok => Left  $ Err (Other msg) line col (index 0 tok)

export
toErrorReason : StopReason -> Maybe ErrorReason
toErrorReason EndInput                = Nothing
toErrorReason NoRuleApply             = Just NoRuleApply
toErrorReason (ComposeNotClosing s e) = Just $ ComposeNotClosing s e

export
lex : String -> Either Error (List (WithBounds Token))
lex str =
  let (res, reason, line, col, str) = lex tokens str in
  case toErrorReason reason of
    Nothing => concatMap check res @{MonoidApplicative}
    Just e  => Left $ Err {reason = e, line, col, char = index 0 str}