module Quox.Parser.Parser

import public Quox.Parser.Lexer
import public Quox.Parser.Syntax

import Data.Bool
import Data.Fin
import Data.Vect
import public Text.Parser
import Derive.Prelude

%language ElabReflection
%default total


public export
0 Grammar : Bool -> Type -> Type
Grammar = Core.Grammar () Token
%hide Core.Grammar


public export
data Error =
    LexError   Lexer.Error
  | ParseError (List1 (ParsingError Token))
%hide Lexer.Error
%runElab derive "Error" [Show]


export
lexParseWith : {c : Bool} -> Grammar c a -> String -> Either Error a
lexParseWith grm input = do
  toks <- mapFst LexError $ lex input
  bimap ParseError fst $ parse (grm <* eof) toks

export
withLoc : {c : Bool} -> FileName -> (Grammar c (Loc -> a)) -> Grammar c a
withLoc fname act = bounds act <&> \res =>
  if res.isIrrelevant then res.val noLoc
  else res.val $ makeLoc fname res.bounds

export
defLoc : FileName -> (Loc -> a) -> Grammar False a
defLoc fname f = position <&> f . makeLoc fname

export
unused : FileName -> Grammar False PatVar
unused fname = defLoc fname Unused


||| reserved token, like punctuation or keywords etc
export
res : (str : String) -> (0 _ : IsReserved str) => Grammar True ()
res str = terminal "expected \"\{str}\"" $ guard . (== Reserved str)

||| optional reserved token, e.g. trailing comma
export
optRes : (str : String) -> (0 _ : IsReserved str) => Grammar False ()
optRes str = ignore $ optional $ res str

||| reserved token, then commit
export
resC : (str : String) -> (0 _ : IsReserved str) => Grammar True ()
resC str = do res str; commit

||| reserved token or fatal error
export
needRes : (str : String) -> (0 _ : IsReserved str) => Grammar True ()
needRes str = resC str <|> fatalError "expected \"\{str}\""


private
terminalMatchN_ : String -> List (TTImp, TTImp) -> Elab (Grammar True a)
terminalMatchN_ what matches = do
  func <- check $ lam (lambdaArg `{x}) $
    iCase `(x) implicitFalse $
    map (\(l, r) => patClause l `(Just ~(r))) matches ++
      [patClause `(_) `(Nothing)]
  pure $ terminal "expected \{what}" func

private %macro
terminalMatchN : String -> List (TTImp, TTImp) -> Elab (Grammar True a)
terminalMatchN = terminalMatchN_

private %macro
terminalMatch : String -> TTImp -> TTImp -> Elab (Grammar True a)
terminalMatch what l r = terminalMatchN_ what [(l, r)]

||| tag without leading `'`
export
bareTag : Grammar True TagVal
bareTag = terminalMatchN "bare tag" [(`(Name t), `(show t)), (`(Str s), `(s))]

||| tag with leading quote
export
tag : Grammar True TagVal
tag = terminalMatch "tag" `(Tag t) `(t)

||| natural number
export
nat : Grammar True Nat
nat = terminalMatch "natural number" `(Nat n) `(n)

||| string literal
export
strLit : Grammar True String
strLit = terminalMatch "string literal" `(Str s) `(s)

||| single-token universe, like ★₀ or Type1
export
universe1 : Grammar True Universe
universe1 = terminalMatch "universe" `(TYPE u) `(u)

||| possibly-qualified name
export
qname : Grammar True PName
qname = terminalMatch "name" `(Name n) `(n)

||| unqualified name
export
baseName : Grammar True PBaseName
baseName = terminalMatch "unqualified name" `(Name (MakePName [<] b)) `(b)

||| dimension constant (0 or 1)
export
dimConst : Grammar True DimConst
dimConst = terminalMatchN "dimension constant"
  [(`(Nat 0), `(Zero)), (`(Nat 1), `(One))]

||| quantity (0, 1, or ω)
export
qtyVal : Grammar True Qty
qtyVal = terminalMatchN "quantity"
  [(`(Nat 0), `(Zero)), (`(Nat 1), `(One)), (`(Reserved "ω"), `(Any))]


||| quantity (0, 1, or ω)
export
qty : FileName -> Grammar True PQty
qty fname = withLoc fname [|PQ qtyVal|]


||| pattern var (unqualified name or _)
export
patVar : FileName -> Grammar True PatVar
patVar fname = withLoc fname $
  [|PV baseName|] <|> Unused <$ res "_"


||| dimension (without `@` prefix)
export
dim : FileName -> Grammar True PDim
dim fname = withLoc fname $ [|K dimConst|] <|> [|V baseName|]

||| dimension argument (with @)
export
dimArg : FileName -> Grammar True PDim
dimArg fname = do resC "@"; mustWork $ dim fname


delim : (o, c : String) -> (0 _ : IsReserved o) => (0 _ : IsReserved c) =>
        {k : Bool} -> Grammar k a -> Grammar True a
delim o c p = resC o *> p <* needRes c

-- this stuff is Like This (rather than just being delim + sepEndBy{1})
-- so that it checks for the close bracket before trying another list element,
-- giving (imo) a better error
parameters (o, c, s : String)
           {auto 0 _ : IsReserved o} {auto 0 _ : IsReserved c}
           {auto 0 _ : IsReserved s}
           (p : Grammar True a)
  private
  dsBeforeDelim, dsAfterDelim : Grammar True (List a)
  dsBeforeDelim = [] <$ resC c <|> resC s *> assert_total dsAfterDelim
  dsAfterDelim  = [] <$ resC c <|> [|p :: assert_total dsBeforeDelim|]

  export
  delimSep1 : Grammar True (List1 a)
  delimSep1 = resC o *> [|p ::: dsBeforeDelim|]

  export
  delimSep : Grammar True (List a)
  delimSep = resC o *> dsAfterDelim


||| enum type, e.g. `{a, b, c.d, "e f g"}`
export
enumType : Grammar True (List TagVal)
enumType = delimSep "{" "}" "," bareTag

||| e.g. `case` or `case 1.`
export
caseIntro : FileName -> Grammar True PQty
caseIntro fname =
      withLoc fname (PQ Zero <$ res "case0")
  <|> withLoc fname (PQ One  <$ res "case1")
  <|> withLoc fname (PQ Any  <$ res "caseω")
  <|> delim "case" "." (qty fname)

export
qtyPatVar : FileName -> Grammar True (PQty, PatVar)
qtyPatVar fname = [|(,) (qty fname) (needRes "." *> patVar fname)|]


export
ptag : FileName -> Grammar True PTagVal
ptag fname = withLoc fname $ [|PT tag|]

public export
data PCasePat =
    PPair PatVar PatVar Loc
  | PTag  PTagVal Loc
  | PZero Loc
  | PSucc PatVar PQty PatVar Loc
  | PBox  PatVar Loc
%runElab derive "PCasePat" [Eq, Ord, Show]

export
Located PCasePat where
  (PPair _ _   loc).loc = loc
  (PTag  _     loc).loc = loc
  (PZero       loc).loc = loc
  (PSucc _ _ _ loc).loc = loc
  (PBox  _     loc).loc = loc

||| either `zero` or `0`
export
zeroPat : Grammar True ()
zeroPat = resC "zero" <|> terminal "expected '0'" (guard . (== Nat 0))

export
casePat : FileName -> Grammar True PCasePat
casePat fname = withLoc fname $
      delim "(" ")" [|PPair (patVar fname) (needRes "," *> patVar fname)|]
  <|> [|PTag (ptag fname)|]
  <|> PZero <$ zeroPat
  <|> do p  <- resC "succ" *> patVar fname
         ih <- resC "," *> qtyPatVar fname
           <|> [|(,) (defLoc fname $ PQ Zero) (unused fname)|]
         pure $ PSucc p (fst ih) (snd ih)
  <|> delim "[" "]" [|PBox (patVar fname)|]
  <|> fatalError "invalid pattern"

export
term : FileName -> Grammar True PTerm
-- defined after all the subterm parsers

export
typeLine : FileName -> Grammar True (PatVar, PTerm)
typeLine fname = do
  resC "["
  mustWork $ do
    i <- patVar fname <* resC "⇒" <|> unused fname
    t <- assert_total term fname <* needRes "]"
    pure (i, t)

||| box term `[t]` or type `[π.A]`
export
boxTerm : FileName -> Grammar True PTerm
boxTerm fname = withLoc fname $ do
  res "["; commit
  q <- optional $ qty fname <* res "."
  t <- mustWork $ assert_total term fname <* needRes "]"
  pure $ maybe (Box t) (\q => BOX q t) q

||| tuple term like `(a, b)`, or parenthesised single term.
||| allows terminating comma. more than two elements are nested on the right:
||| `(a, b, c, d) = (a, (b, (c, d)))`.
export
tupleTerm : FileName -> Grammar True PTerm
tupleTerm fname = withLoc fname $ do
  terms <- delimSep1 "(" ")" "," $ assert_total term fname
  pure $ \loc => foldr1 (\s, t => Pair s t loc) terms

||| argument/atomic term: single-token terms, or those with delimiters e.g.
||| `[t]`
export
termArg : FileName -> Grammar True PTerm
termArg fname = withLoc fname $
      [|TYPE universe1|]
  <|> [|Enum enumType|]
  <|> [|Tag tag|]
  <|> const <$> boxTerm fname
  <|> Nat  <$ res "ℕ"
  <|> Zero <$ res "zero"
  <|> [|fromNat nat|]
  <|> [|V qname|]
  <|> const <$> tupleTerm fname

||| optionally, two dimension arguments. if absent default to `@0 @1`
private
optDirection : FileName -> Grammar False (PDim, PDim)
optDirection fname = withLoc fname $ do
  dims <- optional [|(,) (dimArg fname) (dimArg fname)|]
  pure $ \loc => fromMaybe (K Zero loc, K One loc) dims

export
coeTerm : FileName -> Grammar True PTerm
coeTerm fname = withLoc fname $ do
  resC "coe"
  mustWork $ do
    line   <- typeLine fname
    (p, q) <- optDirection fname
    val    <- termArg fname
    pure $ Coe line p q val

public export
CompBranch : Type
CompBranch = (DimConst, PatVar, PTerm)

export
compBranch : FileName -> Grammar True CompBranch
compBranch fname =
  [|(,,) dimConst (patVar fname) (needRes "⇒" *> assert_total term fname)|]

private
checkCompTermBody : (PatVar, PTerm) -> PDim -> PDim -> PTerm -> PDim ->
                    CompBranch -> CompBranch -> Bounds ->
                    Grammar False (Loc -> PTerm)
checkCompTermBody a p q s r (e0, s0) (e1, s1) bounds =
  case (e0, e1) of
    (Zero, One)  => pure $ Comp a p q s r s0 s1
    (One,  Zero) => pure $ Comp a p q s r s1 s0
    (_,    _)    =>
      fatalLoc bounds "body of 'comp' needs one 0 case and one 1 case"

export
compTerm : FileName -> Grammar True PTerm
compTerm fname = withLoc fname $ do
  resC "comp"
  mustWork $ do
    a <- typeLine fname
    (p, q) <- optDirection fname
    s <- termArg fname; r <- dimArg fname
    bodyStart <- bounds $ needRes "{"
    s0 <- compBranch fname; needRes ";"
    s1 <- compBranch fname; optRes  ";"
    bodyEnd <- bounds $ needRes "}"
    let body = bounds $ mergeBounds bodyStart bodyEnd
    checkCompTermBody a p q s r s0 s1 body

export
splitUniverseTerm : FileName -> Grammar True PTerm
splitUniverseTerm fname = withLoc fname $ resC "★" *> mustWork [|TYPE nat|]

export
eqTerm : FileName -> Grammar True PTerm
eqTerm fname = withLoc fname $
  resC "Eq" *> mustWork [|Eq (typeLine fname) (termArg fname) (termArg fname)|]

export
succTerm : FileName -> Grammar True PTerm
succTerm fname = withLoc fname $
  resC "succ" *> mustWork [|Succ (termArg fname)|]

||| a dimension argument with an `@` prefix, or
||| a term argument with no prefix
export
anyArg : FileName -> Grammar True (Either PDim PTerm)
anyArg fname = dimArg fname <||> termArg fname

export
normalAppTerm : FileName -> Grammar True PTerm
normalAppTerm fname = withLoc fname $ do
  head <- termArg fname
  args <- many $ anyArg fname
  pure $ \loc => foldl (ap loc) head args
where ap : Loc -> PTerm -> Either PDim PTerm -> PTerm
      ap loc f (Left  p) = DApp f p loc
      ap loc f (Right s) = App  f s loc

||| application term `f x @y z`, or other terms that look like application
||| like `succ` or `coe`.
export
appTerm : FileName -> Grammar True PTerm
appTerm fname =
      coeTerm fname
  <|> compTerm fname
  <|> splitUniverseTerm fname
  <|> eqTerm fname
  <|> succTerm fname
  <|> normalAppTerm fname

export
infixEqTerm : FileName -> Grammar True PTerm
infixEqTerm fname = withLoc fname $ do
  l <- appTerm fname; commit
  rest <- optional $ res "≡" *>
    [|(,) (assert_total term fname) (needRes ":" *> appTerm fname)|]
  let u = Unused $ onlyStart l.loc
  pure $ \loc => maybe l (\rest => Eq (u, snd rest) l (fst rest) loc) rest

export
annTerm : FileName -> Grammar True PTerm
annTerm fname = withLoc fname $ do
  tm <- infixEqTerm fname; commit
  ty <- optional $ res "∷" *> assert_total term fname
  pure $ \loc => maybe tm (\ty => Ann tm ty loc) ty

export
lamTerm : FileName -> Grammar True PTerm
lamTerm fname = withLoc fname $ do
  k <- DLam <$ res "δ" <|> Lam <$ res "λ"
  mustWork $ do
    xs   <- some $ patVar fname;     needRes "⇒"
    body <- assert_total term fname; commit
    pure $ \loc => foldr (\x, s => k x s loc) body xs

-- [todo] fix the backtracking in e.g. (F x y z × B)
export
properBinders : FileName -> Grammar True (List1 PatVar, PTerm)
properBinders fname = assert_total $ do
  -- putting assert_total directly on `term`, in this one function,
  -- doesn't work. i cannot tell why
  res "("
  xs <- some $ patVar fname; resC ":"
  t  <- term fname;          needRes ")"
  pure (xs, t)

export
piTerm : FileName -> Grammar True PTerm
piTerm fname = withLoc fname $ do
  q   <- qty fname;               resC "."
  dom <- piBinder;                needRes "→"
  cod <- assert_total term fname; commit
  pure $ \loc => foldr (\x, t => Pi q x (snd dom) t loc) cod (fst dom)
where
  piBinder : Grammar True (List1 PatVar, PTerm)
  piBinder = properBinders fname
         <|> [|(,) [|singleton $ unused fname|] (termArg fname)|]

export
sigmaTerm : FileName -> Grammar True PTerm
sigmaTerm fname =
      (properBinders fname >>= continueDep)
  <|> (annTerm fname       >>= continueNondep)
where
  continueDep : (List1 PatVar, PTerm) -> Grammar True PTerm
  continueDep (names, fst) = withLoc fname $ do
    snd <- needRes "×" *> sigmaTerm fname
    pure $ \loc => foldr (\x, snd => Sig x fst snd loc) snd names

  cross : PTerm -> PTerm -> PTerm
  cross l r = let loc = extend' l.loc r.loc.bounds in
              Sig (Unused $ onlyStart l.loc) l r loc

  continueNondep : PTerm -> Grammar False PTerm
  continueNondep fst = do
    rest <- optional $ resC "×" *> sepBy1 (res "×") (annTerm fname)
    pure $ foldr1 cross $ fst ::: maybe [] toList rest

public export
PCaseArm : Type
PCaseArm = (PCasePat, PTerm)

export
caseArm : FileName -> Grammar True PCaseArm
caseArm fname =
  [|(,) (casePat fname) (needRes "⇒" *> assert_total term fname)|]

export
checkCaseArms : Loc -> List PCaseArm -> Grammar False PCaseBody
checkCaseArms loc [] = pure $ CaseEnum [] loc
checkCaseArms loc ((PPair x y _, rhs) :: rest) =
  if null rest then pure $ CasePair (x, y) rhs loc
  else fatalError "unexpected pattern after pair"
checkCaseArms loc ((PTag tag _, rhs1) :: rest) = do
  let rest = for rest $ \case
        (PTag tag _, rhs) => Just (tag, rhs)
        _                 => Nothing
  maybe (fatalError "expected all patterns to be tags")
        (\rest => pure $ CaseEnum ((tag, rhs1) :: rest) loc) rest
checkCaseArms loc ((PZero _, rhs1) :: rest) = do
  let [(PSucc p q ih _, rhs2)] = rest
    | _ => fatalError "expected succ pattern after zero"
  pure $ CaseNat rhs1 (p, q, ih, rhs2) loc
checkCaseArms loc ((PSucc p q ih _, rhs1) :: rest) = do
  let [(PZero _, rhs2)] = rest
    | _ => fatalError "expected zero pattern after succ"
  pure $ CaseNat rhs2 (p, q, ih, rhs1) loc
checkCaseArms loc ((PBox x _, rhs) :: rest) =
  if null rest then pure $ CaseBox x rhs loc
  else fatalError "unexpected pattern after box"

export
caseBody : FileName -> Grammar True PCaseBody
caseBody fname = do
  body <- bounds $ delimSep "{" "}" ";" $ caseArm fname
  let loc = makeLoc fname body.bounds
  checkCaseArms loc body.val

export
caseReturn : FileName -> Grammar True (PatVar, PTerm)
caseReturn fname = do
  x   <- patVar fname <* resC "⇒" <|> unused fname
  ret <- assert_total term fname
  pure (x, ret)

export
caseTerm : FileName -> Grammar True PTerm
caseTerm fname = withLoc fname $ do
  qty <- caseIntro fname;                     commit
  head <- mustWork $ assert_total term fname; needRes "return"
  ret  <- mustWork $ caseReturn fname;        needRes "of"
  body <- mustWork $ caseBody fname
  pure $ Case qty head ret body

-- export
-- term : FileName -> Grammar True PTerm
term fname = lamTerm fname
         <|> caseTerm fname
         <|> piTerm fname
         <|> sigmaTerm fname


export
decl : FileName -> Grammar True PDecl

||| `def` alone means `defω`
export
defIntro : FileName -> Grammar True PQty
defIntro fname =
      withLoc fname (PQ Zero <$ resC "def0")
  <|> withLoc fname (PQ Any  <$ resC "defω")
  <|> do pos <- bounds $ resC "def"
         let any = PQ Any $ makeLoc fname pos.bounds
         option any $ qty fname <* needRes "."

export
definition : FileName -> Grammar True PDefinition
definition fname = withLoc fname $ do
  qty  <- defIntro fname
  name <- baseName
  type <- optional $ resC ":" *> mustWork (term fname)
  term <- needRes "=" *> mustWork (term fname)
  optRes ";"
  pure $ MkPDef qty name type term

export
namespace_ : FileName -> Grammar True PNamespace
namespace_ fname = withLoc fname $ do
  ns    <- resC "namespace" *> qname; needRes "{"
  decls <- nsInner; optRes ";"
  pure $ MkPNamespace (ns.mods :< ns.base) decls
where
  nsInner : Grammar True (List PDecl)
  nsInner = [] <$ resC "}"
        <|> [|(assert_total decl fname <* commit) :: assert_total nsInner|]

decl fname = [|PDef $ definition fname|] <|> [|PNs $ namespace_ fname|]

export
load : FileName -> Grammar True PTopLevel
load fname = withLoc fname $
  resC "load" *> mustWork [|PLoad strLit|] <* optRes ";"

export
topLevel : FileName -> Grammar True PTopLevel
topLevel fname = load fname <|> [|PD $ decl fname|]

export
input : FileName -> Grammar False (List PTopLevel)
input fname = [] <$ eof
          <|> [|(topLevel fname <* commit) :: assert_total input fname|]

export
lexParseTerm : FileName -> String -> Either Error PTerm
lexParseTerm = lexParseWith . term

export
lexParseInput : FileName -> String -> Either Error (List PTopLevel)
lexParseInput = lexParseWith . input