import std/options
import std/strutils
import std/strformat
import std/collections/sequtils
import std/sugar
import std/collections/tables
import results
import fusion/matching
import fp/maybe
import ./parser_types
import ../utils/str

{.experimental: "caseStmtMacros".}

# -- Parsing Functions

func ch*(expectedChars: set[char]): (Parser -> ParserResult) {.inline.} =
  return func(parser: Parser): ParserResult =
    let state = parser.state
    let newIndex = state.position + 1

    if newIndex > (state.stream.len - 1):
      return err(ParserError(
        kind: endOfStringErr,
        expected: &"{expectedChars.prettyExpectedSet()}",
        index: newIndex,
        parser: parser,
      ))
    else:
      let foundChar = state.stream[newIndex]
      if foundChar in expectedChars:
        return Parser(
          state: ParserState(
            stream: state.stream,
            position: newIndex,
            lastPosition: parser.state.position,
          ),
          tokens: parser.tokens & initParserToken(foundChar)
        ).ok()
      else:
        return err(ParserError(
          kind: charMismatchErr,
          unexpected: &"{foundChar}",
          expected: &"{expectedChars.prettyExpectedSet()}",
          index: newIndex,
          parser: parser,
        ))

func ch*(expectedChar: char): (Parser -> ParserResult) {.inline.} =
  return func(parser: Parser): ParserResult =
    let state = parser.state
    let newIndex = state.position + 1

    if newIndex > (state.stream.len - 1):
      return err(ParserError(
        kind: endOfStringErr,
        expected: &"{expectedChar}",
        index: newIndex,
        parser: parser,
      ))
    else:
      let foundChar = state.stream[newIndex]
      if expectedChar == foundChar:
        return Parser(
          state: ParserState(
            stream: state.stream,
            position: newIndex,
            lastPosition: parser.state.position,
          ),
          tokens: parser.tokens & initParserToken(foundChar)
        ).ok()
      else:
        return err(ParserError(
          kind: charMismatchErr,
          unexpected: &"{foundChar}",
          expected: &"{expectedChar}",
          index: newIndex,
          parser: parser,
        ))

let anyCh* = ch(AllChars)

func str*(s: string): (Parser -> ParserResult) {.inline.} =
  return func(parser: Parser): ParserResult =
    var p = parser.ok()
    for c in s.items:
      p = p.flatMap(ch(c))
    return p


# -- Parsing Helper Functions

func optional*(parserFn: Parser -> ParserResult): (Parser -> ParserResult) {.inline.} =
  ## Parse characters and ignore failure
  return proc(parser: Parser): ParserResult =
    let newParser = parserFn(parser)

    if newParser.isOk():
      newParser
    else:
      parser.ok()

func ignore*(parserFn: Parser -> ParserResult): (Parser -> ParserResult) {.inline.} =
  ## Parse characters but throw success tokens away
  return proc(parser: Parser): ParserResult =
    return parserFn(parser)
    .map((x: Parser) => Parser(
      state: x.state,
      tokens: parser.tokens,
    ))

func manyUntil*(acceptFn: Parser -> ParserResult, stopFn: Parser -> ParserResult): (Parser -> ParserResult) {.inline.} =
  ## Parse characters but throw success tokens away
  return proc(parser: Parser): ParserResult =
    var res: ParserResult = parser.ok()
    while res.isOk() and res.flatMap(stopFn).isErr():
      res = res.flatMap(acceptFn)
    return res

proc anyUntil*(stopFn: Parser -> ParserResult): (Parser -> ParserResult) {.inline.} =
  manyUntil(anyCh, stopFn)

func choice*(parsers: seq[Parser -> ParserResult]): (Parser -> ParserResult) {.inline.} =
  return proc(parser: Parser): ParserResult =
    var errors: seq[ParserResult] = newSeq[ParserResult]()
    var found = Nothing[ParserResult]()

    for fn in parsers:
      let fnResult: ParserResult = fn(parser)

      if fnResult.isOk():
        found = fnResult.just
        break
      else:
        errors = errors & fnResult

    return found
    .fold(
      proc(): ParserResult =
        let prettyErrors = errors.map((x: ParserResult) => x.error().expected)
        err(ParserError(
          kind: choiceMismatchErr,
          index: parser.state.position + 1,
          expected: &"Choice ({prettyErrors})",
          unexpected: errors[0].error().unexpected,
          parser: parser,
        )),
      proc(x: ParserResult): ParserResult = x,
    )


proc `+`*(parserFnA: Parser -> ParserResult, parserFnB: Parser -> ParserResult): (Parser -> ParserResult) {.inline.} =
  ## Parse characters and ignore failure
  return proc(parser: Parser): ParserResult =
    parserFnA(parser).flatMap(parserFnB)

proc parseSeq*(parser: ParserResult, xs: seq[Parser -> ParserResult]): ParserResult =
  xs.foldl(a.flatMap(b), parser)

# -- Parsing Aliases

proc endOfStream*(parser: Parser): ParserResult =
  let index = parser.state.position + 1
  if index == parser.state.stream.len:
    ok(parser)
  else:
    err(ParserError(
      kind: endOfStringErr,
      expected: &"EndOfString",
      index: index,
      parser: parser,
    ))

let newlineParser = choice(@[
  ch(NewLines),
  endOfStream,
])
proc newline*(parser: Parser): ParserResult =
  newlineParser(parser)
  .mapErr((x: ParserError) => x.setErrorExpectedField("Newline"))

let whitespaceParser = choice(@[
  ch(Whitespace),
  newlineParser,
])
proc whitespace*(parser: Parser): ParserResult =
  whitespaceParser(parser)
  .mapErr((x: ParserError) => x.setErrorExpectedField("Whitespace"))

# when isMainModule:
#   proc getTokens(x: ParserResult): seq[string] =
#     x.foldTokens(
#       proc(err: ParserError): seq[string] =
#         echo err
#         @[],
#       proc(xs: seq[ParserToken]): seq[string] = xs.map((x: ParserToken) => x.tokenStringValue()),
#     )

#   proc testParser(x: string, ps: seq[Parser -> ParserResult]): seq[string] =
#     initParserResult(x).parseSeq(ps).getTokens()

#   let optionalPrefixParser = @[
#     optional(ch('_')),
#     str("ABC")
#   ]
#   assert: "_ABC".testParser(optionalPrefixParser) == @["_", "A", "B", "C"]
#   assert: "ABC".testParser(optionalPrefixParser) == @["A", "B", "C"]

#   let andParser = @[
#     (ch('A') + ch('B')),
#     ch('C'),
#   ]
#   assert: "ABC".testParser(andParser) == @["A", "B", "C"]

#   let newlineParserTest = @[
#     str("ABC"),
#     newline
#   ]
#   assert "ABC\n".testParser(newlineParserTest) == @["A", "B", "C", "\n"]