modsemParseEnv <- rlang::env(
  syntaxLines = NULL
)


resetModsemParseEnv <- function() {
  modsemParseEnv$syntaxLines <- NULL
}


getCharsLine <- function(line, i = 1) {
  if (is.null(line) || nchar(line) == 0) {
    return(" ")
  } else if (i > nchar(line)) {
    return(NULL)
  }
  rest <- getCharsLine(line, i + 1)
  c(substr(line, i, i),rest)
}


getLines <- function(syntax) {
  operators <- c("=~", "<~", "<=", ">=", "==", ":=", "~~", "~",
                 "+", "*", "<-", "->", "<", ">", "-", "|", ",")
  for (op in operators) {
    pattern <- paste0("\\", op, "\\s*[\n|;]")
    replace <- paste0(op, " ")
    syntax <- stringr::str_replace_all(syntax, pattern, replace)
  }

  lines <- strsplit(syntax, "\n|;") |>
    unlist() |>
    as.list() |>
    lapply(getCharsLine)
  lines <- purrr::imap(lines,
                  function(x, lNum)
                    structure(x, lineNumber = lNum))
  lines
}


createTokensLine <- function(line, i = 1,
                             token = NULL, listTokens = list()) {
  if (i > length(line)) {
    return(appendToList(listTokens, token))
  }

  if (length(listTokens) > 0 && is.MathOperator(last(listTokens))) {
    lastToken <- last(listTokens)
    offset <- attr(lastToken, "pos") + nchar(lastToken)

    token <- buildMathExprToken(line[offset:length(line)], pos = offset)
    return(appendToList(listTokens, token))
  }


  if (is.null(token)) {
    token <- initializeToken(line[[i]], pos = i, line)
  } else {
    if (fitsToken(token, nextChar = line[[i]])) {
      token <- addCharToken(token, nextChar = line[[i]])

    } else {
      listTokens <- appendToList(listTokens, token)
      token <- initializeToken(line[[i]], pos = i, line)
    }
  }
  if ("LavComment" %in% class(token)) {
      return(listTokens)
    }
  return(createTokensLine(line, i + 1, token, listTokens = listTokens))
}


initializeToken <- function(char, pos, line) {
  nextChar <- if (pos + 1 <= length(line)) line[[pos + 1]] else ""

  nextCharIsAlpha <- grepl("[[:alpha:]\\.]", nextChar)
  nextCharIsNum   <- grepl("[[:digit:]]", nextChar)
  opChars <- c("=", "~", "*", "+", "<", ">", ":", "^", "/", "-", "|", ",")

  # optimaly this should be a switch
  if (grepl("#", char)) {
    type  <- "LavComment"
    priority <- 999
  } else if (grepl("\\s+", char)) {
    type <- "LavBlank"
    priority <- 999
  } else if (grepl("[[:alpha:]_]", char) || (char == "." & nextCharIsAlpha)) {
    type <- "LavName"
    priority <- 10
  } else if (grepl("[\\(\\)]", char)) {
    type <- "LavClosure"
    priority <- 2
  } else if (char %in% opChars) {
    type <- "LavOperator"
    priority <- 0
  } else if (grepl("[[:alnum:]]", char) || (char == "." & nextCharIsNum)) {
    type <- "LavNumeric"
    priority <- 10
  } else if (grepl('\\"' , char)) {
    type <- "LavString"
    priority <- 10
  } else {
    mod_msg_stop(paste0("Unrecognized class of token in line ", attr(line, "lineNumber"),
         " pos ", pos, "\n",
         highlightError(line, pos = pos)))
  }

  structure(char,
            pos = pos,
            lineNumber = attr(line, "lineNumber"),
            priority = priority,
            class = c(type, "LavToken"))
}


buildMathExprToken <- function(restLine, pos) {
  token <- stringr::str_c(restLine, collapse = "")
  structure(token,
            pos = pos,
            lineNumber = attr(restLine, "lineNumber"),
            priority = 10,
            class = c("LavMathExpr", "LavToken"))
}


fitsToken <- function(token, nextChar) {
  UseMethod("fitsToken")
}


#' @export
fitsToken.LavName <- function(token, nextChar) {
  mod_stopif(length(nextChar) != 1, paste0("Wrong length of nextChar", nextChar))
  # if object name ends with ( it is a function,
  # and next char belongs to a new object
  if (grepl("\\($", token)) {
    return(FALSE)
  }
  grepl("[[:alpha:][:digit:]_.\\(]", nextChar)[[1]]
}


#' @export
fitsToken.LavString <- function(token, nextChar) {
  mod_stopif(length(nextChar) != 1, paste0("Wrong length of nextChar", nextChar))
  # if object name ends with ( it is a function,
  # and next char belongs to a new object
  if (grepl('\\"$', token)) {
    return(FALSE)
  }
  grepl("[[:graph:][:space:]]", nextChar)[[1]]
}


#' @export
fitsToken.LavOperator <- function(token, nextChar) {
  mod_stopif(length(nextChar) != 1, paste0("Wrong length of nextChar", nextChar))

  completeToken <- paste0(token, nextChar)
  switch(completeToken,
         "=~" = TRUE,
         "~~" = TRUE,
         "<-" = TRUE,
         "->" = TRUE,
         "==" = TRUE,
         "!=" = TRUE,
         ":=" = TRUE,
         ">=" = TRUE,
         "<=" = TRUE,
         "<~" = TRUE,
         FALSE)
}


#' @export
fitsToken.LavBlank <- function(token, nextChar) {
  mod_stopif(length(nextChar) != 1, paste0("Wrong length of nextChar", nextChar))
  grepl("\\s+", nextChar)
}


#' @export
fitsToken.LavClosure <- function(token, nextChar) {
  FALSE
}


#' @export
fitsToken.LavNumeric <- function(token, nextChar) {
  mod_stopif(length(nextChar) != 1, paste0("Wrong length of nextChar", nextChar))
  grepl("[[:digit:].]", nextChar)
}


#' @export
fitsToken.LavComment <- function(token, nextChar) {
  TRUE
}


assignSubClass <- function(token) {
  UseMethod("assignSubClass")
}


#' @export
assignSubClass.LavOperator <- function(token) {
  switch (getTokenString(token),
          "=~" = {subClass <- "LavMeasure";     priority <- 0},
          "~"  = {subClass <- "LavPredict";     priority <- 0},
          "~~" = {subClass <- "LavCovar";       priority <- 0},
          "+"  = {subClass <- "LavAdd";         priority <- 1},
          "*"  = {subClass <- "LavModify";      priority <- 2},
          "<"  = {subClass <- "LavLessLeft";    priority <- 0},
          ">"  = {subClass <- "LavLessRight";   priority <- 0},
          "==" = {subClass <- "LavEquals";      priority <- 0},
          ":"  = {subClass <- "LavInteraction"; priority <- 2},
          ":=" = {subClass <- "LavCustom";      priority <- 0},
          ","  = {subClass <- "LavSeperator";   priority <- 0},
          "-"  = {subClass <- "LavSubtract";    priority <- 3},
          "|"  = {subClass <- "LavThreshold";   priority <- 0},
          "<~" = {subClass <- "LavMeasure";     priority <- 0},
          mod_msg_stop(paste0("Unrecognized operator: ", highlightErrorToken(token)))
  )
  structure(token,
            class = c(subClass, class(token)),
            priority = priority)
}


#' @export
assignSubClass.LavClosure <- function(token) {
  switch(getTokenString(token),
          "("  = {subClass <- "LeftBracket";    priority <- 3},
          ")"  = {subClass <- "RightBracket";   priority <- 3},
          mod_msg_stop(paste0("Unrecognized operator: ", token))
  )
  structure(token,
            class = c(subClass, class(token)),
            priority = priority)
}


#' @export
assignSubClass.LavName <- function(token) {
  if (grepl("\\($", getTokenString(token))) {
    subClass <- "LavFunction"
    priority <- 3
  } else {
    subClass <- "LavObject"
    priority <- 3
  }
  structure(token,
            class = c(subClass, class(token)),
            priority = priority)
}


#' @export
assignSubClass.LavNumeric <- function(token) {
  token
}


#' @export
assignSubClass.LavToken <- function(token) {
  token
}


#' @export
assignSubClass.LavMathExpr <- function(token) {
  token
}


appendToList <- function(list, elem) {
  list[[length(list) + 1]] <- elem
  list
}


prioritizeTokens <- function(listTokens, i = 1, brackets = list(),
                             nLeftBrackets = 0) {
  if (is.null(listTokens) || i > length(listTokens)) {
    mod_stopif(nLeftBrackets != 0, paste0("Unmatched left bracket",
           highlightErrorToken(brackets[[1]])))
    return(listTokens)
  } else if (is.RightClosure(listTokens[[i]])) {
    brackets <- brackets[-length(brackets)]
    nLeftBrackets <- nLeftBrackets - 1
    mod_stopif(nLeftBrackets < 0, paste0("Unmatched right bracket ",
           highlightErrorToken(listTokens[[i]])))
  }
  getTokenPriority(listTokens[[i]]) <-
    getTokenPriority(listTokens[[i]]) + nLeftBrackets*10

  if (is.LeftClosure(listTokens[[i]])) {
    brackets <- appendToList(brackets, listTokens[[i]])
    nLeftBrackets <- nLeftBrackets + 1
  }
  prioritizeTokens(listTokens, i + 1, brackets = brackets,
                   nLeftBrackets = nLeftBrackets)
}


removeLavBlankLine <- function(line, removeComments = TRUE) {
  if (is.null(line) || length(line) == 0) {
    return(line)
  }
  isBlankOrComment <- vapply(line,
                             FUN.VALUE = logical(1L),
                             FUN = function(token) is.LavBlankOrComment(token))
  line[!isBlankOrComment]
}


tokenizeSyntax <- function(syntax, optimize = TRUE) {
  resetModsemParseEnv()
  mod_stopif(!is.character(syntax), "Syntax must be a string")

  lines <- getLines(syntax)
  modsemParseEnv$syntaxLines <- lines

  tokenizedLines <- lines |>
    lapply(createTokensLine) |>
    lapply(removeLavBlankLine) |>
    lapply(FUN = function(tokens) lapply(tokens, assignSubClass))

  tokenizedLines <- tokenizedLines |>
    lapply(prioritizeTokens)

  isEmpty <- vapply(tokenizedLines, FUN.VALUE = logical(1L),
                    FUN = function(line) is.null(line) || length(line) == 0)

  tokenizedLines[!isEmpty]
}


mergeTokensToString <- function(listTokens) {
  vapply(listTokens, FUN.VALUE = character(1L),
         FUN = getTokenString) |>
    stringr::str_c(collapse = "")
}


addCharToken <- function(token, nextChar) {
  mod_stopif(length(nextChar) != 1, paste0("Wrong length of nextChar ", nextChar))

  out <- paste0(token, nextChar)
  attributes(out) <- attributes(token)
  out
}


highlightError <- function(line, pos) {
  line <- stringr::str_c(line, collapse = "")
  indent <- "      "
  message <- paste0(indent, line, "\n",
                    indent, stringr::str_c(rep(" ", pos - 1),
                                           collapse = ""), "^")
  message
}


highlightErrorToken <- function(token) {
  lineNumber <- attr(token, "lineNumber")
  line <- modsemParseEnv$syntaxLines[[lineNumber]]
  if (is.list(line)) {
    line <- vapply(line,
                   FUN.VALUE = character(1L),
                   FUN = getTokenString)
  }
  line <- stringr::str_c(line, collapse = "")
  pos <- getTokenPosition(token)
  indent <- "      "
  message <- paste0("\n", indent, line, "\n",
                    indent, stringr::str_c(rep(" ", pos - 1),
                                           collapse = ""), "^")
  message
}


getTokenString <- function(token) {
  token[[1]]
}



getTokenPriority <- function(token) {
  attr(token, "priority")
}


`getTokenPriority<-` <- function(token, value) {
  attr(token, "priority") <- value
  token
}


getTokenPosition <- function(token) {
  attr(token, "pos")
}


is.LavToken <- function(token) {
  inherits(token, "LavToken")
}


is.LavName <- function(token, ignore.function=TRUE) {
  isName <- inherits(token, "LavName")

  if (ignore.function) {
    isName <- isName && !grepl("\\($", getTokenString(token))
  }

  isName
}


is.LavOperator <- function(token) {
  inherits(token, "LavOperator")
}


is.MathOperator <- function(token) {
  switch(getTokenString(token),
         "==" = TRUE,
         "<" = TRUE,
         ">" = TRUE,
         ":=" = TRUE,
         FALSE)
}


is.LavBlankOrComment <- function(token) {
  inherits(token, "LavBlank") || inherits(token, "LavComment")
}


is.LeftClosure <- function(token) {
  inherits(token, "LeftBracket") || inherits(token, "LavFunction")
}


is.RightClosure <- function(token) {
  inherits(token, "RightBracket")
}


is.LavClosure <- function(token) {
  inherits(token, "LavClosure")
}


is.LavOperator <- function(token) {
  inherits(token, "LavOperator")
}


is.firstClassOperator <- function(token) {
  switch(getTokenString(token),
         "=~" = TRUE,
         "~"  = TRUE,
         "~~" = TRUE,
         "<"  = TRUE,
         ">"  = TRUE,
         "==" = TRUE,
         FALSE)
}


#' @export
as.character.LavToken <- function(x, ...) {
  attributes(x) <- NULL
  x
}
