import gleam/option.{None, Some}
import gleam/string
import nibble.{type Parser, do, return}
import node.{type Node, EndOfLine}

pub fn exact_string(expected: String, node: Node) -> Parser(Node, String, ctx) {
  use _ <- do(string.to_graphemes(expected) |> match_chars(expected))
  return(node)
}

pub fn consume_exact_string(expected: String) -> Parser(Nil, String, ctx) {
  use _ <- nibble.do(exact_string(expected, node.Let))
  // NOTE: doesn't matter which constructor 

  return(Nil)
}

fn match_chars(chars: List(String), context: String) -> Parser(Nil, String, ctx) {
  case chars {
    [] -> return(Nil)

    [first, ..rest] -> {
      use _ <- do(
        nibble.take_map(
          "expected '" <> first <> "' in keyword '" <> context <> "'",
          fn(tok) {
            case tok == first {
              True -> Some(Nil)
              False -> None
            }
          },
        ),
      )
      match_chars(rest, context)
    }
  }
}

pub fn let_keyword() -> Parser(Node, String, ctx) {
  exact_string("let", node.Let)
}

pub fn end_of_line() -> Parser(Node, String, ctx) {
  use _ <- nibble.do(
    nibble.one_of([nibble.token("\n"), consume_exact_string("\r\n")]),
  )

  return(EndOfLine)
}