"""Lexer for arithmetic calculator."""


class LexError(Exception):
    pass


class Token:
    __slots__ = ("kind", "value")

    def __init__(self, kind: str, value):
        self.kind = kind
        self.value = value

    def __repr__(self):
        return f"Token({self.kind}, {self.value!r})"

    def __eq__(self, other):
        return isinstance(other, Token) and self.kind == other.kind and self.value == other.value


_SINGLE = {
    "+": "PLUS",
    "-": "MINUS",
    "*": "STAR",
    "/": "SLASH",
    "(": "LPAREN",
    ")": "RPAREN",
}


def tokenize(src: str) -> list:
    tokens = []
    i = 0
    n = len(src)
    while i < n:
        ch = src[i]
        if ch in " \t":
            i += 1
        elif ch in _SINGLE:
            tokens.append(Token(_SINGLE[ch], ch))
            i += 1
        elif ch.isdigit() or ch == ".":
            j = i
            has_dot = False
            while j < n and (src[j].isdigit() or (src[j] == "." and not has_dot)):
                if src[j] == ".":
                    has_dot = True
                j += 1
            raw = src[i:j]
            try:
                value = float(raw) if has_dot else int(raw)
            except ValueError:
                raise LexError(f"invalid number literal {raw!r} at position {i}")
            tokens.append(Token("NUMBER", value))
            i = j
        else:
            raise LexError(f"unexpected character {ch!r} at position {i}")
    tokens.append(Token("EOF", None))
    return tokens