import { CaretParser, CaretPrefixParselet, TokensTag } from "@caret-js/core";
import { CharToken } from "@caret-js/core";
import { NegativeNode } from "../nodes/negative";
import { DecimalNode } from "../nodes/decimal";

// This parselet looks for a sequence of `CharToken`s that form a decimal number,
// meaning it has digits, optionally a single decimal point, and more digits. The digits
// are optional on either side of the decimal point, but at least one digit must be present.

export class UnaryMinusParselet extends CaretPrefixParselet {
  parse(parser: CaretParser): NegativeNode | DecimalNode {
    const token = parser.consume();
    this.assert(
      token instanceof CharToken && token.char === "-",
      "Expected '-' token"
    );

    const child = parser.parseMinBP(this);
    return NegativeNode.from(child).addTag(new TokensTag([token]));
  }
}