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

// 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 DecimalParselet extends CaretLeafParselet {
  parse(parser: CaretParser): DecimalNode {
    let value = "";
    let hasLeadingMinus = false;
    let hasDecimalPoint = false;
    let hasDigits = false;
    let consumedTokens: CharToken[] = [];

    // Continue consuming CharTokens that are digits or a decimal point
    const consumedToken = parser.consume();
    this.assert(
      consumedToken instanceof CharToken &&
        ((consumedToken.char >= "0" && consumedToken.char <= "9") ||
          consumedToken.char === "." ||
          consumedToken.char === "-"),
      "Expected CharToken for decimal number"
    );

    let currentToken = consumedToken;
    consumedTokens.push(currentToken);

    while (true) {
      if (currentToken.char === ".") {
        hasDecimalPoint = true;
      } else if (currentToken.char >= "0" && currentToken.char <= "9") {
        hasDigits = true;
      } else if (currentToken.char === "-") {
        hasLeadingMinus = true;
      }
      value += currentToken.char;
      const nextToken = parser.peek();
      if (!nextToken) break;
      if (
        !(
          nextToken instanceof CharToken &&
          ((nextToken.char >= "0" && nextToken.char <= "9") ||
            (nextToken.char === "." && !hasDecimalPoint))
        )
      ) {
        break;
      }
      currentToken = nextToken;
      parser.consume();
      consumedTokens.push(currentToken);
    }

    if (!hasDigits) {
      throw new CannotParseError(this, "Decimal must have at least one digit");
    }

    return DecimalNode.from(value).addTag(new TokensTag(consumedTokens));
  }
}