// @flow
import SourceLocation from "./SourceLocation";

/**
 * Interface required to break circular dependency between Token, Lexer, and
 * ParseError.
 */
export interface LexerInterface {input: string, tokenRegex: RegExp}

/**
 * The resulting token returned from `lex`.
 *
 * It consists of the token text plus some position information.
 * The position information is essentially a range in an input string,
 * but instead of referencing the bare input string, we refer to the lexer.
 * That way it is possible to attach extra metadata to the input string,
 * like for example a file name or similar.
 *
 * The position information is optional, so it is OK to construct synthetic
 * tokens if appropriate. Not providing available position information may
 * lead to degraded error reporting, though.
 */
export class Token {
    text: string;
    loc: ?SourceLocation;

    constructor(
        text: string,           // the text of this token
        loc: ?SourceLocation,
    ) {
        this.text = text;
        this.loc = loc;
    }

    /**
     * Given a pair of tokens (this and endToken), compute a `Token` encompassing
     * the whole input range enclosed by these two.
     */
    range(
        endToken: Token,  // last token of the range, inclusive
        text: string,     // the text of the newly constructed token
    ) {
        return new Token(text, SourceLocation.range(this, endToken));
    }
}