const WHITESPACE_RE = /[ \t]*/

export function escapeRegExp(str: string) {
    return str.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
}

export class MicroParser {
    constructor(str: string, readonly options: { whitespace_regex?: RegExp } = {}) {
        this.stream = str;
        this.options.whitespace_regex ||= WHITESPACE_RE;
    }

    protected stream: string

    // Utilities

    PEEK(n = 1) {
        // if (this.stream.length < n) throw 'EOF';
        return this.stream.slice(0, n);
    }

    TRY_CONSUME(what: string | RegExp): false | string {
        let result: string;
        if (typeof what == 'string' && this.stream.startsWith(what)) {
            result = what;
        } else if (typeof what == 'object') {
            let regex = new RegExp(`^(?:${what.source})`);
            const match = regex.exec(this.stream);
            if (match) {
                result = match[0];
            }
        }
        if (result) {
            this.stream = this.stream.slice(result.length);
            return result;
        }
        return false;
    }

    CONSUME(what: string | RegExp) {
        const result = this.TRY_CONSUME(what);
        if (result === false) throw `Expected token "${what.toString()}"`
        return result;
    }

    TRY_CONSUME_WS(what: string | RegExp) {
        this.TRY_CONSUME(this.options.whitespace_regex);
        return this.TRY_CONSUME(what);
    }

    CONSUME_WS(what?: string | RegExp) {
        this.TRY_CONSUME(this.options.whitespace_regex);
        if (what) return this.CONSUME(what);
    }
}