const suffixes = /(#)+$/;
const trailingHash = /#$/;
const startingHashAndSlash = /^[#/]+/;
const isDomain = /^[^:]+:\/\/[^/]+\//;
const trailingFragments = /\/[^/]*$/;
const idAndPointer = /#.*$/;
const isURN = /^urn:uuid:[0-9A-Fa-f]/;

function _joinScope(previous?: string, id?: string) {
    if (previous == null && (id == null || id === "")) {
        return "#";
    }
    if (id == null || id === "") {
        return previous.replace(trailingHash, "");
    }
    if (isURN.test(id)) {
        return id;
    }
    if (previous == null || previous === "" || previous === "#") {
        return id.replace(trailingHash, "");
    }
    if (id[0] === "#") {
        if (previous[0] === "/") {
            return id;
        }

        return `${previous.replace(idAndPointer, "")}${id.replace(suffixes, "")}`;
    }
    if (isDomain.test(id)) {
        return id.replace(trailingHash, "");
    }

    if (isDomain.test(previous) && id.startsWith("/")) {
        // we have a domain that should be joined with an absolute path
        // thus we have to remove all paths from domain before joining
        return `${previous.replace(/(^[^:]+:\/\/[^/]+)(.*)/, "$1")}/${id.replace(startingHashAndSlash, "")}`;
    }

    return `${previous.replace(trailingFragments, "")}/${id.replace(startingHashAndSlash, "")}`;
}

export function joinId(previous?: string, id?: string) {
    const scope = _joinScope(previous, id);
    return scope === "" ? "#" : scope;
}