/* istanbul ignore next */
const Url = (typeof URL !== 'undefined' ? URL : require('url').URL);
// Matches "..", which must be preceeded by "/" or the start of the string, and
// must be followed by a "/". We do not eat the following "/", so that the next
// iteration can match on it.
const parentRegex = /(^|\/)\.\.(?=\/|$)/g;
function isAbsoluteUrl(url) {
    try {
        return !!new Url(url);
    }
    catch (e) {
        return false;
    }
}
/**
 * Creates a directory name that is guaranteed to not be in `str`.
 */
function uniqInStr(str) {
    let uniq = String(Math.random()).slice(2);
    while (str.indexOf(uniq) > -1) {
        /* istanbul ignore next */
        uniq += uniq;
    }
    return uniq;
}
/**
 * Removes the filename from the path (everything trailing the last "/"). This
 * is only safe to call on a path, never call with an absolute or protocol
 * relative URL.
 */
function stripPathFilename(path) {
    path = normalizePath(path);
    const index = path.lastIndexOf('/');
    return path.slice(0, index + 1);
}
/**
 * Normalizes a protocol-relative URL, but keeps it protocol relative by
 * stripping out the protocl before returning it.
 */
function normalizeProtocolRelative(input, absoluteBase) {
    const { href, protocol } = new Url(input, absoluteBase);
    return href.slice(protocol.length);
}
/**
 * Normalizes a simple path (one that has no ".."s, or is absolute so ".."s can
 * be normalized absolutely).
 */
function normalizeSimplePath(input) {
    const { href } = new Url(input, 'https://foo.com/');
    return href.slice('https://foo.com/'.length);
}
/**
 * Normalizes a path, ensuring that excess ".."s are preserved for relative
 * paths in the output.
 *
 * If the input is absolute, this will return an absolutey normalized path, but
 * it will not have a leading "/".
 *
 * If the input has a leading "..", the output will have a leading "..".
 *
 * If the input has a leading ".", the output will not have a leading "."
 * unless there are too many ".."s, in which case there will be a leading "..".
 */
function normalizePath(input) {
    // If there are no ".."s, we can treat this as if it were an absolute path.
    // The return won't be an absolute path, so it's easy.
    if (!parentRegex.test(input))
        return normalizeSimplePath(input);
    // We already found one "..". Let's see how many there are.
    let total = 1;
    while (parentRegex.test(input))
        total++;
    // If there are ".."s, we need to prefix the the path with the same number of
    // unique directories. This is to ensure that we "remember" how many parent
    // directories we are accessing. Eg, "../../.." must keep 3, and "foo/../.."
    // must keep 1.
    const uniqDirectory = `z${uniqInStr(input)}/`;
    // uniqDirectory is just a "z", followed by numbers, followed by a "/". So
    // generating a runtime regex from it is safe. We'll use this search regex to
    // strip out our uniq directory names and insert any needed ".."s.
    const search = new RegExp(`^(?:${uniqDirectory})*`);
    // Now we can resolve the total path. If there are excess ".."s, they will
    // eliminate one or more of the unique directories we prefix with.
    const relative = normalizeSimplePath(uniqDirectory.repeat(total) + input);
    // We can now count the number of unique directories that were eliminated. If
    // there were 3, and 1 was eliminated, we know we only need to add 1 "..". If
    // 2 were eliminated, we need to insert 2 ".."s. If all 3 were eliminated,
    // then we need 3, etc. This replace is guranteed to match (it may match 0 or
    // more times), and we can count the total match to see how many were eliminated.
    return relative.replace(search, (all) => {
        const leftover = all.length / uniqDirectory.length;
        return '../'.repeat(total - leftover);
    });
}
/**
 * Attempts to resolve `input` URL relative to `base`.
 */
function resolve(input, base) {
    if (!base)
        base = '';
    // Absolute URLs are very easy to resolve right.
    if (isAbsoluteUrl(input))
        return new Url(input).href;
    if (base) {
        // Absolute URLs are easy...
        if (isAbsoluteUrl(base))
            return new Url(input, base).href;
        // If base is protocol relative, we'll resolve with it but keep the result
        // protocol relative.
        if (base.startsWith('//'))
            return normalizeProtocolRelative(input, `https:${base}`);
    }
    // Normalize input, but keep it protocol relative. We know base doesn't supply
    // a protocol, because that would have been handled above.
    if (input.startsWith('//'))
        return normalizeProtocolRelative(input, 'https://foo.com/');
    // We now know that base (if there is one) and input are paths. We've handled
    // both absolute and protocol-relative variations above.
    // Absolute paths don't need any special handling, because they cannot have
    // extra "." or ".."s. That'll all be stripped away. Input takes priority here,
    // because if input is an absolute path, base path won't affect it in any way.
    if (input.startsWith('/'))
        return '/' + normalizeSimplePath(input);
    // Since input and base are paths, we need to join them to do any further
    // processing. Paths are joined at the directory level, so we need to remove
    // the base's filename before joining. We also know that input does not have a
    // leading slash, and that the stripped base will have a trailing slash if
    // there are any directories (or it'll be empty).
    const joined = stripPathFilename(base) + input;
    // If base is an absolute path, then input will be relative to it.
    if (base.startsWith('/'))
        return '/' + normalizeSimplePath(joined);
    // We now know both base (if there is one) and input are relative paths.
    const relative = normalizePath(joined);
    // If base started with a leading ".", or there is no base and input started
    // with a ".", then we need to ensure that the relative path starts with a
    // ".". We don't know if relative starts with a "..", though, so check before
    // prepending.
    if ((base || input).startsWith('.') && !relative.startsWith('.')) {
        return './' + relative;
    }
    return relative;
}

export default resolve;
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