// Matches the scheme of a URL, eg "http://"
const schemeRegex = /^[\w+.-]+:\/\//;
/**
 * Matches the parts of a URL:
 * 1. Scheme, including ":", guaranteed.
 * 2. User/password, including "@", optional.
 * 3. Host, guaranteed.
 * 4. Port, including ":", optional.
 * 5. Path, including "/", optional.
 */
const urlRegex = /^([\w+.-]+:)\/\/([^@/#?]*@)?([^:/#?]*)(:\d+)?(\/[^#?]*)?/;
function isAbsoluteUrl(input) {
    return schemeRegex.test(input);
}
function isSchemeRelativeUrl(input) {
    return input.startsWith('//');
}
function isAbsolutePath(input) {
    return input.startsWith('/');
}
function parseAbsoluteUrl(input) {
    const match = urlRegex.exec(input);
    return {
        scheme: match[1],
        user: match[2] || '',
        host: match[3],
        port: match[4] || '',
        path: match[5] || '/',
        relativePath: false,
    };
}
function parseUrl(input) {
    if (isSchemeRelativeUrl(input)) {
        const url = parseAbsoluteUrl('http:' + input);
        url.scheme = '';
        return url;
    }
    if (isAbsolutePath(input)) {
        const url = parseAbsoluteUrl('http://foo.com' + input);
        url.scheme = '';
        url.host = '';
        return url;
    }
    if (!isAbsoluteUrl(input)) {
        const url = parseAbsoluteUrl('http://foo.com/' + input);
        url.scheme = '';
        url.host = '';
        url.relativePath = true;
        return url;
    }
    return parseAbsoluteUrl(input);
}
function stripPathFilename(path) {
    // If a path ends with a parent directory "..", then it's a relative path with excess parent
    // paths. It's not a file, so we can't strip it.
    if (path.endsWith('/..'))
        return path;
    const index = path.lastIndexOf('/');
    return path.slice(0, index + 1);
}
function mergePaths(url, base) {
    // If we're not a relative path, then we're an absolute path, and it doesn't matter what base is.
    if (!url.relativePath)
        return;
    normalizePath(base);
    // If the path is just a "/", then it was an empty path to begin with (remember, we're a relative
    // path).
    if (url.path === '/') {
        url.path = base.path;
    }
    else {
        // Resolution happens relative to the base path's directory, not the file.
        url.path = stripPathFilename(base.path) + url.path;
    }
    // If the base path is absolute, then our path is now absolute too.
    url.relativePath = base.relativePath;
}
/**
 * The path can have empty directories "//", unneeded parents "foo/..", or current directory
 * "foo/.". We need to normalize to a standard representation.
 */
function normalizePath(url) {
    const { relativePath } = url;
    const pieces = url.path.split('/');
    // We need to preserve the first piece always, so that we output a leading slash. The item at
    // pieces[0] is an empty string.
    let pointer = 1;
    // Positive is the number of real directories we've output, used for popping a parent directory.
    // Eg, "foo/bar/.." will have a positive 2, and we can decrement to be left with just "foo".
    let positive = 0;
    // We need to keep a trailing slash if we encounter an empty directory (eg, splitting "foo/" will
    // generate `["foo", ""]` pieces). And, if we pop a parent directory. But once we encounter a
    // real directory, we won't need to append, unless the other conditions happen again.
    let addTrailingSlash = false;
    for (let i = 1; i < pieces.length; i++) {
        const piece = pieces[i];
        // An empty directory, could be a trailing slash, or just a double "//" in the path.
        if (!piece) {
            addTrailingSlash = true;
            continue;
        }
        // If we encounter a real directory, then we don't need to append anymore.
        addTrailingSlash = false;
        // A current directory, which we can always drop.
        if (piece === '.')
            continue;
        // A parent directory, we need to see if there are any real directories we can pop. Else, we
        // have an excess of parents, and we'll need to keep the "..".
        if (piece === '..') {
            if (positive) {
                addTrailingSlash = true;
                positive--;
                pointer--;
            }
            else if (relativePath) {
                // If we're in a relativePath, then we need to keep the excess parents. Else, in an absolute
                // URL, protocol relative URL, or an absolute path, we don't need to keep excess.
                pieces[pointer++] = piece;
            }
            continue;
        }
        // We've encountered a real directory. Move it to the next insertion pointer, which accounts for
        // any popped or dropped directories.
        pieces[pointer++] = piece;
        positive++;
    }
    let path = '';
    for (let i = 1; i < pointer; i++) {
        path += '/' + pieces[i];
    }
    if (!path || (addTrailingSlash && !path.endsWith('/..'))) {
        path += '/';
    }
    url.path = path;
}
/**
 * Attempts to resolve `input` URL/path relative to `base`.
 */
function resolve(input, base) {
    if (!input && !base)
        return '';
    const url = parseUrl(input);
    // If we have a base, and the input isn't already an absolute URL, then we need to merge.
    if (base && !url.scheme) {
        const baseUrl = parseUrl(base);
        url.scheme = baseUrl.scheme;
        // If there's no host, then we were just a path.
        if (!url.host || baseUrl.scheme === 'file:') {
            // The host, user, and port are joined, you can't copy one without the others.
            url.user = baseUrl.user;
            url.host = baseUrl.host;
            url.port = baseUrl.port;
        }
        mergePaths(url, baseUrl);
    }
    normalizePath(url);
    // If the input (and base, if there was one) are both relative, then we need to output a relative.
    if (url.relativePath) {
        // The first char is always a "/".
        const path = url.path.slice(1);
        if (!path)
            return '.';
        // 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.
        const keepRelative = (base || input).startsWith('.');
        return !keepRelative || path.startsWith('.') ? path : './' + path;
    }
    // If there's no host (and no scheme/user/port), then we need to output an absolute path.
    if (!url.scheme && !url.host)
        return url.path;
    // We're outputting either an absolute URL, or a protocol relative one.
    return `${url.scheme}//${url.user}${url.host}${url.port}${url.path}`;
}

export { resolve as default };
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