// This module provides URI parsing and joining as described
// in RFC 2396.
//
// Usage:
//   <script src="urilib.js"></script>
//   <script type="text/javascript">
//     base = urilib.parse('http://www.site.example/path/to/app');
//     ref = new urilib.URI('', '', 'thing/5', 'a=1');
//     full = urilib.join(base, url);
//     alert(full);     // "http://www.site.example/path/to/thing/5?a=1"
//   </script>

var urilib = {};

urilib.parse_regex = new RegExp(
    // Scheme
    "^(?:([a-zA-Z][a-zA-Z0-9+\\-.]*)[:])?" +
    // Authority
    "(?://([^/]+))?" +
    // Path
    "([^?]+)?" +
    // Query
    "([?](.*))?");

urilib.AbsoluteURIError = function (message) {
    // Error thrown when relativeURI functions are called on an absoluteURI.
    this.message = message || "relativeURI functions cannot be called on an absoluteURI";
}
urilib.AbsoluteURIError.prototype.toString = function () {
    return 'AbsoluteURIError: "' + this.message + '"';
}

urilib.RelativeURIError = function (message) {
    // Error thrown when absoluteURI functions are called on a relativeURI.
    this.message = message || "absoluteURI functions cannot be called on a relativeURI";
}
urilib.RelativeURIError.prototype.toString = function () {
    return 'RelativeURIError: "' + this.message + '"';
}

urilib.URI = function (scheme, authority, path, query) {
    this.scheme = scheme || "";
    this.authority = authority || "";
    this.path = path || "";
    this.query = query || "";
    return this;
};

urilib.URI.prototype.toString = function () {
    // 7) The resulting URI components, including any inherited from the
    // base URI, are recombined to give the absolute form of the URI
    // reference.
    var result = "";
    if (this.scheme != '') result = this.scheme + ":";
    if (this.authority != '') result = result + "//" + this.authority;
    result = result + this.path;
    if (this.query != '') result = result + "?" + this.query;
    return result;
};

urilib.URI.prototype.is_relative = function () {
    return (this.path.length > 0 && this.path.charAt(0) != '/');
}

urilib.URI.prototype.net_path = function () {
    // Return the 'net_path' ("//" authority [ abs_path ]) of this URI.
    if (this.is_relative()) throw urilib.RelativeURIError();
    return "//" + this.authority + this.path;
};

urilib.URI.prototype.abs_path = function () {
    // Return the 'abs_path' ("/" path_segments) of this URI.
    if (this.is_relative()) throw urilib.RelativeURIError();
    return this.path;
};

urilib.URI.prototype.rel_path = function () {
    // Return the 'rel_path' (rel_segment [ abs_path ]) of this URI.
    if (!this.is_relative()) throw urilib.AbsoluteURIError();
    return this.path;
};

urilib.URI.prototype.hier_part = function (include_authority) {
    // Return the 'hier_part' ( net_path | abs_path ) [ "?" query ] of this URI.
    // 
    // If 'include_authority' is false (the default), returns the
    // abs_path [+ query] by omitting the authority component.
    // Otherwise, returns the net_path [+ query] by including the
    // authority component.
    if (this.is_relative()) throw urilib.RelativeURIError();
    var result = include_authority ? this.net_path() : this.path;
    if (this.query != '') result = result + "?" + this.query;
    return result;
};

urilib.URI.prototype.server_relative = function () {
    // Return the 'server relative' ( abs_path | rel_path ) [ "?" query ] form of this URI.
    var result = this.path;
    if (this.query != '') result = result + "?" + this.query;
    return result;
};

urilib.parse = function (uri) {
    // Return a URI object populated by parsing the given uri string.
    uri = uri || "";
    var atoms = urilib.parse_regex.exec(uri);
    return new urilib.URI(atoms[1], atoms[2], atoms[3], atoms[4]);
};

urilib.normalize = function (path) {
    // Return 'path', normalized to remove '.' and '<segment>/..' segments.
    // 
    // 'path' may be either a string or an Array.
    // The return type will match the input type.
    var typ = typeof(path);
    if (typ == 'string') path = path.split("/");
    
    // 5c) All occurrences of "./", where "." is a complete path segment,
    // are removed from the buffer string.
    // 5d) If the buffer string ends with "." as a complete path segment,
    // that "." is removed.
    var pos = 0;
    while (pos < path.length) {
        if (path[pos] == '.') {
            path.splice(pos, 1);
        } else {
            pos++;
        }
    }
    
    // 5e) All occurrences of "<segment>/../", where <segment> is a
    // complete path segment not equal to "..", are removed from the
    // buffer string.  Removal of these path segments is performed
    // iteratively, removing the leftmost matching pattern on each
    // iteration, until no matching pattern remains.
    // 5f) If the buffer string ends with "<segment>/..", where <segment>
    // is a complete path segment not equal to "..", that
    // "<segment>/.." is removed.
    pos = 1;
    while (pos < path.length) {
        if (pos > 0 && path[pos] == '..' && path[pos - 1] != '..') {
            path.splice(pos - 1, 2);
            pos--;
        } else {
            pos++;
        }
    }
    
    // g) If the resulting buffer string still begins with one or more
    // complete path segments of "..", then the reference is
    // considered to be in error.
    if (path.length > 0 && path[0] == '..')
        throw ("Could not normalize. URI begins with illegal '..' segment." +
               path.join('/'));
    
    if (typ == 'string') path = path.join("/");
    return path;
};

urilib.join = function (base, ref) {
    // Return a URI object which combines the two given URI objects.
    
    // 1) The URI reference is parsed into the potential four components
    // and fragment identifier, as described in Section 4.3.
    if (base.constructor != urilib.URI) base = urilib.parse(base);
    if (ref.constructor != urilib.URI) ref = urilib.parse(ref);
    
    // 2) If the path component is empty and the scheme, authority, and
    // query components are undefined, then it is a reference to the
    // current document and we are done.
    if (ref.path == '' && ref.scheme == '' &&
        ref.authority == '' && ref.query == '') return base;
    
    // 3) If the scheme component is defined, indicating that the reference
    // starts with a scheme name, then the reference is interpreted as an
    // absolute URI and we are done.
    if (ref.scheme != '') return ref;
    
    // 2b) Otherwise, the reference URI's
    // query and fragment components are defined as found (or not found)
    // within the URI reference and not inherited from the base URI.
    // 3b) Otherwise, the reference URI's
    // scheme is inherited from the base URI's scheme component.
    var newUri = new urilib.URI(base.scheme, "", "", ref.query);
    
    // 4) If the authority component is defined, then the reference is a
    // network-path and we skip to step 7.
    if (ref.authority == '') {
        // Otherwise, the reference
        // URI's authority is inherited from the base URI's authority
        // component, which will also be undefined if the URI scheme does not
        // use an authority component.
        newUri.authority = base.authority;
        
        // 5) If the path component begins with a slash character ("/"), then
        // the reference is an absolute-path and we skip to step 7.
        if (ref.path.indexOf('/') != 0) {
            // 6) If this step is reached, then we are resolving a relative-path
            // reference.  The relative path needs to be merged with the base
            // URI's path.
            //
            // a) All but the last segment of the base URI's path component is
            // copied to the buffer.  In other words, any characters after the
            // last (right-most) slash character, if any, are excluded.
            var buf = base.path;
            var last_slash = buf.lastIndexOf('/');
            if (last_slash >= 0) buf = buf.substring(0, last_slash + 1);
            
            // b) The reference's path component is appended to the buffer string.
            buf = buf + ref.path;
            
            // c) through g) -- see normalize()
            // h) The remaining buffer string is the reference URI's new path
            // component.
            newUri.path = urilib.normalize(buf);
        }
    }
    return newUri;
}