// A framework for simple tokenizers. Takes care of newlines and
// white-space, and of getting the text from the source stream into
// the token object. A state is a function of two arguments -- a
// string stream and a setState function. The second can be used to
// change the tokenizer's state, and can be ignored for stateless
// tokenizers. This function should advance the stream over a token
// and return a string or object containing information about the next
// token, or null to pass and have the (new) state be called to finish
// the token. When a string is given, it is wrapped in a {style, type}
// object. In the resulting object, the characters consumed are stored
// under the content property. Any whitespace following them is also
// automatically consumed, and added to the value property. (Thus,
// content is the actual meaningful part of the token, while value
// contains all the text it spans.)

function tokenizer(source, state) {
    // Newlines are always a separate token.
    function isWhiteSpace(ch) {
        // The messy regexp is because IE's regexp matcher is of the
        // opinion that non-breaking spaces are no whitespace.
        return ch != "\n" && /^[\s\u00a0]*$/.test(ch);
    }

    var tokenizer = {
        state: state,

        take: function(type) {
            if (typeof(type) == "string")
                type = {style: type, type: type};

            type.content = (type.content || "") + source.get();
            if (!/\n$/.test(type.content))
                source.nextWhile(isWhiteSpace);
            type.value = type.content + source.get();
            return type;
        },

        next: function () {
            if (!source.more()) throw StopIteration;

            var type;
            if (source.equals("\n")) {
                source.next();
                return this.take("whitespace");
            }

            if (source.applies(isWhiteSpace))
                type = "whitespace";
            else
                while (!type)
                    type = this.state(source, function(s) {tokenizer.state = s;});

            return this.take(type);
        }
    };
    return tokenizer;
}
