Prototype/Scriptaculous: Selecting groups of paragraphs (<p>) by clicking on them

Question

A list of paragraphs (<p>) is given. As soon as the user clicks on paragraph A the class of paragraph A changes to "activated". Now the user selects paragraph B and all the paragraphs between A and B change their class to "activated".

By clicking on B again, only A remains with the class "active".

By clicking on A the class "active" gets removed on all paragraphs between A and B (including A and B).

It shouldn't be possible to "deactivate" any paragraph between A and B. The selection between A and B should always be a uninterrupted list of selected paragraphs.

Can anyone give me a hint on how to realize this with Prototype/Scriptaculous? The application is implemented in Rails, so any hint in RJS would even be more appreciated!

Answer 1

OK, in the meantime and with the help of a coworker I came up with an own answer to this problem:

<script type="text/javascript">
    // holds paragraph A (first selected paragraph)
    var a_selected = null;
    // holds paragraph B (second selected paragraph)
    var b_selected = null;
    // holds all 'active' paragraphs
    var selected_paras = [];

    function class_flipper_init() {
        // reset paragraphs A and B
        a_selected = null;
        b_selected = null;
        var paragraphs = $$("#foobar p");
        paragraphs.each(function(paragraph, index) {
            // if user clicks on a paragraph
            paragraph.observe("click", function(event) {
                // if A and B are 'active': reset everything.
                if(b_selected != null) {
                    selected_paras.each(function(i) {
                        toggleStyle(i);
                    })
                    a_selected = null
                    b_selected = null
                    return
                }
                // if A is 'active'
                if(a_selected != null) {
                    // if A is 'active' and selected B is below A:
                    // select all paragraphs between A and B
                    if(a_selected < index) {
                        b_selected = index;
                        for (var i = a_selected + 1; i <= index; i++ ) {
                            toggleStyle(paragraphs[i])
                        }
                    }
                    // if A is 'active' and selected B is above A: 
                    // select all paragraphs between A and B
                    else if(a_selected > index) {
                        b_selected = index;
                        for (var i = a_selected - 1; i >= index; i-- ) {
                            toggleStyle(paragraphs[i])
                        }
                    }
                    // if A == B
                    else {
                        toggleStyle(paragraph)
                        a_selected = null
                    }
                }
                // if A is selected
                else {
                    a_selected = index;
                    toggleStyle(paragraph)
                }
            });
        });
    }

    function toggleStyle(paragraph) {
        // remove active class
        if (paragraph.hasClassName("active")) {
            paragraph.removeClassName("active");
            selected_paras = selected_paras.without(paragraph)
        } 
        // set active class
        else {
            paragraph.addClassName("active");
            selected_paras.push(paragraph)
        }
    }
</script>

class_flipper_init() is called everytime the page (or in my case a certain partial) is loaded.

Please don't hesitate to submit a solution written in "pure" RJS or something more elegant. :-)