Date wizard

Need a javascript for date calculation of items in an <ul>. Website will have an event planner, where by folks can select an event and then extra activities. The GUI will use jQuery's drag & drop functionality to allow items to be added and arrange in sequence. Two type of items will be available, fixed dates and flexible dates. Fixed dates will have a specific start and end date, flexible dates will be designated by number of days, not calendar date. Flexible dates will come in either fixed number (ie: 3 days, 2 days, 1 day lengths) or adjustable, using a <select> dropdown to choose number of days (10 max). Once website visitor has added and arranged sequence of their plan, they will click to "refresh dates" button to trigger to javascript (we are considering also triggering it automatically upon each drop, but that depends on the final script and the processing time/power it needs). When the process is triggered it needs to find the fixed date item and then calculate the start and end dates for all other items in the list based on that fixed date. It will be possible to have multiple fixed dates in the list, if it finds a second fixed date while calculating and the end date of the item before doesn't match the start date of the next fixed item, it needs to generated an error item, by inserting a <li> item </li> in between the two with copy about there being some unaccounted for time. All items are purely number of days, no time of day considerations involved. The GUI using jQuery has already been designed, the html contained within each items <li> event </li> can be edited to provide values needed for js functionality. Date value for fixed dates can be in timestamp or any dd/mm/yy format necessary. Script needs to calculate and then write the new dates to the html (dd mm yy). Each item will have a start and end date, plus an overall start and finish date for entire package.