michael@0: "use strict";
michael@0: 
michael@0: var nil = {}
michael@0: var owns = ({}).hasOwnProperty
michael@0: 
michael@0: function rebase(result, parent, delta) {
michael@0:   var key, current, previous, update
michael@0:   for (key in parent) {
michael@0:     if (owns.call(parent, key)) {
michael@0:       previous = parent[key]
michael@0:       update = owns.call(delta, key) ? delta[key] : nil
michael@0:       if (previous === null) continue
michael@0:       else if (previous === void(0)) continue
michael@0:       else if (update === null) continue
michael@0:       else if (update === void(0)) continue
michael@0:       else result[key] = previous
michael@0:     }
michael@0:   }
michael@0:   for (key in delta) {
michael@0:     if (owns.call(delta, key)) {
michael@0:       update = delta[key]
michael@0:       current = owns.call(result, key) ? result[key] : nil
michael@0:       if (current === update) continue
michael@0:       else if (update === null) continue
michael@0:       else if (update === void(0)) continue
michael@0:       else if (current === nil) result[key] = update
michael@0:       else if (typeof(update) !== "object") result[key] = update
michael@0:       else if (typeof(current) !== "object") result[key] = update
michael@0:       else result[key]= rebase({}, current, update)
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   return result
michael@0: }
michael@0: 
michael@0: module.exports = rebase