using Invercargill.DataStructures;
namespace Invercargill.Modifiers {

    public class Unique<T, TProp> : Enumerable<T> {
        private Enumerable<T> input;
        private EqualityDelegate<TProp> comparison;
        private TransformDelegate<T, TProp> selector;

        public Unique(Enumerable<T> input, owned TransformDelegate<T, TProp> selector, owned EqualityDelegate<TProp> compare) {
            this.input = input;
            comparison = (owned)compare;
            this.selector = (owned)selector;
        }

        public override Tracker<T> get_tracker() {
            var tracker = input.get_tracker();
            var previous = new Vector<T>();
            return new AdvanceTracker<T>((out item) => {
                while(true) {
                    if(!tracker.has_next()) {
                        item = null;
                        return false;
                    }
                    var next = tracker.get_next();
                    if(previous.any(p => comparison(selector(p), selector(next)))) {
                        continue;
                    }
                    previous.add(next);
                    item = next;
                    return true;
                }

            });
        }
    }

}