using System;
using System.Collections.Generic;

namespace Delegates.TreeTraversal
{
    static class Traversal
    {
        public static IEnumerable<Product> GetProducts(ProductCategory data) =>
            Executor<Product, ProductCategory>.Execute(data,
                (d) => d != null,
                (d) => new object[] { d.Categories, d.Products },
                (d) => d as Product);

        public static IEnumerable<int> GetBinaryTreeValues(BinaryTree<int> data) =>
            Executor<int, BinaryTree<int>>.Execute(data,
                (d) => d != null,
                (d) => new object[] { d.Value, d.Left, d.Right },
                (d) => int.Parse(d.ToString()));

        public static IEnumerable<Job> GetEndJobs(Job data) =>
            Executor<Job, Job>.Execute(data,
                (d) => (d is List<Job>) && (d as List<Job>).Count > 0,
                (d) => new object[] { d.Subjobs, d },
                (d) => d as Job);
    }

    class Executor<T1, T2> where T2 : class
    {
        public static IEnumerable<T1> Execute(
            T2 data,
            Func<object, bool> check,
            Func<T2, IEnumerable<object>> getParametrs,
            Func<object, T1> translate)
        {
            var parametrs = getParametrs(data);
            var notChecked = true;
            foreach (var p in parametrs)
                if (check(p))
                {
                    if (p is List<T2>)
                        foreach (var e in p as List<T2>)
                            foreach (var r in Execute(e, check, getParametrs, translate))
                                yield return r;
                    else if (p is T2)
                        foreach (var e in Execute(p as T2, check, getParametrs, translate))
                            yield return e;
                    else if (p is List<T1>)
                        foreach (var e in p as List<T1>)
                            yield return e;
                    else
                        yield return translate(p);
                    notChecked = false;
                }
                else if (p is T1 && notChecked)
                    yield return translate(p);
        }
    }
}