using System;
using System.Collections.Generic;
using System.Linq;
using JD.Kernel.StaticHelpers;

namespace JD.Collections.Utilities
{
    public abstract class GraphWalker<T>
    {
        #region Methods

        protected abstract IEnumerable<T> GetDependenciesOf(T item);

        public bool CanReach(T source, T target)
        {
            Throw.IfNull(source, "source");
            Throw.IfNull(target, "target");

            Set<T> reachable = new Set<T>();
            Predicate<T> isTarget = targetToTest => Equals(target, targetToTest);
            return CanReach(source, isTarget, reachable);
        }

        public bool CanReach(T source, Predicate<T> target)
        {
            Throw.IfNull(source, "source");
            Throw.IfNull(target, "target");

            Set<T> reachable = new Set<T>();
            return CanReach(source, target, reachable);
        }

        private bool CanReach(T source, Predicate<T> isTarget, Set<T> reachable)
        {
            if (isTarget(source))
            {
                return true;
            }

            if (reachable.Add(source))
            {
                return GetDependenciesOf(source).Any(dependency => CanReach(dependency, isTarget, reachable));
            }

            return false;
        }

        /// <summary>
        /// True if the source can reach the target in one step.
        /// </summary>
        public bool IsAdjacent(T source, Predicate<T> isTrarget)
        {
            // It could have used a Func<T, bool> directly but I prefer the predicate (they are more explicit).

            return GetDependenciesOf(source).Any(dependency => isTrarget(dependency));
        }

        #endregion
    }
}