using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SunlightCentralizedControlManagement_SCCM_.UserClass
{
    /// <summary>
    /// Wrapper ProjectManager class
    /// </summary>
    [Serializable]
    public class ProjectManager : ProjectManager<IP_Task, object>
    {
    }

    /// <summary>
    /// Concrete ProjectManager class for the IProjectManager interface
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <typeparam name="R"></typeparam>
    [Serializable]
    public class ProjectManager<T, R> : IProjectManager<T, R>
        where T : IP_Task
        where R : class
    {
        HashSet<T> _mRegister = new HashSet<T>();
        List<T> _mRootIP_Tasks = new List<T>();
        Dictionary<T, List<T>> _mMembersOfGroup = new Dictionary<T, List<T>>(); // Map group to list of members
        Dictionary<T, HashSet<T>> _mDependantsOfPrecedent = new Dictionary<T, HashSet<T>>(); // Map precendent to list of dependents
        Dictionary<T, HashSet<R>> _mResourcesOfIP_Task = new Dictionary<T, HashSet<R>>(); // Map IP_Task to list of resources
        Dictionary<T, List<T>> _mPartsOfSplitIP_Task = new Dictionary<T, List<T>>(); // Map split IP_Task to list of IP_Task parts
        Dictionary<T, T> _mSplitIP_TaskOfPart = new Dictionary<T, T>(); // Map a IP_Task part to the original split IP_Task
        Dictionary<T, T> _mGroupOfMember = new Dictionary<T, T>(); // Map member IP_Task to parent group IP_Task
        Dictionary<T, int> _mIP_TaskIndices = new Dictionary<T, int>(); // Map the IP_Task to its zero-based index order position

        /// <summary>
        /// Create a new Project
        /// </summary>
        public ProjectManager()
        {
            Now = TimeSpan.Zero;
            Start = DateTime.Now;
        }

        /// <summary>
        /// Get or set the TimeSpan we are at now from Start DateTime
        /// </summary>
        public TimeSpan Now { get; set; }

        /// <summary>
        /// Get or set the starting date for this project
        /// </summary>
        public DateTime Start { get; set; }

        /// <summary>
        /// Get the date after the specified TimeSpan
        /// </summary>
        /// <param name="span"></param>
        /// <returns></returns>
        public DateTime GetDateTime(TimeSpan span)
        {
            return this.Start.Add(span);
        }

        /// <summary>
        /// Create a new T for this Project and add it to the T tree
        /// </summary>
        /// <returns></returns>
        public void Add(T IP_Task)
        {
            if (!this._mRegister.Contains(IP_Task))
            {
                _mRegister.Add(IP_Task);
                _mRootIP_Tasks.Add(IP_Task);
                _mMembersOfGroup[IP_Task] = new List<T>();
                _mDependantsOfPrecedent[IP_Task] = new HashSet<T>();
                _mResourcesOfIP_Task[IP_Task] = new HashSet<R>();
                _mGroupOfMember[IP_Task] = null;
            }
        }

        /// <summary>
        /// Remove IP_Task from this Project
        /// </summary>
        /// <param name="IP_Task"></param>
        public void Delete(T IP_Task)
        {
            if (IP_Task != null
                && !_mSplitIP_TaskOfPart.ContainsKey(IP_Task) // not a IP_Task part
                )
            {
                // Check if is group so can ungroup the IP_Task
                if (this.IsGroup(IP_Task))
                    this.Ungroup(IP_Task);

                if (this.IsSplit(IP_Task))
                    this.Merge(IP_Task);

                // Really delete all references
                _mRootIP_Tasks.Remove(IP_Task);
                _mMembersOfGroup.Remove(IP_Task);
                _mDependantsOfPrecedent.Remove(IP_Task);
                _mResourcesOfIP_Task.Remove(IP_Task);
                _mGroupOfMember.Remove(IP_Task);
                _mPartsOfSplitIP_Task.Remove(IP_Task);
                foreach (var g in _mMembersOfGroup) g.Value.Remove(IP_Task); // optimised: no need to check for contains
                foreach (var g in _mDependantsOfPrecedent) g.Value.Remove(IP_Task);
                _mRegister.Remove(IP_Task);
            }
            else if (IP_Task != null
                && _mSplitIP_TaskOfPart.ContainsKey(IP_Task) // must be existing part
                )
            {
                var split = _mSplitIP_TaskOfPart[IP_Task];
                var parts = _mPartsOfSplitIP_Task[split];
                if (parts.Count > 2)
                {
                    parts.Remove(IP_Task); // remove the part from the split IP_Task
                    _mRegister.Remove(IP_Task); // unregister the part
                    _mResourcesOfIP_Task.Remove(IP_Task);
                    _mSplitIP_TaskOfPart.Remove(IP_Task); // remove the reverse lookup
                    
                    split.Start = parts.First().Start; // recalculate the split IP_Task
                    split.End = parts.Last().End;
                    split.Duration = split.End - split.Start;
                }
                else
                {
                    this.Merge(split);
                }
            }
        }

        /// <summary>
        /// Add the member T to the group T
        /// </summary>
        /// <param name="group"></param>
        /// <param name="member"></param>
        public void Group(T group, T member)
        {
            if (group != null
                && member != null
                && _mRegister.Contains(group)
                )
            {
                // if the member is a IP_Task part, assign the split IP_Task to the group instead
                if (_mSplitIP_TaskOfPart.ContainsKey(member)) member = _mSplitIP_TaskOfPart[member];

                if (_mRegister.Contains(member)
                    && !group.Equals(member)
                    && !_mPartsOfSplitIP_Task.ContainsKey(group) // group cannot be split IP_Task
                    && !_mSplitIP_TaskOfPart.ContainsKey(group) // group cannot be parts
                    && !this.MembersOf(member).Contains(group)
                    && !this.HasRelations(group)
                    )
                {
                    _DetachIP_Task(member);

                    // add member to new group
                    _mMembersOfGroup[group].Add(member);
                    _mGroupOfMember[member] = group;

                    _RecalculateAncestorsSchedule();
                    _RecalculateSlack();
                    // clear indices since positions changed
                    _mIP_TaskIndices.Clear();
                }
            }
        }

        /// <summary>
        /// Remove the member IP_Task from its group
        /// </summary>
        public void Ungroup(T group, T member)
        {
            if (group != null
                && member != null
                && _mRegister.Contains(group)
                )
            {
                // change the member to become the split IP_Task is member is a IP_Task part
                if (_mSplitIP_TaskOfPart.ContainsKey(member)) member = _mSplitIP_TaskOfPart[member];
                if (_mRegister.Contains(member) && this.IsGroup(group))
                {
                    var ancestor = this.GroupsOf(group).LastOrDefault();
                    if(ancestor == null) // group is in root
                        _mRootIP_Tasks.Insert(_mRootIP_Tasks.IndexOf(group) + 1, member);
                    else // group is not in root, we get the ancestor that is in root
                        _mRootIP_Tasks.Insert(_mRootIP_Tasks.IndexOf(ancestor) + 1, member);
                    _mMembersOfGroup[group].Remove(member);
                    _mGroupOfMember[member] = null;

                    _RecalculateAncestorsSchedule();
                }
            }
        }

        /// <summary>
        /// Ungroup all member IP_Task under the specfied group IP_Task. The specified group IP_Task will become a normal IP_Task.
        /// If the there is a grandparent group, the members will become members of the grandparent group.
        /// </summary>
        /// <param name="group"></param>
        public void Ungroup(T group)
        {
            if (group != null
                //&& _mRegister.Contains(group)
                && _mMembersOfGroup.TryGetValue(group, out List<T> members))
            {
                var newgroup = this.DirectGroupOf(group);
                if (newgroup == null)
                {
                    foreach (var member in members)
                    {
                        _mRootIP_Tasks.Add(member);
                        _mGroupOfMember[member] = null;
                    }
                }
                else
                {
                    foreach (var member in members)
                    {
                        _mMembersOfGroup[newgroup].Add(member);
                        _mGroupOfMember[member] = null;
                    }
                }

                members.Clear();

                _RecalculateAncestorsSchedule();
            }
        }

        /// <summary>
        /// Get the zero-based index of the IP_Task in this Project
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <returns></returns>
        public int IndexOf(T IP_Task)
        {
            if (_mRegister.Contains(IP_Task))
            {
                if (_mIP_TaskIndices.ContainsKey(IP_Task))
                    return _mIP_TaskIndices[IP_Task];

                int i = 0;
                foreach (var x in IP_Tasks)
                {
                    if (x.Equals(IP_Task))
                    {
                        _mIP_TaskIndices[IP_Task] = i;
                        return i;
                    }
                    i++;
                }
            }
            return -1;
        }

        /// <summary>
        /// Re-order position of the IP_Task by offset amount of places
        /// If IP_Task is moved between members, the IP_Task is added to the members' group
        /// If IP_Task is a member and it is moved above it's group or below last sibling member, then it is moved out of its group
        /// If IP_Task is a part, then its parent split-IP_Task will be move instead
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <param name="offset"></param>
        public void Move(T IP_Task, int offset)
        {
            if (IP_Task != null && _mRegister.Contains(IP_Task) && offset != 0)
            {
                if (IsPart(IP_Task)) IP_Task = SplitIP_TaskOf(IP_Task);

                int indexofIP_Task = IndexOf(IP_Task);
                if (indexofIP_Task > -1)
                {
                    int newindexofIP_Task = indexofIP_Task + offset;
                    // check for out of index bounds
                    var IP_Taskcount = IP_Tasks.Count();
                    if (newindexofIP_Task < 0) newindexofIP_Task = 0;
                    else if (newindexofIP_Task > IP_Taskcount) newindexofIP_Task = IP_Taskcount;
                    // get the index of the IP_Task that will be displaced
                    var displacedIP_Task = IP_Tasks.ElementAtOrDefault(newindexofIP_Task);

                    if(displacedIP_Task == IP_Task)
                    {
                        return;
                    }
                    if (displacedIP_Task == null)
                    {
                        // adding to the end of the IP_Task list
                        _DetachIP_Task(IP_Task);
                        _mRootIP_Tasks.Add(IP_Task);
                    }
                    else if (!displacedIP_Task.Equals(IP_Task))
                    {
                        int indexofdestinationIP_Task;
                        var displacedIP_Taskparent = this.DirectGroupOf(displacedIP_Task);
                        if (displacedIP_Taskparent == null) // displacedIP_Task is in root
                        {
                            indexofdestinationIP_Task = _mRootIP_Tasks.IndexOf(displacedIP_Task);
                            _DetachIP_Task(IP_Task);
                            _mRootIP_Tasks.Insert(indexofdestinationIP_Task, IP_Task);
                        }
                        else if (!displacedIP_Taskparent.Equals(IP_Task)) // displaced IP_Task is not under the moving IP_Task
                        {
                            var memberlist = _mMembersOfGroup[displacedIP_Taskparent];
                            indexofdestinationIP_Task = memberlist.IndexOf(displacedIP_Task);
                            _DetachIP_Task(IP_Task);
                            memberlist.Insert(indexofdestinationIP_Task, IP_Task);
                            _mGroupOfMember[IP_Task] = displacedIP_Taskparent;
                        }
                    }

                    _RecalculateAncestorsSchedule();
                    _RecalculateSlack();

                    // clear indices since positions changed
                    _mIP_TaskIndices.Clear();
                }
            }
        }

        /// <summary>
        /// Get the T tree
        /// </summary>
        public IEnumerable<T> IP_Tasks
        {
            get
            {
                var stack = new Stack<T>(1024);
                var rstack = new Stack<T>(30);
                foreach (var IP_Task in _mRootIP_Tasks)
                {
                    stack.Push(IP_Task);
                    while (stack.Count > 0)
                    {
                        var visited = stack.Pop();
                        yield return visited;

                        foreach (var member in _mMembersOfGroup[visited])
                            rstack.Push(member);

                        while (rstack.Count > 0) stack.Push(rstack.Pop());
                    }
                }
            }
        }
        
        /// <summary>
        /// Enumerate upwards from member to and through all the parents and grandparents of the specified IP_Task
        /// </summary>
        public IEnumerable<T> GroupsOf(T member)
        {
            T parent = DirectGroupOf(member);
            while (parent != null)
            {
                yield return parent;
                parent = DirectGroupOf(parent);
            }
        }

        /// <summary>
        /// Enumerate through all the children and grandchildren of the specified group
        /// </summary>
        /// <param name="group"></param>
        /// <returns></returns>
        public IEnumerable<T> MembersOf(T group)
        {
            if (_mRegister.Contains(group))
            {
                Stack<T> stack = new Stack<T>(20);
                Stack<T> rstack = new Stack<T>(10);
                foreach (var child in _mMembersOfGroup[group])
                {
                    stack.Push(child);
                    while (stack.Count > 0)
                    {
                        var visitedchild = stack.Pop();
                        yield return visitedchild;

                        // push the grandchild
                        rstack.Clear();
                        foreach (var grandchild in _mMembersOfGroup[visitedchild])
                            rstack.Push(grandchild);

                        // put in the right visiting order
                        while (rstack.Count > 0)
                            stack.Push(rstack.Pop());
                    }
                }
            }
        }

        /// <summary>
        /// Get the parent group of the specified IP_Task
        /// </summary>
        /// <param name="member"></param>
        /// <returns></returns>
        public T DirectGroupOf(T member)
        {
            if (_mGroupOfMember.ContainsKey(member)) // _mRegister.Contains(IP_Task))
            {
                return _mGroupOfMember[member];
            }
            else
            {
                return null;
            }
        }

        /// <summary>
        /// Enumerate through all the direct children of the specified group
        /// </summary>
        /// <param name="group"></param>
        /// <returns></returns>
        public IEnumerable<T> DirectMembersOf(T group)
        {
            if (group == null) yield break;

            if (_mMembersOfGroup.TryGetValue(group, out List<T> list))
            {
                var iter = list.GetEnumerator();
                while (iter.MoveNext()) yield return iter.Current;
            }
        }

        /// <summary>
        /// Enumerate through all the direct precedents and indirect precedents of the specified IP_Task
        /// </summary>
        /// <param name="dependant"></param>
        /// <returns></returns>
        public IEnumerable<T> PrecedentsOf(T dependant)
        {
            if (_mRegister.Contains(dependant))
            {
                var stack = new Stack<T>(20);
                foreach (var p in DirectPrecedentsOf(dependant))
                {
                    stack.Push(p);
                    while (stack.Count > 0)
                    {
                        var visited = stack.Pop();
                        yield return visited;
                        foreach (var grandp in DirectPrecedentsOf(visited))
                            stack.Push(grandp);
                    }
                }
            }
        }

        /// <summary>
        /// Enumerate through all the direct dependants and indirect dependants of the specified IP_Task
        /// </summary>
        /// <param name="precendent"></param>
        /// <returns></returns>
        public IEnumerable<T> DependantsOf(T precendent)
        {
            if (!_mDependantsOfPrecedent.ContainsKey(precendent)) yield break;

            var stack = new Stack<T>(20);
            foreach (var d in _mDependantsOfPrecedent[precendent])
            {
                stack.Push(d);
                while (stack.Count > 0)
                {
                    var visited = stack.Pop();
                    yield return visited;
                    foreach (var grandd in _mDependantsOfPrecedent[visited])
                        stack.Push(grandd);
                }
            }
        }

        /// <summary>
        /// Enumerate through all the direct precedents of the specified IP_Task
        /// </summary>
        /// <param name="dependants"></param>
        /// <returns></returns>
        public IEnumerable<T> DirectPrecedentsOf(T dependants)
        {
            return _mDependantsOfPrecedent.Where(x => x.Value.Contains(dependants)).Select(x => x.Key);
        }

        /// <summary>
        /// Enumerate through all the direct dependants of the specified IP_Task
        /// </summary>
        /// <param name="precedent"></param>
        /// <returns></returns>
        public IEnumerable<T> DirectDependantsOf(T precedent)
        {
            if (precedent == null) yield break;

            if (_mDependantsOfPrecedent.TryGetValue(precedent, out HashSet<T> dependants))
            {
                var iter = dependants.GetEnumerator();
                while (iter.MoveNext()) yield return iter.Current;
            }
        }

        /// <summary>
        /// Enumerate through all IP_Tasks that is a precedent, having dependants.
        /// </summary>
        public IEnumerable<T> Precedents
        {
            get { return _mDependantsOfPrecedent.Where(x => _mDependantsOfPrecedent[x.Key].Count > 0).Select(x => x.Key); }
        }

        /// <summary>
        /// Enumerate list of critical paths in Project
        /// </summary>
        public IEnumerable<IEnumerable<T>> CriticalPaths
        {
            get
            {
                Dictionary<TimeSpan, List<T>> endtimelookp = new Dictionary<TimeSpan, List<T>>(1024);
                TimeSpan max_end = TimeSpan.MinValue;
                foreach (var IP_Task in this.IP_Tasks)
                {
                    if (!endtimelookp.TryGetValue(IP_Task.End, out List<T> list))
                        endtimelookp[IP_Task.End] = new List<T>(10);
                    endtimelookp[IP_Task.End].Add(IP_Task);

                    if (IP_Task.End > max_end) max_end = IP_Task.End;
                }

                if (max_end != TimeSpan.MinValue)
                {
                    foreach (var IP_Task in endtimelookp[max_end])
                    {
                        yield return new T[] { IP_Task }.Concat(PrecedentsOf(IP_Task));
                    }
                }
            }
        }

        /// <summary>
        /// Get whether the specified IP_Task is a group
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <returns></returns>
        public bool IsGroup(T IP_Task)
        {
            if (_mMembersOfGroup.TryGetValue(IP_Task, out List<T> list))
                return list.Count > 0;
            else
                return false;
        }

        /// <summary>
        /// Get whether the specified IP_Task is a member
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <returns></returns>
        public bool IsMember(T IP_Task)
        {
            return this.DirectGroupOf(IP_Task) != null;
        }

        /// <summary>
        /// Get whether the specified IP_Task has relations, either has dependants or has precedents connecting to it.
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <returns></returns>
        public bool HasRelations(T IP_Task)
        {
            if (_mRegister.Contains(IP_Task) && _mDependantsOfPrecedent.ContainsKey(IP_Task))
            {
                return _mDependantsOfPrecedent[IP_Task].Count > 0 || DirectPrecedentsOf(IP_Task).FirstOrDefault() != null;
            }
            else
            {
                return false;
            }
        }

        /// <summary>
        /// Set a relation between the precedent and dependant IP_Task
        /// </summary>
        /// <param name="precedent"></param>
        /// <param name="dependant"></param>
        public void Relate(T precedent, T dependant)
        {
            if (_mRegister.Contains(precedent)
                && _mRegister.Contains(dependant)
                )
            {
                if (_mSplitIP_TaskOfPart.ContainsKey(precedent)) precedent = _mSplitIP_TaskOfPart[precedent];
                if (_mSplitIP_TaskOfPart.ContainsKey(dependant)) dependant = _mSplitIP_TaskOfPart[dependant];

                if (!precedent.Equals(dependant)
                    &&!this.DependantsOf(dependant).Contains(precedent)
                    && !this.IsGroup(precedent)
                    && !this.IsGroup(dependant)
                    )
                {
                    _mDependantsOfPrecedent[precedent].Add(dependant);

                    _RecalculateDependantsOf(precedent);
                    _RecalculateAncestorsSchedule();
                    _RecalculateSlack();
                }
            }
        }
        
        /// <summary>
        /// Unset the relation between the precedent and dependant IP_Task, if any.
        /// </summary>
        /// <param name="precedent"></param>
        /// <param name="dependant"></param>
        public void Unrelate(T precedent, T dependant)
        {
            if (_mRegister.Contains(precedent) && _mRegister.Contains(dependant))
            {
                if (_mSplitIP_TaskOfPart.ContainsKey(precedent)) precedent = _mSplitIP_TaskOfPart[precedent];
                if (_mSplitIP_TaskOfPart.ContainsKey(dependant)) dependant = _mSplitIP_TaskOfPart[dependant];

                _mDependantsOfPrecedent[precedent].Remove(dependant);

                _RecalculateSlack();
            }
        }

        /// <summary>
        /// Remove all dependant IP_Task from specified precedent IP_Task
        /// </summary>
        /// <param name="precedent"></param>
        public void Unrelate(T precedent)
        {
            if (_mRegister.Contains(precedent))
            {
                if (_mSplitIP_TaskOfPart.ContainsKey(precedent))
                    precedent = _mSplitIP_TaskOfPart[precedent];

                _mDependantsOfPrecedent[precedent].Clear();

                _RecalculateSlack();
            }
        }

        /// <summary>
        /// Assign the specified resource to the specified IP_Task
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <param name="resource"></param>
        public void Assign(T IP_Task, R resource)
        {
            if (_mRegister.Contains(IP_Task) && !_mResourcesOfIP_Task[IP_Task].Contains(resource))
                _mResourcesOfIP_Task[IP_Task].Add(resource);
        }

        /// <summary>
        /// Unassign the specified resource from the specfied IP_Task
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <param name="resource"></param>
        public void Unassign(T IP_Task, R resource)
        {
            _mResourcesOfIP_Task[IP_Task].Remove(resource);
        }

        /// <summary>
        /// Unassign the all resources from the specfied IP_Task
        /// </summary>
        /// <param name="IP_Task"></param>
        public void Unassign(T IP_Task)
        {
            if(_mRegister.Contains(IP_Task))
                _mResourcesOfIP_Task[IP_Task].Clear();
        }

        /// <summary>
        /// Unassign the specified resource from all IP_Tasks that has this resource assigned
        /// </summary>
        /// <param name="resource"></param>
        public void Unassign(R resource)
        {
            foreach (var r in _mResourcesOfIP_Task.Where(x => x.Value.Contains(resource)))
                r.Value.Remove(resource);
        }

        /// <summary>
        /// Enumerate through all the resources that has been assigned to some IP_Task.
        /// </summary>
        public IEnumerable<R> Resources
        {
            get
            {
                return _mResourcesOfIP_Task.SelectMany(x => x.Value).Distinct();
            }
        }

        /// <summary>
        /// Enumerate through all the resources that has been assigned to the specified IP_Task.
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <returns></returns>
        public IEnumerable<R> ResourcesOf(T IP_Task)
        {
            if (IP_Task == null || !_mRegister.Contains(IP_Task))
                yield break;

            if (_mResourcesOfIP_Task.TryGetValue(IP_Task, out HashSet<R> list))
            {
                foreach (var item in list)
                    yield return item;
            }
        }

        /// <summary>
        /// Enumerate through all the IP_Tasks that has the specified resource assigned to it.
        /// </summary>
        /// <param name="resource"></param>
        /// <returns></returns>
        public IEnumerable<T> IP_TasksOf(R resource)
        {
            return _mResourcesOfIP_Task.Where(x => x.Value.Contains(resource)).Select(x => x.Key);
        }

        /// <summary>
        /// Set the start value. Affects group start/end and dependants start time.
        /// </summary>
        public void SetStart(T IP_Task, TimeSpan value)
        {
            if (_mRegister.Contains(IP_Task) && value != IP_Task.Start && !this.IsGroup(IP_Task))
            {
                _SetStartHelper(IP_Task, value);

                _RecalculateAncestorsSchedule();
                _RecalculateSlack();
            }
            // Set start for a group IP_Task
            else if (_mRegister.Contains(IP_Task) && value != IP_Task.Start && this.IsGroup(IP_Task))
            {
                _SetGroupStartHelper(IP_Task, value);

                _RecalculateAncestorsSchedule();
                _RecalculateSlack();
            }
        }

        /// <summary>
        /// Set the end time. Affects group end and dependants start time.
        /// </summary>
        public void SetEnd(T IP_Task, TimeSpan value)
        {
            if (_mRegister.Contains(IP_Task) && value != IP_Task.End && !this.IsGroup(IP_Task))
            {
                this._SetEndHelper(IP_Task, value);

                _RecalculateAncestorsSchedule();
                _RecalculateSlack();
            }
        }

        /// <summary>
        /// Set the duration of the specified IP_Task from start to end.
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <param name="duration">Number of timescale units between ProjectManager.Start</param>
        public void SetDuration(T IP_Task, TimeSpan duration)
        {
            this.SetEnd(IP_Task, IP_Task.Start + duration);
        }

        /// <summary>
        /// Set the percentage complete of the specified IP_Task from 0.0f to 1.0f.
        /// No effect on group IP_Tasks as they will get the aggregated percentage complete of all child IP_Tasks
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <param name="complete"></param>
        public void SetComplete(T IP_Task, float complete)
        {
            if (_mRegister.Contains(IP_Task)
                && complete != IP_Task.Complete
                && !this.IsGroup(IP_Task) // not a group
                && !_mPartsOfSplitIP_Task.ContainsKey(IP_Task) // not a split IP_Task
                )
            {
                _SetCompleteHelper(IP_Task, complete);

                _RecalculateComplete();
            }
        }

        /// <summary>
        /// Set whether to collapse the specified group IP_Task. No effect on regular IP_Tasks.
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <param name="collasped"></param>
        public void SetCollapse(T IP_Task, bool collasped)
        {
            if (_mRegister.Contains(IP_Task) && this.IsGroup(IP_Task))
            {
                IP_Task.IsCollapsed = collasped;
            }
        }
        
        /// <summary>
        /// Split the specified IP_Task into consecutive parts part1 and part2.
        /// </summary>
        /// <param name="IP_Task">The regular IP_Task to split which has duration of at least 2 to make two parts of 1 time unit duration each.</param>
        /// <param name="part1">New IP_Task part (1) of the split IP_Task, with the start time of the original IP_Task and the specified duration value.</param>
        /// <param name="part2">New IP_Task part (2) of the split IP_Task, starting 1 time unit after part (1) ends and having the remaining of the duration of the origina IP_Task.</param>
        /// <param name="duration">The duration of part (1) will be set to the specified duration value but will also be adjusted to approperiate value if necessary.</param>
        public void Split(T IP_Task, T part1, T part2, TimeSpan duration)
        {
            if (IP_Task != null
                && part1 != null
                && part2 != null
                && !part1.Equals(part2) // parts cannot be the same
                && _mRegister.Contains(IP_Task) // IP_Task must be registered
                && !_mPartsOfSplitIP_Task.ContainsKey(IP_Task) // IP_Task must not already be a split IP_Task
                && !_mSplitIP_TaskOfPart.ContainsKey(IP_Task) // IP_Task must not be a IP_Task part
                && _mMembersOfGroup[IP_Task].Count == 0 // IP_Task cannot be a group
                && !_mRegister.Contains(part1) // part1 and part2 must have never existed
                && !_mRegister.Contains(part2)
                )
            {
                _mRegister.Add(part1);  // register part1
                _mResourcesOfIP_Task[part1] = new HashSet<R>(); // create container for holding resource
                
                // add part1 to split IP_Task
                IP_Task.Complete = 0.0f; // reset the complete status
                var parts = _mPartsOfSplitIP_Task[IP_Task] = new List<T>(2); 
                parts.Add(part1);
                _mSplitIP_TaskOfPart[part1] = IP_Task; // make a reverse lookup

                // allign the schedule
                if (duration <= TimeSpan.Zero || duration >= IP_Task.Duration) duration = TimeSpan.FromTicks(IP_Task.Duration.Ticks / 2);
                part1.Start = IP_Task.Start;
                part1.End = IP_Task.End;
                part1.Duration = IP_Task.Duration;

                // split part1 to give part2
                this.Split(part1, part2, duration);
            }
        }
        
        /// <summary>
        /// Split the specified part and obtain another part from it.
        /// </summary>
        /// <param name="part">The IP_Task part to split which has duration of at least 2 to make two parts of 1 time unit duration each. Its duration will be set to the specified duration value.</param>
        /// <param name="other">New IP_Task part of the original part, starting 1 time unit after it ends and having the remaining of the duration of the original part.</param>
        /// <param name="duration">The duration of part (1) will be set to the specified duration value but will also be adjusted to approperiate value if necessary.</param>
        public void Split(T part, T other, TimeSpan duration)
        {
            if (part != null
                && other != null
                && _mSplitIP_TaskOfPart.ContainsKey(part) // part must be an existing part
                && !_mRegister.Contains(other) // other must not have existed
                )
            {
                _mRegister.Add(other); // register other part
                _mResourcesOfIP_Task[other] = new HashSet<R>(); // create container for holding resource

                var split = _mSplitIP_TaskOfPart[part]; // get the split IP_Task
                var parts = _mPartsOfSplitIP_Task[split]; // get the list of ordered parts

                parts.Insert(parts.IndexOf(part) + 1, other); // insert the other part after the existing part
                _mSplitIP_TaskOfPart[other] = split; // set the reverse lookup

                System.Diagnostics.Debug.Write("Project::Split(T part, T other, TimeSpan duration): Need to define minimum duration for splitting.");

                // limit the duration point within the split IP_Task duration
                if (duration <= TimeSpan.Zero || duration >= part.Duration) duration = TimeSpan.FromTicks(part.Duration.Ticks / 2);
                
                // the real split
                var one_duration = duration;
                var two_duration = part.Duration - duration;
                part.Duration = one_duration;
                part.End = part.Start + one_duration;
                other.Duration = two_duration;
                other.Start = part.End;
                other.End = other.Start + two_duration;

                _PackPartsForward(parts);
                split.Start = parts.First().Start; // recalculate the split IP_Task
                split.End = parts.Last().End;
                split.Duration = split.End - split.Start;

                _RecalculateDependantsOf(split);
                _RecalculateAncestorsSchedule();                
            }
        }
        
        /// <summary>
        /// Join part1 and part2 in a split IP_Task into a single part represented by part1, and part2 will be deleted from the ProjectManager.
        /// The resulting part will have a duration total of the two parts.
        /// Part1 and part2 must be actual parts and must be consecutive parts in the split IP_Task.
        /// If the join results in only one part remaining, the all parts will be deleted and the split IP_Task will promote to a regular IP_Task
        /// Schedule of other parts will not be affected.
        /// TODO: Join option: EarlyStartLateEnd, EarlyStartEarlyEnd, LateStartLateEnd
        /// </summary>
        /// <param name="part1">The part to keep in the ProjectManager after the join completes successfully.</param>
        /// <param name="part2">The part to join into part1 and be deleted afterwards from the ProjectManager.</param>
        public void Join(T part1, T part2)
        {
            if (part1 != null
                && part2 != null
                && _mSplitIP_TaskOfPart.ContainsKey(part1) // part1 and part2 must already be existing parts
                && _mSplitIP_TaskOfPart.ContainsKey(part2) 
                && _mSplitIP_TaskOfPart[part1] == _mSplitIP_TaskOfPart[part2] // part1 and part2 must be of the same split IP_Task
                )
            {

                var split = _mSplitIP_TaskOfPart[part1];
                var parts = _mPartsOfSplitIP_Task[split];
                if (parts.Count > 2)
                {
                    // Aggregate part2 into part1, and determine join type
                    TimeSpan min; bool join_backwards;
                    if (part1.Start < part2.Start) { min = part1.Start; join_backwards = true; }
                    else { min = part2.Start; join_backwards = false; }
                    TimeSpan duration = part1.Duration + part2.Duration;

                    part1.Start = min;
                    part1.Duration = duration;
                    part1.End = min + duration;

                    // aggregate resouces
                    // TODO: Ask whether to aggregate resources?
                    foreach (var r in this.ResourcesOf(part2))
                        this.Assign(part1, r);
                    this.Unassign(part2);

                    // remove all traces of part2
                    parts.Remove(part2);
                    _mResourcesOfIP_Task.Remove(part2);
                    _mSplitIP_TaskOfPart.Remove(part2);
                    _mRegister.Remove(part2);

                    // pack the remaining parts
                    if (join_backwards) _PackPartsForward(parts);
                    else _PackPartsBackwards(parts);

                    // set the duration
                    split.End = parts.Last().End;
                    split.Duration = split.End - split.Start;
                    split.Start = parts.First().Start;

                    _RecalculateAncestorsSchedule();
                }
                else
                {
                    this.Merge(split);
                }
            }
        }
        
        /// <summary>
        /// Merge all the parts of the splitted IP_Task back into one IP_Task, having duration equal to sum of total duration of individual IP_Task parts, and aggregating the resources onto the resulting IP_Task.
        /// </summary>
        /// <param name="split">The split IP_Task to merge</param>
        public void Merge(T split)
        {
            if (split != null
                && _mPartsOfSplitIP_Task.ContainsKey(split) // must be existing split IP_Task
                )
            {
                TimeSpan duration = TimeSpan.Zero;
                _mPartsOfSplitIP_Task[split].ForEach(x => {

                    // sum durations
                    duration += x.Duration;

                    // merge resources onto split IP_Task
                    foreach (var r in _mResourcesOfIP_Task[x])
                        this.Assign(split, r);

                    // remove traces of all parts
                    _mSplitIP_TaskOfPart.Remove(x);
                    _mRegister.Remove(x);
                    _mResourcesOfIP_Task.Remove(x);
                });
                _mPartsOfSplitIP_Task.Remove(split); // remove split as a split IP_Task

                // set the duration
                this.SetDuration(split, duration);
            }
        }
        
        /// <summary>
        /// Get the parts of the split IP_Task
        /// </summary>
        /// <param name="split"></param>
        /// <returns></returns>
        public IEnumerable<T> PartsOf(T split)
        {
            if (split != null
                && _mPartsOfSplitIP_Task.ContainsKey(split) // must be existing split IP_Task
                )
            {
                return _mPartsOfSplitIP_Task[split].Select(x => x);
            }
            else
            {
                return new T[0];
            }
        }
        
        /// <summary>
        /// Get the split IP_Task that the specified part belogs to.
        /// </summary>
        /// <param name="part"></param>
        /// <returns></returns>
        public T SplitIP_TaskOf(T part)
        {
            if (_mSplitIP_TaskOfPart.ContainsKey(part))
                return _mSplitIP_TaskOfPart[part];
            return null;
        }
        
        /// <summary>
        /// Get whether the specified IP_Task is a split IP_Task
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <returns></returns>
        public bool IsSplit(T IP_Task)
        {
            return IP_Task != null && _mPartsOfSplitIP_Task.ContainsKey(IP_Task);
        }
        
        /// <summary>
        /// Get whether the specified IP_Task is a part of a split IP_Task
        /// </summary>
        /// <param name="IP_Task"></param>
        /// <returns></returns>
        public bool IsPart(T IP_Task)
        {
            return IP_Task != null && _mSplitIP_TaskOfPart.ContainsKey(IP_Task);
        }

        /// <summary>
        /// Detach the specified IP_Task from ProjectManager.IP_Tasks (i.e. remove from its parent group, or if not it goes not have a parent group, unregister from root IP_Task status).
        /// The specified IP_Task will remain registered in ProjectManager.
        /// After execution of this helper method, the IP_Task is expected to be re-attached to ProjectManager.IP_Tasks by regaining root IP_Task status, or joining a new group.
        /// </summary>
        /// <param name="IP_Task"></param>
        private void _DetachIP_Task(T IP_Task)
        {
            var group = this.DirectGroupOf(IP_Task);
            if (group == null) // member is actually not in any group, so it must be in _mRootIP_Tasks
                _mRootIP_Tasks.Remove(IP_Task);
            else
            {
                _mMembersOfGroup[group].Remove(IP_Task);
                _mGroupOfMember[IP_Task] = null;
            }
        }

        private void _SetStartHelper(T IP_Task, TimeSpan value)
        {
            if (IP_Task.Start != value)
            {
                if (_mSplitIP_TaskOfPart.ContainsKey(IP_Task)) 
                {
                    // IP_Task part belonging to a split IP_Task needs special treatment
                    _SetPartStartHelper(IP_Task, value);
                }
                else // regular IP_Task or a split IP_Task, which we will treat normally
                {
                    // check out of bounds
                    if (value < TimeSpan.Zero) value = TimeSpan.Zero;
                    if (this.DirectPrecedentsOf(IP_Task).Any())
                    {
                        var max_end = this.DirectPrecedentsOf(IP_Task).Max(x => x.End);
                        if (value <= max_end) value = max_end; // + One;
                    }

                    // save offset just in case we need to use for moving IP_Task parts
                    var offset = value - IP_Task.Start;

                    // cache value
                    IP_Task.Duration = IP_Task.End - IP_Task.Start;
                    IP_Task.Start = value;

                    // affect self
                    IP_Task.End = IP_Task.Start + IP_Task.Duration;

                    // calculate dependants
                    _RecalculateDependantsOf(IP_Task);

                    // shift the IP_Task parts accordingly if IP_Task was a split IP_Task
                    if (_mPartsOfSplitIP_Task.ContainsKey(IP_Task))
                    {
                        _mPartsOfSplitIP_Task[IP_Task].ForEach(x => {
                            x.Start += offset;
                            x.End += offset;
                        });
                    }
                }
            }
        }

        /// <summary>
        /// Set the start date for a group IP_Task. The relative dates between the IP_Tasks in the group will not be affected
        /// </summary>
        /// <param name="group"></param>
        /// <param name="value"></param>
        private void _SetGroupStartHelper(T group, TimeSpan value)
        {
            if (_mRegister.Contains(group) && value != group.Start && this.IsGroup(group))
            {
                bool earlier = value < group.Start;
                TimeSpan offset = value - group.Start;
                var decendants = earlier ? MembersOf(group).OrderBy((t) => t.Start) : MembersOf(group).OrderByDescending((t) => t.Start);

                foreach(T decendant in decendants)
                {
                    if (this.IsGroup(decendant)) continue;
                   
                    decendant.Start += offset;
                    decendant.End += offset;

                    if (this.IsSplit(decendant))
                    {
                        var parts = _mPartsOfSplitIP_Task[decendant];
                        foreach (T part in parts)
                        {
                            part.Start += offset;
                            part.End += offset;
                        }
                    }

                    _RecalculateDependantsOf(decendant);
                }

                _RecalculateAncestorsSchedule();
                _RecalculateSlack();
            }
        }

        private void _SetEndHelper(T IP_Task, TimeSpan value)
        {
            if (IP_Task.End != value)
            {
                if (_mSplitIP_TaskOfPart.ContainsKey(IP_Task))
                {
                    // IP_Task part belonging to a split IP_Task needs special treatment
                    _SetPartEndHelper(IP_Task, value);
                }
                else // regular IP_Task or a split IP_Task, which we will treat normally
                {
                    // check bounds
                    bool isSplitIP_Task = _mPartsOfSplitIP_Task.ContainsKey(IP_Task);
                    T last_part = null;
                    if (isSplitIP_Task)
                    {
                        last_part = _mPartsOfSplitIP_Task[IP_Task].Last();
                        if (value <= last_part.Start) value = last_part.Start + TimeSpan.FromMinutes(30);
                    }
                    if (value <= IP_Task.Start) value = IP_Task.Start + TimeSpan.FromMinutes(30); // end cannot be less than start
                    
                    // assign end value
                    IP_Task.End = value;
                    IP_Task.Duration = IP_Task.End - IP_Task.Start;

                    _RecalculateDependantsOf(IP_Task);

                    if (isSplitIP_Task)
                    {
                        last_part.End = value;
                        last_part.Duration = last_part.End - last_part.Start;
                    }
                }
            }
        }

        private void _SetPartStartHelper(T part, TimeSpan value)
        {
            var split = _mSplitIP_TaskOfPart[part];
            var parts = _mPartsOfSplitIP_Task[split];

            // check bounds
            if (this.DirectPrecedentsOf(split).Any())
            {
                var max_end = this.DirectPrecedentsOf(split).Max(x => x.End);
                if (value < max_end) value = max_end;
            }
            if (value < TimeSpan.Zero) value = TimeSpan.Zero;

            // flag whether we need to pack parts forward or backwards
            bool backwards = value < part.Start;

            // assign start value, maintining duration and modifying end
            var duration = part.End - part.Start;
            part.Start = value;
            part.End = value + duration;

            // pack packs
            if (backwards) _PackPartsBackwards(parts);
            else _PackPartsForward(parts);

            // recalculate the split
            split.Start = parts.First().Start; // recalculate the split IP_Task
            split.End = parts.Last().End;
            split.Duration = split.End - split.Start;

            _RecalculateDependantsOf(split);
        }

        private void _SetPartEndHelper(T part, TimeSpan value)
        {
            var split = _mSplitIP_TaskOfPart[part];
            var parts = _mPartsOfSplitIP_Task[split];

            // check for bounds
            if (value <= part.Start) value = part.Start + TimeSpan.FromMinutes(30);

            // flag whether duration is increased or reduced
            bool increased = value > part.End;

            // set end value and duration
            part.End = value;
            part.Duration = part.End - part.Start;

            // pack parts
            if (increased) _PackPartsForward(parts);

            // recalculate the split
            split.Start = parts.First().Start; // recalculate the split IP_Task
            split.End = parts.Last().End;
            split.Duration = split.End - split.Start;

            _RecalculateDependantsOf(split);
        }

        private void _PackPartsBackwards(List<T> parts)
        {
            // pack backwards first before packing forward again
            for (int i = parts.Count - 2; i > 0; i--) // Cannot pack beyond first part (i > 0)
            {
                var earlier = parts[i];
                var later = parts[i + 1];
                if (later.Start <= earlier.End)
                {
                    earlier.End = later.Start;
                    earlier.Start = earlier.End - earlier.Duration;
                }
            }

            _PackPartsForward(parts);
        }

        private void _PackPartsForward(List<T> parts)
        {
            for (int i = 1; i < parts.Count; i++)
            {
                var current = parts[i];
                var previous = parts[i - 1];
                if (previous.End >= current.Start)
                {
                    current.Start = previous.End;
                    current.End = current.Start + current.Duration;
                }
            }
        }

        private void _SetCompleteHelper(T IP_Task, float value)
        {
            if (IP_Task.Complete != value)
            {
                if (value > 1) value = 1;
                else if (value < 0) value = 0;
                IP_Task.Complete = value;

                if (_mSplitIP_TaskOfPart.ContainsKey(IP_Task))
                {
                    var split = _mSplitIP_TaskOfPart[IP_Task];
                    var parts = _mPartsOfSplitIP_Task[split];
                    float complete = 0;
                    TimeSpan duration = TimeSpan.Zero;
                    foreach (var part in parts)
                    {
                        complete += part.Complete * part.Duration.Ticks;
                        duration += part.Duration;
                    }
                    split.Complete = complete / duration.Ticks;
                }
            }
        }

        private void _RecalculateComplete()
        {
            Stack<T> groups = new Stack<T>();
            foreach (var IP_Task in _mRootIP_Tasks.Where(x => this.IsGroup(x)))
            {
                _RecalculateCompletedHelper(IP_Task);
            }
        }

        private float _RecalculateCompletedHelper(T groupOrSplit)
        {
            float t_complete = 0;
            TimeSpan t_duration = TimeSpan.Zero;

            if (_mPartsOfSplitIP_Task.ContainsKey(groupOrSplit))
            {
                foreach (var part in _mPartsOfSplitIP_Task[groupOrSplit])
                {
                    t_complete += part.Complete * part.Duration.Ticks;
                    t_duration += part.Duration;
                }
            }
            else
            {
                foreach (var member in this.DirectMembersOf(groupOrSplit))
                {
                    t_duration += member.Duration;
                    if (this.IsGroup(member)) t_complete += _RecalculateCompletedHelper(member) * member.Duration.Ticks;
                    else t_complete += member.Complete * member.Duration.Ticks;
                }
            }

            groupOrSplit.Complete = t_complete / t_duration.Ticks;
            

            return groupOrSplit.Complete;
        }

        private void _RecalculateDependantsOf(T precedent)
        {
            // affect decendants
            foreach (var dependant in this.DirectDependantsOf(precedent))
            {
                if (dependant.Start < precedent.End)
                    this._SetStartHelper(dependant, precedent.End);
            }
        }

        private void _RecalculateAncestorsSchedule()
        {
            // affects parent group
            foreach(var group in _mRootIP_Tasks.Where(x => this.IsGroup(x)))
            {
                _RecalculateAncestorsScheduleHelper(group);
            }
        }

        private void _RecalculateAncestorsScheduleHelper(T group)
        {
            float t_complete = 0;
            TimeSpan t_duration = TimeSpan.Zero;
            var start = TimeSpan.MaxValue;
            var end = TimeSpan.MinValue;
            foreach (var member in this.DirectMembersOf(group))
            {
                if (this.IsGroup(member))
                    _RecalculateAncestorsScheduleHelper(member);

                t_duration += member.Duration;
                t_complete += member.Complete * member.Duration.Ticks;
                if (member.Start < start) start = member.Start;
                if (member.End > end) end = member.End;
            }

            this._SetStartHelper(group, start);
            this._SetEndHelper(group, end);
            this._SetCompleteHelper(group, t_complete / t_duration.Ticks);
        }

        private void _RecalculateSlack()
        {
            var max_end = this.IP_Tasks.Max(x => x.End);
            foreach (var IP_Task in this.IP_Tasks)
            {
                // affects slack for current IP_Task
                if (this.DirectDependantsOf(IP_Task).Any())
                {
                    // slack until the earliest dependant needs to start
                    var min = this.DirectDependantsOf(IP_Task).Min(x => x.Start);
                    IP_Task.Slack = min - IP_Task.End;
                }
                else
                {
                    // no dependants, so we have all the time until the last IP_Task ends
                    IP_Task.Slack = max_end - IP_Task.End;
                }
            }
        }

        
    }
}