using System;
using System.Collections.Generic;
using System.Linq;

namespace Terminal.Gui {
	class Branch<T> where T : class {
		/// <summary>
		/// True if the branch is expanded to reveal child branches.
		/// </summary>
		public bool IsExpanded { get; set; }

		/// <summary>
		/// The users object that is being displayed by this branch of the tree.
		/// </summary>
		public T Model { get; private set; }

		/// <summary>
		/// The depth of the current branch.  Depth of 0 indicates root level branches.
		/// </summary>
		public int Depth { get; private set; } = 0;

		/// <summary>
		/// The children of the current branch.  This is null until the first call to 
		/// <see cref="FetchChildren"/> to avoid enumerating the entire underlying hierarchy.
		/// </summary>
		public Dictionary<T, Branch<T>> ChildBranches { get; set; }

		/// <summary>
		/// The parent <see cref="Branch{T}"/> or null if it is a root.
		/// </summary>
		public Branch<T> Parent { get; private set; }

		private TreeView<T> tree;

		/// <summary>
		/// Declares a new branch of <paramref name="tree"/> in which the users object 
		/// <paramref name="model"/> is presented.
		/// </summary>
		/// <param name="tree">The UI control in which the branch resides.</param>
		/// <param name="parentBranchIfAny">Pass null for root level branches, otherwise
		/// pass the parent.</param>
		/// <param name="model">The user's object that should be displayed.</param>
		public Branch (TreeView<T> tree, Branch<T> parentBranchIfAny, T model)
		{
			this.tree = tree;
			this.Model = model;

			if (parentBranchIfAny != null) {
				Depth = parentBranchIfAny.Depth + 1;
				Parent = parentBranchIfAny;
			}
		}


		/// <summary>
		/// Fetch the children of this branch. This method populates <see cref="ChildBranches"/>.
		/// </summary>
		public virtual void FetchChildren ()
		{
			if (tree.TreeBuilder == null) {
				return;
			}

			var children = tree.TreeBuilder.GetChildren (this.Model) ?? Enumerable.Empty<T> ();

			this.ChildBranches = children.ToDictionary (k => k, val => new Branch<T> (tree, this, val));
		}

		/// <summary>
		/// Returns the width of the line including prefix and the results 
		/// of <see cref="TreeView{T}.AspectGetter"/> (the line body).
		/// </summary>
		/// <returns></returns>
		public virtual int GetWidth (ConsoleDriver driver)
		{
			return
				GetLinePrefix (driver).Sum (Rune.ColumnWidth) +
				Rune.ColumnWidth (GetExpandableSymbol (driver)) +
				(tree.AspectGetter (Model) ?? "").Length;
		}

		/// <summary>
		/// Renders the current <see cref="Model"/> on the specified line <paramref name="y"/>.
		/// </summary>
		/// <param name="driver"></param>
		/// <param name="colorScheme"></param>
		/// <param name="y"></param>
		/// <param name="availableWidth"></param>
		public virtual void Draw (ConsoleDriver driver, ColorScheme colorScheme, int y, int availableWidth)
		{
			// true if the current line of the tree is the selected one and control has focus
			bool isSelected = tree.IsSelected (Model);

			Attribute textColor = isSelected ? (tree.HasFocus ? colorScheme.Focus : colorScheme.HotNormal) : colorScheme.Normal;
			Attribute symbolColor = tree.Style.HighlightModelTextOnly ? colorScheme.Normal : textColor;

			// Everything on line before the expansion run and branch text
			Rune [] prefix = GetLinePrefix (driver).ToArray ();
			Rune expansion = GetExpandableSymbol (driver);
			string lineBody = tree.AspectGetter (Model) ?? "";

			tree.Move (0, y);

			// if we have scrolled to the right then bits of the prefix will have dispeared off the screen
			int toSkip = tree.ScrollOffsetHorizontal;

			driver.SetAttribute (symbolColor);
			// Draw the line prefix (all parallel lanes or whitespace and an expand/collapse/leaf symbol)
			foreach (Rune r in prefix) {

				if (toSkip > 0) {
					toSkip--;
				} else {
					driver.AddRune (r);
					availableWidth -= Rune.ColumnWidth (r);
				}
			}

			// pick color for expanded symbol
			if (tree.Style.ColorExpandSymbol || tree.Style.InvertExpandSymbolColors) {
				Attribute color = symbolColor;

				if (tree.Style.ColorExpandSymbol) {
					if (isSelected) {
						color = tree.Style.HighlightModelTextOnly ? colorScheme.HotNormal : (tree.HasFocus ? tree.ColorScheme.HotFocus : tree.ColorScheme.HotNormal);
					} else {
						color = tree.ColorScheme.HotNormal;
					}
				} else {
					color = symbolColor;
				}

				if (tree.Style.InvertExpandSymbolColors) {
					color = new Attribute (color.Background, color.Foreground);
				}

				driver.SetAttribute (color);
			}

			if (toSkip > 0) {
				toSkip--;
			} else {
				driver.AddRune (expansion);
				availableWidth -= Rune.ColumnWidth (expansion);
			}

			// horizontal scrolling has already skipped the prefix but now must also skip some of the line body
			if (toSkip > 0) {
				if (toSkip > lineBody.Length) {
					lineBody = "";
				} else {
					lineBody = lineBody.Substring (toSkip);
				}
			}

			// If body of line is too long
			if (lineBody.Sum (l => Rune.ColumnWidth (l)) > availableWidth) {
				// remaining space is zero and truncate the line
				lineBody = new string (lineBody.TakeWhile (c => (availableWidth -= Rune.ColumnWidth (c)) >= 0).ToArray ());
				availableWidth = 0;
			} else {

				// line is short so remaining width will be whatever comes after the line body
				availableWidth -= lineBody.Length;
			}


			// default behaviour is for model to use the color scheme
			// of the tree view
			var modelColor = textColor;

			// if custom color delegate invoke it
			if (tree.ColorGetter != null) {
				var modelScheme = tree.ColorGetter (Model);

				// if custom color scheme is defined for this Model
				if (modelScheme != null) {
					// use it
					modelColor = isSelected ? modelScheme.Focus : modelScheme.Normal;
				}
			}

			driver.SetAttribute (modelColor);
			driver.AddStr (lineBody);

			if (availableWidth > 0) {
				driver.SetAttribute (symbolColor);
				driver.AddStr (new string (' ', availableWidth));
			}
			driver.SetAttribute (colorScheme.Normal);
		}

		/// <summary>
		/// Gets all characters to render prior to the current branches line.  This includes indentation
		/// whitespace and any tree branches (if enabled).
		/// </summary>
		/// <param name="driver"></param>
		/// <returns></returns>
		private IEnumerable<Rune> GetLinePrefix (ConsoleDriver driver)
		{
			// If not showing line branches or this is a root object.
			if (!tree.Style.ShowBranchLines) {
				for (int i = 0; i < Depth; i++) {
					yield return new Rune (' ');
				}

				yield break;
			}

			// yield indentations with runes appropriate to the state of the parents
			foreach (var cur in GetParentBranches ().Reverse ()) {
				if (cur.IsLast ()) {
					yield return new Rune (' ');
				} else {
					yield return driver.VLine;
				}

				yield return new Rune (' ');
			}

			if (IsLast ()) {
				yield return driver.LLCorner;
			} else {
				yield return driver.LeftTee;
			}
		}

		/// <summary>
		/// Returns all parents starting with the immediate parent and ending at the root.
		/// </summary>
		/// <returns></returns>
		private IEnumerable<Branch<T>> GetParentBranches ()
		{
			var cur = Parent;

			while (cur != null) {
				yield return cur;
				cur = cur.Parent;
			}
		}

		/// <summary>
		/// Returns an appropriate symbol for displaying next to the string representation of 
		/// the <see cref="Model"/> object to indicate whether it <see cref="IsExpanded"/> or
		/// not (or it is a leaf).
		/// </summary>
		/// <param name="driver"></param>
		/// <returns></returns>
		public Rune GetExpandableSymbol (ConsoleDriver driver)
		{
			var leafSymbol = tree.Style.ShowBranchLines ? driver.HLine : ' ';

			if (IsExpanded) {
				return tree.Style.CollapseableSymbol ?? leafSymbol;
			}

			if (CanExpand ()) {
				return tree.Style.ExpandableSymbol ?? leafSymbol;
			}

			return leafSymbol;
		}

		/// <summary>
		/// Returns true if the current branch can be expanded according to 
		/// the <see cref="TreeBuilder{T}"/> or cached children already fetched.
		/// </summary>
		/// <returns></returns>
		public bool CanExpand ()
		{
			// if we do not know the children yet
			if (ChildBranches == null) {

				//if there is a rapid method for determining whether there are children
				if (tree.TreeBuilder.SupportsCanExpand) {
					return tree.TreeBuilder.CanExpand (Model);
				}

				//there is no way of knowing whether we can expand without fetching the children
				FetchChildren ();
			}

			//we fetched or already know the children, so return whether we have any
			return ChildBranches.Any ();
		}

		/// <summary>
		/// Expands the current branch if possible.
		/// </summary>
		public void Expand ()
		{
			if (ChildBranches == null) {
				FetchChildren ();
			}

			if (ChildBranches.Any ()) {
				IsExpanded = true;
			}
		}

		/// <summary>
		/// Marks the branch as collapsed (<see cref="IsExpanded"/> false).
		/// </summary>
		public void Collapse ()
		{
			IsExpanded = false;
		}

		/// <summary>
		/// Refreshes cached knowledge in this branch e.g. what children an object has.
		/// </summary>
		/// <param name="startAtTop">True to also refresh all <see cref="Parent"/> 
		/// branches (starting with the root).</param>
		public void Refresh (bool startAtTop)
		{
			// if we must go up and refresh from the top down
			if (startAtTop) {
				Parent?.Refresh (true);
			}

			// we don't want to loose the state of our children so lets be selective about how we refresh
			//if we don't know about any children yet just use the normal method
			if (ChildBranches == null) {
				FetchChildren ();
			} else {
				// we already knew about some children so preserve the state of the old children

				// first gather the new Children
				var newChildren = tree.TreeBuilder?.GetChildren (this.Model) ?? Enumerable.Empty<T> ();

				// Children who no longer appear need to go
				foreach (var toRemove in ChildBranches.Keys.Except (newChildren).ToArray ()) {
					ChildBranches.Remove (toRemove);

					//also if the user has this node selected (its disapearing) so lets change selection to us (the parent object) to be helpful
					if (Equals (tree.SelectedObject, toRemove)) {
						tree.SelectedObject = Model;
					}
				}

				// New children need to be added
				foreach (var newChild in newChildren) {
					// If we don't know about the child yet we need a new branch
					if (!ChildBranches.ContainsKey (newChild)) {
						ChildBranches.Add (newChild, new Branch<T> (tree, this, newChild));
					} else {
						//we already have this object but update the reference anyway incase Equality match but the references are new
						ChildBranches [newChild].Model = newChild;
					}
				}
			}

		}

		/// <summary>
		/// Calls <see cref="Refresh(bool)"/> on the current branch and all expanded children.
		/// </summary>
		internal void Rebuild ()
		{
			Refresh (false);

			// if we know about our children
			if (ChildBranches != null) {
				if (IsExpanded) {
					//if we are expanded we need to updatethe visible children
					foreach (var child in ChildBranches) {
						child.Value.Rebuild ();
					}

				} else {
					// we are not expanded so should forget about children because they may not exist anymore
					ChildBranches = null;
				}
			}

		}

		/// <summary>
		/// Returns true if this branch has parents and it is the last node of it's parents 
		/// branches (or last root of the tree).
		/// </summary>
		/// <returns></returns>
		private bool IsLast ()
		{
			if (Parent == null) {
				return this == tree.roots.Values.LastOrDefault ();
			}

			return Parent.ChildBranches.Values.LastOrDefault () == this;
		}

		/// <summary>
		/// Returns true if the given x offset on the branch line is the +/- symbol.  Returns 
		/// false if not showing expansion symbols or leaf node etc.
		/// </summary>
		/// <param name="driver"></param>
		/// <param name="x"></param>
		/// <returns></returns>
		internal bool IsHitOnExpandableSymbol (ConsoleDriver driver, int x)
		{
			// if leaf node then we cannot expand
			if (!CanExpand ()) {
				return false;
			}

			// if we could theoretically expand
			if (!IsExpanded && tree.Style.ExpandableSymbol != null) {
				return x == GetLinePrefix (driver).Count ();
			}

			// if we could theoretically collapse
			if (IsExpanded && tree.Style.CollapseableSymbol != null) {
				return x == GetLinePrefix (driver).Count ();
			}

			return false;
		}

		/// <summary>
		/// Expands the current branch and all children branches.
		/// </summary>
		internal void ExpandAll ()
		{
			Expand ();

			if (ChildBranches != null) {
				foreach (var child in ChildBranches) {
					child.Value.ExpandAll ();
				}
			}
		}

		/// <summary>
		/// Collapses the current branch and all children branches (even though those branches are 
		/// no longer visible they retain collapse/expansion state).
		/// </summary>
		internal void CollapseAll ()
		{
			Collapse ();

			if (ChildBranches != null) {
				foreach (var child in ChildBranches) {
					child.Value.CollapseAll ();
				}
			}
		}
	}
}