// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System;
using System.Collections.Generic;
using Microsoft.CodeAnalysis.Shared.Collections;
using Microsoft.CodeAnalysis.Shared.Extensions;
 
namespace Microsoft.CodeAnalysis.Formatting;
 
/// <summary>
/// a tweaked version of our interval tree to meet the formatting engine's need
/// 
/// it now has an ability to return a smallest span that contains a position rather than
/// all Intersecting or overlapping spans
/// </summary>
internal sealed class ContextMutableIntervalTree<T, TIntrospector> : SimpleMutableIntervalTree<T, TIntrospector>
    where TIntrospector : struct, IIntervalIntrospector<T>
{
    public ContextMutableIntervalTree(in TIntrospector introspector)
        : base(introspector, values: null)
    {
    }
 
    public T? GetSmallestEdgeExclusivelyContainingInterval(int start, int length)
        => GetSmallestContainingIntervalWorker(start, length, ContainsEdgeExclusive);
 
    public T? GetSmallestEdgeInclusivelyContainingInterval(int start, int length)
        => GetSmallestContainingIntervalWorker(start, length, ContainsEdgeInclusive);
 
    public T? GetSmallestContainingInterval(int start, int length)
        => GetSmallestContainingIntervalWorker(start, length, Contains);
 
    private static bool ContainsEdgeExclusive(T value, int start, int length, TIntrospector introspector)
    {
        var otherStart = start;
        var otherEnd = start + length;
 
        var thisSpan = introspector.GetSpan(value);
        var thisStart = thisSpan.Start;
        var thisEnd = thisSpan.End;
 
        return thisStart < otherStart && otherEnd < thisEnd;
    }
 
    private static bool ContainsEdgeInclusive(T value, int start, int length, TIntrospector introspector)
    {
        var otherStart = start;
        var otherEnd = start + length;
 
        var thisSpan = introspector.GetSpan(value);
        var thisStart = thisSpan.Start;
        var thisEnd = thisSpan.End;
 
        return thisStart <= otherStart && otherEnd <= thisEnd;
    }
 
    private static bool Contains(T value, int start, int length, TIntrospector introspector)
        => IntervalTreeAlgorithms<T, ContextMutableIntervalTree<T, TIntrospector>>.Contains(value, start, length, introspector);
 
    private T? GetSmallestContainingIntervalWorker(int start, int length, Func<T, int, int, TIntrospector, bool> predicate)
    {
        var result = default(T);
        if (root == null || MaxEndValue(root) < start)
        {
            return result;
        }
 
        var end = start + length;
 
        // * our interval tree is a binary tree that is ordered by a start position.
        //
        // this method works by
        // 1. find a sub tree that has biggest "start" position that is smaller than given "start" by going down right side of a tree
        // 2. once it encounters a right sub tree that it can't go down anymore, move down to left sub tree once and try #1 again
        // 3. once it gets to the position where it can't find any smaller span (both left and
        //    right sub tree doesn't contain given span) start to check whether current node
        //    contains the given "span"
        // 4. move up the spin until it finds one that contains the "span" which should be smallest span that contains the given "span"
        // 5. if it is going up from right side, it make sure to check left side of tree first.
        using var pooledObject = SharedPools.Default<Stack<Node>>().GetPooledObject();
 
        var spineNodes = pooledObject.Object;
 
        spineNodes.Push(root);
        while (spineNodes.Count > 0)
        {
            var currentNode = spineNodes.Peek();
 
            // only goes to right if right tree contains given span
            if (Introspector.GetSpan(currentNode.Value).Start <= start)
            {
                var right = currentNode.Right;
                if (right != null && end < MaxEndValue(right))
                {
                    spineNodes.Push(right);
                    continue;
                }
            }
 
            // right side, sub tree doesn't contain the given span, put current node on
            // stack, and move down to left sub tree
            var left = currentNode.Left;
            if (left != null && end <= MaxEndValue(left))
            {
                spineNodes.Push(left);
                continue;
            }
 
            // we reached the point, where we can't go down anymore.
            // now, go back up to find best answer
            while (spineNodes.TryPop(out currentNode))
            {
                // check whether current node meets condition
                if (predicate(currentNode.Value, start, length, Introspector))
                {
                    // hold onto best answer
                    if (EqualityComparer<T?>.Default.Equals(result, default))
                    {
                        result = currentNode.Value;
                    }
                    else
                    {
                        var resultSpan = Introspector.GetSpan(result!);
                        var currentNodeSpan = Introspector.GetSpan(currentNode.Value);
 
                        if (resultSpan.Start <= currentNodeSpan.Start &&
                            currentNodeSpan.Length < resultSpan.Length)
                        {
                            result = currentNode.Value;
                        }
                    }
                }
 
                // there is no parent, result we currently have is the best answer
                if (spineNodes.Count == 0)
                {
                    return result;
                }
 
                var parentNode = spineNodes.Peek();
 
                // if we are under left side of parent node
                if (parentNode.Left == currentNode)
                {
                    // go one level up again
                    continue;
                }
 
                // okay, we are under right side of parent node
                if (parentNode.Right == currentNode)
                {
                    // try left side of parent node if it can have better answer
                    if (parentNode.Left != null && end <= MaxEndValue(parentNode.Left))
                    {
                        // right side tree doesn't have any answer or if the right side has
                        // an answer but left side can have better answer then try left side
                        if (EqualityComparer<T?>.Default.Equals(result, default) ||
                            Introspector.GetSpan(parentNode.Value).Start == Introspector.GetSpan(currentNode.Value).Start)
                        {
                            // put left as new root, and break out inner loop
                            spineNodes.Push(parentNode.Left);
                            break;
                        }
                    }
 
                    // no left side, go one more level up
                    continue;
                }
            }
        }
 
        return result;
    }
 
#if DEBUG
    public override string ToString()
        => $"Interval tree with '{System.Linq.Enumerable.Count(this)}' entries. Use '.ToList()' to visualize contents.";
#endif
}