// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE

using System;
using System.Collections.Generic;
using System.Linq;
using osu.Framework.Configuration;
using osu.Framework.Graphics;
using osu.Framework.Graphics.Containers;
using osu.Game.Rulesets.Objects.Drawables;

namespace osu.Game.Rulesets.Timing
{
    /// <summary>
    /// A collection of <see cref="SpeedAdjustmentContainer"/>s.
    ///
    /// <para>
    /// This container redirects any <see cref="DrawableHitObject"/>'s added to it to the <see cref="SpeedAdjustmentContainer"/>
    /// which provides the speed adjustment active at the start time of the hit object. Furthermore, this container provides the
    /// necessary <see cref="VisibleTimeRange"/> for the contained <see cref="SpeedAdjustmentContainer"/>s.
    /// </para>
    /// </summary>
    public class SpeedAdjustmentCollection : Container<SpeedAdjustmentContainer>
    {
        private readonly BindableDouble visibleTimeRange = new BindableDouble();
        /// <summary>
        /// Gets or sets the range of time that is visible by the length of this container.
        /// For example, only hit objects with start time less than or equal to 1000 will be visible with <see cref="VisibleTimeRange"/> = 1000.
        /// </summary>
        public Bindable<double> VisibleTimeRange
        {
            get { return visibleTimeRange; }
            set { visibleTimeRange.BindTo(value); }
        }

        protected override int Compare(Drawable x, Drawable y)
        {
            var xSpeedAdjust = x as SpeedAdjustmentContainer;
            var ySpeedAdjust = y as SpeedAdjustmentContainer;

            // If either of the two drawables are not hit objects, fall back to the base comparer
            if (xSpeedAdjust?.ControlPoint == null || ySpeedAdjust?.ControlPoint == null)
                return CompareReverseChildID(x, y);

            // Compare by start time
            int i = ySpeedAdjust.ControlPoint.StartTime.CompareTo(xSpeedAdjust.ControlPoint.StartTime);

            return i != 0 ? i : CompareReverseChildID(x, y);
        }

        /// <summary>
        /// Hit objects that are to be re-processed on the next update.
        /// </summary>
        private readonly Queue<DrawableHitObject> queuedHitObjects = new Queue<DrawableHitObject>();

        private readonly Axes scrollingAxes;

        /// <summary>
        /// Creates a new <see cref="SpeedAdjustmentCollection"/>.
        /// </summary>
        /// <param name="scrollingAxes">The axes upon which hit objects should appear to scroll inside this container.</param>
        public SpeedAdjustmentCollection(Axes scrollingAxes)
        {
            this.scrollingAxes = scrollingAxes;
        }

        public override void Add(SpeedAdjustmentContainer speedAdjustment)
        {
            speedAdjustment.VisibleTimeRange.BindTo(VisibleTimeRange);
            speedAdjustment.ScrollingAxes = scrollingAxes;
            base.Add(speedAdjustment);
        }

        /// <summary>
        /// Adds a hit object to this <see cref="SpeedAdjustmentCollection"/>. The hit objects will be kept in a queue
        /// and will be processed when new <see cref="SpeedAdjustmentContainer"/>s are added to this <see cref="SpeedAdjustmentCollection"/>.
        /// </summary>
        /// <param name="hitObject">The hit object to add.</param>
        public void Add(DrawableHitObject hitObject)
        {
            if (!(hitObject is IScrollingHitObject))
                throw new InvalidOperationException($"Hit objects added to a {nameof(SpeedAdjustmentCollection)} must implement {nameof(IScrollingHitObject)}.");

            queuedHitObjects.Enqueue(hitObject);
        }

        protected override void Update()
        {
            base.Update();

            // Todo: At the moment this is going to re-process every single Update, however this will only be a null-op
            // when there are no SpeedAdjustmentContainers available. This should probably error or something, but it's okay for now.

            // An external count is kept because hit objects that can't be added are re-queued
            int count = queuedHitObjects.Count;
            while (count-- > 0)
            {
                var hitObject = queuedHitObjects.Dequeue();

                var target = adjustmentContainerFor(hitObject);
                if (target == null)
                {
                    // We can't add this hit object to a speed adjustment container yet, so re-queue it
                    // for re-processing when the layout next invalidated
                    queuedHitObjects.Enqueue(hitObject);
                    continue;
                }

                if (hitObject.RelativePositionAxes != target.ScrollingAxes)
                    throw new InvalidOperationException($"Make sure to set all {nameof(DrawableHitObject)}'s {nameof(RelativePositionAxes)} are equal to the correct axes of scrolling ({target.ScrollingAxes}).");

                target.Add(hitObject);
            }
        }

        /// <summary>
        /// Finds the <see cref="SpeedAdjustmentContainer"/> which provides the speed adjustment active at the start time
        /// of a hit object. If there is no <see cref="SpeedAdjustmentContainer"/> active at the start time of the hit object,
        /// then the first (time-wise) speed adjustment is returned.
        /// </summary>
        /// <param name="hitObject">The hit object to find the active <see cref="SpeedAdjustmentContainer"/> for.</param>
        /// <returns>The <see cref="SpeedAdjustmentContainer"/> active at <paramref name="hitObject"/>'s start time. Null if there are no speed adjustments.</returns>
        private SpeedAdjustmentContainer adjustmentContainerFor(DrawableHitObject hitObject) => Children.FirstOrDefault(c => c.CanContain(hitObject)) ?? Children.LastOrDefault();

        /// <summary>
        /// Finds the <see cref="SpeedAdjustmentContainer"/> which provides the speed adjustment active at a time.
        /// If there is no <see cref="SpeedAdjustmentContainer"/> active at the time, then the first (time-wise) speed adjustment is returned.
        /// </summary>
        /// <param name="time">The time to find the active <see cref="SpeedAdjustmentContainer"/> at.</param>
        /// <returns>The <see cref="SpeedAdjustmentContainer"/> active at <paramref name="time"/>. Null if there are no speed adjustments.</returns>
        private SpeedAdjustmentContainer adjustmentContainerAt(double time) => Children.FirstOrDefault(c => c.CanContain(time)) ?? Children.LastOrDefault();
    }
}