// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using osu.Framework.Graphics;
using osu.Framework.Graphics.Containers;
using osu.Framework.Graphics.Sprites;
using osu.Game.Graphics.Sprites;
using System;
using System.Collections.Generic;
using osu.Framework.Allocation;
using osu.Framework.Bindables;

namespace osu.Game.Graphics.UserInterface
{
    public abstract class RollingCounter<T> : Container
        where T : struct, IEquatable<T>
    {
        /// <summary>
        /// The current value.
        /// </summary>
        public Bindable<T> Current = new Bindable<T>();

        private SpriteText displayedCountSpriteText;

        /// <summary>
        /// If true, the roll-up duration will be proportional to change in value.
        /// </summary>
        protected virtual bool IsRollingProportional => false;

        /// <summary>
        /// If IsRollingProportional = false, duration in milliseconds for the counter roll-up animation for each
        /// element; else duration in milliseconds for the counter roll-up animation in total.
        /// </summary>
        protected virtual double RollingDuration => 0;

        /// <summary>
        /// Easing for the counter rollover animation.
        /// </summary>
        protected virtual Easing RollingEasing => Easing.OutQuint;

        private T displayedCount;

        /// <summary>
        /// Value shown at the current moment.
        /// </summary>
        public virtual T DisplayedCount
        {
            get => displayedCount;
            set
            {
                if (EqualityComparer<T>.Default.Equals(displayedCount, value))
                    return;

                displayedCount = value;
                if (displayedCountSpriteText != null)
                    displayedCountSpriteText.Text = FormatCount(value);
            }
        }

        /// <summary>
        /// Skeleton of a numeric counter which value rolls over time.
        /// </summary>
        protected RollingCounter()
        {
            AutoSizeAxes = Axes.Both;
        }

        [BackgroundDependencyLoader]
        private void load()
        {
            displayedCountSpriteText = CreateSpriteText();
            displayedCountSpriteText.Text = FormatCount(DisplayedCount);
            Child = displayedCountSpriteText;
        }

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

            Current.BindValueChanged(val => TransformCount(DisplayedCount, val.NewValue), true);
        }

        /// <summary>
        /// Sets count value, bypassing rollover animation.
        /// </summary>
        /// <param name="count">New count value.</param>
        public virtual void SetCountWithoutRolling(T count)
        {
            Current.Value = count;
            StopRolling();
        }

        /// <summary>
        /// Stops rollover animation, forcing the displayed count to be the actual count.
        /// </summary>
        public virtual void StopRolling()
        {
            FinishTransforms(false, nameof(DisplayedCount));
            DisplayedCount = Current.Value;
        }

        /// <summary>
        /// Resets count to default value.
        /// </summary>
        public virtual void ResetCount()
        {
            SetCountWithoutRolling(default);
        }

        /// <summary>
        /// Calculates the duration of the roll-up animation by using the difference between the current visible value
        /// and the new final value.
        /// </summary>
        /// <remarks>
        /// To be used in conjunction with IsRollingProportional = true.
        /// Unless a derived class needs to have a proportional rolling, it is not necessary to override this function.
        /// </remarks>
        /// <param name="currentValue">Current visible value.</param>
        /// <param name="newValue">New final value.</param>
        /// <returns>Calculated rollover duration in milliseconds.</returns>
        protected virtual double GetProportionalDuration(T currentValue, T newValue)
        {
            return RollingDuration;
        }

        /// <summary>
        /// Used to format counts.
        /// </summary>
        /// <param name="count">Count to format.</param>
        /// <returns>Count formatted as a string.</returns>
        protected virtual string FormatCount(T count)
        {
            return count.ToString();
        }

        /// <summary>
        /// Called when the count is updated to add a transformer that changes the value of the visible count (i.e.
        /// implement the rollover animation).
        /// </summary>
        /// <param name="currentValue">Count value before modification.</param>
        /// <param name="newValue">Expected count value after modification.</param>
        protected virtual void TransformCount(T currentValue, T newValue)
        {
            double rollingTotalDuration =
                IsRollingProportional
                    ? GetProportionalDuration(currentValue, newValue)
                    : RollingDuration;

            this.TransformTo(nameof(DisplayedCount), newValue, rollingTotalDuration, RollingEasing);
        }

        protected virtual OsuSpriteText CreateSpriteText() => new OsuSpriteText
        {
            Font = OsuFont.Numeric.With(size: 40f),
        };
    }
}