using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using MLEM.Misc;
using MLEM.Textures;

namespace MLEM.Animations {
    /// <summary>
    /// A sprite animation that allows for any number of frames that each last any number of seconds
    /// </summary>
    public class SpriteAnimation : GenericDataHolder {

        private readonly AnimationFrame[] frames;
        /// <summary>
        /// Returns the <see cref="AnimationFrame"/> at the given index.
        /// Index ordering is based on the order that animation frames were added in.
        /// </summary>
        /// <param name="index">The index in the list of animation frames</param>
        public AnimationFrame this[int index] => this.frames[index];
        /// <summary>
        /// The frame that the animation is currently on.
        /// </summary>
        public AnimationFrame CurrentFrame {
            get {
                // we might have overshot the end time by a little bit, so just return the last frame
                if (this.TimeIntoAnimation >= this.TotalTime)
                    return this.frames[this.frames.Length - 1];
                var accum = 0D;
                foreach (var frame in this.frames) {
                    accum += frame.Seconds;
                    if (accum >= this.TimeIntoAnimation)
                        return frame;
                }
                // if we're here then the time is negative for some reason, so just return the first frame
                return this.frames[0];
            }
        }
        /// <summary>
        /// The texture region that this animation's <see cref="CurrentFrame"/> should render.
        /// If there are multiple regions, <see cref="CurrentRegions"/> should be used instead.
        /// </summary>
        public TextureRegion CurrentRegion => this.CurrentFrame.Region;
        /// <summary>
        /// The texture regions that this animation's <see cref="CurrentFrame"/> should render.
        /// If there is only one region, <see cref="CurrentRegion"/> can be used for convenience.
        /// </summary>
        public IList<TextureRegion> CurrentRegions => this.CurrentFrame.Regions;
        /// <summary>
        /// The total amount of time that this animation has.
        /// This is auatomatically calculated based on the frame time of each frame.
        /// </summary>
        public readonly double TotalTime;
        /// <summary>
        /// The amount of seconds that the animation has been going on for.
        /// If <see cref="TotalTime"/> is reached, this value resets to 0.
        /// </summary>
        public double TimeIntoAnimation { get; private set; }
        /// <summary>
        /// The finished state of this animation.
        /// This is only true for longer than a frame if <see cref="IsLooping"/> is false.
        /// </summary>
        public bool IsFinished { get; private set; }
        /// <summary>
        /// The name of this animation. This is useful if used in combination with <see cref="SpriteAnimationGroup"/>.
        /// </summary>
        public string Name;
        /// <summary>
        /// The speed multiplier that this animation should run with.
        /// Numbers higher than 1 will increase the speed.
        /// </summary>
        public float SpeedMultiplier = 1;
        /// <summary>
        /// Set to false to stop this animation from looping.
        /// To check if the animation has finished playing, see <see cref="IsFinished"/>.
        /// </summary>
        public bool IsLooping = true;
        /// <summary>
        /// A callback that gets fired when the animation completes.
        /// </summary>
        public event Completed OnCompleted;
        /// <summary>
        /// Set this to true to pause the playback of the animation.
        /// <see cref="TimeIntoAnimation"/> will not continue and the <see cref="CurrentFrame"/> will not change.
        /// </summary>
        public bool IsPaused;

        /// <summary>
        /// Creates a new sprite animation that contains the given frames.
        /// </summary>
        /// <param name="frames">The frames this animation should have</param>
        public SpriteAnimation(params AnimationFrame[] frames) {
            if (frames.Length <= 0)
                throw new ArgumentException("Cannot create a sprite animation without any frames");
            this.frames = frames;
            foreach (var frame in frames)
                this.TotalTime += frame.Seconds;
        }

        /// <summary>
        /// Creates a new sprite animation that contains the given texture regions as frames.
        /// </summary>
        /// <param name="timePerFrame">The amount of time that each frame should last for</param>
        /// <param name="regions">The texture regions that should make up this animation</param>
        public SpriteAnimation(double timePerFrame, params TextureRegion[] regions) : this(Array.ConvertAll(regions, r => new AnimationFrame(timePerFrame, r))) {}

        /// <summary>
        /// Creates a new sprite animation that contains the given texture region arrays as frames, where each frame represents one set of texture regions.
        /// </summary>
        /// <param name="timePerFrame">The amount of time that each frame should last for</param>
        /// <param name="regions">The texture regions that should make up this animation</param>
        public SpriteAnimation(double timePerFrame, params TextureRegion[][] regions) : this(Array.ConvertAll(regions, r => new AnimationFrame(timePerFrame, r))) {}

        /// <summary>
        /// Creates a new sprite animation based on the given texture regions in rectangle-based format.
        /// </summary>
        /// <param name="timePerFrame">The amount of time that each frame should last for</param>
        /// <param name="texture">The texture that the regions should come from</param>
        /// <param name="regions">The texture regions that should make up this animation</param>
        public SpriteAnimation(double timePerFrame, Texture2D texture, params Rectangle[] regions) : this(timePerFrame, Array.ConvertAll(regions, r => new TextureRegion(texture, r))) {}

        /// <summary>
        /// Updates this animation, causing <see cref="TimeIntoAnimation"/> to be increased and the <see cref="CurrentFrame"/> to be updated.
        /// </summary>
        /// <param name="time">The game's time</param>
        public void Update(GameTime time) {
            this.Update(time.ElapsedGameTime);
        }

        /// <summary>
        /// Updates this animation, causing <see cref="TimeIntoAnimation"/> to be increased and the <see cref="CurrentFrame"/> to be updated.
        /// </summary>
        /// <param name="elapsed">The amount of time that has passed</param>
        public void Update(TimeSpan elapsed) {
            if (this.IsFinished || this.IsPaused)
                return;
            this.TimeIntoAnimation += elapsed.TotalSeconds * this.SpeedMultiplier;
            if (this.TimeIntoAnimation >= this.TotalTime) {
                if (!this.IsLooping) {
                    this.IsFinished = true;
                } else {
                    this.Restart();
                }
                this.OnCompleted?.Invoke(this);
            }
        }

        /// <summary>
        /// Restarts this animation from the first frame.
        /// </summary>
        public void Restart() {
            this.TimeIntoAnimation = 0;
            this.IsFinished = false;
            this.IsPaused = false;
        }

        /// <summary>
        /// A callback for when a sprite animation is completed.
        /// </summary>
        /// <param name="animation">The animation that has completed</param>
        public delegate void Completed(SpriteAnimation animation);

    }

    /// <summary>
    /// Represents a single frame of a <see cref="SpriteAnimation"/>
    /// </summary>
    public class AnimationFrame : GenericDataHolder {

        /// <summary>
        /// The texture regions that this frame should render.
        /// If there is only one region, <see cref="Region"/> can be used for convenience.
        /// </summary>
        public readonly IList<TextureRegion> Regions;
        /// <summary>
        /// The total amount of seconds that this frame should last for.
        /// </summary>
        public readonly double Seconds;
        /// <summary>
        /// The texture region that this frame should render.
        /// If there are multiple regions, <see cref="Regions"/> should be used instead.
        /// </summary>
        /// <exception cref="InvalidOperationException">Thrown if this animation frame has more than one region, in which case <see cref="Regions"/> should be used instead.</exception>
        public TextureRegion Region => this.Regions.Count == 1 ? this.Regions[0] : throw new InvalidOperationException("Cannot return single region for an animation frame with multiple regions");

        /// <summary>
        /// Creates a new animation frame based on a set of texture regions and a time.
        /// </summary>
        /// <param name="regions">The texture regions that this frame should render</param>
        /// <param name="seconds">The total amount of seconds that this frame should last for</param>
        public AnimationFrame(double seconds, params TextureRegion[] regions) {
            if (regions.Length <= 0)
                throw new ArgumentException("Cannot create an animation frame without any regions");
            this.Regions = new ReadOnlyCollection<TextureRegion>(regions);
            this.Seconds = seconds;
        }

    }
}