using System.Collections.Generic;
using System.Drawing;
using Amphora;
using Azimuth;
using Blacklight.Core;
using Blacklight.Core.Cameras;
using Blacklight.Core.Drawables;
using Konis.Blacklight;

namespace Konis.Testbed
{
    /// <summary>
    /// A particle world and what it takes to draw it with Blacklight.
    /// </summary>
    public class ParticleDemo
    {
        private const SpriteBatch.Varying WrittenColumns =
            SpriteBatch.Varying.TintColor | SpriteBatch.Varying.Transform;

        private readonly WindowHandle window;
        private readonly Camera camera;
        private readonly Scene scene = new Scene();
        private readonly Cel cel = new Cel();
        private readonly SpriteSheet sheet;
        private readonly SpriteSource source;

        // One set for each emitter, since a batch reads its set in place until the cel is next cleared.
        private readonly List<SpriteBatch.EntrySet> entrySets = new List<SpriteBatch.EntrySet>();

        /// <summary>
        /// Makes a demo that draws into <paramref name="window"/>, which must already be bound.
        /// </summary>
        public ParticleDemo(WindowHandle window, Camera camera, Rand random)
        {
            this.window = window;
            this.camera = camera;
            World = new ParticleWorld(random);
            scene.Cels.Add(cel);

            sheet = SpriteSheet.Create(
                window, SoftDisc.Build(), spriteSize: new Size(SoftDisc.Side, SoftDisc.Side), borderSize: 0);
            source = sheet.Frame(new Point(0, 0));
        }

        /// <summary>
        /// Gets the world the demo runs.
        /// </summary>
        public ParticleWorld World { get; }

        /// <summary>
        /// Gets or sets which of <see cref="Effects.All"/> a spawn makes.
        /// </summary>
        public int EffectIndex { get; set; }

        /// <summary>
        /// Gets or sets how the world's three dimensions land on the screen.
        /// </summary>
        public ViewProjection Projection { get; set; } = ViewProjection.Dimetric2To1;

        /// <summary>
        /// Starts the chosen effect at <paramref name="position"/>.
        /// </summary>
        public Emitter Spawn(Vector3 position, float preWarmSeconds)
        {
            return World.Spawn(Effects.All[EffectIndex].Def, position, preWarmSeconds);
        }

        /// <summary>
        /// Draws one complete frame.
        /// </summary>
        public void Draw()
        {
            // Only FrameReset empties the batch pools, so the reset/queue/submit triple has to stay together.
            window.FrameReset();
            cel.Clear();

            for (int i = 0; i < World.Count; i++)
            {
                var emitter = (StandardEmitter)World[i];
                if (i == entrySets.Count)
                {
                    entrySets.Add(new SpriteBatch.EntrySet());
                }

                int count = ParticleSpriteWriter.Write(emitter, Projection, source, entrySets[i]);
                if (count == 0)
                {
                    continue;
                }

                SpriteBatch batch = cel.NewSpriteBatchView(entrySets[i], count, WrittenColumns);
                batch.Texture = sheet.Texture;
                if (Effects.IsAdditive(emitter.Def))
                {
                    batch.Additiveness = 1;
                }

                cel.AddEntity(batch, AffineMatrix.Identity);
            }

            window.DrawScene(scene, camera);
            window.SubmitDrawCalls();
        }
    }
}