using System;
using System.Drawing;
using Azimuth;
using Blacklight.Core;
using Blacklight.Core.Drawables;
using Prism;

namespace Konis.Blacklight
{
    /// <summary>
    /// Writes a standard emitter's particles into the entries of a sprite batch, so Blacklight can draw them.
    /// </summary>
    public static class ParticleSpriteWriter
    {
        private const SpriteBatch.Varying WrittenColumns =
            SpriteBatch.Varying.TintColor | SpriteBatch.Varying.Transform;

        /// <summary>
        /// Writes one entry per live particle, in the order the emitter keeps them, and returns how many that was.
        /// </summary>
        /// <remarks>
        /// A batch drawing the entries must vary <see cref="SpriteBatch.Varying.TintColor"/> and <see
        /// cref="SpriteBatch.Varying.Transform"/>.  A particle's size is the width in world units it draws at, and its
        /// rotation turns the way an <see cref="AffineMatrix"/> turns for a positive angle.
        /// </remarks>
        /// <param name="emitter">The emitter whose particles are written.</param>
        /// <param name="projection">How the emitter's three-dimensional positions land on the screen.</param>
        /// <param name="source">The sprite every particle draws, which is centered on the particle.</param>
        /// <param name="entries">
        /// The set to write into.  It grows to fit, and gains the columns the writer fills if it lacks them.
        /// </param>
        public static int Write(
            StandardEmitter emitter, ViewProjection projection, in SpriteSource source, SpriteBatch.EntrySet entries)
        {
            Particle[] particles = emitter.Store.Items;
            int count = emitter.Store.Count;

            entries.EnsureCapacity(count);
            entries.AddColumns(WrittenColumns);

            Size size = source.Size;
            var destination = new SpriteDestination(new Vector(size.Width / 2.0, size.Height / 2.0), size);
            var entry = new SpriteBatch.Entry(in source, in destination);
            Vector3 origin = emitter.Position;

            for (int i = 0; i < count; i++)
            {
                var position = new Vector3(
                    origin.X + particles[i].PositionX,
                    origin.Y + particles[i].PositionY,
                    origin.Z + particles[i].PositionZ);
                double angle = emitter.RotationOf(i) * 2.0 * Math.PI;
                double scale = emitter.SizeOf(i) / (double)size.Width;

                entries.Entries[i] = entry;
                entries.Transforms[i] = new AffineMatrix(angle, projection.Project(position), scale);
                entries.TintColors[i] = Prism.Color.FromArgb(emitter.TintOf(i));
            }

            return count;
        }
    }
}