using System.IO;
using UnityEngine;

namespace Luneraria.UI
{
    /// <summary>
    /// Screenshots of the scene with the HUD on top, also in batch mode: the camera renders into
    /// one texture, the HUD panel into its own (premultiplied alpha), and both are composed on the
    /// CPU. Used by the U3 tests and captures; the player can also capture the real screen.
    /// </summary>
    public static class LuneHudCapture
    {
        public static Texture2D Read(RenderTexture texture)
        {
            RenderTexture previous = RenderTexture.active;
            RenderTexture.active = texture;
            var image = new Texture2D(texture.width, texture.height, TextureFormat.RGBA32, false);
            image.ReadPixels(new Rect(0, 0, texture.width, texture.height), 0, 0);
            image.Apply();
            RenderTexture.active = previous;
            return image;
        }

        public static Texture2D RenderScene(Camera camera, int width, int height)
        {
            var target = new RenderTexture(width, height, 24, RenderTextureFormat.ARGB32) { antiAliasing = 4 };
            RenderTexture previous = camera.targetTexture;
            float aspect = camera.aspect;
            camera.aspect = (float)width / height;
            camera.targetTexture = target;
            camera.Render();
            camera.targetTexture = previous;
            camera.aspect = aspect;
            Texture2D image = Read(target);
            target.Release();
            Object.Destroy(target);
            return image;
        }

        /// <summary>HUD (premultiplied alpha) over the scene: out = hud + scene · (1 − hud alpha).</summary>
        public static Texture2D Compose(Texture2D scene, Texture2D hud)
        {
            Color32[] under = scene.GetPixels32();
            Color32[] over = hud.GetPixels32();
            var result = new Color32[under.Length];
            for (int index = 0; index < under.Length; index++)
            {
                Color32 a = over[index];
                Color32 b = under[index];
                int keep = 255 - a.a;
                result[index] = new Color32((byte)Mathf.Min(255, a.r + b.r * keep / 255), (byte)Mathf.Min(255, a.g + b.g * keep / 255), (byte)Mathf.Min(255, a.b + b.b * keep / 255), 255);
            }
            var image = new Texture2D(scene.width, scene.height, TextureFormat.RGBA32, false);
            image.SetPixels32(result);
            image.Apply();
            return image;
        }

        public static void Save(Texture2D image, string file)
        {
            Directory.CreateDirectory(Path.GetDirectoryName(file));
            File.WriteAllBytes(file, image.EncodeToPNG());
        }
    }
}