// Copyright (c) Six Labors.
// Licensed under the Apache License, Version 2.0.

using System;
using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Processing.Processors.Quantization;
using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
using Xunit;

namespace SixLabors.ImageSharp.Tests.Quantization
{
    public class PixelSamplingStrategyTests
    {
        public static readonly TheoryData<int, int, int, int> DefaultPixelSamplingStrategy_Data = new TheoryData<int, int, int, int>()
            {
                { 100, 100, 1, 10000 },
                { 100, 100, 1, 5000 },
                { 100, 100, 10, 50000 },
                { 99, 100, 11, 30000 },
                { 97, 99, 11, 80000 },
                { 99, 100, 11, 20000 },
                { 99, 501, 20, 100000 },
                { 97, 500, 20, 10000 },
                { 103, 501, 20, 1000 },
            };

        [Fact]
        public void ExtensivePixelSamplingStrategy_EnumeratesAll()
        {
            using Image<L8> image = CreateTestImage(100, 100, 100);
            var strategy = new ExtensivePixelSamplingStrategy();

            foreach (Buffer2DRegion<L8> region in strategy.EnumeratePixelRegions(image))
            {
                PaintWhite(region);
            }

            using Image<L8> expected = CreateTestImage(100, 100, 100, true);

            ImageComparer.Exact.VerifySimilarity(expected, image);
        }

        [Theory]
        [WithBlankImages(nameof(DefaultPixelSamplingStrategy_Data), 1, 1, PixelTypes.L8)]
        public void DefaultPixelSamplingStrategy_IsFair(TestImageProvider<L8> dummyProvider, int width, int height, int noOfFrames, int maximumNumberOfPixels)
        {
            using Image<L8> image = CreateTestImage(width, height, noOfFrames);

            var strategy = new DefaultPixelSamplingStrategy(maximumNumberOfPixels, 0.1);

            long visitedPixels = 0;
            foreach (Buffer2DRegion<L8> region in strategy.EnumeratePixelRegions(image))
            {
                PaintWhite(region);
                visitedPixels += region.Width * region.Height;
            }

            image.DebugSaveMultiFrame(
                dummyProvider,
                $"W{width}_H{height}_noOfFrames_{noOfFrames}_maximumNumberOfPixels_{maximumNumberOfPixels}",
                appendPixelTypeToFileName: false);

            int maximumPixels = image.Width * image.Height * image.Frames.Count / 10;
            maximumPixels = Math.Max(maximumPixels, (int)strategy.MaximumPixels);

            // allow some inaccuracy:
            double visitRatio = visitedPixels / (double)maximumPixels;
            Assert.True(visitRatio <= 1.1, $"{visitedPixels}>{maximumPixels}");
        }

        private static void PaintWhite(Buffer2DRegion<L8> region)
        {
            var white = new L8(255);
            for (int y = 0; y < region.Height; y++)
            {
                region.GetRowSpan(y).Fill(white);
            }
        }

        private static Image<L8> CreateTestImage(int width, int height, int noOfFrames, bool paintWhite = false)
        {
            L8 bg = paintWhite ? new L8(255) : default;
            var image = new Image<L8>(width, height, bg);

            for (int i = 1; i < noOfFrames; i++)
            {
                ImageFrame<L8> f = image.Frames.CreateFrame();
                if (paintWhite)
                {
                    f.PixelBuffer.MemoryGroup.Fill(bg);
                }
            }

            return image;
        }
    }
}