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

using System.Linq;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Processing.Drawing.Brushes;

using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing.Drawing;
using Xunit;

namespace SixLabors.ImageSharp.Tests.Drawing
{
    public class FillLinearGradientBrushTests : FileTestBase
    {
        [Fact]
        public void LinearGradientBrushWithEqualColorsReturnsUnicolorImage()
        {
            string path = TestEnvironment.CreateOutputDirectory("Fill", "LinearGradientBrush");
            using (var image = new Image<Rgba32>(10, 10))
            {
                LinearGradientBrush<Rgba32> unicolorLinearGradientBrush =
                    new LinearGradientBrush<Rgba32>(
                        new SixLabors.Primitives.Point(0, 0),
                        new SixLabors.Primitives.Point(10, 0),
                        new LinearGradientBrush<Rgba32>.ColorStop(0, Rgba32.Red),
                        new LinearGradientBrush<Rgba32>.ColorStop(1, Rgba32.Red));

                image.Mutate(x => x.Fill(unicolorLinearGradientBrush));
                image.Save($"{path}/UnicolorGradient.png");

                using (PixelAccessor<Rgba32> sourcePixels = image.Lock())
                {
                    Assert.Equal(Rgba32.Red, sourcePixels[0, 0]);
                    Assert.Equal(Rgba32.Red, sourcePixels[9, 9]);
                    Assert.Equal(Rgba32.Red, sourcePixels[5, 5]);
                    Assert.Equal(Rgba32.Red, sourcePixels[3, 8]);
                }
            }
        }

        [Fact]
        public void HorizontalLinearGradientBrushReturnsUnicolorColumns()
        {
            int width = 500;
            int height = 10;
            int lastColumnIndex = width - 1;

            string path = TestEnvironment.CreateOutputDirectory("Fill", "LinearGradientBrush");
            using (var image = new Image<Rgba32>(width, height))
            {
                LinearGradientBrush<Rgba32> unicolorLinearGradientBrush =
                    new LinearGradientBrush<Rgba32>(
                        new SixLabors.Primitives.Point(0, 0),
                        new SixLabors.Primitives.Point(500, 0),
                        new LinearGradientBrush<Rgba32>.ColorStop(0, Rgba32.Red),
                        new LinearGradientBrush<Rgba32>.ColorStop(1, Rgba32.Yellow));

                image.Mutate(x => x.Fill(unicolorLinearGradientBrush));
                image.Save($"{path}/horizontalRedToYellow.png");

                using (PixelAccessor<Rgba32> sourcePixels = image.Lock())
                {
                    Rgba32 columnColor0 = sourcePixels[0, 0];
                    Rgba32 columnColor23 = sourcePixels[23, 0];
                    Rgba32 columnColor42 = sourcePixels[42, 0];
                    Rgba32 columnColor333 = sourcePixels[333, 0];

                    Rgba32 lastColumnColor = sourcePixels[lastColumnIndex, 0];

                    for (int i = 0; i < height; i++)
                    {
                        // check first and last column:
                        Assert.Equal(columnColor0, sourcePixels[0, i]);
                        Assert.Equal(lastColumnColor, sourcePixels[lastColumnIndex, i]);

                        // check the random colors:
                        Assert.True(columnColor23 == sourcePixels[23, i], $"at {i}");
                        Assert.Equal(columnColor42, sourcePixels[42, i]);
                        Assert.Equal(columnColor333, sourcePixels[333, i]);
                    }
                }
            }
        }

        [Theory]
        [InlineData(new[] { 0.5f })]
        [InlineData(new[] { 0.2f, 0.4f, 0.6f, 0.8f })]
        [InlineData(new[] { 0.1f, 0.3f, 0.6f })]
        public void LinearGradientsWithDoubledStopsProduceDashedPatterns(
            float[] pattern)
        {
            int width = 200;
            int height = 10;

            // ensure the input data is valid
            Assert.True(pattern.Length > 0);

            // create the input pattern: 0, followed by each of the arguments twice, followed by 1.0 - toggling black and white.
            LinearGradientBrush<Rgba32>.ColorStop[] colorStops =
                Enumerable.Repeat(new LinearGradientBrush<Rgba32>.ColorStop(0, Rgba32.Black), 1)
                .Concat(
                        pattern
                            .SelectMany((f, index) => new[]
                                                      {
                                                          new LinearGradientBrush<Rgba32>.ColorStop(f, index % 2 == 0 ? Rgba32.Black : Rgba32.White),
                                                          new LinearGradientBrush<Rgba32>.ColorStop(f, index % 2 == 0 ? Rgba32.White : Rgba32.Black)
                                                      }))
                .Concat(Enumerable.Repeat(new LinearGradientBrush<Rgba32>.ColorStop(1, pattern.Length % 2 == 0 ? Rgba32.Black : Rgba32.White), 1))
                .ToArray();

            string path = TestEnvironment.CreateOutputDirectory("Fill", "LinearGradientBrush");
            using (var image = new Image<Rgba32>(width, height))
            {
                LinearGradientBrush<Rgba32> unicolorLinearGradientBrush =
                    new LinearGradientBrush<Rgba32>(
                        new SixLabors.Primitives.Point(0, 0),
                        new SixLabors.Primitives.Point(width, 0),
                        colorStops);

                image.Mutate(x => x.Fill(unicolorLinearGradientBrush));
                image.Save($"{path}/blackAndWhite{pattern[0]}.png");

                using (PixelAccessor<Rgba32> sourcePixels = image.Lock())
                {
                    // the result must be a black and white pattern, no other color should occur:
                    Assert.All(
                        Enumerable.Range(0, width).Select(i => sourcePixels[i, 0]),
                        color => Assert.True(color == Rgba32.Black || color == Rgba32.White));
                }
            }
        }

        [Fact]
        public void VerticalLinearGradientBrushReturnsUnicolorColumns()
        {
            int width = 10;
            int height = 500;
            int lastRowIndex = height - 1;

            string path = TestEnvironment.CreateOutputDirectory("Fill", "LinearGradientBrush");
            using (var image = new Image<Rgba32>(width, height))
            {
                LinearGradientBrush<Rgba32> unicolorLinearGradientBrush =
                    new LinearGradientBrush<Rgba32>(
                        new SixLabors.Primitives.Point(0, 0),
                        new SixLabors.Primitives.Point(0, 500),
                        new LinearGradientBrush<Rgba32>.ColorStop(0, Rgba32.Red),
                        new LinearGradientBrush<Rgba32>.ColorStop(1, Rgba32.Yellow));

                image.Mutate(x => x.Fill(unicolorLinearGradientBrush));
                image.Save($"{path}/verticalRedToYellow.png");

                using (PixelAccessor<Rgba32> sourcePixels = image.Lock())
                {
                    Rgba32 firstRowColor = sourcePixels[0, 0];
                    
                    Rgba32 columnColor23 = sourcePixels[0, 23];
                    Rgba32 columnColor42 = sourcePixels[0, 42];
                    Rgba32 columnColor333 = sourcePixels[0, 333];

                    Rgba32 lastRowColor = sourcePixels[0, lastRowIndex];

                    for (int i = 0; i < width; i++)
                    {
                        // check first and last column, these are known:
                        Assert.Equal(firstRowColor, sourcePixels[i, 0]);
                        Assert.Equal(lastRowColor, sourcePixels[i, lastRowIndex]);

                        // check the random colors:
                        Assert.Equal(columnColor23, sourcePixels[i, 23]);
                        Assert.Equal(columnColor42, sourcePixels[i, 42]);
                        Assert.Equal(columnColor333, sourcePixels[i, 333]);
                    }
                }
            }
        }

        [Theory]
        [InlineData(0, 0, 499, 499)]
        [InlineData(0, 499, 499, 0)]
        [InlineData(499, 499, 0, 0)]
        [InlineData(499, 0, 0, 499)]
        public void DiagonalLinearGradientBrushReturnsUnicolorColumns(
            int startX, int startY, int endX, int endY)
        {
            int size = 500;

            string path = TestEnvironment.CreateOutputDirectory("Fill", "LinearGradientBrush");
            using (var image = new Image<Rgba32>(size, size))
            {
                LinearGradientBrush<Rgba32> unicolorLinearGradientBrush =
                    new LinearGradientBrush<Rgba32>(
                        new SixLabors.Primitives.Point(startX, startY),
                        new SixLabors.Primitives.Point(endX, endY),
                        new LinearGradientBrush<Rgba32>.ColorStop(0, Rgba32.Red),
                        new LinearGradientBrush<Rgba32>.ColorStop(1, Rgba32.Yellow));

                image.Mutate(x => x.Fill(unicolorLinearGradientBrush));
                image.Save($"{path}/diagonalRedToYellowFrom{startX}_{startY}.png");

                using (PixelAccessor<Rgba32> sourcePixels = image.Lock())
                {
                    // check first and last pixel, these are known:
                    Assert.Equal(Rgba32.Red, sourcePixels[startX, startY]);
                    Assert.Equal(Rgba32.Yellow, sourcePixels[endX, endY]);

                    for (int i = 0; i < size; i++)
                    {
                        // it's diagonal, so for any (a, a) on the gradient line, for all (a-x, b+x) - +/- depending on the diagonal direction - must be the same color)
                    }
                }
            }
        }

        [Theory]
        [InlineData("a", 0, 0, 499, 499, new[] { 0f, .2f, .5f, .9f }, new[] { 0, 0, 1, 1 })]
        [InlineData("b", 0, 499, 499, 0, new[] { 0f, 0.2f, 0.5f, 0.9f }, new[] { 0, 1, 2, 3 })]
        [InlineData("c", 499, 499, 0, 0, new[] { 0f, 0.7f, 0.8f, 0.9f}, new[] { 0, 1, 2, 0 })]
        [InlineData("d", 0, 0, 499, 499, new[] { 0f, .5f, 1f}, new[]{0, 1, 3})]
        public void ArbitraryLinearGradientsProduceImagesVisualCheckOnly(
            string filenameSuffix,
            int startX, int startY,
            int endX, int endY,
            float[] stopPositions,
            int[] stopColorCodes)
        {
            var colors = new Rgba32[]
                             {
                                 Rgba32.Navy,
                                 Rgba32.LightGreen,
                                 Rgba32.Yellow,
                                 Rgba32.Red
                             };

            var colorStops = new LinearGradientBrush<Rgba32>.ColorStop[stopPositions.Length];
            for (int i = 0; i < stopPositions.Length; i++)
            {
                colorStops[i] = new LinearGradientBrush<Rgba32>.ColorStop(
                    stopPositions[i],
                    colors[stopColorCodes[i]]);
            }

            int size = 500;

            string path = TestEnvironment.CreateOutputDirectory("Fill", "LinearGradientBrush");
            using (var image = new Image<Rgba32>(size, size))
            {
                LinearGradientBrush<Rgba32> unicolorLinearGradientBrush =
                    new LinearGradientBrush<Rgba32>(
                        new SixLabors.Primitives.Point(startX, startY),
                        new SixLabors.Primitives.Point(endX, endY),
                        colorStops);

                image.Mutate(x => x.Fill(unicolorLinearGradientBrush));
                image.Save($"{path}/arbitraryGradient_{filenameSuffix}.png");
            }
        }
    }
}