using OpenTK.Graphics.OpenGL4;
using OpenTK.Mathematics;
using OpenTK.Windowing.Common;
using OpenTK.Windowing.Common.Input;
using OpenTK.Windowing.Desktop;
using OpenTK.Windowing.GraphicsLibraryFramework;
// https://docs.sixlabors.com/api/ImageSharp/SixLabors.ImageSharp.Image.html
using Image = SixLabors.ImageSharp.Image;
using SixLabors.Fonts;
using SixLabors.ImageSharp.Metadata.Profiles.Exif;
using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
using SixLabors.ImageSharp.Drawing.Processing;
using SixLabors.ImageSharp.Drawing;
using SixLabors.ImageSharp.Formats.Jpeg;
using System;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Text;
using System.Xml.Linq;

namespace SemiColinGames;

public class FpsCounter {
  private readonly int[] frameTimes = new int[30];
  private double fps = 0;
  private int idx = 0;

  public int Fps {
    get => (int) Math.Ceiling(fps);
  }

  public void Update() {
    var now = Environment.TickCount;  // ms
    if (frameTimes[idx] != 0) {
      var timeElapsed = now - frameTimes[idx];
      fps = 1000.0 * frameTimes.Length / timeElapsed;
    }
    frameTimes[idx] = now;
    idx = (idx + 1) % frameTimes.Length;
  }
}

public class CameraInfo {
  public readonly Vector2i Resolution;

  private CameraInfo(Vector2i resolution) {
    Resolution = resolution;
  }

  public static readonly CameraInfo NIKON_D7000 = new(new Vector2i(4928, 3264));
  public static readonly CameraInfo CANON_EOS_R6M2 = new(new Vector2i(6000, 4000));
  public static readonly CameraInfo IPHONE_12_MINI = new(new Vector2i(4032, 3024));
}

// FIXME: switch to immediate mode??
// https://gamedev.stackexchange.com/questions/198805/opentk-immediate-mode-on-net-core-doesnt-work
// https://www.youtube.com/watch?v=Q23Kf9QEaO4
public class Shader : IDisposable {
  public int Handle;
  private bool init = false;

  public Shader() {}

  public void Init() {
    init = true;
    int VertexShader;
    int FragmentShader;

    string VertexShaderSource = @"
#version 330

layout(location = 0) in vec3 aPosition;
layout(location = 1) in vec2 aTexCoord;

out vec2 texCoord;

uniform mat4 projection;

void main(void) {
    texCoord = aTexCoord;
    gl_Position = vec4(aPosition, 1.0) * projection;
}";

    string FragmentShaderSource = @"
#version 330

out vec4 outputColor;
in vec2 texCoord;
uniform sampler2D texture0;
uniform vec4 color;

void main() {
    outputColor = texture(texture0, texCoord) * color;
}";

    VertexShader = GL.CreateShader(ShaderType.VertexShader);
    GL.ShaderSource(VertexShader, VertexShaderSource);

    FragmentShader = GL.CreateShader(ShaderType.FragmentShader);
    GL.ShaderSource(FragmentShader, FragmentShaderSource);

    GL.CompileShader(VertexShader);

    int success;
    GL.GetShader(VertexShader, ShaderParameter.CompileStatus, out success);
    if (success == 0) {
      string infoLog = GL.GetShaderInfoLog(VertexShader);
      Console.WriteLine(infoLog);
    }

    GL.CompileShader(FragmentShader);

    GL.GetShader(FragmentShader, ShaderParameter.CompileStatus, out success);
    if (success == 0) {
      string infoLog = GL.GetShaderInfoLog(FragmentShader);
      Console.WriteLine(infoLog);
    }
    Handle = GL.CreateProgram();

    GL.AttachShader(Handle, VertexShader);
    GL.AttachShader(Handle, FragmentShader);

    GL.LinkProgram(Handle);

    GL.GetProgram(Handle, GetProgramParameterName.LinkStatus, out success);
    if (success == 0) {
      string infoLog = GL.GetProgramInfoLog(Handle);
      Console.WriteLine(infoLog);
    }

    GL.DetachShader(Handle, VertexShader);
    GL.DetachShader(Handle, FragmentShader);
    GL.DeleteShader(FragmentShader);
    GL.DeleteShader(VertexShader);
  }

  public void Use() {
    if (!init) {
      Console.WriteLine("Shader.Use(): must call Init() first");
    }
    GL.UseProgram(Handle);
  }

  private bool disposedValue = false;

  protected virtual void Dispose(bool disposing) {
    if (!disposedValue) {
      GL.DeleteProgram(Handle);
      disposedValue = true;
    }
  }

  ~Shader() {
    if (disposedValue == false) {
      Console.WriteLine("~Shader(): resource leak? Dispose() should be called manually.");
    }
  }

  public void Dispose() {
    Dispose(true);
    GC.SuppressFinalize(this);
  }

  public int GetAttribLocation(string name) {
    return GL.GetAttribLocation(Handle, name);
  }

  public int GetUniformLocation(string name) {
    return GL.GetUniformLocation(Handle, name);
  }
}

// FIXME: this should probably be IDisposable?
public class Photo {
  public string Filename;
  public bool Loaded = false;
  public long LastTouch = 0;
  public Vector2i Size;
  public DateTime DateTimeOriginal;
  public string CameraModel = "";
  public string LensModel = "";
  public string FocalLength = "<unk>";
  public string FNumber = "<unk>";
  public string ExposureTime = "<unk>";
  public string IsoSpeed = "<unk>";
  public int Rating = 0;
  public ushort Orientation = 1;

  private static long touchCounter = 0;
  private Texture texture;
  private Texture placeholder;
  private Image<Rgba32>? image = null;

  public Photo(string filename, Texture placeholder) {
    Filename = filename;
    this.placeholder = placeholder;
    texture = placeholder;

    DateTime creationTime = File.GetCreationTime(filename);  // Local time.
    DateTimeOriginal = creationTime;
    ImageInfo info = Image.Identify(filename);
    Size = new(info.Size.Width, info.Size.Height);
    Rating = ParseRating(info.Metadata.XmpProfile);
    ParseExif(info.Metadata.ExifProfile);
  }

  public async void LoadAsync() {
    // We don't assign to this.image until Load() is done, because we might
    // edit the image due to rotation (etc) and don't want to try generating
    // a texture for it until that's already happened.
    LastTouch = touchCounter++;
    Image<Rgba32> tmp = await Image.LoadAsync<Rgba32>(Filename);
    Util.RotateImageFromExif(tmp, Orientation);
    image = tmp;
  }

  public void Unload() {
    Loaded = false;
    if (texture != placeholder) {
      texture.Dispose();
      texture = placeholder;
    }
  }

  public async void SaveAsJpegAsync(string outputRoot, JpegEncoder encoder) {
    // FIXME: if nothing was changed about this image, just copy the file bytes directly, possibly with metadata changed?
    string directory = System.IO.Path.Combine(
        outputRoot,
        String.Format("{0:D4}", DateTimeOriginal.Year),
        String.Format("{0:D2}", DateTimeOriginal.Month),
        String.Format("{0:D2}", DateTimeOriginal.Day));
    Directory.CreateDirectory(directory);
    string filename = System.IO.Path.Combine(directory, System.IO.Path.GetFileName(Filename));
    Console.WriteLine("saving " + filename);
    // FIXME: add comments / captions as ImageDescription?
    // FIXME: strip some Exif tags for privacy reasons?
    // FIXME: warn if the file already exists?
    using (Image<Rgba32> image = await Image.LoadAsync<Rgba32>(Filename)) {
      Util.RotateImageFromExif(image, Orientation);

      ExifProfile exif = image.Metadata.ExifProfile ?? new();
      exif.SetValue<ushort>(ExifTag.Orientation, 1);
      exif.SetValue<string>(ExifTag.Artist, "Colin McMillen");
      exif.SetValue<string>(ExifTag.Copyright, "Colin McMillen");
      exif.SetValue<string>(ExifTag.Software, "Totte");
      exif.SetValue<ushort>(ExifTag.Rating, (ushort) Rating);
      DateTime now = DateTime.Now;
      string datetime = String.Format(
        "{0:D4}:{1:D2}:{2:D2} {3:D2}:{4:D2}:{5:D2}",
        now.Year, now.Month, now.Day, now.Hour, now.Minute, now.Second);
      exif.SetValue<string>(ExifTag.DateTime, datetime);

      image.Metadata.XmpProfile = UpdateXmp(image.Metadata.XmpProfile);

      await image.SaveAsync(filename, encoder);
    }
  }

  private XElement? GetXmpRoot(XmpProfile? xmp) {
    if (xmp == null) {
      return null;
    }
    XDocument? doc = xmp.GetDocument();
    if (doc == null) {
      return null;
    }
    return doc.Root;
  }

  private int ParseRating(XmpProfile? xmp) {
    XElement? root = GetXmpRoot(xmp);
    if (root == null) {
      return 0;
    }
    foreach (XElement elt in root.Descendants()) {
      if (elt.Name == "{http://ns.adobe.com/xap/1.0/}Rating") {
        int rating = 0;
        if (int.TryParse(elt.Value, out rating)) {
          return rating;
        }
      }
    }
    return 0;
  }

  private XmpProfile? UpdateXmp(XmpProfile? xmp) {
    if (xmp == null) {
      return null;
    }
    string xmlIn = Encoding.UTF8.GetString(xmp.ToByteArray());
    int index = xmlIn.IndexOf("</xmp:Rating>");
    if (index == -1) {
      return xmp;
    }
    string xmlOut = xmlIn.Substring(0, index - 1) + Rating.ToString() + xmlIn.Substring(index);
    return new XmpProfile(Encoding.UTF8.GetBytes(xmlOut));
  }

  // Exif (and other image metadata) reference, from the now-defunct Metadata Working Group:
  // https://web.archive.org/web/20180919181934/http://www.metadataworkinggroup.org/pdf/mwg_guidance.pdf
  //
  // Specifically:
  //
  // In general, date/time metadata is being used to describe the following scenarios:
  // * Date/time original specifies when a photo was taken
  // * Date/time digitized specifies when an image was digitized
  // * Date/time modified specifies when a file was modified by the user
  //
  // Original Date/Time – Creation date of the intellectual content (e.g. the photograph), rather than the creation date of the content being shown
  // Exif DateTimeOriginal (36867, 0x9003) and SubSecTimeOriginal (37521, 0x9291)
  // IPTC DateCreated (IIM 2:55, 0x0237) and TimeCreated (IIM 2:60, 0x023C)
  // XMP (photoshop:DateCreated)
  //
  // Digitized Date/Time – Creation date of the digital representation
  // Exif DateTimeDigitized (36868, 0x9004) and SubSecTimeDigitized (37522, 0x9292)
  // IPTC DigitalCreationDate (IIM 2:62, 0x023E) and DigitalCreationTime (IIM 2:63, 0x023F)
  // XMP (xmp:CreateDate)
  //
  // Modification Date/Time – Modification date of the digital image file
  // Exif DateTime (306, 0x132) and SubSecTime (37520, 0x9290)
  // XMP (xmp:ModifyDate)
  //
  // See also: https://exiftool.org/TagNames/EXIF.html
  private void ParseExif(ExifProfile? exifs) {
    if (exifs == null) {
      return;
    }

    IExifValue<ushort>? orientation;
    if (exifs.TryGetValue(ExifTag.Orientation, out orientation)) {
      Orientation = orientation.Value;
    }

    IExifValue<string>? model;
    if (exifs.TryGetValue(ExifTag.Model, out model)) {
      CameraModel = model.Value ?? "";
    }

    IExifValue<string>? lensModel;
    if (exifs.TryGetValue(ExifTag.LensModel, out lensModel)) {
      LensModel = lensModel.Value ?? "";
    }

    IExifValue<Rational>? focalLength;
    if (exifs.TryGetValue(ExifTag.FocalLength, out focalLength)) {
      Rational r = focalLength.Value;
      FocalLength = $"{r.Numerator / r.Denominator}mm";
    }

    IExifValue<Rational>? fNumber;
    if (exifs.TryGetValue(ExifTag.FNumber, out fNumber)) {
      Rational r = fNumber.Value;
      if (r.Numerator % r.Denominator == 0) {
        FNumber = $"f/{r.Numerator / r.Denominator}";
      } else {
        int fTimesTen = (int) Math.Round(10f * r.Numerator / r.Denominator);
        FNumber = $"f/{fTimesTen / 10}.{fTimesTen % 10}";
      }
    }

    // FIXME: could also show ExposureBiasValue, ExposureMode, ExposureProgram?
    IExifValue<Rational>? exposureTime;
    if (exifs.TryGetValue(ExifTag.ExposureTime, out exposureTime)) {
      Rational r = exposureTime.Value;
      if (r.Numerator == 1) {
        ExposureTime = $"1/{r.Denominator}";
      } else if (r.Numerator == 10) {
        ExposureTime = $"1/{r.Denominator / 10}";
      } else if (r.Denominator == 1) {
        ExposureTime = $"{r.Numerator }\"";
      } else if (r.Denominator == 10) {
        ExposureTime = $"{r.Numerator / 10}.{r.Numerator % 10}\"";
      } else {
        Console.WriteLine($"*** WARNING: unexpected ExposureTime: {r.Numerator}/{r.Denominator}");
        ExposureTime = r.ToString();
      }
    }

    IExifValue<ushort[]>? isoSpeed;
    if (exifs.TryGetValue(ExifTag.ISOSpeedRatings, out isoSpeed)) {
      ushort[]? iso = isoSpeed.Value;
      if (iso != null) {
        if (iso.Length != 1) {
          Console.WriteLine($"*** WARNING: unexpected ISOSpeedRatings array length: {iso.Length}");
        }
        if (iso.Length >= 1) {
          IsoSpeed = $"ISO {iso[0]}";
        }
      }
    }

    // FIXME: there is also a SubSecTimeOriginal tag we could use to get fractional seconds.
    // FIXME: I think the iPhone stores time in UTC but other cameras report it in local time.
    IExifValue<string>? dateTimeOriginal;
    if (exifs.TryGetValue(ExifTag.DateTimeOriginal, out dateTimeOriginal)) {
      DateTime date;
      if (DateTime.TryParseExact(
          dateTimeOriginal.Value ?? "",
          "yyyy:MM:dd HH:mm:ss",
          System.Globalization.CultureInfo.InvariantCulture,
          System.Globalization.DateTimeStyles.AssumeLocal,
          out date)) {
        DateTimeOriginal = date;
      } else {
        Console.WriteLine($"*** WARNING: unexpected DateTimeOriginal value: {dateTimeOriginal.Value}");
      }
    }
  }

  public Texture Texture() {
    LastTouch = touchCounter++;
    if (texture == placeholder && image != null) {
      // The texture needs to be created on the GL thread, so we instantiate
      // it here (since this is called from OnRenderFrame), as long as the
      // image is ready to go.
      texture = new Texture(image);
      image.Dispose();
      image = null;
      Loaded = true;
    }
    return texture;
  }

  public string Description() {
    string date = DateTimeOriginal.ToString("yyyy-MM-dd HH:mm:ss");
    string shootingInfo = $"{date}   {FocalLength}, {FNumber} at {ExposureTime}, {IsoSpeed}";
    return String.Format("{0,-60} {1,-50} {2}", shootingInfo, $"{CameraModel} {LensModel}", Filename);
  }
}

public class Texture : IDisposable {
  public int Handle;
  public Vector2i Size;

  private static int maxHandle = -1;
  private bool disposedValue = false;

  public Texture(Image<Rgba32> image) {
    Size = new Vector2i(image.Width, image.Height);
    byte[] pixelBytes = new byte[Size.X * Size.Y * Unsafe.SizeOf<Rgba32>()];
    image.CopyPixelDataTo(pixelBytes);

    Handle = GL.GenTexture();
    if (Handle > maxHandle) {
      // Console.WriteLine("GL.GenTexture #" + Handle);
      maxHandle = Handle;
    }
    GL.ActiveTexture(TextureUnit.Texture0);
    GL.BindTexture(TextureTarget.Texture2D, Handle);
    GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, Size.X, Size.Y, 0, PixelFormat.Rgba, PixelType.UnsignedByte, pixelBytes);
    //GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int) TextureMinFilter.LinearMipmapLinear);
    GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int) TextureMinFilter.Linear);
    GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int) TextureMagFilter.Nearest);
    GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapS, (int) TextureWrapMode.ClampToBorder);
    GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapT, (int) TextureWrapMode.ClampToBorder);
    float[] borderColor = { 0.0f, 0.0f, 0.0f, 1.0f };
    GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureBorderColor, borderColor);
    // FIXME: should we use mipmaps?
    //GL.GenerateMipmap(GenerateMipmapTarget.Texture2D);
  }

  protected virtual void Dispose(bool disposing) {
    if (!disposedValue) {
      GL.DeleteTexture(Handle);
      disposedValue = true;
    }
  }

  ~Texture() {
    if (!disposedValue) {
      Console.WriteLine("~Texture(): resource leak? Dispose() should be called manually.");
    }
  }

  public void Dispose() {
    Dispose(true);
    GC.SuppressFinalize(this);
  }
}

public class UiGeometry {
  public static Vector2i MIN_WINDOW_SIZE = new(1024, 768);
  private static CameraInfo activeCamera = CameraInfo.CANON_EOS_R6M2;

  public readonly Vector2i WindowSize;
  public readonly Box2i ThumbnailBox;
  public readonly List<Box2i> ThumbnailBoxes = new();
  public readonly List<Box2i> StarBoxes = new();
  public readonly Box2i PhotoBox;
  public readonly Box2i StatusBox;

  public UiGeometry() : this(MIN_WINDOW_SIZE, 0) {}

  public UiGeometry(Vector2i windowSize, int starSize) {
    WindowSize = windowSize;

    int numThumbnails = Math.Max(WindowSize.Y / 100, 1);
    int thumbnailHeight = WindowSize.Y / numThumbnails;
    int thumbnailWidth = (int) 1.0 * thumbnailHeight * activeCamera.Resolution.X / activeCamera.Resolution.Y;

    Console.WriteLine($"thumbnail size: {thumbnailWidth} x {thumbnailHeight}");
    for (int i = 0; i < numThumbnails; i++) {
      Box2i box = Util.MakeBox(WindowSize.X - thumbnailWidth, i * thumbnailHeight, thumbnailWidth, thumbnailHeight);
      ThumbnailBoxes.Add(box);
    }

    int statusBoxHeight = 20;
    int statusBoxPadding = 4;
    PhotoBox = new Box2i(0, 0, WindowSize.X - thumbnailWidth, WindowSize.Y - statusBoxHeight - statusBoxPadding);
    StatusBox = new Box2i(0, WindowSize.Y - statusBoxHeight, WindowSize.X - thumbnailWidth, WindowSize.Y);
    ThumbnailBox = new Box2i(ThumbnailBoxes[0].Min.X, ThumbnailBoxes[0].Min.Y, WindowSize.X, WindowSize.Y);

    int starSpacing = 10;
    int starBoxLeft = (int) (PhotoBox.Center.X - 2.5 * starSize - starSpacing * 2);
    for (int i = 0; i < 5; i++) {
      Box2i box = Util.MakeBox(starBoxLeft + i * (starSize + starSpacing), PhotoBox.Max.Y - starSize - 10, starSize, starSize);
      StarBoxes.Add(box);
    }
  }
}

public static class Util {
  public const float PI = (float) Math.PI;

  public static int Lerp(int start, int end, double fraction) {
    return start + (int) ((end - start) * fraction);
  }

  public static Box2i MakeBox(int left, int top, int width, int height) {
    return new Box2i(left, top, left + width, top + height);
  }

  public static Image<Rgba32> MakeImage(float width, float height) {
    return new((int) Math.Ceiling(width), (int) Math.Ceiling(height));
  }

  // https://sirv.com/help/articles/rotate-photos-to-be-upright/
  public static void RotateImageFromExif(Image<Rgba32> image, ushort orientation) {
    if (orientation <= 1) {
      return;
    }
    // FIXME: I'm not convinced that all of these are correct, especially the
    // cases that involve flipping (because whether you're flipping before or
    // after rotation matters.).
    var operations = new Dictionary<ushort, (RotateMode, FlipMode)> {
      { 2, (RotateMode.None, FlipMode.Horizontal) },
      { 3, (RotateMode.Rotate180, FlipMode.None) },
      { 4, (RotateMode.None, FlipMode.Vertical) },
      { 5, (RotateMode.Rotate90, FlipMode.Vertical) },
      { 6, (RotateMode.Rotate90, FlipMode.None) },
      { 7, (RotateMode.Rotate270, FlipMode.Vertical) },
      { 8, (RotateMode.Rotate270, FlipMode.None) },
    };
    var (rotate, flip) = operations[orientation];
    image.Mutate(x => x.RotateFlip(rotate, flip));
  }

  public static Texture RenderText(string text) {
    return RenderText(text, 16);
  }

  public static Texture RenderText(string text, int size) {
    Font font = SystemFonts.CreateFont("Consolas", size, FontStyle.Bold);
    TextOptions options = new(font);
    FontRectangle rect = TextMeasurer.Measure(text, new TextOptions(font));
    Image<Rgba32> image = MakeImage(rect.Width, rect.Height);
    IBrush brush = Brushes.Solid(Color.White);
    image.Mutate(x => x.DrawText(options, text, brush));
    Texture texture = new Texture(image);
    image.Dispose();
    return texture;
  }

  // FIXME: make a real icon stored as a PNG...
  public static OpenTK.Windowing.Common.Input.Image[] RenderAppIcon() {
    int size = 64;
    Font font = SystemFonts.CreateFont("MS Mincho", size, FontStyle.Bold);
    TextOptions options = new(font);
    Image<Rgba32> image = MakeImage(size, size);
    IBrush brush = Brushes.Solid(Color.Black);
    image.Mutate(x => x.DrawText(options, "撮", brush));
    byte[] pixelBytes = new byte[size * size * 4];
    image.CopyPixelDataTo(pixelBytes);
    image.Dispose();
    OpenTK.Windowing.Common.Input.Image opentkImage = new(size, size, pixelBytes);
    return new OpenTK.Windowing.Common.Input.Image[]{ opentkImage };
  }

  public static Texture RenderStar(float radius, bool filled) {
    IPath path = new Star(x: radius, y: radius + 1, prongs: 5, innerRadii: radius * 0.4f, outerRadii: radius, angle: Util.PI);
    // We add a little bit to the width & height because the reported
    // path.Bounds are often a little tighter than they should be & a couple
    // pixels end up obviously missing...
    Image<Rgba32> image = MakeImage(path.Bounds.Width + 2, path.Bounds.Height + 2);
    IBrush brush = Brushes.Solid(Color.White);
    IPen white = Pens.Solid(Color.White, 1.5f);
    IPen black = Pens.Solid(Color.Black, 3f);
    image.Mutate(x => x.Draw(black, path));
    if (filled) {
      image.Mutate(x => x.Fill(brush, path));
    }
    image.Mutate(x => x.Draw(white, path));
    Texture texture = new Texture(image);
    image.Dispose();
    return texture;
  }
}

public class Game : GameWindow {
  public Game(GameWindowSettings gwSettings, NativeWindowSettings nwSettings) : base(gwSettings, nwSettings) {}

  private static Texture TEXTURE_WHITE = new(new Image<Rgba32>(1, 1, new Rgba32(255, 255, 255)));
  private static Texture TEXTURE_BLACK = new(new Image<Rgba32>(1, 1, new Rgba32(0, 0, 0)));
  private static Texture STAR_FILLED = Util.RenderStar(20, true);
  private static Texture STAR_EMPTY = Util.RenderStar(20, false);
  private static Texture STAR_SMALL = Util.RenderStar(6, true);

  UiGeometry geometry = new();
  FpsCounter fpsCounter = new();

  // Four points, each consisting of (x, y, z, tex_x, tex_y).
  float[] vertices = new float[20];

  // Indices to draw a rectangle from two triangles.
  uint[] indices = {
    0, 1, 3,   // first triangle
    1, 2, 3    // second triangle
  };

  int VertexBufferObject;
  int ElementBufferObject;
  int VertexArrayObject;
  List<Photo> allPhotos = new();
  List<Photo> photos = new();
  HashSet<Photo> loadedImages = new();
  HashSet<Photo> loadingImages = new();
  readonly object loadedImagesLock = new();
  int photoIndex = 0;
  int ribbonIndex = 0;
  Vector2i mouseDragStart;
  Vector2i mouseDragEnd;
  Shader shader = new();
  Matrix4 projection;
  float zoomLevel = 0f;

  protected override void OnUpdateFrame(FrameEventArgs e) {
    base.OnUpdateFrame(e);

    KeyboardState input = KeyboardState;

    bool shiftIsDown = input.IsKeyDown(Keys.LeftShift) || input.IsKeyDown(Keys.RightShift);
    bool altIsDown = input.IsKeyDown(Keys.LeftAlt) || input.IsKeyDown(Keys.RightAlt);
    bool ctrlIsDown = input.IsKeyDown(Keys.LeftControl) || input.IsKeyDown(Keys.RightControl);

    // FIXME: add a confirm dialog before closing. (Also for the window-close button.)
    // FIXME: don't quit if there's pending file-write operations.
    // Close when Ctrl-Q is pressed.
    if (input.IsKeyPressed(Keys.Q) && ctrlIsDown) {
      Close();
    }

    int lastPhotoIndex = photoIndex;

    Vector2i mousePosition = (Vector2i) MouseState.Position;

    // Look for mouse clicks on thumbnails or stars.
    //
    // Note that we don't bounds-check photoIndex until after all the possible
    // inputs that might affect it. That simplifies this logic significantly.
    if (MouseState.IsButtonPressed(MouseButton.Button1)) {

      for (int i = 0; i < geometry.StarBoxes.Count; i++) {
        if (geometry.StarBoxes[i].ContainsInclusive(mousePosition)) {
          photos[photoIndex].Rating = i + 1;
        }
      }

      for (int i = 0; i < geometry.ThumbnailBoxes.Count; i++) {
        if (geometry.ThumbnailBoxes[i].ContainsInclusive(mousePosition)) {
          photoIndex = ribbonIndex + i;
        }
      }

      if (geometry.PhotoBox.ContainsInclusive(mousePosition)) {
        mouseDragStart = mousePosition;
      }
    }

    if (MouseState.IsButtonDown(MouseButton.Button1)) {
      if (geometry.PhotoBox.ContainsInclusive(mousePosition)) {
        // FIXME: really this should be clipped to the active photo's drawable area, not the whole photobox.
        mouseDragEnd = mousePosition;
      }
    }

    if (input.IsKeyPressed(Keys.Escape)) {
      mouseDragStart = new(-1, -1);
      mouseDragEnd = new(-1, -1);
    }

    if (MouseState.IsButtonPressed(MouseButton.Button4)) {
      photoIndex--;
    }

    if (MouseState.IsButtonPressed(MouseButton.Button5)) {
      photoIndex++;
    }

    if (MouseState.ScrollDelta.Y < 0) {
      photoIndex++;
    }

    if (MouseState.ScrollDelta.Y > 0) {
      photoIndex--;
    }

    if (input.IsKeyPressed(Keys.Down)) {
      photoIndex++;
    }
    if (input.IsKeyPressed(Keys.Up)) {
      photoIndex--;
    }

    if (input.IsKeyPressed(Keys.Home)) {
      photoIndex = 0;
    }

    if (input.IsKeyPressed(Keys.End)) {
      photoIndex = photos.Count - 1;
    }

    if (input.IsKeyPressed(Keys.PageDown)) {
      photoIndex += 5;
    }

    if (input.IsKeyPressed(Keys.PageUp)) {
      photoIndex -= 5;
    }

    if (input.IsKeyPressed(Keys.P) && altIsDown) {
      ExportPhotos();
    }

    // Make sure the photoIndex is actually valid.
    if (photos.Count == 0) {
      photoIndex = 0;
    } else {
      photoIndex = Math.Clamp(photoIndex, 0, photos.Count - 1);
    }

    if (photoIndex != lastPhotoIndex) {
      mouseDragStart = new(-1, -1);
      mouseDragEnd = new(-1, -1);
    }

    // Handle presses of the "rating" keys -- 0-5 and `.
    // A normal press just sets the rating of the current photo.
    // If the user is holding "shift", we instead filter to only show photos of that rating or higher.
    int rating = -1;

    if (input.IsKeyPressed(Keys.D0) || input.IsKeyPressed(Keys.GraveAccent)) {
      rating = 0;
    }

    if (input.IsKeyPressed(Keys.D1)) {
      rating = 1;
    }

    if (input.IsKeyPressed(Keys.D2)) {
      rating = 2;
    }

    if (input.IsKeyPressed(Keys.D3)) {
      rating = 3;
    }

    if (input.IsKeyPressed(Keys.D4)) {
      rating = 4;
    }

    if (input.IsKeyPressed(Keys.D5)) {
      rating = 5;
    }

    if (rating >= 0) {
      if (shiftIsDown) {
        FilterByRating(rating);
      } else {
        if (photos.Count > 0) {
          photos[photoIndex].Rating = rating;
        }
      }
    }

    if (input.IsKeyPressed(Keys.Q)) {
      zoomLevel = 0f;
    }

    if (input.IsKeyPressed(Keys.W)) {
      zoomLevel = 1f;
    }

    if (input.IsKeyPressed(Keys.E)) {
      zoomLevel = 2f;
    }

    if (input.IsKeyPressed(Keys.R)) {
      zoomLevel = 4f;
    }

    if (input.IsKeyPressed(Keys.T)) {
      zoomLevel = 8f;
    }

    if (input.IsKeyPressed(Keys.Y)) {
      zoomLevel = 16f;
    }
  }

  void FilterByRating(int rating) {
    Console.WriteLine("filter to " + rating);
    Photo previouslyActive = photos.Count > 0 ? photos[photoIndex] : allPhotos[0];
    photos = allPhotos.Where(p => p.Rating >= rating).ToList();
    // Move photoIndex to wherever the previously active photo was, or if it
    // was filtered out, to whichever unfiltered photo comes before it. This
    // is O(n) in the length of allPhotos, but how bad can it be? :)
    photoIndex = -1;
    for (int i = 0; i < allPhotos.Count; i++) {
      Photo candidate = allPhotos[i];
      if (candidate.Rating >= rating) {
        photoIndex++;
      }
      if (candidate == previouslyActive) {
        break;
      }
    }
    photoIndex = Math.Max(0, photoIndex);
  }

  protected override void OnLoad() {
    base.OnLoad();

    GL.ClearColor(0f, 0f, 0f, 1f);

    GL.Enable(EnableCap.Blend);
    GL.BlendFunc(BlendingFactor.SrcAlpha, BlendingFactor.OneMinusSrcAlpha);

    VertexArrayObject = GL.GenVertexArray();
    GL.BindVertexArray(VertexArrayObject);

    VertexBufferObject = GL.GenBuffer();
    ElementBufferObject = GL.GenBuffer();

    GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);
    GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices, BufferUsageHint.DynamicDraw);
    GL.BindBuffer(BufferTarget.ElementArrayBuffer, ElementBufferObject);
    GL.BufferData(BufferTarget.ElementArrayBuffer, indices.Length * sizeof(uint), indices, BufferUsageHint.DynamicDraw);

    shader.Init();
    shader.Use();

    // Because there's 5 floats between the start of the first vertex and the start of the second,
    // the stride is 5 * sizeof(float).
    // This will now pass the new vertex array to the buffer.
    var vertexLocation = shader.GetAttribLocation("aPosition");
    GL.EnableVertexAttribArray(vertexLocation);
    GL.VertexAttribPointer(vertexLocation, 3, VertexAttribPointerType.Float, false, 5 * sizeof(float), 0);

    // Next, we also setup texture coordinates. It works in much the same way.
    // We add an offset of 3, since the texture coordinates comes after the position data.
    // We also change the amount of data to 2 because there's only 2 floats for texture coordinates.
    var texCoordLocation = shader.GetAttribLocation("aTexCoord");
    GL.EnableVertexAttribArray(texCoordLocation);
    GL.VertexAttribPointer(texCoordLocation, 2, VertexAttribPointerType.Float, false, 5 * sizeof(float), 3 * sizeof(float));

    // Load photos from a directory.
    // string[] files = Directory.GetFiles(@"c:\users\colin\desktop\photos-test\");
    // string[] files = Directory.GetFiles(@"c:\users\colin\pictures\photos\2023\07\14\");
    string[] files = Directory.GetFiles(@"G:\DCIM\100EOSR6\");
    // string[] files = Directory.GetFiles(@"c:\users\colin\desktop\totte-output\2023\07\31");
    // string[] files = Directory.GetFiles(@"C:\Users\colin\Pictures\photos\2018\06\23");
    // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\Germany all\104D7000");
    // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\many-birds\");

    for (int i = 0; i < files.Count(); i++) {
      string file = files[i];
      if (file.ToLower().EndsWith(".jpg")) {
        Photo photo = new Photo(file, TEXTURE_BLACK);
        allPhotos.Add(photo);
      }
    }

    allPhotos.Sort(ComparePhotosByDate);
    photos = allPhotos;
  }

  private static int ComparePhotosByDate(Photo x, Photo y) {
    int compare = x.DateTimeOriginal.CompareTo(y.DateTimeOriginal);
    if (compare != 0) {
      return compare;
    }
    // If the photos have the same seconds value, sort by filename
    // (since cameras usually increment the filename for successive shots.)
    return x.Filename.CompareTo(y.Filename);
  }

  protected override void OnUnload() {
    base.OnUnload();
  }

  private void UnloadImages() {
    // Unload images that haven't been touched in a while.
    // FIXME: keep around thumbnail-sized textures?
    lock (loadedImagesLock) {
      while (loadedImages.Count > 100) {
        long earliestTime = long.MaxValue;
        Photo? earliest = null;
        foreach (Photo photo in loadedImages) {
          if (photo.LastTouch < earliestTime) {
            earliest = photo;
            earliestTime = photo.LastTouch;
          }
        }
        if (earliest != null) {
          Console.WriteLine($"loadedImages.Count: {loadedImages.Count}, evicting {earliest.Filename} @ {earliestTime}");
          // TODO: we have to free textures on the GL thread, but could we do that async'ly to keep the UI responsive?
          earliest.Unload();
          loadedImages.Remove(earliest);
        }
      }
    }
  }

  private async void LoadImagesAsync() {
    foreach (Photo p in loadingImages) {
      if (p.Loaded) {
        lock (loadedImagesLock) {
          loadedImages.Add(p);
          loadingImages.Remove(p);
        }
      }
    }
    // Start loading any images that are in our window but not yet loaded.
    int minLoadedImage = Math.Max(0, photoIndex - 30);
    int maxLoadedImage = Math.Min(photoIndex + 30, photos.Count - 1);
    List<Photo> toLoad = new();
    for (int i = minLoadedImage; i <= maxLoadedImage; i++) {
      lock (loadedImagesLock) {
        if (!loadedImages.Contains(photos[i]) && !loadingImages.Contains(photos[i])) {
          Console.WriteLine("loading " + i);
          loadingImages.Add(photos[i]);
          toLoad.Add(photos[i]);
        }
      }
    }
    foreach (Photo p in toLoad) {
      await Task.Run( () => { p.LoadAsync(); });
    }
  }

  // To find the JPEG compression level of a file from the command line:
  // $ identify -verbose image.jpg | grep Quality:
  // FIXME: don't ExportPhotos() if another export is already active.
  // FIXME: show a progress bar or something.
  private async void ExportPhotos() {
    JpegEncoder encoder = new JpegEncoder() { Quality = 100 };
    string outputRoot = @"c:\users\colin\desktop\totte-output";
    // string outputRoot = @"c:\users\colin\pictures\photos";
    foreach (Photo p in photos) {
      await Task.Run( () => { p.SaveAsJpegAsync(outputRoot, encoder); });
    }
  }

  protected override void OnRenderFrame(FrameEventArgs e) {
    base.OnRenderFrame(e);
    fpsCounter.Update();

    UnloadImages();
    LoadImagesAsync();

    GL.Clear(ClearBufferMask.ColorBufferBit);
    GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);
    GL.ActiveTexture(TextureUnit.Texture0);

    if (photos.Count > 0) {
      DrawPhotos();
    } else {
      DrawText("No photos found.", 10, 10);
    }

    DrawCropBox();

    SwapBuffers();
  }

  void DrawCropBox() {
    Vector2i start = mouseDragStart;
    Vector2i end = mouseDragEnd;
    end.Y = Math.Min(end.Y, start.Y + (end.X - start.X) * 4 / 6);
    end.X = start.X + (end.Y - start.Y) * 6 / 4;
    int left = Math.Min(start.X, end.X);
    int right = Math.Max(start.X, end.X);
    int top = Math.Min(start.Y, end.Y);
    int bottom = Math.Max(start.Y, end.Y);
    int area = (right - left) * (bottom - top);

    if (area < 100) {
      return;
    }
    Color4 shadeColor = new Color4(0, 0, 0, 0.75f);
    DrawFilledBox(new Box2i(0, 0, left, geometry.PhotoBox.Max.Y), shadeColor);
    DrawFilledBox(new Box2i(left, 0, geometry.PhotoBox.Max.X, top), shadeColor);
    DrawFilledBox(new Box2i(left, bottom, geometry.PhotoBox.Max.X, geometry.PhotoBox.Max.Y), shadeColor);
    DrawFilledBox(new Box2i(right, top, geometry.PhotoBox.Max.X, bottom), shadeColor);
    DrawBox(new Box2i(left, top, right, bottom), 1, Color4.White);
    DrawBox(new Box2i(left - 1, top - 1 , right + 1, bottom + 1), 1, Color4.Black);
    DrawBox(new Box2i(left - 2, top - 2 , right + 2, bottom + 2), 1, Color4.White);
    DrawHorizontalLine(left, Util.Lerp(top, bottom, 1.0 / 3), right, Color4.White);
    DrawHorizontalLine(left, Util.Lerp(top, bottom, 2.0 / 3), right, Color4.White);
    DrawVerticalLine(Util.Lerp(left, right, 1.0 / 3), top, bottom, Color4.White);
    DrawVerticalLine(Util.Lerp(left, right, 2.0 / 3), top, bottom, Color4.White);
  }

  void DrawPhotos() {
    Photo activePhoto = photos[photoIndex];
    Texture active = activePhoto.Texture();

    // FIXME: make a function for scaling & centering one box on another.
    float scaleX = 1f * geometry.PhotoBox.Size.X / active.Size.X;
    float scaleY = 1f * geometry.PhotoBox.Size.Y / active.Size.Y;
    float scale = Math.Min(scaleX, scaleY);
    if (zoomLevel > 0f) {
      scale = zoomLevel;
    }

    Vector2i renderSize = (Vector2i) (((Vector2) active.Size) * scale);
    Vector2i center = (Vector2i) geometry.PhotoBox.Center;
    Box2i photoBox = Util.MakeBox(center.X - renderSize.X / 2, center.Y - renderSize.Y / 2, renderSize.X, renderSize.Y);
    DrawTexture(active, photoBox);
    for (int i = 0; i < 5; i++) {
      Texture star = (activePhoto.Rating > i) ? STAR_FILLED : STAR_EMPTY;
      DrawTexture(star, geometry.StarBoxes[i].Min.X, geometry.StarBoxes[i].Min.Y);
    }

    // Draw thumbnail boxes.
    ribbonIndex = Math.Clamp(photoIndex - (geometry.ThumbnailBoxes.Count - 1) / 2, 0, Math.Max(0, photos.Count - geometry.ThumbnailBoxes.Count));
    DrawFilledBox(geometry.ThumbnailBox, Color4.Black);
    for (int i = 0; i < geometry.ThumbnailBoxes.Count; i++) {
      if (ribbonIndex + i >= photos.Count) {
        break;
      }
      Photo photo = photos[ribbonIndex + i];
      Box2i box = geometry.ThumbnailBoxes[i];
      DrawTexture(photo.Texture(), box);
      for (int j = 0; j < photo.Rating; j++) {
        DrawTexture(STAR_SMALL, box.Min.X + 8 + ((STAR_SMALL.Size.X + 2) * j), box.Min.Y + 8);
      }
      if (ribbonIndex + i == photoIndex) {
        DrawBox(box, 5, Color4.Black);
        DrawBox(box, 3, Color4.White);
      }
    }

    // Draw status box.
    int statusPadding = 2;
    DrawFilledBox(geometry.StatusBox, Color4.Black);
    DrawText(String.Format("{0,4}/{1,-4}", photoIndex + 1, photos.Count), geometry.StatusBox.Min.X + 72, geometry.StatusBox.Min.Y + statusPadding);
    DrawText(activePhoto.Description(), geometry.StatusBox.Min.X + 160, geometry.StatusBox.Min.Y + statusPadding);
    DrawText(String.Format("FPS: {0,2}", fpsCounter.Fps), geometry.StatusBox.Max.X - 66, geometry.StatusBox.Min.Y + statusPadding);

    if (activePhoto.Loaded) {
      DrawText($"{(scale * 100):F1}%", geometry.StatusBox.Min.X, geometry.StatusBox.Min.Y + statusPadding);
    }
  }

  void DrawTexture(Texture texture, int x, int y) {
    DrawTexture(texture, Util.MakeBox(x, y, texture.Size.X, texture.Size.Y));
  }

  void DrawTexture(Texture texture, Box2i box) {
    DrawTexture(texture, box, Color4.White);
  }

  void DrawTexture(Texture texture, Box2i box, Color4 color) {
    GL.Uniform4(shader.GetUniformLocation("color"), color);
    SetVertices(box.Min.X, box.Min.Y, box.Size.X, box.Size.Y);
    GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices, BufferUsageHint.DynamicDraw);
    GL.BindTexture(TextureTarget.Texture2D, texture.Handle);
    GL.DrawElements(PrimitiveType.Triangles, indices.Length, DrawElementsType.UnsignedInt, 0);
  }

  void DrawHorizontalLine(int left, int top, int right, Color4 color) {
    DrawTexture(TEXTURE_WHITE, Util.MakeBox(left, top, right - left, 1), color);
  }

  void DrawVerticalLine(int left, int top, int bottom, Color4 color) {
    DrawTexture(TEXTURE_WHITE, Util.MakeBox(left, top, 1, bottom - top), color);
  }

  void DrawBox(Box2i box, int thickness, Color4 color) {
    DrawTexture(TEXTURE_WHITE, Util.MakeBox(box.Min.X, box.Min.Y, box.Size.X, thickness), color);
    DrawTexture(TEXTURE_WHITE, Util.MakeBox(box.Min.X, box.Min.Y, thickness, box.Size.Y), color);
    DrawTexture(TEXTURE_WHITE, Util.MakeBox(box.Min.X, box.Max.Y - thickness, box.Size.X, thickness), color);
    DrawTexture(TEXTURE_WHITE, Util.MakeBox(box.Max.X - thickness, box.Min.Y, thickness, box.Size.Y), color);
  }

  void DrawFilledBox(Box2i box, Color4 color) {
    DrawTexture(TEXTURE_WHITE, Util.MakeBox(box.Min.X, box.Min.Y, box.Size.X, box.Size.Y), color);
  }

  void DrawText(string text, int x, int y) {
    Texture label = Util.RenderText(text);
    DrawTexture(label, x, y);
    label.Dispose();
  }

  protected override void OnResize(ResizeEventArgs e) {
    base.OnResize(e);
    Console.WriteLine($"OnResize: {e.Width}x{e.Height}");

    geometry = new UiGeometry(e.Size, STAR_FILLED.Size.X);

    projection = Matrix4.CreateOrthographicOffCenter(0f, e.Width, e.Height, 0f, -1f, 1f);
    GL.UniformMatrix4(shader.GetUniformLocation("projection"), true, ref projection);
    GL.Viewport(0, 0, e.Width, e.Height);
  }

  private void SetVertices(float left, float top, float width, float height) {
    // top left
    vertices[0] = left;
    vertices[1] = top;
    vertices[2] = 0f;
    vertices[3] = 0f;
    vertices[4] = 0f;

    // top right
    vertices[5] = left + width;
    vertices[6] = top;
    vertices[7] = 0f;
    vertices[8] = 1f;
    vertices[9] = 0f;

    // bottom right
    vertices[10] = left + width;
    vertices[11] = top + height;
    vertices[12] = 0f;
    vertices[13] = 1f;
    vertices[14] = 1f;

    // bottom left
    vertices[15] = left;
    vertices[16] = top + height;
    vertices[17] = 0f;
    vertices[18] = 0f;
    vertices[19] = 1f;
  }
}

static class Program {
  static void Main(string[] args) {
    List<MonitorInfo> monitors = Monitors.GetMonitors();
    MonitorInfo bestMonitor = monitors[0];
    int bestResolution = bestMonitor.HorizontalResolution * bestMonitor.VerticalResolution;
    for (int i = 1; i < monitors.Count; i++) {
      MonitorInfo monitor = monitors[i];
      int resolution = monitor.HorizontalResolution * monitor.VerticalResolution;
      if (resolution > bestResolution) {
        bestResolution = resolution;
        bestMonitor = monitor;
      }
    }
    Console.WriteLine($"best monitor: {bestMonitor.HorizontalResolution}x{bestMonitor.VerticalResolution}");
    GameWindowSettings gwSettings = new();
    gwSettings.UpdateFrequency = 30.0;
    gwSettings.RenderFrequency = 30.0;

    NativeWindowSettings nwSettings = new();
    nwSettings.WindowState = WindowState.Normal;
    nwSettings.CurrentMonitor = bestMonitor.Handle;
    nwSettings.Location = new Vector2i(bestMonitor.WorkArea.Min.X + 1, bestMonitor.WorkArea.Min.Y + 31);
    // nwSettings.Size = new Vector2i(bestMonitor.WorkArea.Size.X - 2, bestMonitor.WorkArea.Size.Y - 32);
    nwSettings.Size = new Vector2i(1600, 900);
    nwSettings.MinimumSize = UiGeometry.MIN_WINDOW_SIZE;
    nwSettings.Title = "Totte";
    nwSettings.IsEventDriven = false;
    nwSettings.Icon = new WindowIcon(Util.RenderAppIcon());

    using (Game game = new(gwSettings, nwSettings)) {
      game.Run();
    }
  }
}