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 SixLabors.Fonts;
using SixLabors.ImageSharp.Drawing.Processing;
using SixLabors.ImageSharp.Drawing;
using SixLabors.ImageSharp.Formats.Jpeg;
using System;
using System.Diagnostics;

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 static float AspectRatio = 6000f / 4000f;
}


public enum ToolStatus {
  Active,
  Done,
  Canceled
}


public class Transform {
  // FIXME: move scale and offset into Photo itself?
  float activeScale;
  Vector2i activeOffset;
  Vector2i photoSize;

  public Transform(float scale, Vector2i offset, Vector2i photoSize) {
    activeScale = scale;
    activeOffset = offset;
    this.photoSize = photoSize;
  }

  public Vector2i ScreenToImageDelta(int x, int y) {
    return new((int) (x / activeScale), (int) (y / activeScale));
  }

  public Vector2i ScreenToImage(int x, int y) {
    int rx = (int) ((x - activeOffset.X) / activeScale);
    int ry = (int) ((y - activeOffset.Y) / activeScale);
    rx = Math.Clamp(rx, 0, photoSize.X);
    ry = Math.Clamp(ry, 0, photoSize.Y);
    return new(rx, ry);
  }

  public Vector2i ScreenToImage(Vector2i position) {
    return ScreenToImage(position.X, position.Y);
  }

  public Vector2i ImageToScreen(int x, int y) {
    int rx = (int) ((x * activeScale) + activeOffset.X);
    int ry = (int) ((y * activeScale) + activeOffset.Y);
    return new(rx, ry);
  }

  public Vector2i ImageToScreen(Vector2i position) {
    return ImageToScreen(position.X, position.Y);
  }
}

public interface ITool {
  ToolStatus HandleInput(KeyboardState input, MouseState mouse, Transform transform);
  string Status();
  void Draw(UiGeometry geometry, Game game);
}


public class ViewTool : ITool {
  public ToolStatus HandleInput(KeyboardState input, MouseState mouse, Transform transform) {
    return ToolStatus.Active;
  }

  public string Status() {
    return "";
  }

  public void Draw(UiGeometry geometry, Game game) {
  }
}


public class CropTool : ITool {

  Photo photo;
  Vector2i mouseDragStart;
  Vector2i mouseDragEnd;
  bool dragging;
  string status = "";

  public CropTool(Photo photo) {
    this.photo = photo;
    mouseDragStart = new(photo.CropRectangle.Left, photo.CropRectangle.Top);
    mouseDragEnd = new(photo.CropRectangle.Right, photo.CropRectangle.Bottom);
  }

  public ToolStatus HandleInput(KeyboardState input, MouseState mouse, Transform transform) {
    Vector2i mousePosition = (Vector2i) mouse.Position;
    Vector2i imagePosition = transform.ScreenToImage(mousePosition);

    if (mouse.IsButtonPressed(MouseButton.Button1)) {
      dragging = photo.CropRectangle.Contains(imagePosition.X, imagePosition.Y);
    }

    if (!dragging) {
      if (mouse.IsButtonPressed(MouseButton.Button1)) {
        mouseDragStart = imagePosition;
      }
      if (mouse.IsButtonDown(MouseButton.Button1)) {
        mouseDragEnd = imagePosition;
      }

      var (left, right, top, bottom) = GetCrop();
      if (left != right && top != bottom) {
        photo.CropRectangle = Rectangle.FromLTRB(left, top, right, bottom);
      } else {
        photo.CropRectangle = Rectangle.Empty;
      }
    } else {
      if (mouse.IsButtonDown(MouseButton.Button1)) {
        Vector2 delta = mouse.Delta;
        Vector2i imageDelta = transform.ScreenToImageDelta((int) delta.X, (int) delta.Y);
        photo.CropRectangle.Offset(imageDelta.X, imageDelta.Y);
        if (photo.CropRectangle.Left < 0) {
          photo.CropRectangle.Offset(-photo.CropRectangle.Left, 0);
        }
        if (photo.CropRectangle.Right > photo.Size.X) {
          int overshoot = photo.CropRectangle.Right - photo.Size.X;
          photo.CropRectangle.Offset(-overshoot, 0);
        }
        if (photo.CropRectangle.Top < 0) {
          photo.CropRectangle.Offset(0, -photo.CropRectangle.Top);
        }
        if (photo.CropRectangle.Bottom > photo.Size.Y) {
          int overshoot = photo.CropRectangle.Bottom - photo.Size.Y;
          photo.CropRectangle.Offset(0, -overshoot);
        }
      }
    }

    Rectangle r = photo.CropRectangle;
    status = $"({r.Left}, {r.Top}, {r.Right}, {r.Bottom}) {r.Width}x{r.Height}";

    if (input.IsKeyPressed(Keys.Enter)) {
      return ToolStatus.Done;
    }

    if (input.IsKeyPressed(Keys.Escape)) {
      photo.CropRectangle = Rectangle.Empty;
      return ToolStatus.Canceled;
    }

    return ToolStatus.Active;
  }

  // left, right, top, bottom
  (int, int, int, int) GetCrop() {
    // FIXME: this expects the start point in the top left and the end point
    // in the bottom right; some sign flipping needs to occur to make anchors
    // in other directions work well.
    Vector2i start = mouseDragStart;
    Vector2i end = mouseDragEnd;
    // FIXME: choose the aspect ratio based on the original image aspect ratio.
    // FIXME: allow for unconstrained crop, 1:1, etc.
    end.Y = Math.Min(end.Y, (int) (start.Y + (end.X - start.X) / CameraInfo.AspectRatio));
    end.X = (int) (start.X + (end.Y - start.Y) * CameraInfo.AspectRatio);
    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);
    return (left, right, top, bottom);
  }

  public void Draw(UiGeometry geometry, Game game) {
  }

  public string Status() {
    return "[crop] " + status;
  }
}


public class UiGeometry {
  public static Vector2i MIN_WINDOW_SIZE = new(1024, 768);

  public readonly Vector2i WindowSize;
  public readonly Vector2i ThumbnailSize;
  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 * CameraInfo.AspectRatio);
    ThumbnailSize = new(thumbnailWidth, thumbnailHeight);

    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 = 40;
    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) {
    // Make sure that 0-length text doesn't end up as a 0-size texture, which
    // might cause problems.
    if (text.Length == 0) {
      text = " ";
    }
    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) {
    activeTool = viewTool;
    geometry = new UiGeometry(nwSettings.Size, STAR_FILLED.Size.X);
  }

  private static string outputRoot = @"c:\users\colin\desktop\totte-output";
  // private static string outputRoot = @"c:\users\colin\pictures\photos";

  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;
  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();
  readonly ViewTool viewTool = new ViewTool();
  ITool activeTool;
  int photoIndex = 0;
  int ribbonIndex = 0;
  Vector2i mousePosition;
  float activeScale = 1f;
  Vector2i activeOffset;
  Transform transform = new(1f, Vector2i.Zero, Vector2i.Zero);
  Shader shader = new();
  Matrix4 projection;
  float zoomLevel = 0f;

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

    Photo previousPhoto = photos[photoIndex];

    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();
    }

    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 (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) && ctrlIsDown) {
      ExportPhotos();
    }

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

    // Handle tool switching.
    if (photos[photoIndex] != previousPhoto) {
      activeTool = viewTool;
    }

    if (activeTool == viewTool) {
      if (input.IsKeyPressed(Keys.C)) {
        activeTool = new CropTool(photos[photoIndex]);
      }
    }

    // Delegate input to the active tool.
    ToolStatus status = activeTool.HandleInput(KeyboardState, MouseState, transform);

    // Change back to the default tool if the active tool is done.
    if (status != ToolStatus.Active) {
      activeTool = viewTool;
    }
  }

  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);
  }

  // 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
  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(@"c:\users\colin\pictures\photos\2023\07\23\");
    // 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\desktop\import");
    // 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;

    LoadThumbnailsAsync();
  }

  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.
    lock (loadedImagesLock) {
      while (loadedImages.Count > 30) {
        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 - 10);
    int maxLoadedImage = Math.Min(photoIndex + 10, 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(geometry.PhotoBox.Size); });
    }
  }

  private async void LoadThumbnailsAsync() {
    foreach (Photo p in allPhotos) {
      await Task.Run( () => { p.LoadThumbnailAsync(geometry.ThumbnailSize); });
    }
  }

  // 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.
  // FIXME: if there's a photo missing GPS information, copy the information
  // from the previous photo in the export.
  private async void ExportPhotos() {
    JpegEncoder encoder = new JpegEncoder() { Quality = 100 };
    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);
    }

    activeTool.Draw(geometry, this);

    SwapBuffers();
  }

  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;
    }
    activeScale = scale;

    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);
    activeOffset = new(photoBox.Min.X, photoBox.Min.Y);
    transform = new Transform(activeScale, activeOffset, activePhoto.Size);
    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);
    }
    bool cropActive = activeTool is CropTool;
    DrawCropRectangle(cropActive);

    // 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.ThumbnailTexture(), 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);
    // First line.
    int y = geometry.StatusBox.Min.Y + statusPadding;
    DrawText(String.Format("{0,4}/{1,-4}", photoIndex + 1, photos.Count),
             geometry.StatusBox.Min.X, y);
    DrawText(activePhoto.Description(), geometry.StatusBox.Min.X + 88, y);

    // Second line.
    y += 20;
    DrawText(activeTool.Status(), geometry.StatusBox.Min.X, y);
    DrawText(String.Format("FPS: {0,2}", fpsCounter.Fps), geometry.StatusBox.Max.X - 66, y);
    if (activePhoto.Loaded) {
      DrawText($"{(scale * 100):F1}%", geometry.StatusBox.Max.X - 136, y);
    }
  }

  void DrawCropRectangle(bool active) {
    Photo activePhoto = photos[photoIndex];
    if (activePhoto.CropRectangle == Rectangle.Empty) {
      return;
    }

    Vector2i leftTop = transform.ImageToScreen(activePhoto.CropRectangle.Left,
                                               activePhoto.CropRectangle.Top);
    Vector2i rightBottom = transform.ImageToScreen(activePhoto.CropRectangle.Right,
                                                   activePhoto.CropRectangle.Bottom);
    var (left, top) = leftTop;
    var (right, bottom) = rightBottom;

    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 - 1, top - 1, right + 1, bottom + 1), 1, Color4.White);
    if (active) {
      // handles
      int handleThickness = 3;
      int handleLength = 16;
      // top-left
      DrawFilledBox(new Box2i(left - handleThickness, top - handleThickness,
                              left + handleLength, top), Color4.White);
      DrawFilledBox(new Box2i(left - handleThickness, top - handleThickness,
                              left, top + handleLength), Color4.White);
      // top-right
      DrawFilledBox(new Box2i(right - handleLength, top - handleThickness,
                              right + handleThickness, top), Color4.White);
      DrawFilledBox(new Box2i(right, top - handleThickness,
                              right + handleThickness, top + handleLength), Color4.White);
      // bottom-left
      DrawFilledBox(new Box2i(left - handleThickness, bottom,
                              left + handleLength, bottom + handleThickness), Color4.White);
      DrawFilledBox(new Box2i(left - handleThickness, bottom - handleLength,
                              left, bottom + handleThickness), Color4.White);
      // bottom-right
      DrawFilledBox(new Box2i(right - handleLength, bottom,
                              right + handleThickness, bottom + handleThickness), Color4.White);
      DrawFilledBox(new Box2i(right + handleThickness, bottom - handleLength,
                              right, bottom + handleThickness), Color4.White);

      // thirds
      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);
    }
  }

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

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

  public 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);
  }

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

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

  public 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);
  }

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

  public 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 = true;
    nwSettings.Icon = new WindowIcon(Util.RenderAppIcon());

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