emulsion 12.0.0

use std::{
	borrow::Cow,
	collections::BTreeMap,
	ffi::{OsStr, OsString},
	fs, mem,
	path::{Path, PathBuf},
	rc::Rc,
	sync::atomic::Ordering,
	time::SystemTime,
};

use log::trace;

use gelatin::{
	glium::{
		self,
		texture::{MipmapsOption, RawImage2d, SrgbTexture2d},
		CapabilitiesSource,
	},
	image,
};

pub mod image_loader;

use self::{directory::DirItem, image_loader::*};

mod pending_requests;
use pending_requests::PendingRequests;

pub mod directory;
use directory::Directory;

#[derive(Debug, thiserror::Error)]
pub enum TextureError {
	#[error("ImageCache is waiting for the image loader to send result")]
	WaitingOnLoader,

	#[error("Other texture error: {0}")]
	Other(Cow<'static, str>),
}
impl From<directory::Error> for TextureError {
	fn from(value: directory::Error) -> Self {
		Self::Other(format!("Directory error: {}", value).into())
	}
}
impl From<glium::texture::TextureCreationError> for TextureError {
	fn from(value: glium::texture::TextureCreationError) -> Self {
		Self::Other(format!("glium failed to create the texture: {value}").into())
	}
}
impl From<std::io::Error> for TextureError {
	fn from(value: std::io::Error) -> Self {
		Self::Other(format!("IO error occured during texture creation: {value}").into())
	}
}
impl TextureError {
	pub fn from_failed_request(req_id: u32) -> Self {
		Self::Other(format!("Failed to load #{req_id}").into())
	}
}

pub type TextureResult<T> = std::result::Result<T, TextureError>;

// use self::texture_load_errors::*;

#[derive(Debug, thiserror::Error)]
pub enum PathResolutionError {
	#[error("No image path has been specified. (Eg emulsion was started without it being requested to open an image or folder)")]
	NotYetSpecified,

	#[error("Could not find file path matching the request, because the Directory Filter hasn't finished yet")]
	WaitingOnDirFilter,
}

/// Some operations eg "load the next image" doesn't only have to load the image but
/// also have to determine the path to the image. It's possible that we successfuly
/// determined the path, but cannot load the image for some reason.
pub type PathedTextureResult =
	std::result::Result<(PathBuf, TextureResult<AnimationFrameTexture>), PathResolutionError>;

pub fn get_image_size_estimate(width: u32, height: u32) -> isize {
	// In an RGBA image, each pixel is 4 bytes.
	// counting all the mipmaps would add an additionnal multiplier of around ~1.6
	// but only the gpu textures have mip maps so just multiply by 1.5
	// 4 x 1.5 gives the factor 6.
	(width * height * 6) as isize
}

pub fn get_anim_size_estimate(frames: &[AnimationFrameTexture]) -> isize {
	frames.iter().map(|frame| get_image_size_estimate(frame.w, frame.h)).sum()
}

/// The request sender function must process all prefetched requests to avoid
/// hitting the pending request limit (MAX_PENDING_REQUESTS). The display is needed
/// for this processing but it would be incorrect to require the dispaly for prefetch
/// requests
enum RequestKind<'a> {
	NonPriority,
	Priority { display: &'a gelatin::Display },
}

impl<'a> RequestKind<'a> {
	pub fn priority(self) -> bool {
		match self {
			RequestKind::Priority { .. } => true,
			RequestKind::NonPriority => false,
		}
	}
}

pub struct TextureGridItem {
	pub tex: SrgbTexture2d,
	pub col: u32,
	pub row: u32,
}

#[derive(Clone)]
pub struct AnimationFrameTexture {
	/// The maximum texture size supported by GPUs is limited. However it may be
	/// the I want to view a 16k*16k image while my GPU only supports 4k*4k
	/// textures. To work around this, we split up large images into a grid of
	/// smaller ones, which are displayed to appear as one continous surface.
	pub tex_grid: Rc<Vec<TextureGridItem>>,
	/// Number of physical pixels between two adjacent cells in one dimension.
	/// For example the pixel offset from the corner of the image to the corner
	/// of the cell at the 3rd column and 2nd row is
	/// (3*cell_step_size, 2*cell_step_size)
	pub cell_step_size: u32,

	pub delay_nano: u64,
	pub orientation: Orientation,

	/// The total width of the image. This equals to the sum of the widths of the
	/// textures from a single row of the grid
	pub w: u32,
	/// The total height of the image. This equals to the sum of the heights of the
	/// textures from a single column of the grid
	pub h: u32,
}
impl AnimationFrameTexture {
	pub fn from_image(
		display: &gelatin::Display,
		image: image::RgbaImage,
		delay_nano: u64,
		orientation: Orientation,
	) -> TextureResult<Self> {
		let (w, h) = image.dimensions();
		let img_bytes = image.into_raw();
		let mut tex_grid = Vec::new();

		// The reasoning behind dividing by 2 and taking the min with 4*1024, is
		// that if the textures are going to be swaped out from GPU memory it
		// might be easier to shuffle smaller chunks of memory around. (Because
		// I believe that if the memory is fragmented, it is easier to find
		// space for a smaller texture)
		let max_size = (display.get_capabilities().max_texture_size as u32 / 2).min(4 * 1024);

		// DEBUG
		// let max_size = 1024;

		let grid_cols = ((w - 1) / max_size) + 1;
		let grid_rows = ((h - 1) / max_size) + 1;

		for row in 0..grid_rows {
			for col in 0..grid_cols {
				let offset_x = col * max_size;
				let offset_y = row * max_size;
				let cell_w = (w - offset_x).min(max_size);
				let cell_h = (h - offset_y).min(max_size);
				let tex = texture_from_img_rect(
					display, w, h, &img_bytes, offset_x, offset_y, cell_w, cell_h,
				)?;
				let item = TextureGridItem { tex, col, row };
				tex_grid.push(item);
			}
		}

		Ok(AnimationFrameTexture {
			tex_grid: Rc::new(tex_grid),
			delay_nano,
			orientation,
			w,
			h,
			cell_step_size: max_size,
		})
	}

	pub fn oriented_dimensions(&self) -> (u32, u32) {
		use Orientation::*;
		match self.orientation {
			Deg0 | Deg0HorFlip | Deg180 | Deg180HorFlip => (self.w, self.h),
			Deg90 | Deg90VerFlip | Deg270 | Deg270VerFlip => (self.h, self.w),
		}
	}
}

/// img_bytes has to be an rgba8 buffer.
#[allow(clippy::too_many_arguments)]
fn texture_from_img_rect(
	display: &gelatin::Display,
	img_w: u32,
	img_h: u32,
	img_bytes: &[u8],
	offset_x: u32,
	offset_y: u32,
	cell_w: u32,
	cell_h: u32,
) -> TextureResult<SrgbTexture2d> {
	let raw_image;
	if img_w == cell_w {
		assert!(offset_x == 0);
		let start = (offset_y as usize * img_w as usize) * 4;
		let end = start + (cell_h as usize * cell_w as usize * 4);
		raw_image = RawImage2d {
			data: Cow::Borrowed(&img_bytes[start..end]),
			format: glium::texture::ClientFormat::U8U8U8U8,
			width: cell_w,
			height: cell_h,
		};
	} else {
		let cell_size = cell_w as usize * cell_h as usize * 4;
		let mut cell_pixels = Vec::with_capacity(cell_size);
		for y in offset_y..(offset_y + cell_h) {
			// We multiply by four becase we need to convert from a pixel offset to
			// a byte offset and each pixel is 4 bytes wide.
			let start = (y as usize * img_w as usize + offset_x as usize) * 4;
			let end = start + (cell_w as usize * 4);
			cell_pixels.extend_from_slice(&img_bytes[start..end]);
		}
		raw_image = RawImage2d::from_raw_rgba(cell_pixels, (cell_w, cell_h));
	}

	let x_pow = 31 - img_w.leading_zeros();
	let y_pow = 31 - img_h.leading_zeros();

	let max_mipmap_levels = x_pow.min(y_pow).min(4);

	let mipmaps = if max_mipmap_levels == 1 {
		MipmapsOption::NoMipmap
	} else {
		MipmapsOption::AutoGeneratedMipmapsMax(max_mipmap_levels)
		//MipmapsOption::AutoGeneratedMipmaps
	};
	Ok(SrgbTexture2d::with_mipmaps(display, raw_image, mipmaps)?)
}

struct CachedTexture {
	/// Contains the load request id
	_req_id: u32,
	needs_update: bool,
	mod_time: Option<SystemTime>,

	/// This is false if there are frames from the animation that haven't been added.
	/// This is used when requesting a frame that's outside of `frames`.
	/// In such a case the value of `fully_loaded` is inspected and if the image
	/// is loaded the frame number is wrapped around so that it falls onto the range.
	/// If it's not fully loaded yet a `WaitingOnLoader` error is returned.
	fully_loaded: bool,

	/// - `false` if loading is still in progress or if succeeded.
	/// - `true` if this failed to load,
	failed: bool,

	/// If the target file is an image this vector will have a single texture once the
	/// image uploaded to the GPU. If the target file is an animated image like a gif,
	/// these the frames
	frames: Vec<AnimationFrameTexture>,
}

/// The process of loading an image (or animation frame) consists of the following steps.
/// Note that even still images are handled as 1 frame long animations as there is
/// semantically no difference between those and this keeps the code relatively simple.
///
/// - ImageCache - Load request sent
///     - An entry representing the request is created in `ImageCache::ongoing_requests`
/// - Worker thread - Decodes an image from the byte stream into a CPU-side buffer. Send this back on a channel
///     - Decoded pixel data on channel (CPU)
/// - ImageCache - Prefetched image received from worker thread
///     - Decoded pixel data in `ImageCache::prefetched`
/// - ImageCache - Prefetched image is uploaded to a GPU texture from the CPU
///     - Pixel data is on the gpu referred to by `ImageCache::texture_cache`
///
pub struct ImageCache {
	dir: Directory,

	//current_name: OsString,
	//current_file_idx: usize,
	current_frame_idx: usize,

	remaining_capacity: isize,
	total_capacity: isize,
	curr_est_size: isize,

	pending_requests: PendingRequests,
	texture_cache: BTreeMap<u32, CachedTexture>,
	loader: ImageLoader,
}

/// This is a store for the supported images loaded from a folder
///
/// The basic idea is to have a few images already in the memory while an image is shown on the screen
impl ImageCache {
	const MAX_PENDING_REQUESTS: usize = 5;

	/// # Arguments
	/// * `capacity` - Number of bytes. The last image loaded will be the one at which the allocated memory reaches or exceeds capacity
	pub fn new(capacity: isize, threads: u32) -> ImageCache {
		ImageCache {
			dir: Directory::new(),
			//current_file_idx: 0,
			current_frame_idx: 0,

			remaining_capacity: capacity,
			total_capacity: capacity,
			curr_est_size: 1000, // 1 kb, an optimistic estimate for the image size before anything is loaded

			pending_requests: PendingRequests::new(),
			texture_cache: BTreeMap::new(),
			loader: ImageLoader::new(threads),
		}
	}

	pub fn current_filename(&self) -> Option<OsString> {
		self.dir.curr_filename()
	}

	pub fn current_file_path(&self) -> Option<PathBuf> {
		self.current_filename().map(|name| self.dir.path().join(name))
	}

	/// Returns `None` when the directory hasn't finished filtering image files.
	pub fn current_file_index(&mut self) -> Option<usize> {
		self.dir.curr_img_index()
	}

	/// Returns `None` when the directory hasn't finished filtering image files.
	pub fn current_dir_len(&mut self) -> Option<usize> {
		self.dir.image_count()
	}

	fn curr_dir_item(&self) -> Option<DirItem> {
		self.dir.curr_descriptor().cloned()
	}

	/// Returns tru if and only if the current image has been fully loaded and it has a single frame.
	pub fn loaded_still_image(&self) -> bool {
		if let Some(desc) = self.dir.curr_descriptor() {
			if let Some(img) = self.texture_cache.get(&desc.request_id) {
				if img.fully_loaded && img.frames.len() == 1 {
					return true;
				}
			}
		}
		false
	}

	/// Fetches the contents of the folder and stores the list of image filenames to know which
	/// files will be the next and previous.
	///
	/// Tries to locate the image that was the current image before calling the function and
	/// keeping it current. If that filename is not found, than it tries to preserve the previous
	/// file index instead of the filename. If there is no such an index in the folder, it resets
	/// the index to 0 making the current file the first one in the folder.
	///
	/// Returns the error that might occure while fetching the files from the directory. Otherwise
	/// returns `Ok(())`
	pub fn update_directory(&mut self) -> directory::Result<()> {
		self.dir.update_directory()?;

		// indicate that the an update directory
		// call was made since those were created and they should all be
		// checked against the modification time of the file system file.
		for texture in self.texture_cache.values_mut() {
			texture.needs_update = true;
		}

		Ok(())
	}

	pub fn load_at_index(
		&mut self,
		display: &gelatin::Display,
		index: usize,
		frame_id: Option<isize>,
	) -> PathedTextureResult {
		let path = self
			.dir
			.image_by_index(index)
			.ok_or(PathResolutionError::WaitingOnDirFilter)?
			.path
			.clone();

		let result = self.load_specific(display, &path, frame_id);
		Ok((path, result))
	}

	/// Returns `Err(errors::Error::from_kind(errors::ErrorKind::WaitingOnLoader))`
	/// when the image
	pub fn load_specific(
		&mut self,
		display: &gelatin::Display,
		path: &Path,
		frame_id: Option<isize>,
	) -> TextureResult<AnimationFrameTexture> {
		trace!("Begin `load_specific`");
		self.receive_prefetched();
		trace!("Receive prefetched done");
		let target_file_name;
		let parent;
		if path.is_dir() {
			parent = path.to_owned();
			target_file_name = None;
		} else {
			let filename_and_parent = get_file_name_and_parent(path)?;
			target_file_name = Some(filename_and_parent.0);
			parent = filename_and_parent.1;
		}

		let prev_img_index = self.dir.curr_img_index();
		if let Some(target_file_name) = target_file_name {
			self.change_directory_with_filename(&parent, &target_file_name)?;
		} else {
			self.change_directory(&parent)?;
			self.current_frame_idx = 0;
		}
		if self.dir.path() != parent {
			let DirItem { path, request_id } = self.curr_dir_item().ok_or_else(|| {
				TextureError::Other("Could not get path for current image".into())
			})?;
			self.send_request_for_file(path, request_id, RequestKind::Priority { display });
			return Err(TextureError::WaitingOnLoader);
		}
		if let Some(img_index) = self.dir.curr_img_index() {
			self.dir.set_curr_img_index(img_index)?;
		}
		let requested_frame_id = match frame_id {
			Some(frame_id) => frame_id,
			None => {
				let mut retval = 0;
				if let Some(prev_img_index) = prev_img_index {
					if let Some(curr_img_index) = self.dir.curr_img_index() {
						if curr_img_index == prev_img_index {
							retval = self.current_frame_idx as isize;
						}
					}
				}
				retval
			}
		};
		self.refresh_cache();
		self.try_getting_requested_image(display, requested_frame_id)
	}

	fn refresh_cache(&mut self) {
		trace!("Begin `refresh_cache`");
		if let Some(curr_index) = self.dir.curr_img_index() {
			let cache = mem::take(&mut self.texture_cache);

			// Delete all entries that are outside the range of files around the current file
			// allowed by the capacity.
			// Walk through our list of directory entries sorted by their distance from the current
			// file and in each step remove an entry from the cache until we reach the desired cache
			// size
			let mut sorted_files: Vec<_> = cache.into_iter().enumerate().collect();
			sorted_files
				.sort_unstable_by_key(|&(index, _)| (index as isize - curr_index as isize).abs());
			self.remaining_capacity = self.total_capacity;
			sorted_files.retain(|(_, (_, texture))| {
				// TODO consider retaining individual frames.
				let all_frames_size = get_anim_size_estimate(&texture.frames);

				if self.remaining_capacity > (all_frames_size + self.curr_est_size) {
					self.remaining_capacity -= all_frames_size;
					true
				} else {
					false
				}
			});

			self.texture_cache = sorted_files.into_iter().map(|(_, entry)| entry).collect();
		}
	}

	pub fn load_next(&mut self, display: &gelatin::Display) -> PathedTextureResult {
		self.load_jump(display, 1, 0)
	}
	pub fn load_prev(&mut self, display: &gelatin::Display) -> PathedTextureResult {
		self.load_jump(display, -1, 0)
	}

	pub fn load_jump(
		&mut self,
		display: &gelatin::Display,
		file_jump_count: i32,
		frame_jump_count: isize,
	) -> PathedTextureResult {
		if file_jump_count == 0 {
			// Here, it is possible that the current image was already
			// requested but not yet loaded.
			let target_frame = self.current_frame_idx as isize + frame_jump_count;
			let requested = self.try_getting_requested_image(display, target_frame);
			if let Some(path) = self.current_file_path() {
				return Ok((path, requested));
			} else {
				return Err(PathResolutionError::NotYetSpecified);
			}
		} else {
			self.current_frame_idx = 0;
		}

		let target_path;
		if file_jump_count.abs() == 1 {
			if file_jump_count > 0 {
				self.dir.jump_to_next();
			} else {
				self.dir.jump_to_prev();
			}
			target_path = self.dir.curr_descriptor().unwrap().path.clone();
		} else if let (Some(curr_index), Some(img_count)) =
			(self.dir.curr_img_index(), self.dir.image_count())
		{
			// rem_euclid calculates the least nonnegative remainder
			let target_index = (curr_index as isize + file_jump_count as isize)
				.rem_euclid(img_count as isize) as usize;

			target_path = self.dir.image_by_index(target_index).unwrap().path.clone();
		} else {
			log::info!("Folder is empty, no folder was open, or folder hasn't finished filtering when trying to jump to an image by index.");
			return Err(PathResolutionError::NotYetSpecified);
		}
		let result = self.load_specific(display, &target_path, None);
		Ok((target_path, result))
	}

	fn receive_prefetched(&mut self) {
		use std::sync::mpsc::TryRecvError;
		loop {
			match self.loader.try_recv_prefetched() {
				Ok(load_result) => {
					self.pending_requests.add_load_result(load_result);
				}
				Err(TryRecvError::Disconnected) => panic!("Channel disconnected unexpectidly."),
				Err(TryRecvError::Empty) => break,
			}
		}
	}

	pub fn process_prefetched(&mut self, display: &gelatin::Display) -> TextureResult<()> {
		self.receive_prefetched();
		let mut uploaded_one = false;
		let req_ids = self.pending_requests.get_all_ids();
		let mut retval = Ok(());
		for id in req_ids {
			if let Some(results) = self.pending_requests.take_results(id) {
				for result in results {
					match self.upload_to_texture(display, result) {
						Ok(_) => uploaded_one = true,
						// it's okay to ignore if the image falied to load here, this is just pre-fetch.
						// so we don't break the loop
						Err(e) => {
							retval = Err(e);
						}
					}
				}
			}

			// Clippy suggests an alternative that does not compile so we allow this case
			#[allow(clippy::question_mark)]
			if retval.is_err() {
				return retval;
			}
			if uploaded_one {
				break;
			}
		}
		Ok(())
	}

	/// This funciton will check if the image which we are at, is already avaialbe.
	///
	///
	///
	/// Negative frame numbers are allowed. So are larger-than-total-frame-count frame numbers.
	///
	/// This is because this function call will often happen when the animation is not fully loaded yet.
	/// So in order to minimize complexity of the functions calling this one, frame ids that are out of
	/// bounds are allowed and will be wraped around if needed within this function.
	fn try_getting_requested_image(
		&mut self,
		display: &gelatin::Display,
		frame_id: isize,
	) -> TextureResult<AnimationFrameTexture> {
		trace!("Begin `try_getting_requested_image` in `image_cache`");
		let DirItem { path, request_id: req_id } = self
			.curr_dir_item()
			.ok_or_else(|| TextureError::Other("Could not get path for current image".into()))?;

		// Check if it's among the prefetched, and upload it, if it is
		if let Some(results) = self.pending_requests.take_results(req_id) {
			for load_result in results {
				self.upload_to_texture(display, load_result)?;
			}
			// And just let the next blok deal with locating the appropriate frame.
		}

		// Check if it is inside the texture cache first
		if let Some(tex) = self.texture_cache.get(&req_id) {
			if tex.failed {
				return Err(TextureError::from_failed_request(req_id));
			}
			let modified = fs::metadata(&path).ok().and_then(|m| m.modified().ok());
			let mut get_from_cache = false;
			if let Some(curr_mod_time) = modified {
				if let Some(mod_time) = tex.mod_time {
					if mod_time == curr_mod_time {
						get_from_cache = true;
					}
				}
			} else {
				get_from_cache = true;
			}
			if get_from_cache {
				let count = tex.frames.len() as isize;
				if tex.fully_loaded || (frame_id >= 0 && frame_id < count) {
					let wrapped_id;
					if frame_id < 0 {
						wrapped_id = count + (frame_id % count);
					} else {
						wrapped_id = frame_id % count;
					}
					if let Some(frame) = tex.frames.get(wrapped_id as usize) {
						self.current_frame_idx = wrapped_id as usize;
						return Ok(frame.clone());
					}
				}
			}
			return Err(TextureError::WaitingOnLoader);
		}
		if self.pending_requests.contains(&req_id) {
			PRIORITY_REQUEST_ID.store(req_id, Ordering::SeqCst);
			return Err(TextureError::WaitingOnLoader);
		}
		self.send_request_for_file(path, req_id, RequestKind::Priority { display });
		// If the texture is not in the cache just throw our hands in the air
		// and tell the caller that we gotta wait for the loader to load this texture.
		Err(TextureError::WaitingOnLoader)
	}

	fn upload_to_texture(
		&mut self,
		display: &gelatin::Display,
		load_result: LoadResult,
	) -> TextureResult<Option<AnimationFrameTexture>> {
		use std::collections::btree_map::Entry;
		match load_result {
			LoadResult::Start { req_id, metadata } => {
				let curr_mod_time = metadata.modified().ok();
				if let Some(cancelled) = self.pending_requests.cancelled(&req_id) {
					if cancelled {
						return Ok(None);
					}
				} else {
					return Ok(None);
				}
				match self.texture_cache.entry(req_id) {
					Entry::Vacant(entry) => {
						entry.insert(CachedTexture {
							_req_id: req_id,
							needs_update: false,
							fully_loaded: false,
							mod_time: curr_mod_time,
							failed: false,
							frames: Vec::new(),
						});
					}
					Entry::Occupied(mut entry) => {
						let mut overwrite = true;
						if let Some(curr_mod_time) = curr_mod_time {
							let cached = entry.get();
							if let Some(existing_mod_time) = cached.mod_time {
								if existing_mod_time == curr_mod_time {
									overwrite = false;
								}
							}
						}
						if overwrite {
							let old_size_estimate = get_anim_size_estimate(&entry.get().frames);
							self.remaining_capacity += old_size_estimate;
							let mut_entry = entry.get_mut();
							mut_entry.frames.clear();
							mut_entry.mod_time = curr_mod_time;
						}
					}
				}
				Ok(None)
			}
			LoadResult::Frame { req_id, image, delay_nano, orientation } => {
				if let Some(cancelled) = self.pending_requests.cancelled(&req_id) {
					if cancelled {
						return Ok(None);
					}
				} else {
					return Ok(None);
				}
				let size_estimate = get_image_size_estimate(image.width(), image.height());
				if let Some(entry) = self.texture_cache.get_mut(&req_id) {
					let anim_frame =
						AnimationFrameTexture::from_image(display, image, delay_nano, orientation)?;
					entry.frames.push(anim_frame.clone());
					self.remaining_capacity -= size_estimate;
					return Ok(Some(anim_frame));
				}
				Ok(None)
			}
			LoadResult::Done { req_id } => {
				if let Some(tex) = self.texture_cache.get_mut(&req_id) {
					tex.fully_loaded = true;
				}
				let _ = PRIORITY_REQUEST_ID.compare_exchange(
					req_id,
					NON_EXISTENT_REQUEST_ID,
					Ordering::SeqCst,
					Ordering::SeqCst,
				);
				self.pending_requests.set_finished(&req_id);
				Ok(None)
			}
			LoadResult::Failed { req_id } => {
				if let Some(tex) = self.texture_cache.get_mut(&req_id) {
					tex.fully_loaded = true;
					tex.failed = true;
				}
				let _ = PRIORITY_REQUEST_ID.compare_exchange(
					req_id,
					NON_EXISTENT_REQUEST_ID,
					Ordering::SeqCst,
					Ordering::SeqCst,
				);
				self.pending_requests.set_finished(&req_id);
				Err(TextureError::from_failed_request(req_id))
			}
		}
	}

	pub fn prefetch_neighbors(&mut self) {
		if let Some(mut index) = self.dir.curr_img_index() {
			// Send enough load requests so that the estimated total will just fill the cache
			let mut estimated_remaining_cap = self.remaining_capacity;

			while estimated_remaining_cap > self.curr_est_size {
				// Send a load request for the closest file not in the cache or outdated
				index += 1;
				if self.prefetch_at_index(index) {
					estimated_remaining_cap -= self.curr_est_size;
				} else {
					break;
				}
			}
		}
	}

	pub fn prefetch_at_index(&mut self, index: usize) -> bool {
		if self.remaining_capacity > self.curr_est_size {
			let params =
				self.dir.image_by_index(index).map(|desc| (desc.path.clone(), desc.request_id));
			if let Some((path, req_id)) = params {
				return self.send_request_for_file(path, req_id, RequestKind::NonPriority);
			} else {
				return false;
			}
		}
		false
	}

	/// This is almost identical to `prefetch_at_index` but this function
	/// does not check the `remaining_capacity`.
	fn send_request_for_file(
		&mut self,
		file_path: PathBuf,
		req_id: u32,
		kind: RequestKind,
	) -> bool {
		if let RequestKind::Priority { display } = kind {
			if self.pending_requests.len() >= Self::MAX_PENDING_REQUESTS {
				if let Err(e) = self.process_prefetched(display) {
					eprintln!("Error while processing prefetched images:\n{}", e);
				}
			}
		}
		if self.pending_requests.len() >= Self::MAX_PENDING_REQUESTS {
			return false;
		}
		let mut cache_enty_invalid = false;
		if let Some(texture) = self.texture_cache.get_mut(&req_id) {
			if !texture.needs_update {
				return false;
			} else {
				texture.needs_update = false;
				if let Some(existing_mod_time) = texture.mod_time {
					let new_mod_time =
						fs::metadata(&file_path).ok().and_then(|m| m.modified().ok());
					if let Some(new_mod_time) = new_mod_time {
						if new_mod_time == existing_mod_time {
							return false;
						} else {
							cache_enty_invalid = true;
						}
					}
				}
			}
		}
		if cache_enty_invalid {
			self.texture_cache.remove(&req_id);
		}
		if kind.priority() {
			PRIORITY_REQUEST_ID.store(req_id, Ordering::SeqCst);
		}
		if self.pending_requests.contains(&req_id) {
			return false;
		}
		let request = LoadRequest { req_id, path: file_path };
		self.pending_requests.add_request(request.clone());
		self.loader.send_load_request(request);
		true
	}

	fn change_directory(&mut self, dir_path: &Path) -> directory::Result<()> {
		if self.dir.path() == dir_path {
			return Ok(());
		}
		self.texture_cache.clear();
		self.remaining_capacity = self.total_capacity;

		// Cancel all pending load requests
		for (_, request) in self.pending_requests.iter_mut() {
			request.cancel();
		}

		self.dir.change_directory(dir_path)?;
		Ok(())
	}

	fn change_directory_with_filename(
		&mut self,
		dir_path: &Path,
		filename: &OsStr,
	) -> directory::Result<()> {
		self.dir.change_directory_with_filename(dir_path, filename)
	}

	// fn collect_directory(&mut self) -> Result<Vec<DirItem>> {
	// 	let start = std::time::Instant::now();
	// 	let mut dir_files: Vec<_> = fs::read_dir(&self.dir.path)?
	// 		.filter_map(|x| match x {
	// 			Ok(entry) => match entry.file_type() {
	// 				Ok(file_type) => {
	// 					if file_type.is_file() || file_type.is_symlink() {
	// 						if is_file_supported(entry.path().as_path()) {
	// 							self.current_req_id += 1;
	// 							Some(DirItem { dir_entry: entry, request_id: self.current_req_id })
	// 						} else {
	// 							None
	// 						}
	// 					} else {
	// 						None
	// 					}
	// 				}
	// 				Err(_) => None,
	// 			},
	// 			Err(_) => None,
	// 		})
	// 		.collect();

	// 	let total_time = start.elapsed();
	// 	println!("Collected directory in: {} ms", total_time.as_millis());
	// 	dir_files.sort_unstable_by(|a, b| {
	// 		lexical_sort::natural_lexical_cmp(
	// 			&a.dir_entry.file_name().to_string_lossy(),
	// 			&b.dir_entry.file_name().to_string_lossy(),
	// 		)
	// 	});

	// 	Ok(dir_files)
	// }
}

fn get_file_name_and_parent(path: &Path) -> std::io::Result<(OsString, PathBuf)> {
	use std::io;

	let file_name = match path.file_name() {
		Some(f) => f.to_owned(),
		None => {
			return Err(io::Error::new(
				io::ErrorKind::Other,
				format!("Could not get file name from path {:?}", path),
			))
		}
	};
	let parent = match path.parent() {
		Some(p) => {
			if p == Path::new("") {
				Path::new(".").canonicalize()?
			} else {
				p.canonicalize()?
			}
		}
		None => {
			let mut path = path.canonicalize()?;
			if !path.pop() {
				return Err(io::Error::new(
					io::ErrorKind::Other,
					format!("Could not get parent directory of {:?}", path),
				));
			}
			path
		}
	};

	Ok((file_name, parent))
}