use std::{borrow::Cow, io::stdout, num::NonZeroUsize};

use crossterm::{
	event::{Event, KeyCode, KeyModifiers, MouseEventKind},
	execute,
	terminal::{
		BeginSynchronizedUpdate, EnterAlternateScreen, LeaveAlternateScreen, disable_raw_mode,
		enable_raw_mode
	}
};
use kittage::display::DisplayLocation;
use nix::{
	sys::signal::{Signal::SIGSTOP, kill},
	unistd::Pid
};
use ratatui::{
	Frame,
	layout::{Constraint, Flex, Layout, Position, Rect},
	prelude::{Line, Text},
	style::{Color, Style},
	symbols::border,
	text::Span,
	widgets::{Block, Borders, Clear, Padding, Paragraph, Wrap}
};
use ratatui_image::{FontSize, Image};

use crate::{
	FitOrFill,
	converter::{ConvertedImage, MaybeTransferred},
	kitty::{KittyDisplay, KittyReadyToDisplay},
	renderer::{RenderError, fill_default},
	skip::Skip
};

pub struct Tui {
	name: String,
	pub page: usize,
	last_render: LastRender,
	bottom_msg: BottomMessage,
	// we use `prev_msg` to, for example, restore the 'search results' message on the bottom after
	// jumping to a specific page
	prev_msg: Option<BottomMessage>,
	rendered: Vec<RenderedInfo>,
	page_constraints: PageConstraints,
	showing_help_msg: bool,
	is_kitty: bool,
	zoom: Option<Zoom>
}

#[derive(Default)]
struct LastRender {
	// Used as a way to track if we need to draw the images, to save ratatui from doing a lot of
	// diffing work
	rect: Rect,
	pages_shown: usize,
	unused_width: u16
}

#[derive(Default)]
pub enum BottomMessage {
	#[default]
	Help,
	SearchResults(String),
	Error(String),
	Input(InputCommand),
	Reloaded
}

pub enum InputCommand {
	GoToPage(usize),
	Search(String)
}

struct PageConstraints {
	max_wide: Option<NonZeroUsize>,
	r_to_l: bool
}

#[derive(Default, Debug)]
struct Zoom {
	// just how much 'zoom' you have. 0 means it fills the screen (instead of fits), such
	// that one axis is fully on-screen
	level: i16,
	// how many terminal-cells worth of content overflow the left side of the screen (and are thus
	// not displayed)
	cell_pan_from_left: u16,
	// how many terminal-cells worth of content overflow the top side of the screen (and are thus
	// not displayed)
	cell_pan_from_top: u16
}
impl Zoom {
	/// Returns the zoom factor, where 1 is the default and means fill-screen
	fn factor(&self) -> f32 {
		// TODO: Make these configurable once we have a good way to set options after startup
		const ZOOM_RATE: f32 = 1.1;
		const ZOOM_RATE_GRANULAR: f32 = 1.05;

		if self.level > 0 {
			ZOOM_RATE.powi(self.level.into())
		} else {
			// use a more granular zoom rate for the steps between fit-screen and fill-screen
			ZOOM_RATE_GRANULAR.powi(self.level.into())
		}
	}
}

// This seems like a kinda weird struct because it holds two optionals but any representation
// within it is valid; I think it's the best way to represent it
#[derive(Default)]
pub struct RenderedInfo {
	// The image, if it has been rendered by `Converter` to that struct
	img: Option<ConvertedImage>,
	// The number of results for the current search term that have been found on this page. None if
	// we haven't checked this page yet
	// Also this isn't the most efficient representation of this value, but it's accurate, so like
	// whatever I guess
	num_results: Option<usize>
}

#[derive(PartialEq)]
pub struct RenderLayout {
	pub page_area: Rect,
	pub top_and_bottom: Option<(Rect, Rect)>
}

impl Tui {
	#[must_use]
	pub fn new(name: String, max_wide: Option<NonZeroUsize>, r_to_l: bool, is_kitty: bool) -> Self {
		Self {
			name,
			page: 0,
			prev_msg: None,
			bottom_msg: BottomMessage::Help,
			last_render: LastRender::default(),
			rendered: vec![],
			page_constraints: PageConstraints { max_wide, r_to_l },
			showing_help_msg: false,
			is_kitty,
			zoom: None
		}
	}

	#[must_use]
	pub fn main_layout(frame: &Frame<'_>, fullscreened: bool) -> RenderLayout {
		if fullscreened {
			RenderLayout {
				page_area: frame.area(),
				top_and_bottom: None
			}
		} else {
			let layout = Layout::default()
				.constraints([
					Constraint::Length(3),
					Constraint::Fill(1),
					Constraint::Length(3)
				])
				.horizontal_margin(2)
				.vertical_margin(1)
				.split(frame.area());

			RenderLayout {
				page_area: layout[1],
				top_and_bottom: Some((layout[0], layout[2]))
			}
		}
	}

	fn render_zoomed<'s>(
		// area of the 'fit-screen' page
		mut img_area: Rect,
		font_size: FontSize,
		zoom: &mut Zoom,
		img: &'s mut MaybeTransferred,
		page_num: usize,
		img_cell_w: u16,
		img_cell_h: u16
	) -> KittyDisplay<'s> {
		log::debug!("zoom is {zoom:#?}");
		log::debug!("page area is {img_area:#?}");
		log::debug!("img dimensions are {img_cell_w}x{img_cell_h}");

		// Dimensions of the section of the image to be displayed.
		// Kittage calls this the "image area to display".
		// We need to shrink this or the page area in order to zoom in or out,
		// respectively.
		let mut img_section_w = f32::from(img_cell_w);
		let mut img_section_h = f32::from(img_cell_h);

		let zoom_factor = zoom.factor();

		if zoom_factor >= 1.0 {
			// Use a smaller section of the image. This efficively zooms into that section.
			img_section_w /= zoom_factor;
			img_section_h /= zoom_factor;
		} else {
			// Shrink the page area, such that the fill-screen conversion
			// will zoom out of the image.
			let initial_page_w = f32::from(img_area.width);
			let initial_page_h = f32::from(img_area.height);

			// how many pages the image is wide/high
			let img_page_w_ratio = img_section_w / initial_page_w;
			let img_page_h_ratio = img_section_h / initial_page_h;

			let shrink_move_page = |dim: &mut u16, pos: &mut u16, axis_zoom_factor: f32| {
				let old_dim = *dim;
				// The axis zoom factor tells us what portion of the axis
				// we need to show.
				*dim = (f32::from(*dim) * axis_zoom_factor) as u16;

				*pos += old_dim
					.checked_sub(*dim)
					.expect("zooming out should shrink the image")
					/ 2;
			};

			// TODO: Detect max zoom-out in zoom levels
			if img_page_w_ratio < img_page_h_ratio {
				// vertical scroll / tall image. zooming out means decreasing the width of the page area
				shrink_move_page(
					&mut img_area.width,
					&mut img_area.x,
					// disallow zooming out past fit-screen
					zoom_factor.max(1.0 / img_page_h_ratio)
				);
			} else {
				// horizontal scroll / wide image. zooming out means decreasing the width of the page area
				shrink_move_page(
					&mut img_area.height,
					&mut img_area.y,
					// disallow zooming out past fit-screen
					zoom_factor.max(1.0 / img_page_w_ratio)
				);
			}
		}
		log::debug!("after adjustment, page area is {img_area:#?}");

		// Crop the image such that in the end, the aspect ratio of the section
		// is the same as that of the page area. This effectively performs the
		// conversion to fill-screen.
		// Note that this only works because cell_w, cell_h is in fit-screen
		// format, i.e. the cell size and the page area already share at
		// least one dimension.
		{
			let page_area_w = f32::from(img_area.width);
			let page_area_h = f32::from(img_area.height);

			// how many pages the image is wide/high
			// Note that this is not the same as during the
			// zoom-out calculation, since it changed the page
			// dimensions.
			let img_page_w_ratio = img_section_w / page_area_w;
			let img_page_h_ratio = img_section_h / page_area_h;

			if img_page_w_ratio < img_page_h_ratio {
				img_section_h = page_area_h * img_page_w_ratio;
			} else {
				img_section_w = page_area_w * img_page_h_ratio;
			}
		}

		let width = (img_section_w * f32::from(font_size.0)) as u32;
		let height = (img_section_h * f32::from(font_size.1)) as u32;

		zoom.cell_pan_from_left = zoom
			.cell_pan_from_left
			.min(img_cell_w.saturating_sub(img_section_w.ceil() as u16));
		zoom.cell_pan_from_top = zoom
			.cell_pan_from_top
			.min(img_cell_h.saturating_sub(img_section_h.ceil() as u16));

		KittyDisplay::DisplayImages(vec![KittyReadyToDisplay {
			img,
			page_num,
			pos: Position {
				x: img_area.x,
				y: img_area.y
			},
			display_loc: DisplayLocation {
				x: u32::from(zoom.cell_pan_from_left) * u32::from(font_size.0),
				y: u32::from(zoom.cell_pan_from_top) * u32::from(font_size.1),
				width,
				height,
				columns: img_area.width,
				rows: img_area.height,
				..DisplayLocation::default()
			}
		}])
	}

	// TODO: Make a way to fill the width of the screen with one page and scroll down to view it
	#[must_use]
	pub fn render<'s>(
		&'s mut self,
		frame: &mut Frame<'_>,
		full_layout: &RenderLayout,
		font_size: FontSize
	) -> KittyDisplay<'s> {
		if self.showing_help_msg {
			self.render_help_msg(frame);
			return KittyDisplay::ClearImages;
		}

		if let Some(t_and_b) = full_layout.top_and_bottom {
			Self::render_top_and_bottom(
				t_and_b,
				self.page,
				&self.rendered,
				&self.name,
				frame,
				&self.bottom_msg
			);
		}

		let mut img_area = full_layout.page_area;

		let size = frame.area();
		if size == self.last_render.rect {
			// If we haven't resized (and haven't used the Rect as a way to mark that we need to
			// resize this time), then go through every element in the buffer where any Image would
			// be written and set to skip it so that ratatui doesn't spend a lot of time diffing it
			// each re-render
			frame.render_widget(Skip::new(true), img_area);
			return KittyDisplay::NoChange;
		}

		if let Some(ref mut zoom) = self.zoom {
			// yes this is ugly and I hate it. it's due to the limitations that currently exist
			// in the borrow checker. Once `-Zpolonius=next` is stabilized, we can rework this
			// to look like what we expect.
			// See https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md#problem-case-3-conditional-control-flow-across-functions
			// You can also rewrite this to just if an `if let` and run it under
			// `RUSTFLAGS="-Zpolonius=next"` and see that it works
			if self.rendered[self.page]
				.img
				.as_ref()
				.is_some_and(|c| matches!(c, ConvertedImage::Kitty { .. }))
			{
				let Some(ConvertedImage::Kitty {
					ref mut img,
					cell_w,
					cell_h
				}) = self.rendered[self.page].img
				else {
					unreachable!()
				};

				self.last_render = LastRender {
					rect: size,
					pages_shown: 1,
					unused_width: 0
				};
				return Self::render_zoomed(
					img_area, font_size, zoom, img, self.page, cell_w, cell_h
				);
			}
		}

		// here we calculate how many pages can fit in the available area.
		let mut test_area_w = img_area.width;
		// go through our pages, starting at the first one we want to view
		let mut page_sizes = self.rendered[self.page..]
			.iter_mut()
			// and get this to represent a count of how many we're looking at so far to render
			.enumerate()
			// and only take as many as are ready to be rendered
			.take_while(|(idx, page)| {
				let mut take = page.img.is_some();
				if let Some(max) = self.page_constraints.max_wide {
					take &= *idx < max.get();
				}
				take
			})
			// and map it to their width (in cells on the terminal, not pixels)
			.filter_map(|(_, page)| {
				page.img.as_mut().map(|img| {
					let (w, h) = img.w_h();
					(w, h, img)
				})
			})
			// and then take them as long as they won't overflow the available area.
			.take_while(|(width, _, _)| match test_area_w.checked_sub(*width) {
				Some(new_val) => {
					test_area_w = new_val;
					true
				}
				None => false
			})
			.collect::<Vec<_>>();

		if self.page_constraints.r_to_l {
			page_sizes.reverse();
		}

		if page_sizes.is_empty() {
			// If none are ready to render, just show the loading thing
			Self::render_loading_in(frame, img_area);
			KittyDisplay::ClearImages
		} else {
			execute!(stdout(), BeginSynchronizedUpdate).unwrap();

			let total_width = page_sizes.iter().map(|(w, _, _)| w).sum::<u16>();

			self.last_render.pages_shown = page_sizes.len();

			let unused_width = img_area.width - total_width;
			self.last_render.unused_width = unused_width;
			img_area.x += unused_width / 2;

			if let Some(total_height) = page_sizes.iter().map(|(_, h, _)| h).max() {
				// This subtraction might sporadicly fail while shrinking the window.
				if let Some(unused_height) = img_area.height.checked_sub(*total_height) {
					img_area.y += unused_height / 2;
				}
			}

			let to_display = page_sizes
				.into_iter()
				.enumerate()
				.filter_map(|(idx, (width, _, img))| {
					let maybe_img =
						Self::render_single_page(frame, img, Rect { width, ..img_area });
					img_area.x += width;
					maybe_img.map(|(img, pos)| KittyReadyToDisplay {
						img,
						page_num: idx + self.page,
						pos,
						display_loc: DisplayLocation::default()
					})
				})
				.collect::<Vec<_>>();

			// we want to set this at the very end so it doesn't get set somewhere halfway through and
			// then the whole diffing thing messes it up
			self.last_render.rect = size;

			KittyDisplay::DisplayImages(to_display)
		}
	}

	fn render_single_page<'img>(
		frame: &mut Frame<'_>,
		page_img: &'img mut ConvertedImage,
		img_area: Rect
	) -> Option<(&'img mut MaybeTransferred, Position)> {
		match page_img {
			ConvertedImage::Generic(page_img) => {
				frame.render_widget(Image::new(page_img), img_area);
				None
			}
			ConvertedImage::Kitty {
				img,
				cell_h: _,
				cell_w: _
			} => Some((img, Position {
				x: img_area.x,
				y: img_area.y
			}))
		}
	}

	fn render_loading_in(frame: &mut Frame<'_>, area: Rect) {
		const LOADING_STR: &str = "Loading...";
		let inner_space =
			Layout::horizontal([Constraint::Length(const { LOADING_STR.len() as u16 })])
				.flex(Flex::Center)
				.split(area);

		let loading_span = Span::styled(LOADING_STR, Style::new().fg(Color::Cyan));

		frame.render_widget(loading_span, inner_space[0]);
	}

	fn change_page(&mut self, mut change: PageChange, amt: ChangeAmount) -> Option<InputAction> {
		let diff = match amt {
			ChangeAmount::Single => 1,
			ChangeAmount::WholeScreen => self.last_render.pages_shown
		};

		// This is a kinda weird way to switch around the controls for this sort of thing but it
		// allows it to be pretty centralized and avoids annoyingly duplicated match arms (since
		// we'd have to do `match key { 'h' if r_to_l | 'l' => {}}` and that doesn't play well with
		// `if` guards on match arms)
		if self.page_constraints.r_to_l {
			change = match change {
				PageChange::Next => PageChange::Prev,
				PageChange::Prev => PageChange::Next
			};
		}

		let old = self.page;
		match change {
			PageChange::Next =>
				self.set_page((self.page + diff).min(self.rendered.len().saturating_sub(1))),
			PageChange::Prev => self.set_page(self.page.saturating_sub(diff))
		}

		// Yes these conversions could wrap around if you have > isize::MAX pages, but we already
		// decided that you deserve to suffer if you have more than u32::MAX pages, so that's fine.
		match self.page as isize - old as isize {
			0 => None,
			_ => Some(InputAction::JumpingToPage(self.page))
		}
	}

	pub fn set_n_pages(&mut self, n_pages: usize) {
		fill_default(&mut self.rendered, n_pages);
		self.page = self.page.min(n_pages - 1);
	}

	pub fn page_ready(&mut self, img: ConvertedImage, page_num: usize, num_results: usize) {
		// If this new image woulda fit within the available space on the last render AND it's
		// within the range where it might've been rendered with the last shown pages, then reset
		// the last rect marker so that all images are forced to redraw on next render and this one
		// is drawn with them
		if page_num >= self.page && page_num <= self.page + self.last_render.pages_shown {
			self.last_render.rect = Rect::default();
		} else {
			let img_w = img.w_h().0;
			if img_w <= self.last_render.unused_width {
				let num_fit = self.last_render.unused_width / img_w;
				if page_num >= self.page && (self.page + num_fit as usize) >= page_num {
					self.last_render.rect = Rect::default();
				}
			}
		}

		// We always just set this here because we handle reloading in the `set_n_pages` function.
		// If the document was reloaded, then It'll have the `set_n_pages` called to set the new
		// number of pages, so the vec will already be cleared
		self.rendered[page_num] = RenderedInfo {
			img: Some(img),
			num_results: Some(num_results)
		};
	}

	pub fn page_failed_display(&mut self, page_num: usize) {
		self.rendered[page_num].img = None;
	}

	pub fn got_num_results_on_page(&mut self, page_num: usize, num_results: usize) {
		self.rendered[page_num].num_results = Some(num_results);
	}

	pub fn render_top_and_bottom(
		(top_area, bottom_area): (Rect, Rect),
		page_num: usize,
		rendered: &[RenderedInfo],
		doc_name: &str,
		frame: &mut Frame<'_>,
		bottom_msg: &BottomMessage
	) {
		// use the extra space here to add some padding to the right side
		let page_nums_text = format!("{} / {} ", page_num + 1, rendered.len());

		let top_block = Block::new()
			// use this first title to add a bit of padding to the left side
			.title_top(" ")
			.title_top(Span::styled(doc_name, Style::new().fg(Color::Cyan)))
			.title_top(
				Span::styled(&page_nums_text, Style::new().fg(Color::Cyan))
					.into_right_aligned_line()
			)
			.padding(Padding {
				bottom: 1,
				..Padding::default()
			})
			.borders(Borders::BOTTOM);

		frame.render_widget(top_block, top_area);

		let bottom_block = Block::new()
			.padding(Padding {
				top: 1,
				right: 2,
				left: 2,
				bottom: 0
			})
			.borders(Borders::TOP);
		let bottom_inside_block = bottom_block.inner(bottom_area);

		frame.render_widget(bottom_block, bottom_area);

		let rendered_str = if !rendered.is_empty() {
			format!(
				"Rendered: {}%",
				(rendered.iter().filter(|i| i.img.is_some()).count() * 100) / rendered.len()
			)
		} else {
			String::new()
		};
		let bottom_layout = Layout::horizontal([
			Constraint::Fill(1),
			Constraint::Length(rendered_str.len() as u16)
		])
		.split(bottom_inside_block);

		let rendered_span = Span::styled(&rendered_str, Style::new().fg(Color::Cyan));
		frame.render_widget(rendered_span, bottom_layout[1]);

		let (msg_str, color): (Cow<'_, str>, _) = match bottom_msg {
			BottomMessage::Help => ("?: Show help page".into(), Color::Blue),
			BottomMessage::Error(e) => (e.as_str().into(), Color::Red),
			BottomMessage::Input(input_state) => (
				match input_state {
					InputCommand::GoToPage(page) => format!("Go to: {page}"),
					InputCommand::Search(s) => format!("Search: {s}")
				}
				.into(),
				Color::Blue
			),
			BottomMessage::SearchResults(term) => {
				let num_found = rendered.iter().filter_map(|r| r.num_results).sum::<usize>();
				let num_searched =
					rendered.iter().filter(|r| r.num_results.is_some()).count() * 100;
				(
					format!(
						"Results for '{term}': {num_found} (searched: {}%)",
						num_searched / rendered.len()
					)
					.into(),
					Color::Blue
				)
			}
			BottomMessage::Reloaded => ("Document was reloaded!".into(), Color::Blue)
		};

		let span = Span::styled(msg_str, Style::new().fg(color));
		frame.render_widget(span, bottom_layout[0]);
	}

	pub fn handle_event(&mut self, ev: &Event) -> Option<InputAction> {
		fn jump_to_page(page: &mut usize, rect: &mut Rect, new_page: usize) -> InputAction {
			*page = new_page;
			// Make sure we re-render
			*rect = Rect::default();
			InputAction::JumpingToPage(new_page)
		}

		match ev {
			Event::Key(key) => {
				match key.code {
					KeyCode::Char(c) => {
						// TODO: refactor back to `if let` arm guards when those are stabilized
						if let BottomMessage::Input(InputCommand::Search(ref mut term)) =
							self.bottom_msg
						{
							term.push(c);
							return Some(InputAction::Redraw);
						}

						if let BottomMessage::Input(InputCommand::GoToPage(ref mut page)) =
							self.bottom_msg
						{
							if c == 'g' && self.is_kitty {
								self.update_zoom(|z| z.cell_pan_from_top = 0);
								self.set_msg(MessageSetting::Pop);
								return Some(InputAction::Redraw);
							}

							return c.to_digit(10).map(|input_num| {
								*page = (*page * 10) + input_num as usize;
								InputAction::Redraw
							});
						}

						match c {
							'l' => self.change_page(PageChange::Next, ChangeAmount::Single),
							'j' => self.change_page(PageChange::Next, ChangeAmount::WholeScreen),
							'h' => self.change_page(PageChange::Prev, ChangeAmount::Single),
							'k' => self.change_page(PageChange::Prev, ChangeAmount::WholeScreen),
							'q' => Some(InputAction::QuitApp),
							'g' => {
								self.set_msg(MessageSetting::Some(BottomMessage::Input(
									InputCommand::GoToPage(0)
								)));
								Some(InputAction::Redraw)
							}
							'/' => {
								self.set_msg(MessageSetting::Some(BottomMessage::Input(
									InputCommand::Search(String::new())
								)));
								Some(InputAction::Redraw)
							}
							'i' => Some(InputAction::Invert),
							'?' => {
								self.showing_help_msg = true;
								Some(InputAction::Redraw)
							}
							'f' => Some(InputAction::Fullscreen),
							'n' if self.page < self.rendered.len() - 1 => {
								// TODO: If we can't find one, then maybe like block until we've verified
								// all the pages have been checked?
								self.rendered[(self.page + 1)..]
									.iter()
									.enumerate()
									.find_map(|(idx, p)| {
										p.num_results
											.is_some_and(|num| num > 0)
											.then_some(self.page + 1 + idx)
									})
									.map(|next_page| {
										jump_to_page(
											&mut self.page,
											&mut self.last_render.rect,
											next_page
										)
									})
							}
							'N' if self.page > 0 => self.rendered[..(self.page)]
								.iter()
								.rev()
								.enumerate()
								.find_map(|(idx, p)| {
									p.num_results
										.is_some_and(|num| num > 0)
										.then_some(self.page - (idx + 1))
								})
								.map(|prev_page| {
									jump_to_page(
										&mut self.page,
										&mut self.last_render.rect,
										prev_page
									)
								}),
							'z' if key.modifiers.contains(KeyModifiers::CONTROL) => {
								// [todo] better error handling here?

								let mut backend = stdout();
								execute!(
									&mut backend,
									LeaveAlternateScreen,
									crossterm::cursor::Show,
									crossterm::event::DisableMouseCapture
								)
								.unwrap();
								disable_raw_mode().unwrap();

								// This process will hang after the SIGSTOP call until we get
								// foregrounded again by something else, at which point we need to
								// re-setup everything so that it all gets drawn again.
								kill(Pid::this(), SIGSTOP).unwrap();

								enable_raw_mode().unwrap();
								execute!(
									&mut backend,
									EnterAlternateScreen,
									crossterm::cursor::Hide,
									crossterm::event::EnableMouseCapture
								)
								.unwrap();

								self.last_render.rect = Rect::default();
								Some(InputAction::Redraw)
							}
							'z' if self.is_kitty => {
								let (zoom, f_or_f) = match self.zoom {
									None => (Some(Zoom::default()), FitOrFill::Fill),
									Some(_) => (None, FitOrFill::Fit)
								};
								self.zoom = zoom;
								self.last_render.rect = Rect::default();
								Some(InputAction::SwitchRenderZoom(f_or_f))
							}
							'o' if self.is_kitty =>
								self.update_zoom(|z| z.level = z.level.saturating_add(1)),
							'O' if self.is_kitty =>
								self.update_zoom(|z| z.level = z.level.saturating_sub(1)),
							'L' if self.is_kitty => self.update_zoom(|z| {
								z.cell_pan_from_left = z.cell_pan_from_left.saturating_add(1);
							}),
							'H' if self.is_kitty => self.update_zoom(|z| {
								z.cell_pan_from_left = z.cell_pan_from_left.saturating_sub(1);
							}),
							'J' if self.is_kitty => self.update_zoom(|z| {
								z.cell_pan_from_top = z.cell_pan_from_top.saturating_add(1);
							}),
							'K' if self.is_kitty => self.update_zoom(|z| {
								z.cell_pan_from_top = z.cell_pan_from_top.saturating_sub(1);
							}),
							'G' if self.is_kitty =>
								self.update_zoom(|z| z.cell_pan_from_top = u16::MAX),
							_ => None
						}
					}
					KeyCode::Backspace => {
						if let BottomMessage::Input(InputCommand::Search(ref mut term)) =
							self.bottom_msg
						{
							term.pop();
							return Some(InputAction::Redraw);
						}
						None
					}
					KeyCode::Right => self.change_page(PageChange::Next, ChangeAmount::Single),
					KeyCode::Down | KeyCode::PageDown =>
						self.change_page(PageChange::Next, ChangeAmount::WholeScreen),
					KeyCode::Left => self.change_page(PageChange::Prev, ChangeAmount::Single),
					KeyCode::Up | KeyCode::PageUp =>
						self.change_page(PageChange::Prev, ChangeAmount::WholeScreen),
					KeyCode::Esc => match (self.showing_help_msg, &self.bottom_msg) {
						(false, BottomMessage::Help) => Some(InputAction::QuitApp),
						_ => {
							// When we hit escape, we just want to pop off the current message and
							// show the underlying one.
							self.set_msg(MessageSetting::Pop);
							Some(InputAction::Redraw)
						}
					},
					KeyCode::Enter => {
						let mut default = BottomMessage::default();
						std::mem::swap(&mut self.bottom_msg, &mut default);
						let BottomMessage::Input(ref cmd) = default else {
							std::mem::swap(&mut self.bottom_msg, &mut default);
							return None;
						};

						match cmd {
							// Only forward the command if it's within range
							InputCommand::GoToPage(page) => {
								// We need to subtract 1 b/c they're tracked internally as
								// 0-indexed but input and displayed as 1-indexed
								let zero_page = page.saturating_sub(1);
								let rendered_len = self.rendered.len();

								if zero_page < rendered_len {
									self.set_page(zero_page);
									Some(InputAction::JumpingToPage(zero_page))
								} else {
									self.set_msg(MessageSetting::Some(BottomMessage::Error(
										format!(
											"Cannot jump to page {page}; there are only {rendered_len} pages in the document"
										)
									)));
									Some(InputAction::Redraw)
								}
							}
							InputCommand::Search(term) => {
								let term = term.clone();

								// We only want to show search results if there would actually be
								// data to show
								if !term.is_empty() {
									self.set_msg(MessageSetting::Some(
										BottomMessage::SearchResults(term.clone())
									));
								} else {
									// else, if it's not empty, we just want to reset the bottom
									// area to show the default data; we don't want it to like show
									// the data from a previous search
									self.set_msg(MessageSetting::Reset);
								}

								// Reset all the search results
								for img in &mut self.rendered {
									img.num_results = None;
								}
								// but we still want to tell the rest of the system that we set the
								// search term to '' so that they can re-render the pages wthout
								// the highlighting
								Some(InputAction::Search(term))
							}
						}
					}
					_ => None
				}
			}
			Event::Mouse(mouse) => {
				if mouse.modifiers.contains(KeyModifiers::CONTROL)
					&& self.is_kitty
					&& self.zoom.is_some()
				{
					match mouse.kind {
						MouseEventKind::ScrollUp =>
							self.update_zoom(|z| z.level = z.level.saturating_add(1).min(0)),
						MouseEventKind::ScrollDown =>
							self.update_zoom(|z| z.level = z.level.saturating_sub(1)),
						_ => None
					}
				} else {
					match mouse.kind {
						MouseEventKind::ScrollRight =>
							self.change_page(PageChange::Next, ChangeAmount::Single),
						MouseEventKind::ScrollDown =>
							self.change_page(PageChange::Next, ChangeAmount::WholeScreen),
						MouseEventKind::ScrollLeft =>
							self.change_page(PageChange::Prev, ChangeAmount::Single),
						MouseEventKind::ScrollUp =>
							self.change_page(PageChange::Prev, ChangeAmount::WholeScreen),
						_ => None
					}
				}
			}
			Event::Resize(_, _) => Some(InputAction::Redraw),
			_ => None
		}
	}

	// I want this to always return an option 'cause I just use it to return from `Self::handle_event`
	#[expect(clippy::unnecessary_wraps)]
	fn update_zoom(&mut self, f: impl FnOnce(&mut Zoom)) -> Option<InputAction> {
		if let Some(z) = &mut self.zoom {
			f(z);
		}
		self.last_render.rect = Rect::default();
		Some(InputAction::Redraw)
	}

	pub fn show_error(&mut self, err: RenderError) {
		self.set_msg(MessageSetting::Some(BottomMessage::Error(match err {
			RenderError::Notify(e) => format!("Auto-reload failed: {e}"),
			RenderError::Doc(e) => format!("Couldn't process document: {e}"),
			RenderError::Converting(e) => format!("Couldn't convert page after rendering: {e}")
		})));
	}

	fn set_page(&mut self, page: usize) {
		if page != self.page {
			// mark that we need to re-render the images
			self.last_render.rect = Rect::default();
			self.page = page;
		}
	}

	// We have `msg` as optional so that if they reset it to none, it'll replace it with
	// `prev_msg`, but if they reset it to something else, it'll put the current thing in prev_msg
	pub fn set_msg(&mut self, msg: MessageSetting) {
		match msg {
			MessageSetting::Some(mut msg) => {
				std::mem::swap(&mut self.bottom_msg, &mut msg);
				self.prev_msg = Some(msg);
			}
			MessageSetting::Default => self.set_msg(MessageSetting::Some(BottomMessage::default())),
			MessageSetting::Reset => {
				self.prev_msg = None;
				self.bottom_msg = BottomMessage::default();
			}
			MessageSetting::Pop =>
				if self.showing_help_msg {
					self.last_render.rect = Rect::default();
					self.showing_help_msg = false;
				} else {
					self.bottom_msg = self.prev_msg.take().unwrap_or_default();
				},
		}
	}

	pub fn render_help_msg(&self, frame: &mut Frame<'_>) {
		let frame_area = frame.area();
		frame.render_widget(Clear, frame_area);

		let block = Block::new()
			.title("Help")
			.padding(Padding::proportional(1))
			.borders(Borders::ALL)
			.border_set(border::ROUNDED)
			.border_style(Color::Blue);

		let help_sections = [
			Text::from(HELP_PAGE),
			// just some spacing
			Text::from(""),
			if self.is_kitty {
				Text::from(KITTY_HELP)
			} else {
				Text::from("Not using kitty, kitty-specific keybindings hidden")
					.style(Color::DarkGray)
			}
		];

		let max_w: u16 = help_sections
			.iter()
			.flat_map(|section| section.lines.as_slice())
			// We don't really need full unicode-width since we're using all ascii for the help
			// pages, but this is the function they give us.
			.map(Line::width)
			.max()
			.unwrap_or_default()
			.try_into()
			.expect("Every help text line must be shorter than u16::MAX");

		let layout = Layout::horizontal([
			Constraint::Fill(1),
			Constraint::Length(max_w + 6),
			Constraint::Fill(1)
		])
		.split(frame_area);

		let block_area = Layout::vertical([
			Constraint::Fill(1),
			Constraint::Length(
				u16::try_from(help_sections.iter().map(|s| s.lines.len()).sum::<usize>()).unwrap()
					+ 4
			),
			Constraint::Fill(1)
		])
		.split(layout[1]);

		let mut block_inner = block.inner(block_area[1]);

		frame.render_widget(block, block_area[1]);

		for section in help_sections {
			let section_lines = section.lines.len();
			let span = Paragraph::new(section).wrap(Wrap { trim: false });
			frame.render_widget(span, block_inner);
			block_inner.y += u16::try_from(section_lines).unwrap();
		}
	}
}

static HELP_PAGE: &str = "\
l, h, left, right:
    Go forward/backwards a single page
j, k, down, up:
    Go forwards/backwards a screen's worth of pages
q, esc:
    Quit
g:
    Go to specific page (type numbers after 'g')
/:
    Search
n, N:
    Next/Previous search result
i:
    Invert colors
f:
    Remove borders/fullscreen
?:
    Show this page
ctrl+z:
    Suspend & background tdf \
";

static KITTY_HELP: &str = "\
When using Kitty Protocol:
z:
    Toggle between fill-screen and fit-screen
o/O (when on fill-screen):
    Zoom in and out, respectively
gg/G (when on fill-screen):
    Scroll to top/bottom of page
H, J, K, L (when zoomed in):
    Pan direction around page
";

pub enum InputAction {
	Redraw,
	JumpingToPage(usize),
	Search(String),
	QuitApp,
	Invert,
	Fullscreen,
	SwitchRenderZoom(crate::FitOrFill)
}

#[derive(Copy, Clone)]
enum PageChange {
	Prev,
	Next
}

#[derive(Copy, Clone)]
enum ChangeAmount {
	WholeScreen,
	Single
}

pub enum MessageSetting {
	Some(BottomMessage),
	Default,
	Reset,
	Pop
}
