/*
 gifski pngquant-based GIF encoder
 © 2017 Kornel Lesiński

 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU Affero General Public License as
 published by the Free Software Foundation, either version 3 of the
 License, or (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU Affero General Public License for more details.

 You should have received a copy of the GNU Affero General Public License
 along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/
#![doc(html_logo_url = "https://gif.ski/icon.png")]

use encoderust::RustEncoder;
use gif::DisposalMethod;
use imagequant::{Image, QuantizationResult, Attributes};
use imgref::*;
use rgb::*;

mod error;
pub use crate::error::*;
mod ordqueue;
use crate::ordqueue::{OrdQueue, OrdQueueIter};
pub mod progress;
use crate::progress::*;
pub mod c_api;
mod denoise;
use crate::denoise::*;
mod encoderust;

// #[cfg(feature = "gifsicle")]
// mod encodegifsicle;

mod minipool;

use crossbeam_channel::{Receiver, Sender};
use std::cell::Cell;
use std::io::prelude::*;
use std::num::NonZeroU8;
use std::path::PathBuf;
use std::rc::Rc;
use std::thread;
use std::sync::atomic::Ordering::Relaxed;


enum FrameSource {
    Pixels(ImgVec<RGBA8>),
    #[cfg(feature = "png")]
    Path(PathBuf),
}
struct InputFrameUnresized {
    /// The pixels to resize and encode
    frame: FrameSource,
    /// Time in seconds when to display the frame. First frame should start at 0.
    presentation_timestamp: f64,
    frame_index: usize,
}

struct InputFrame {
    /// The pixels to encode
    frame: ImgVec<RGBA8>,
    /// The same as above, but with smart blur applied (for denoiser)
    frame_blurred: ImgVec<RGB8>,
    /// Time in seconds when to display the frame. First frame should start at 0.
    presentation_timestamp: f64,
}

/// Number of repetitions
pub type Repeat = gif::Repeat;

/// Encoding settings for the `new()` function
#[derive(Copy, Clone)]
pub struct Settings {
    /// Resize to max this width if non-0.
    pub width: Option<u32>,
    /// Resize to max this height if width is non-0. Note that aspect ratio is not preserved.
    pub height: Option<u32>,
    /// 1-100, but useful range is 50-100. Recommended to set to 100.
    pub quality: u8,
    /// Lower quality, but faster encode.
    pub fast: bool,
    /// Sets the looping method for the image sequence.
    pub repeat: Repeat,
}

#[derive(Copy, Clone)]
#[non_exhaustive]
struct SettingsExt {
    pub s: Settings,
    pub max_threads: NonZeroU8,
    pub extra_effort: bool,
    pub motion_quality: u8,
    pub giflossy_quality: u8,
    pub matte: Option<RGB8>,
}

impl Settings {
    /// quality is used in other places, like gifsicle or frame differences,
    /// and it's better to lower quality there before ruining quantization
    pub(crate) fn color_quality(&self) -> u8 {
        (u16::from(self.quality) * 4 / 3).min(100) as u8
    }

    /// `add_frame` is going to resize the images to this size.
    #[must_use]
    #[inline]
    pub fn dimensions_for_image(&self, width: usize, height: usize) -> (usize, usize) {
        dimensions_for_image((width, height), (self.width, self.height))
    }
}

impl SettingsExt {
    pub(crate) fn gifsicle_loss(&self) -> u32 {
        if cfg!(feature = "gifsicle") && self.giflossy_quality < 100 {
            (100. / 5. - f32::from(self.giflossy_quality) / 5.).powf(1.8).ceil() as u32 + 10
        } else {
            0
        }
    }
}

impl Default for Settings {
    #[inline]
    fn default() -> Self {
        Self {
            width: None, height: None,
            quality: 100,
            fast: false,
            repeat: Repeat::Infinite,
        }
    }
}

/// Collect frames that will be encoded
///
/// Note that writing will finish only when the collector is dropped.
/// Collect frames on another thread, or call `drop(collector)` before calling `writer.write()`!
pub struct Collector {
    queue: Sender<InputFrameUnresized>,
}

/// Perform GIF writing
pub struct Writer {
    /// Input frame decoder results
    queue_iter: Option<Receiver<InputFrameUnresized>>,
    settings: SettingsExt,
    /// Colors the caller has specified as fixed (i.e. key colours)
    /// This can't be in settings because that would cause it to lose Copy.
    /// Additionally to avoid breaking C API compatibility this has to be mutable there too.
    fixed_colors: Vec<RGB8>,
}

struct GIFFrame {
    left: u16,
    top: u16,
    image: ImgVec<u8>,
    pal: Vec<RGBA8>,
    dispose: DisposalMethod,
    transparent_index: Option<u8>,
}

/// Frame before quantization
struct DiffMessage {
    /// 1..
    ordinal_frame_number: usize,
    pts: f64, frame_duration: f64,
    image: ImgVec<RGBA8>,
    importance_map: Vec<u8>,
}

/// Frame post quantization, before remap
struct RemapMessage {
    /// 1..
    ordinal_frame_number: usize,
    end_pts: f64,
    dispose: DisposalMethod,
    liq: Attributes,
    remap: QuantizationResult,
    liq_image: Image<'static>,
    out_buf: Vec<u8>,
}

/// Frame post quantization and remap
struct FrameMessage {
    /// 0..
    frame_index: usize,
    /// 1..
    ordinal_frame_number: usize,
    end_pts: f64,
    frame: GIFFrame,
    screen_width: u16,
    screen_height: u16,
}

/// Start new encoding
///
/// Encoding is multi-threaded, and the `Collector` and `Writer`
/// can be used on sepate threads.
///
/// You feed input frames to the `Collector`, and ask the `Writer` to
/// start writing the GIF.
#[inline]
pub fn new(settings: Settings) -> CatResult<(Collector, Writer)> {
    if settings.quality == 0 || settings.quality > 100 {
        return Err(Error::WrongSize("quality must be 1-100".into())); // I forgot to add a better error variant
    }
    if settings.width.unwrap_or(0) > 1<<16 || settings.height.unwrap_or(0) > 1<<16 {
        return Err(Error::WrongSize("image size too large".into()));
    }

    let max_threads = thread::available_parallelism().map(|t| t.get().min(255) as u8).unwrap_or(8);
    let (queue, queue_iter) = crossbeam_channel::bounded(5.min(max_threads.into())); // should be sufficient for denoiser lookahead
    Ok((
        Collector {
            queue,
        },
        Writer {
            queue_iter: Some(queue_iter),
            settings: SettingsExt {
                s: settings,
                max_threads: max_threads.try_into()?,
                motion_quality: settings.quality,
                giflossy_quality: settings.quality,
                extra_effort: false,
                matte: None,
            },
            fixed_colors: Vec::new(),
        },
    ))
}

impl Collector {
    /// Frame index starts at 0.
    ///
    /// Set each frame (index) only once, but you can set them in any order.
    ///
    /// Presentation timestamp is time in seconds (since file start at 0) when this frame is to be displayed.
    ///
    /// If the first frame doesn't start at pts=0, the delay will be used for the last frame.
    pub fn add_frame_rgba(&self, frame_index: usize, frame: ImgVec<RGBA8>, presentation_timestamp: f64) -> CatResult<()> {
        debug_assert!(frame_index == 0 || presentation_timestamp > 0.);
        self.queue.send(InputFrameUnresized {
            frame_index,
            frame: FrameSource::Pixels(frame),
            presentation_timestamp,
        })?;
        Ok(())
    }

    /// Read and decode a PNG file from disk.
    ///
    /// Frame index starts at 0.
    ///
    /// Presentation timestamp is time in seconds (since file start at 0) when this frame is to be displayed.
    ///
    /// If the first frame doesn't start at pts=0, the delay will be used for the last frame.
    #[cfg(feature = "png")]
    pub fn add_frame_png_file(&self, frame_index: usize, path: PathBuf, presentation_timestamp: f64) -> CatResult<()> {
        self.queue.send(InputFrameUnresized {
            frame: FrameSource::Path(path),
            presentation_timestamp,
            frame_index,
        })?;
        Ok(())
    }
}

#[inline(never)]
fn resized_binary_alpha(image: ImgVec<RGBA8>, width: Option<u32>, height: Option<u32>, matte: Option<RGB8>) -> CatResult<ImgVec<RGBA8>> {
    let (width, height) = dimensions_for_image((image.width(), image.height()), (width, height));

    let mut image = if width != image.width() || height != image.height() {
        let tmp = image.as_ref();
        let (buf, img_width, img_height) = tmp.to_contiguous_buf();
        assert_eq!(buf.len(), img_width * img_height);

        let mut r = resize::new(img_width, img_height, width, height, resize::Pixel::RGBA8P, resize::Type::Lanczos3)?;
        let mut dst = vec![RGBA8::new(0, 0, 0, 0); width * height];
        r.resize(&buf, &mut dst)?;
        ImgVec::new(dst, width, height)
    } else {
        image
    };

    if let Some(matte) = matte {
        image.pixels_mut().filter(|px| px.a < 255 && px.a > 0).for_each(move |px| {
            let alpha = px.a as u16;
            let inv_alpha = 255 - alpha;

            *px = RGBA8 {
                r: ((px.r as u16 * alpha + matte.r as u16 * inv_alpha) / 255) as u8,
                g: ((px.g as u16 * alpha + matte.g as u16 * inv_alpha) / 255) as u8,
                b: ((px.b as u16 * alpha + matte.b as u16 * inv_alpha) / 255) as u8,
                a: 255,
            };
        });
    } else {
        dither_image(image.as_mut());
    }

    Ok(image)
}

#[allow(clippy::identity_op)]
#[allow(clippy::erasing_op)]
#[inline(never)]
fn dither_image(mut image: ImgRefMut<RGBA8>) {
    let width = image.width();
    let height = image.height();

    // dithering of anti-aliased edges can look very fuzzy, so disable it near the edges
    let mut anti_aliasing = vec![false; width * height];
    loop9::loop9(image.as_ref(), 0, 0, width, height, |x,y, top, mid, bot| {
        if mid.curr.a != 255 && mid.curr.a != 0 {
            fn is_edge(a: u8, b: u8) -> bool {
                a < 12 && b >= 240 ||
                b < 12 && a >= 240
            }
            if is_edge(top.curr.a, bot.curr.a) ||
            is_edge(mid.prev.a, mid.next.a) ||
            is_edge(top.prev.a, bot.next.a) ||
            is_edge(top.next.a, bot.prev.a) {
                anti_aliasing[x + y * width] = true;
            }
        }
    });

    // this table is already biased, so that px.a doesn't need to be changed
    const DITHER: [u8; 64] = [
     0*2+8,48*2+8,12*2+8,60*2+8, 3*2+8,51*2+8,15*2+8,63*2+8,
    32*2+8,16*2+8,44*2+8,28*2+8,35*2+8,19*2+8,47*2+8,31*2+8,
     8*2+8,56*2+8, 4*2+8,52*2+8,11*2+8,59*2+8, 7*2+8,55*2+8,
    40*2+8,24*2+8,36*2+8,20*2+8,43*2+8,27*2+8,39*2+8,23*2+8,
     2*2+8,50*2+8,14*2+8,62*2+8, 1*2+8,49*2+8,13*2+8,61*2+8,
    34*2+8,18*2+8,46*2+8,30*2+8,33*2+8,17*2+8,45*2+8,29*2+8,
    10*2+8,58*2+8, 6*2+8,54*2+8, 9*2+8,57*2+8, 5*2+8,53*2+8,
    42*2+8,26*2+8,38*2+8,22*2+8,41*2+8,25*2+8,37*2+8,21*2+8];

    // Make transparency binary
    for (y, (row, aa)) in image.rows_mut().zip(anti_aliasing.chunks_exact(width)).enumerate() {
        for (x, (px, aa)) in row.iter_mut().zip(aa.iter().copied()).enumerate() {
            if px.a < 255 {
                if aa {
                    px.a = if px.a < 89 { 0 } else { 255 };
                } else {
                    px.a = if px.a < DITHER[(y & 7) * 8 + (x & 7)] { 0 } else { 255 };
                }
            }
        }
    }
}

/// `add_frame` is going to resize the image to this size.
/// The `Option` args are user-specified max width and max height
#[inline(never)]
fn dimensions_for_image((img_w, img_h): (usize, usize), resize_to: (Option<u32>, Option<u32>)) -> (usize, usize) {
    match resize_to {
        (None, None) => {
            let factor = ((img_w * img_h + 800 * 600 / 2) as f64 / f64::from(800 * 600)).sqrt().round() as usize;
            if factor > 1 {
                (img_w / factor, img_h / factor)
            } else {
                (img_w, img_h)
            }
        },
        (Some(w), Some(h)) => {
            ((w as usize).min(img_w), (h as usize).min(img_h))
        },
        (Some(w), None) => {
            let w = (w as usize).min(img_w);
            (w, img_h * w / img_w)
        }
        (None, Some(h)) => {
            let h = (h as usize).min(img_h);
            (img_w * h / img_h, h)
        },
    }
}

#[derive(Copy, Clone)]
enum LastFrameDuration {
    FixedOffset(f64),
    FrameRate(f64),
}

impl LastFrameDuration {
    #[inline]
    pub fn value(&self) -> f64 {
        match self {
            Self::FixedOffset(val) | Self::FrameRate(val) => *val,
        }
    }

    #[inline]
    pub fn shift_every_pts_by(&self) -> f64 {
        match self {
            Self::FixedOffset(offset) => *offset,
            Self::FrameRate(_) => 0.,
        }
    }
}

/// Encode collected frames
impl Writer {
    #[deprecated(note = "please don't use, it will be in Settings eventually")]
    #[doc(hidden)]
    pub fn set_extra_effort(&mut self, enabled: bool) {
        self.settings.extra_effort = enabled;
    }

    #[deprecated(note = "please don't use, it will be in Settings eventually")]
    #[doc(hidden)]
    pub fn set_motion_quality(&mut self, q: u8) {
        self.settings.motion_quality = q;
    }

    #[deprecated(note = "please don't use, it will be in Settings eventually")]
    #[doc(hidden)]
    pub fn set_lossy_quality(&mut self, q: u8) {
        self.settings.giflossy_quality = q;
    }

    /// Adds a fixed color that will be kept in the palette at all times.
    ///
    /// This may increase file size, because every frame will use a larger palette.
    /// Max 255 allowed, because one more is reserved for transparency.
    pub fn add_fixed_color(&mut self, col: RGB8) {
        if self.fixed_colors.len() < 255 {
            self.fixed_colors.push(col);
        }
    }

    #[deprecated(note = "please don't use, it will be in Settings eventually")]
    #[doc(hidden)]
    pub fn set_matte_color(&mut self, col: RGB8) {
        self.settings.matte = Some(col);
    }

    /// `importance_map` is computed from previous and next frame.
    /// Improves quality of pixels visible for longer.
    /// Avoids wasting palette on pixels identical to the background.
    ///
    /// `background` is the previous frame.
    fn quantize(image: ImgVec<RGBA8>, importance_map: &[u8], first_frame: bool, needs_transparency: bool, prev_frame_keeps: bool, settings: &SettingsExt, fixed_colors: &[RGB8]) -> CatResult<(Attributes, QuantizationResult, Image<'static>, Vec<u8>)> {
        let mut liq = Attributes::new();
        if settings.s.fast {
            liq.set_speed(10)?;
        } else if settings.extra_effort {
            liq.set_speed(1)?;
        }
        let quality = if !first_frame {
            settings.s.color_quality()
        } else {
            100 // the first frame is too important to ruin it
        };
        liq.set_quality(0, quality)?;
        if settings.s.quality < 50 {
            liq.set_max_colors(u32::from(settings.s.quality * 2).max(16).next_power_of_two())?;
        }
        let (buf, width, height) = image.into_contiguous_buf();
        let mut img = liq.new_image(buf, width, height, 0.)?;
        // only later remapping tracks which area has been damaged by transparency
        // so for previous-transparent background frame the importance map may be invalid
        // because there's a transparent hole in the background not taken into account,
        // and palette may lack colors to fill that hole
        if first_frame || prev_frame_keeps {
            img.set_importance_map(importance_map)?;
        }
        // first frame may be transparent too, so it's not just for diffs
        if needs_transparency {
            img.add_fixed_color(RGBA8::new(0, 0, 0, 0))?;
        }
        // user may have colors which need to be preserved and left undithered
        for color in fixed_colors {
            img.add_fixed_color(RGBA8::new(color.r, color.g, color.b, 255))?;
        }

        let mut res = liq.quantize(&mut img)?;
        res.set_dithering_level((f32::from(settings.s.quality) / 50.0 - 1.).max(0.2))?;

        let mut out = Vec::new();
        out.try_reserve_exact(width*height).map_err(imagequant::liq_error::from)?;
        res.optionally_prepare_for_dithering_with_background_set(&mut img, &mut out.spare_capacity_mut()[..width*height])?;

        Ok((liq, res, img, out))
    }

    fn remap<'a>(liq: Attributes, mut res: QuantizationResult, mut img: Image<'a>, background: Option<ImgRef<'a, RGBA8>>, mut pal_img: Vec<u8>) -> CatResult<(ImgVec<u8>, Vec<RGBA8>)> {
        if let Some(bg) = background {
            img.set_background(Image::new_stride_borrowed(&liq, bg.buf(), bg.width(), bg.height(), bg.stride(), 0.)?)?;
        }

        let pal = res.remap_into_vec(&mut img, &mut pal_img)?;
        debug_assert_eq!(img.width() * img.height(), pal_img.len());

        Ok((Img::new(pal_img, img.width(), img.height()), pal))
    }

    #[inline(never)]
    fn write_frames(write_queue: Receiver<FrameMessage>, writer: &mut dyn Write, settings: &SettingsExt, reporter: &mut dyn ProgressReporter) -> CatResult<()> {
        let (send, recv) = ordqueue::new(2);
        minipool::new_scope((if settings.s.fast || settings.gifsicle_loss() > 0 { 3 } else { 1 }).try_into().unwrap(), "lzw", move || {
            let mut pts_in_delay_units = 0_u64;

            let written = Rc::new(Cell::new(0));
            let mut enc = RustEncoder::new(writer, written.clone());

            let mut n_done = 0;
            for tmp in recv {
                let (end_pts, ordinal_frame_number, frame, screen_width, screen_height): (f64, _, _, _, _) = tmp;
                let delay = ((end_pts * 100_f64).round() as u64)
                    .saturating_sub(pts_in_delay_units)
                    .min(30000) as u16;
                pts_in_delay_units += u64::from(delay);

                debug_assert_ne!(0, delay);

                // skip frames with bad pts
                if delay != 0 {
                    enc.write_frame(frame, delay, screen_width, screen_height, &settings.s)?;
                }

                // loop to report skipped frames too
                while n_done < ordinal_frame_number {
                    n_done += 1;
                    if !reporter.increase() {
                        return Err(Error::Aborted);
                    }
                }
                reporter.written_bytes(written.get());
            }
            if n_done == 0 {
                Err(Error::NoFrames)
            } else {
                Ok(())
            }
        }, move |abort| {
            for FrameMessage {frame, frame_index, ordinal_frame_number, end_pts, screen_width, screen_height } in write_queue {
                if abort.load(Relaxed) {
                    return Err(Error::Aborted);
                }

                let frame = RustEncoder::<&mut dyn std::io::Write>::compress_frame(frame, settings)?;
                send.push(frame_index, (end_pts, ordinal_frame_number, frame, screen_width, screen_height))?;
            }
            Ok(())
        })
    }

    /// Start writing frames. This function will not return until `Collector` is dropped.
    ///
    /// `outfile` can be any writer, such as `File` or `&mut Vec`.
    ///
    /// `ProgressReporter.increase()` is called each time a new frame is being written.
    #[inline]
    pub fn write<W: Write>(self, mut writer: W, reporter: &mut dyn ProgressReporter) -> CatResult<()> {
        self.write_inner(&mut writer, reporter)
    }

    #[inline(never)]
    fn write_inner(mut self, writer: &mut dyn Write, reporter: &mut dyn ProgressReporter) -> CatResult<()> {
        let decode_queue_recv = self.queue_iter.take().ok_or(Error::Aborted)?;

        let settings_ext = self.settings;
        let (diff_queue, diff_queue_recv) = ordqueue::new(0);
        let resize_thread = thread::Builder::new().name("resize".into()).spawn(move || {
            Self::make_resize(decode_queue_recv, diff_queue, &settings_ext)
        })?;
        let (quant_queue, quant_queue_recv) = crossbeam_channel::bounded(0);
        let diff_thread = thread::Builder::new().name("diff".into()).spawn(move || {
            Self::make_diffs(diff_queue_recv, quant_queue, &settings_ext)
        })?;
        let (remap_queue, remap_queue_recv) = ordqueue::new(0);
        let quant_thread = thread::Builder::new().name("quant".into()).spawn(move || {
            Self::quantize_frames(quant_queue_recv, remap_queue, &settings_ext, &self.fixed_colors)
        })?;
        let (write_queue, write_queue_recv) = crossbeam_channel::bounded(0);
        let remap_thread = thread::Builder::new().name("remap".into()).spawn(move || {
            Self::remap_frames(remap_queue_recv, write_queue)
        })?;
        let res0 = Self::write_frames(write_queue_recv, writer, &settings_ext, reporter);
        let res1 = resize_thread.join().map_err(handle_join_error)?;
        let res2 = diff_thread.join().map_err(handle_join_error)?;
        let res3 = quant_thread.join().map_err(handle_join_error)?;
        let res4 = remap_thread.join().map_err(handle_join_error)?;
        combine_res(combine_res(combine_res(res0, res1), combine_res(res2, res3)), res4)
    }

    /// Apply resizing and crate a blurred version for the diff/denoise phase
    fn make_resize(inputs: Receiver<InputFrameUnresized>, diff_queue: OrdQueue<InputFrame>, settings: &SettingsExt) -> CatResult<()> {
        minipool::new_scope(settings.max_threads.min(if settings.s.fast || settings.extra_effort { 6 } else { 4 }.try_into()?), "resize", move || {
            Ok(())
        }, move |abort| {
            for frame in inputs {
                if abort.load(Relaxed) {
                    return Err(Error::Aborted);
                }
                let image = match frame.frame {
                    FrameSource::Pixels(image) => image,
                    #[cfg(feature = "png")]
                    FrameSource::Path(path) => {
                        let image = lodepng::decode32_file(&path)
                            .map_err(|err| Error::PNG(format!("Can't load {}: {err}", path.display())))?;
                        Img::new(image.buffer, image.width, image.height)
                    },
                };
                let resized = resized_binary_alpha(image, settings.s.width, settings.s.height, settings.matte)?;
                let frame_blurred = if settings.extra_effort { smart_blur(resized.as_ref()) } else { less_smart_blur(resized.as_ref()) };
                diff_queue.push(frame.frame_index, InputFrame {
                    frame: resized,
                    frame_blurred,
                    presentation_timestamp: frame.presentation_timestamp,
                })?;
            }
            Ok(())
        })
    }

    /// Find differences between frames, and compute importance maps
    fn make_diffs(mut inputs: OrdQueueIter<InputFrame>, quant_queue: Sender<DiffMessage>, settings: &SettingsExt) -> CatResult<()> {
        let first_frame = inputs.next().ok_or(Error::NoFrames)?;

        let mut last_frame_duration = if first_frame.presentation_timestamp > 1. / 100. {
            // this is gifski's weird rule that a non-zero first-frame pts
            // shifts the whole anim and is the delay of the last frame
            LastFrameDuration::FixedOffset(first_frame.presentation_timestamp)
        } else {
            LastFrameDuration::FrameRate(0.)
        };

        let mut denoiser = Denoiser::new(first_frame.frame.width(), first_frame.frame.height(), settings.motion_quality)?;

        let mut next_frame = Some(first_frame);
        let mut ordinal_frame_number = 0;
        let mut last_frame_pts = 0.;
        loop {
            // NB! There are two interleaved loops here:
            //  - one to feed the denoiser
            //  - the other to process denoised frames
            //
            // The denoiser buffers five frames, so these two loops process different frames!
            // But need to be interleaved in one `loop{}` to get frames falling out of denoiser's buffer.

            ////////////////////// Feed denoiser: /////////////////////

            let curr_frame = next_frame.take();
            next_frame = inputs.next();

            if let Some(InputFrame { frame, frame_blurred, presentation_timestamp: raw_pts }) = curr_frame {
                ordinal_frame_number += 1;

                let pts = raw_pts - last_frame_duration.shift_every_pts_by();
                if let LastFrameDuration::FrameRate(duration) = &mut last_frame_duration {
                    *duration = pts - last_frame_pts;
                }
                last_frame_pts = pts;

                denoiser.push_frame(frame.as_ref(), frame_blurred.as_ref(), (ordinal_frame_number, pts, last_frame_duration)).map_err(|_| {
                    Error::WrongSize(format!("Frame {ordinal_frame_number} has wrong size ({}×{})", frame.width(), frame.height()))
                })?;
                if next_frame.is_none() {
                    denoiser.flush();
                }
            }

            ////////////////////// Consume denoised frames /////////////////////

            let (importance_map, image, (ordinal_frame_number, pts, last_frame_duration)) = match denoiser.pop() {
                Denoised::Done => {
                    debug_assert!(next_frame.is_none());
                    break
                },
                Denoised::NotYet => continue,
                Denoised::Frame { importance_map, frame, meta } => ( importance_map, frame, meta ),
            };

            let (importance_map, ..) = importance_map.into_contiguous_buf();

            quant_queue.send(DiffMessage {
                importance_map,
                ordinal_frame_number,
                image,
                pts, frame_duration: last_frame_duration.value().max(1. / 100.),
            })?;
        }

        Ok(())
    }

    fn quantize_frames(inputs: Receiver<DiffMessage>, remap_queue: OrdQueue<RemapMessage>, settings: &SettingsExt, fixed_colors: &Vec<RGB8>) -> CatResult<()> {
        minipool::new_channel(settings.max_threads.min(4.try_into()?), "quant", move |to_remap| {
        let mut inputs = inputs.into_iter().peekable();

        let DiffMessage {image: first_frame, ..} = inputs.peek().ok_or(Error::NoFrames)?;
        let first_frame_has_transparency = first_frame.pixels().any(|px| px.a < 128);

        let mut prev_frame_keeps = false;
        let mut frame_index = 0;
        let mut importance_map = None;
        while let Some(DiffMessage { image, pts, frame_duration, ordinal_frame_number, importance_map: new_importance_map }) = inputs.next() {

            if importance_map.is_none() {
                importance_map = Some(new_importance_map);
            }

            let dispose = if let Some(DiffMessage { image: next_image, .. }) = inputs.peek() {
                // Skip identical frames
                if next_image.as_ref() == image.as_ref() {
                    // this keeps importance_map of the previous frame in the identical-frame series
                    // (important, because subsequent identical frames have all-zero importance_map and would be dropped too)
                    continue;
                }

                // If the next frame becomes transparent, this frame has to clear to bg for it
                if next_image.pixels().zip(image.pixels()).any(|(next, curr)| next.a < curr.a) {
                    DisposalMethod::Background
                } else {
                    DisposalMethod::Keep
                }
            } else if first_frame_has_transparency {
                // Last frame should reset to background to avoid breaking transparent looped anims
                DisposalMethod::Background
            } else {
                // macOS preview gets Background wrong
                DisposalMethod::Keep
            };

            let importance_map = importance_map.take().ok_or(Error::ThreadSend)?; // always set at the beginning

            if !prev_frame_keeps || importance_map.iter().any(|&px| px > 0) {
                let end_pts = if let Some(&DiffMessage { pts: next_pts, .. }) = inputs.peek() {
                    next_pts
                } else {
                    pts + frame_duration
                };
                debug_assert!(end_pts > 0.);

                to_remap.send((end_pts, image, importance_map, ordinal_frame_number, frame_index, dispose, first_frame_has_transparency, prev_frame_keeps))?;

                frame_index += 1;
                prev_frame_keeps = dispose == DisposalMethod::Keep;
            }
        }
        Ok(())
        }, move |(end_pts, mut image, importance_map, ordinal_frame_number, frame_index, dispose, first_frame_has_transparency, prev_frame_keeps)| {
            if prev_frame_keeps {
                // if denoiser says the background didn't change, then believe it
                // (except higher quality settings, which try to improve it every time)
                let bg_keep_likelihood = u32::from(settings.s.quality.saturating_sub(80) / 4);
                if settings.s.fast || (settings.s.quality < 100 && (frame_index % 5) >= bg_keep_likelihood) {
                    image.pixels_mut().zip(&importance_map).filter(|&(_, &m)| m == 0).for_each(|(px, _)| *px = RGBA8::new(0,0,0,0));
                }
            }

            let needs_transparency = frame_index > 0 || (frame_index == 0 && first_frame_has_transparency);
            let (liq, remap, liq_image, out_buf) = Self::quantize(image, &importance_map, frame_index == 0, needs_transparency, prev_frame_keeps, settings, fixed_colors)?;

            remap_queue.push(frame_index as usize, RemapMessage {
                ordinal_frame_number,
                end_pts,
                dispose,
                liq, remap,
                liq_image,
                out_buf,
            })
        })
    }

    fn remap_frames(inputs: OrdQueueIter<RemapMessage>, write_queue: Sender<FrameMessage>) -> CatResult<()> {
        let mut inputs = inputs.into_iter().peekable();
        let first_frame = inputs.peek().ok_or(Error::NoFrames)?;
        let mut screen = gif_dispose::Screen::new(first_frame.liq_image.width(), first_frame.liq_image.height(), RGBA8::new(0, 0, 0, 0), None);

        let mut frame_index = 0;
        while let Some(RemapMessage {ordinal_frame_number, end_pts, dispose, liq, remap, liq_image, out_buf}) = inputs.next() {
            let screen_width = screen.pixels.width() as u16;
            let screen_height = screen.pixels.height() as u16;
            let mut screen_after_dispose = screen.dispose();

            let (mut image8, mut image8_pal) = {
                let bg = if frame_index != 0 { Some(screen_after_dispose.pixels()) } else { None };
                Self::remap(liq, remap, liq_image, bg, out_buf)?
            };

            let transparent_index = transparent_index_from_palette(&mut image8_pal, image8.as_mut());

            let next_frame = inputs.peek();
            let (left, top, image8) = if frame_index != 0 && next_frame.is_some() {
                match trim_image(image8, &image8_pal, transparent_index, dispose, screen_after_dispose.pixels()) {
                    Some(trimmed) => trimmed,
                    None => continue, // no pixels need to be changed after dispose
                }
            } else {
                // must keep first and last frame
                (0, 0, image8)
            };

            screen_after_dispose.then_blit(Some(&image8_pal), dispose, left, top as _, image8.as_ref(), transparent_index)?;

            write_queue.send(FrameMessage {
                frame_index,
                ordinal_frame_number,
                end_pts,
                screen_width,
                screen_height,
                frame: GIFFrame {
                    left,
                    top,
                    image: image8,
                    pal: image8_pal,
                    transparent_index,
                    dispose,
                },
            })?;
            frame_index += 1;
        }
        Ok(())
    }
}

fn transparent_index_from_palette(image8_pal: &mut [RGBA<u8>], mut image8: ImgRefMut<u8>) -> Option<u8> {
    // Palette may have multiple transparent indices :(
    let mut transparent_index = None;
    for (i, p) in image8_pal.iter_mut().enumerate() {
        if p.a <= 128 {
            p.a = 0;
            let new_index = i as u8;
            if let Some(old_index) = transparent_index {
                image8.pixels_mut().filter(|px| **px == new_index).for_each(|px| *px = old_index);
            } else {
                transparent_index = Some(new_index);
            }
        }
    }

    // Check that palette is fine and has no duplicate transparent indices
    debug_assert!(image8_pal.iter().enumerate().all(|(idx, color)| {
        Some(idx as u8) == transparent_index || color.a > 128 || !image8.pixels().any(|px| px == idx as u8)
    }));

    transparent_index
}

/// When one thread unexpectedly fails, all other threads fail with Aborted, but that Aborted isn't the relevant cause
#[inline]
fn combine_res(res1: Result<(), Error>, res2: Result<(), Error>) -> Result<(), Error> {
    use Error::*;
    match (res1, res2) {
        (Err(e), Ok(())) | (Ok(()), Err(e)) => Err(e),
        (Err(ThreadSend), res) | (res, Err(ThreadSend)) => res,
        (Err(Aborted), res) | (res, Err(Aborted)) => res,
        (Err(NoFrames), res) | (res, Err(NoFrames)) => res,
        (_, res2) => res2,
    }
}

fn trim_image(mut image8: ImgVec<u8>, image8_pal: &[RGBA8], transparent_index: Option<u8>, dispose: DisposalMethod, mut screen: ImgRef<RGBA8>) -> Option<(u16, u16, ImgVec<u8>)> {
    let mut image_trimmed = image8.as_ref();

    let is_matching_pixel = move |px: u8, bg: RGBA8| -> bool {
        if Some(px) == transparent_index {
            if dispose == DisposalMethod::Keep {
                // if dispose == keep, then transparent pixels do nothing, so they can be cropped out
                true
            } else {
                // if disposing to background, then transparent pixels paint transparency, so bg has to actually be transparent to match
                bg.a == 0
            }
        } else {
            image8_pal.get(px as usize).copied().unwrap_or_default() == bg
        }
    };

    let bottom = image_trimmed.rows().zip(screen.rows()).rev()
        .take_while(|(img_row, screen_row)| {
            img_row.iter().copied().zip(screen_row.iter().copied())
                .all(|(px, bg)| is_matching_pixel(px, bg))
        })
        .count();

    if bottom > 0 {
        if bottom == image_trimmed.height() {
            return None;
        }
        image_trimmed = image_trimmed.sub_image(0, 0, image_trimmed.width(), image_trimmed.height() - bottom);
        screen = screen.sub_image(0, 0, screen.width(), screen.height() - bottom);
    }

    let top = image_trimmed.rows().zip(screen.rows())
        .take_while(|(img_row, screen_row)| {
            img_row.iter().copied().zip(screen_row.iter().copied())
                .all(|(px, bg)| is_matching_pixel(px, bg))
        })
        .count();

    if top > 0 {
        image_trimmed = image_trimmed.sub_image(0, top, image_trimmed.width(), image_trimmed.height() - top);
        screen = screen.sub_image(0, top, screen.width(), screen.height() - top);
    }

    let left = (0..image_trimmed.width()-1)
        .take_while(|&x| {
            (0..image_trimmed.height()).all(|y| {
                let px = image_trimmed[(x, y)];
                is_matching_pixel(px, screen[(x, y)])
            })
        }).count();
    if left > 0 {
        image_trimmed = image_trimmed.sub_image(left, 0, image_trimmed.width() - left, image_trimmed.height());
    }

    if image_trimmed.height() != image8.height() || image_trimmed.width() != image8.width() {
        let (buf, width, height) = image_trimmed.to_contiguous_buf();
        image8 = Img::new(buf.into_owned(), width, height);
    }

    Some((left as _, top as _, image8))
}

trait PushInCapacity<T> {
    fn push_in_cap(&mut self, val: T);
}

impl<T> PushInCapacity<T> for Vec<T> {
    #[track_caller]
    #[inline(always)]
    fn push_in_cap(&mut self, val: T) {
        debug_assert!(self.capacity() != self.len());
        if self.capacity() != self.len() {
            self.push(val);
        }
    }
}

fn handle_join_error(err: Box<dyn std::any::Any + Send>) -> Error {
    let msg = err.downcast_ref::<String>().map(|s| s.as_str())
    .or_else(|| err.downcast_ref::<&str>().copied()).unwrap_or("unknown panic");
    eprintln!("thread crashed (this is a bug): {msg}");
    Error::ThreadSend
}