use crate::{
    block::{AdvancedReference, Block},
    frame::Frame,
    helpers::{pixel::Pixel, threading::both_par, vector::Vec2},
    refsampler::Sampler,
    view::View,
};
use clap::ValueEnum;
use log::{debug, trace};

#[derive(Debug, Clone)]
pub struct EncodeConfig {
    pub mode: EncodeMode,
    pub ref_thres: f64,
    pub max_diff_area: isize,
    pub min_block_size: isize,
    pub max_threads: usize,
}

#[derive(Debug, Clone, ValueEnum)]
pub enum EncodeMode {
    Trivial,
    Default,
    Advanced,
}

pub fn encode_block(view: View<&Frame>, prev: View<&Frame>, config: &EncodeConfig) -> Block {
    let (diff, refblock) = if view.area() > config.max_diff_area {
        (
            f64::INFINITY,
            Block::Reference {
                translation: Vec2::<isize>::ZERO,
            },
        )
    } else {
        match config.mode {
            EncodeMode::Trivial => (
                View::diff(&view, &prev) / view.area() as f64,
                Block::Reference {
                    translation: Vec2::<isize>::ZERO,
                },
            ),
            EncodeMode::Default => {
                let mut best_diff = f64::INFINITY;
                let mut best_translation = Vec2::<isize>::ZERO;
                const OFFSETS: &[isize] =
                    &[-64, -32, -16, -8, -4, -2, -1, 0, 1, 2, 4, 8, 16, 32, 64];
                for x in OFFSETS {
                    for y in OFFSETS {
                        let translation = Vec2 { x: *x, y: *y };
                        let diff = View::diff(&view, &prev.offset(translation));
                        if diff < best_diff {
                            best_translation = translation;
                            best_diff = diff;
                        }
                    }
                }
                (
                    best_diff,
                    Block::Reference {
                        translation: best_translation,
                    },
                )
            }
            EncodeMode::Advanced => {
                let mut params = AdvancedReference::default();
                let sampler = Sampler::from_refblock(prev.clone(), &params);
                let mut diff = View::diff_sampler(&view, &sampler);

                loop {
                    pub fn pk<F: FnMut(&mut AdvancedReference) -> ()>(
                        view: &View<&Frame>,
                        prev: &View<&Frame>,
                        diff: &mut f64,
                        params: &mut AdvancedReference,
                        mut f: F,
                    ) {
                        let mut p = params.clone();
                        f(&mut p);
                        let d = View::diff_sampler(view, &Sampler::from_refblock(prev.clone(), &p));
                        trace!("best={diff} try={d}");
                        if d < *diff {
                            *diff = d;
                            *params = p;
                        }
                    }

                    let (mut d, mut p) = (diff, params.clone());
                    pk(&view, &prev, &mut d, &mut p, |p| p.translation.x += 2);
                    pk(&view, &prev, &mut d, &mut p, |p| p.translation.x -= 2);
                    pk(&view, &prev, &mut d, &mut p, |p| p.translation.y += 2);
                    pk(&view, &prev, &mut d, &mut p, |p| p.translation.y -= 2);
                    debug!("{diff} -> {d}");

                    if d >= diff {
                        break (diff, Block::AdvancedReference(params));
                    }

                    diff = d;
                    params = p;
                }
            }
        }
    };
    if diff < config.ref_thres {
        refblock
    } else {
        if view.size.x < config.min_block_size || view.size.y < config.min_block_size {
            Block::Literal(view.pixels())
        } else {
            let [av, bv] =
                unsafe { std::mem::transmute::<_, [View<&'static Frame>; 2]>(view.split()) };
            let [ap, bp] =
                unsafe { std::mem::transmute::<_, [View<&'static Frame>; 2]>(prev.split()) };
            let config = unsafe { std::mem::transmute::<_, &'static EncodeConfig>(config) };

            // only bother to do multithreading, when the block is big.
            let (a, b) = if view.size.x > 64 {
                both_par(
                    || encode_block(av, ap, config),
                    || encode_block(bv, bp, config),
                    config.max_threads,
                )
            } else {
                (encode_block(av, ap, config), encode_block(bv, bp, config))
            };

            if a.is_literal() && b.is_literal() {
                Block::Literal(view.pixels())
            } else {
                Block::Split(Box::new([a, b]))
            }
        }
    }
}

pub fn importance(view: &View<&Frame>) -> f64 {
    let mut acc = 0;
    for x in 0..view.size.x {
        for y in 0..view.size.y {
            let p = Vec2 { x, y };
            if x > 0 {
                acc += Pixel::distance(view[p], view[p + Vec2::<isize>::LEFT]);
            }
            if y > 0 {
                acc += Pixel::distance(view[p], view[p + Vec2::<isize>::UP]);
            }
        }
    }
    (acc / view.area() as usize) as f64
}