//
// This is an abstraction over a drawing environment.
// Future note: z-Buffer is described here:
// https://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation/perspective-correct-interpolation-vertex-attributes
//
// Georg Hopp <georg@steffers.org>
//
// Copyright © 2019 Georg Hopp
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.
//
use std::cmp;
use std::fmt::{Formatter, Debug, Display, Result};
use std::ops::{Add, Sub, Div};
use std::sync::mpsc;

pub trait Easel {
    //fn canvas(&mut self, width :u16, height :u16) -> Option<&dyn Canvas>;
}

pub trait Canvas<T> {
    fn init_events(&self);
    fn start_events(&self, tx :mpsc::Sender<i32>);

    fn width(&self) -> u16;
    fn height(&self) -> u16;

    fn clear(&mut self);
    fn draw(&mut self, c :&dyn Drawable<T>, ofs :Coordinate<T>, color :u32);
    fn put_text(&self, ofs :Coordinate<T>, s :&str);
    fn set_pixel(&mut self, c :Coordinate<T>, color :u32);
    fn show(&self);
}

pub trait Drawable<T> {
    fn plot(&self) -> Coordinates<T>;
}

pub trait Fillable<T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Copy + From<i32> {
    fn fill(&self, canvas :&mut dyn Canvas<T>, color :u32);
}

#[derive(Debug, Clone, Copy)]
pub struct Coordinate<T>(pub i32, pub i32, pub T);

#[derive(Debug, Clone)]
pub struct Coordinates<T>(pub Vec<Coordinate<T>>);

#[derive(Debug, Clone, Copy)]
pub struct LineIterator<T> where T: Debug {
               a :Option<Coordinate<T>>
    ,          b :Coordinate<T>
    ,         dx :i32
    ,         dy :i32
    ,         dz :T
    ,         sx :i32
    ,         sy :i32
    ,        err :i32
    , only_edges :bool
}

impl<T> Iterator for LineIterator<T>
where T: Add<Output = T> + Debug + Copy + From<i32> {
    type Item = Coordinate<T>;

    fn next(&mut self) -> Option<Self::Item> {
        match self.a {
            None    => None,
            Some(a) => {
                let Coordinate(ax, ay, az) = a;
                let Coordinate(bx, by,  _) = self.b;

                if ax != bx || ay != by {
                    match (2 * self.err >= self.dy, 2 * self.err <= self.dx ) {
                        (true, false) => {
                            let r    = self.a;
                            self.a   = Some(Coordinate( ax + self.sx
                                                      , ay
                                                      , az + self.dz ));
                            self.err = self.err + self.dy;
                            if self.only_edges { self.next() } else { r }
                        },
                        (false, true) => {
                            let r    = self.a;
                            self.a   = Some(Coordinate( ax
                                                      , ay + self.sy
                                                      , az + self.dz ));
                            self.err = self.err + self.dx;
                            r
                        },
                        _             => {
                            let r    = self.a;
                            self.a   = Some(Coordinate( ax + self.sx
                                                      , ay + self.sy
                                                      , az + self.dz ));
                            self.err = self.err + self.dx + self.dy;
                            r
                        },
                    }
                } else {
                    self.a = None;
                    Some(self.b)
                }
            }
        }
    }
}

impl<T> Coordinate<T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Clone + Copy + From<i32> {
    fn iter(self, b :&Self, only_edges :bool) -> LineIterator<T> {
        let Coordinate(ax, ay, az) = self;
        let Coordinate(bx, by, bz) = *b;

        let dx = (bx - ax).abs();
        let dy = -(by - ay).abs();

        LineIterator {    a: Some(self)
                     ,    b: *b
                     ,   dx: dx
                     ,   dy: dy
                     ,   dz: (bz - az) / cmp::max(dx, -dy).into()
                     ,   sx: if ax < bx { 1 } else { -1 }
                     ,   sy: if ay < by { 1 } else { -1 }
                     , err: dx + dy
                     , only_edges: only_edges
        }
    }

    fn line_iter(self, b :&Self) -> LineIterator<T> {
        self.iter(b, false)
    }

    fn line(self, b :&Self) -> Vec<Self> {
        self.line_iter(b).collect()
    }

    fn edge_iter(self, b :&Self) -> LineIterator<T> {
        self.iter(b, true)
    }

    fn edge(self, b :&Self) -> Vec<Self> {
        self.edge_iter(b).collect()
    }

    fn face(edges :&[Self]) -> Vec<Self> {
        edges.to_vec()
    }
}

impl<T> Display for Coordinate<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        write!(f, "<{},{}>", self.0, self.1)
    }
}

impl<T> Display for Coordinates<T> where T: Copy {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        let Coordinates(is) = self;

        let c = match is[..] {
            []  => String::from(""),
            [a] => format!("{}", a),
            _   => {
                let mut a = format!("{}", is[0]);
                for i in is[1..].iter() {
                    a = a + &format!(",{}", i);
                }
                a
            }
        };

        write!(f, "Coordinates[{}]", c)
    }
}


#[derive(Debug, Clone, Copy)]
pub struct Point<T>(pub Coordinate<T>);

impl<T> Drawable<T> for Point<T> where T: Copy {
    fn plot(&self) -> Coordinates<T> {
        let Point(c) = *self;
        Coordinates(vec!(c))
    }
}

impl<T> Display for Point<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        let Point(p) = self;
        write!(f, "Point[{}]", p)
    }
}

#[derive(Debug, Clone, Copy)]
pub struct Line<T>(pub Coordinate<T>, pub Coordinate<T>);

impl<T> Drawable<T> for Line<T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Clone + Copy + From<i32> {
    fn plot(&self) -> Coordinates<T> {
        let Line(a, b) = *self;
        Coordinates(a.line(&b))
    }
}

impl<T> Display for Line<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        let Line(a, b) = self;
        write!(f, "Line[{},{}]", a, b)
    }
}

#[derive(Debug, Clone)]
pub struct Polyline<T>(pub Coordinates<T>);

impl<T> Drawable<T> for Polyline<T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Clone + Copy + From<i32> {
    fn plot(&self) -> Coordinates<T> {
        let Polyline(Coordinates(cs)) = self;

        match cs[..] {
            []     => Coordinates(Vec::<Coordinate<T>>::new()),
            [a]    => Coordinates(vec!(a)),
            [a, b] => Coordinates(a.line(&b)),
            _      => {
                let (a, b) = (cs[0], cs[1]);
                let mut r = a.line(&b);
                let mut i = b;
                for j in cs[2..].iter() {
                    r.append(&mut i.line(j)[1..].to_vec());
                    i = *j;
                }
                Coordinates(r)
            },
        }
    }
}

impl<T> Display for Polyline<T> where T: Copy {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        let Polyline(a) = self;
        write!(f, "PLine[{}]", a)
    }
}

#[derive(Debug, Clone, Copy)]
enum Direction { Left, Right }

#[derive(Debug, Clone)]
pub struct Polygon<T>(pub Coordinates<T>);

#[derive(Debug, Clone)]
enum VertexIteratorMode { Vertex, Edge }
#[derive(Debug, Clone)]
pub struct VertexIterator<'a,T> where T: Debug {
    p         :&'a Polygon<T>,
    top       :usize,
    current   :Option<usize>,
    edge      :Option<LineIterator<T>>,
    mode      :VertexIteratorMode,
    direction :Direction,
}

impl<'a,T> VertexIterator<'a,T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Copy + From<i32> {
    fn edge(p :&'a Polygon<T>, direction :Direction) -> Self {
        let top  = p.vert_min(direction);
        let next = p.next_y(top, direction);
        let edge = match next {
            None       => None,
            Some(next) => Some(p.vertex(top).edge_iter(&p.vertex(next))),
        };

        VertexIterator { p:         p
                       , top:       top
                       , current:   next
                       , edge:      edge
                       , mode:      VertexIteratorMode::Edge
                       , direction: direction }
    }

    fn vertex(p :&'a Polygon<T>, direction :Direction) -> Self {
        let top  = p.vert_min(direction);
        let next = p.next_y(top, direction);

        VertexIterator { p:         p
                       , top:       top
                       , current:   next
                       , edge:      None
                       , mode:      VertexIteratorMode::Vertex
                       , direction: direction }
    }

    // if this yields "None" we are finished.
    fn next_edge(&mut self) -> Option<LineIterator<T>> {
        let current  = self.current?;
        let next     = self.p.next_y(current, self.direction)?;
        let mut edge = self.p.vertex(current).edge_iter(&self.p.vertex(next));

        match edge.next() {
            // It should be impossible that a new edge iterator has no values
            // at all… anyway, just in case I handle it here.
            None    => self.next_edge(),
            Some(_) => {
                self.current = Some(next);
                self.edge    = Some(edge);
                self.edge
            },
        }
    }
}

impl<'a,T> Iterator for VertexIterator<'a,T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Copy + From<i32> {
    type Item = Coordinate<T>;

    fn next(&mut self) -> Option<Self::Item> {
        match self.mode {
            VertexIteratorMode::Edge => {
                // if for whatever reason edge is "None" finish this iterator.
                let next = self.edge.as_mut()?.next();

                match next {
                    Some(_) => next,
                    None    => {
                        self.next_edge()?;
                        self.next()
                    },
                }
            },
            VertexIteratorMode::Vertex => {
                let current  = self.current?;
                self.current = self.p.next_y(current, self.direction);
                Some(self.p.vertex(current))
            },
        }
    }
}

impl<T> Polygon<T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Copy + Debug + From<i32> {
    #[inline]
    fn vertex(&self, v :usize) -> Coordinate<T> {
        let Polygon(Coordinates(cs)) = self;
        cs[v]
    }

    fn vert_min<'a>(&'a self, d :Direction) -> usize {
        let Polygon(Coordinates(cs)) = self;

        type ICoord<'a,T> = (usize, &'a Coordinate<T>);

        // TODO I guess the problem here is that it does not account for the
        //      same y vertex on the beggining and the end. So i guess correct
        //      would be finding the first one and then dependings on the
        //      given direction either search left or right for same y's.
        let fold = |acc :Option<ICoord<'a,T>>, x :ICoord<'a,T>|
            match acc {
                None    => Some(x),
                Some(a) => {
                    let Coordinate(_, ay, _) = a.1;
                    let Coordinate(_, xy, _) = x.1;
                    if xy < ay {Some(x)} else {Some(a)}
                },
            };

        let mut  min = cs.iter().enumerate().fold(None, fold).unwrap().0;
        let mut next = self.step(min, d);

        while self.vertex(min).1 == self.vertex(next).1 {
            min = next;
            next = self.step(min, d);
        }

        min
    }

    fn left_edge(&self) -> VertexIterator<T> {
        VertexIterator::edge(self, Direction::Left)
    }

    fn right_edge(&self) -> VertexIterator<T> {
        VertexIterator::edge(self, Direction::Right)
    }

    fn left_vertices(&self) -> VertexIterator<T> {
        VertexIterator::vertex(self, Direction::Left)
    }

    fn right_vertices(&self) -> VertexIterator<T> {
        VertexIterator::vertex(self, Direction::Right)
    }

    fn left(&self, v :usize) -> usize {
        let Polygon(Coordinates(cs)) = self;

        match v {
            0 => cs.len() - 1,
            _ => v - 1,
        }
    }

    fn right(&self, v :usize) -> usize {
        let Polygon(Coordinates(cs)) = self;

        (v + 1) % cs.len()
    }

    fn step(&self, v :usize, d :Direction) -> usize {
        match d {
            Direction::Left  => self.left(v),
            Direction::Right => self.right(v),
        }
    }

    fn next_y(&self, c :usize, d :Direction) -> Option<usize> {
        fn inner<T>( p :&Polygon<T>
                   , c :usize
                   , n :usize
                   , d :Direction) -> Option<usize>
        where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
               + Copy + Debug + From<i32> {
            if c == n {
                None
            } else {
                let Coordinate(_, cy, _) = p.vertex(c);
                let Coordinate(_, ny, _) = p.vertex(n);

                if ny < cy { None } else { Some(n) }
            }
        }

        inner(self, c, self.step(c, d), d)
    }

    pub fn debug(&self) {
        let mut left  = self.left_vertices();
        let mut right = self.right_vertices();

        if left.find(|l| right.find(|r| l.0 == r.0).is_some()).is_some() {
            let left  :Vec<Coordinate<T>> = self.left_vertices().collect();
            let right :Vec<Coordinate<T>> = self.right_vertices().collect();

            println!("===");
            println!("==  poly : {:?}", self);
            println!("==  ltop : {:?}", self.vert_min(Direction::Left));
            println!("==  rtop : {:?}", self.vert_min(Direction::Right));
            println!("==  left : {:?}", left);
            println!("== right : {:?}", right);
            println!("===");
        }
    }
}

impl<T> Drawable<T> for Polygon<T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Clone + Copy + From<i32> {
    fn plot(&self) -> Coordinates<T> {
        let Polygon(Coordinates(cs)) = self;

        match cs[..] {
            []     => Coordinates(Vec::<Coordinate<T>>::new()),
            [a]    => Coordinates(vec!(a)),
            [a, b] => Coordinates(a.line(&b)),
            _      => {
                let (a, b) = (cs[0], cs[1]);
                let mut r = a.line(&b);
                let mut i = b;
                for j in cs[2..].iter() {
                    r.append(&mut i.line(j)[1..].to_vec());
                    i = *j;
                }
                let mut j = a.line(&i);
                let     l = j.len();
                if l > 1 {
                    r.append(&mut j[1..l-1].to_vec());
                }
                Coordinates(r)
            },
        }
    }
}

impl<T> Fillable<T> for Polygon<T>
where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
       + Debug + Clone + Copy + From<i32> {
    fn fill(&self, canvas :&mut dyn Canvas<T>, color :u32) {
        let scanlines = self.left_edge().zip(self.right_edge());

        for l in scanlines.flat_map(|(l, r)| l.line_iter(&r)) {
            canvas.set_pixel(l, color);
        }
    }
}

impl<T> Display for Polygon<T> where T: Copy {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        let Polygon(a) = self;
        write!(f, "Poly[{}]", a)
    }
}