use std::fmt;

use super::{eqn, Expr, Point2, Rot2, Scalar, Value};

// pub type Vec2 = nalgebra::Vector2<Value>;
// pub type Point2 = nalgebra::Point2<Value>;

// pub type Rot2 = nalgebra::UnitComplex<Value>;

pub trait GenericRegion {
    fn full() -> Self;
    fn intersection(self, other: Self) -> Self;
    fn simplify(self) -> Self;
    fn evaluate_with(self, eqns: &eqn::Eqns) -> Self;
}

pub trait Region<T>: GenericRegion {
    fn singleton(value: T) -> Self;

    fn nearest(&self, value: &T) -> Option<T>;
    fn contains(&self, value: &T) -> Option<bool>;
}

#[derive(Clone, Debug)]
pub enum Region1 {
    Empty,
    Singleton(Value),
    Range(Value, Value),
    Intersection(Box<Region1>, Box<Region1>),
    // Union(Box<Region1>, Box<Region1>),
    Full,
}

impl fmt::Display for Region1 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        use Region1::*;
        match self {
            Empty => write!(f, "Ø"),
            Singleton(v) => write!(f, "{{ {} }}", v),
            Range(l, u) => write!(f, "[ {}, {} ]", l, u),
            Intersection(r1, r2) => write!(f, "{} ∩ {}", r1, r2),
            Full => write!(f, "ℝ"),
        }
    }
}

impl GenericRegion for Region1 {
    fn intersection(self, other: Region1) -> Self {
        Region1::Intersection(Box::new(self), Box::new(other))
    }

    fn full() -> Self {
        Region1::Full
    }

    fn simplify(self) -> Self {
        use Region1::*;
        match self {
            Singleton(n) => Singleton(n.simplify()),
            Range(l, u) => Range(l.simplify(), u.simplify()),
            Intersection(r1, r2) => r1.simplify().intersection(r2.simplify()),
            other => other,
        }
    }

    fn evaluate_with(self, eqns: &eqn::Eqns) -> Self {
        use Region1::*;
        match self {
            Singleton(n) => Singleton(n.evaluate_with(eqns)),
            Range(l, u) => Range(l.evaluate_with(eqns), u.evaluate_with(eqns)),
            Intersection(r1, r2) => r1.evaluate_with(eqns).intersection(r2.evaluate_with(eqns)),
            other => other,
        }
    }
}

impl Region<Scalar> for Region1 {
    fn singleton(value: Scalar) -> Self {
        Region1::Singleton(value.into())
    }

    fn contains(&self, n: &Scalar) -> Option<bool> {
        use Expr::Const;
        use Region1::*;
        match self {
            Empty => Some(false),
            Singleton(n1) => match n1 {
                Const(c) => Some(relative_eq!(c, n)),
                _ => None,
            },
            Range(l, u) => match (l, u) {
                (Const(cl), Const(cu)) => Some(*cl <= *n && *n <= *cu),
                _ => None,
            },
            Intersection(r1, r2) => r1
                .contains(n)
                .and_then(|c1| r2.contains(n).map(|c2| c1 && c2)),
            // Union(r1, r2) => r1.contains(n) || r2.contains(n),
            Full => Some(true),
        }
    }

    fn nearest(&self, s: &Scalar) -> Option<Scalar> {
        use Expr::Const;
        use Region1::*;
        match self {
            Empty => None,
            Full => Some(*s),
            Singleton(n) => match n {
                Const(c) => Some(*c),
                _ => None,
            },
            Range(l, u) => match (l, u) {
                (Const(cl), Const(cu)) => match (cl < s, s < cu) {
                    (true, true) => Some(*s),
                    (true, false) => Some(*cu),
                    (false, true) => Some(*cl),
                    _ => None,
                },
                _ => None,
            },
            Intersection(r1, r2) => unimplemented!(), /*Union(r1, r2) => {
                                                          let distance = |a: Scalar, b: Scalar| (a - b).abs();
                                                          match (r1.nearest(s), r2.nearest(s)) {
                                                              (None, None) => None,
                                                              (Some(n), None) | (None, Some(n)) => Some(n),
                                                              (Some(n1), Some(n2)) => Some({
                                                                  if distance(*s, n1) <= distance(*s, n2) {
                                                                      n1
                                                                  } else {
                                                                      n2
                                                                  }
                                                              }),
                                                          }
                                                      }*/
        }
    }
}

// line starting at start, point at angle dir, with range extent
// ie. start + (cos dir, sin dir) * t for t in extent
#[derive(Clone, Debug)]
pub struct Line2 {
    start: Point2<Value>,
    dir: Rot2,
    extent: Region1,
}

impl fmt::Display for Line2 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(
            f,
            "{{ <x, y> = {} + {} * {} }}",
            self.start, self.dir, self.extent
        )
    }
}

impl Line2 {
    pub fn new(start: Point2<Value>, dir: Rot2, extent: Region1) -> Self {
        Self { start, dir, extent }
    }

    pub fn evaluate(&self, t: Value) -> Point2<Value> {
        self.start.clone() + self.dir.clone() * t
    }

    pub fn evaluate_extent(&self) -> Option<Point2<Value>> {
        match &self.extent {
            Region1::Singleton(t) => Some(self.evaluate(t.clone())),
            _ => None,
        }
    }

    pub fn with_extent(self, new_extent: Region1) -> Line2 {
        Line2 {
            start: self.start,
            dir: self.dir,
            extent: new_extent,
        }
    }

    pub fn nearest(&self, p: &Point2<Value>) -> Point2<Value> {
        // rotate angle 90 degrees
        let perp_dir = self.dir.clone() + Rot2::cardinal(1);
        let perp = Line2::new(p.clone(), perp_dir, Region1::Full);
        match self.intersect(&perp) {
            Region2::Singleton(np) => np,
            Region2::Line(l) => l.evaluate_extent().expect("Line2::nearest not found"),
            _ => panic!("Line2::nearest not found!"),
        }
    }

    pub fn intersect(&self, other: &Line2) -> Region2 {
        // if the two lines are parallel...
        let dirs = self.dir.clone() - other.dir.clone();
        if relative_eq!(dirs.sin(), 0.) {
            let starts = self.dir.conj() * (other.start.clone() - self.start.clone());
            return if starts.y.simplify().is_zero() {
                // and they are colinear
                Region2::Line(self.clone())
            } else {
                // they are parallel and never intersect
                Region2::Empty
            };
        }
        // TODO: respect extent
        let (a, b) = (self, other);
        let (a_0, a_v, b_0, b_v) = (
            a.start.clone(),
            a.dir.clone(),
            b.start.clone(),
            b.dir.clone(),
        );
        let (a_c, a_s, b_c, b_s) = (a_v.cos(), a_v.sin(), b_v.cos(), b_v.sin());
        let t_b = (a_0.x.clone() * a_s.clone()
            - a_0.y.clone() * a_c.clone()
            - b_0.x.clone() * a_s.clone()
            + b_0.y.clone() * a_c.clone())
            / (a_s.clone() * b_c.clone() - a_c.clone() * b_s.clone());
        // Region2::Singleton(b.evaluate(t_b))
        trace!("intersect a: {}, b: {}, t_b = {}", a, b, t_b);
        let res = Region2::Line(b.clone().with_extent(Region1::Singleton(t_b.simplify())));
        trace!("intersect a: {}, b: {} = {}", a, b, res);
        res
    }

    pub fn simplify(self) -> Region2 {
        let new_l = Line2 {
            start: self.start.simplify(),
            dir: self.dir,
            extent: self.extent.simplify(),
        };
        trace!(
            "line {}: simplify evaluate extent: {:?}",
            new_l,
            new_l.evaluate_extent()
        );
        if let Some(p) = new_l.evaluate_extent() {
            return Region2::Singleton(p.simplify());
        }
        Region2::Line(new_l)
    }

    pub fn evaluate_with(self, eqns: &eqn::Eqns) -> Self {
        Line2 {
            start: self.start.evaluate_with(eqns),
            dir: self.dir,
            extent: self.extent.evaluate_with(eqns),
        }
    }
}

#[derive(Clone, Debug)]
pub enum Region2 {
    Empty,
    // single point at 0
    Singleton(Point2<Value>),
    Line(Line2),
    // #[allow(dead_code)]
    // Union(Box<Region2>, Box<Region2>),
    Intersection(Box<Region2>, Box<Region2>),
    Full,
}

impl fmt::Display for Region2 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        use Region2::*;
        match self {
            Empty => write!(f, "ز"),
            Singleton(v) => write!(f, "{{ {} }}", v),
            Line(l) => l.fmt(f),
            Intersection(r1, r2) => write!(f, "{} ∩ {}", r1, r2),
            Full => write!(f, "ℝ²"),
        }
    }
}

impl GenericRegion for Region2 {
    fn full() -> Self {
        Region2::Full
    }

    fn intersection(self, other: Self) -> Self {
        use Region2::*;
        match (self, other) {
            (Empty, _) | (_, Empty) => Empty,
            (Full, r) | (r, Full) => r,
            (r1, r2) => Intersection(Box::new(r1), Box::new(r2)),
        }
    }

    fn simplify(self) -> Region2 {
        use Region2::*;
        match self {
            Singleton(n) => Singleton(n.simplify()),
            Line(l) => l.simplify(),
            Intersection(r1, r2) => r1.simplify().intersect(r2.simplify()),
            other => other,
        }
    }

    fn evaluate_with(self, eqns: &eqn::Eqns) -> Self {
        use Region2::*;
        match self {
            Singleton(n) => Singleton(n.evaluate_with(eqns)),
            Line(l) => Line(l.evaluate_with(eqns)),
            Intersection(r1, r2) => r1.evaluate_with(eqns).intersection(r2.evaluate_with(eqns)),
            other => other,
        }
    }
}

impl Region<Point2<Scalar>> for Region2 {
    fn singleton(value: Point2<Scalar>) -> Self {
        Region2::Singleton(value.into())
    }

    fn contains(&self, p: &Point2<Scalar>) -> Option<bool> {
        self.nearest(p).map(|n| n == *p)
    }

    fn nearest(&self, p: &Point2<Scalar>) -> Option<Point2<Scalar>> {
        use Expr::Const;
        use Region2::*;
        match self {
            Empty => None,
            Full => Some(p.clone()),
            Singleton(n) => match (&n.x, &n.y) {
                (Const(cx), Const(cy)) => Some(Point2::new(*cx, *cy)),
                _ => None,
            },
            Line(line) => {
                let pv: Point2<Value> = p.clone().into();
                let n = line.nearest(&pv).simplify();
                trace!("line {} nearest to {}: {}", line, pv, n);
                match (n.x, n.y) {
                    (Const(cx), Const(cy)) => Some(Point2::new(cx, cy)),
                    _ => None,
                }
            }
            Intersection(r1, r2) => {
                None
                // r1.clone().intersect((**r2).clone()).nearest(p)
            } /*Union(r1, r2) => {
                  use nalgebra::distance;
                  match (r1.nearest(p), r2.nearest(p)) {
                      (None, None) => None,
                      (Some(n), None) | (None, Some(n)) => Some(n),
                      (Some(n1), Some(n2)) => Some({
                          if distance(p, &n1) <= distance(p, &n2) {
                              n1
                          } else {
                              n2
                          }
                      }),
                  }
              }*/
        }
    }
}

impl Region<Point2<Value>> for Region2 {
    fn singleton(value: Point2<Value>) -> Self {
        Region2::Singleton(value)
    }

    fn contains(&self, p: &Point2<Value>) -> Option<bool> {
        self.nearest(p)
            .map(|n| n.simplify() == p.clone().simplify())
    }

    fn nearest(&self, p: &Point2<Value>) -> Option<Point2<Value>> {
        use Region2::*;
        match self {
            Empty => None,
            Full => Some(p.clone()),
            Singleton(n) => Some(n.clone()),
            Line(line) => Some(line.nearest(p)),
            Intersection(r1, r2) => r1.clone().intersect((**r2).clone()).nearest(p), /*Union(r1, r2) => {
                                                                                         use nalgebra::distance;
                                                                                         match (r1.nearest(p), r2.nearest(p)) {
                                                                                             (None, None) => None,
                                                                                             (Some(n), None) | (None, Some(n)) => Some(n),
                                                                                             (Some(n1), Some(n2)) => Some({
                                                                                                 if distance(p, &n1) <= distance(p, &n2) {
                                                                                                     n1
                                                                                                 } else {
                                                                                                     n2
                                                                                                 }
                                                                                             }),
                                                                                         }
                                                                                     }*/
        }
    }
}

impl Region2 {
    /*
    pub fn union(r1: Region2, r2: Region2) -> Region2 {
        use Region2::*;
        match (r1, r2) {
            (Empty, r) | (r, Empty) => r,
            (Full, _) | (_, Full) => Full,
            (r1, r2) => Union(Box::new(r1), Box::new(r2)),
        }
    }
    */

    pub fn intersect(self, other: Region2) -> Region2 {
        use Region2::*;
        match (self, other) {
            (Empty, _) | (_, Empty) => Empty,
            (Full, r) | (r, Full) => r.clone(),
            (Singleton(n1), Singleton(n2)) => {
                if n1 == n2 {
                    Singleton(n1)
                } else {
                    Region2::intersection(Singleton(n1), Singleton(n2))
                }
            }
            (Singleton(n), o) | (o, Singleton(n)) => {
                if o.contains(&n).unwrap_or(false) {
                    Singleton(n)
                } else {
                    Region2::intersection(Singleton(n), o)
                }
            }
            (Intersection(r1, r2), o) | (o, Intersection(r1, r2)) => r1.intersect(*r2).intersect(o),
            (Line(l1), Line(l2)) => l1.intersect(&l2).simplify(),
            /*(Union(un1, un2), o) | (o, Union(un1, un2)) => {
                Self::union(un1.intersect(o), un2.intersect(o))
            }*/
            (r1, r2) => Intersection(Box::new(r1), Box::new(r2)),
        }
    }
}