//! Rectangles where the sides are parallel to the x and y-axes.

use std::ops::{Add, AddAssign, Sub};

//use alga::general::{Additive, Identity};
use nalgebra::Scalar;
use num_traits::sign::{self, Signed};
use num_traits::Zero;
use serde::{Deserialize, Serialize};

use super::Vec2;

/// Represents a Rectangle with the value type T.
#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
pub struct Rect<T: Scalar + Copy>
{
    /// The x coordinate, or leftmost coordinate of the Rect.
    pub x: T,
    /// The y coordinate, or rightmost coordinate of the Rect.
    pub y: T,
    /// The width of the Rect.
    pub w: T,
    /// The height of the Rect.
    pub h: T,
}

impl<T: Scalar + Copy> Rect<T>
{
    /// Create a new Rectangle from the internal values, where it might be nicer
    /// to use a function instead of setting the values directly.
    pub fn new(x: T, y: T, w: T, h: T) -> Self { Self { x, y, w, h } }

    /// Create a Rectangle from a slice. Indices are [x, y, w, h].
    pub fn from_slice(slice: [T; 4]) -> Rect<T>
    where
        T: Copy,
    {
        Rect {
            x: slice[0],
            y: slice[1],
            w: slice[2],
            h: slice[3],
        }
    }

    /// Move by the Vec provided.
    pub fn translate(&mut self, by: Vec2<T>)
    where
        T: AddAssign,
    {
        self.x += by.x;
        self.y += by.y;
    }

    /// Set the posiotien of the rectangle to the given one without changing its
    /// size
    pub fn set_pos(&mut self, pos: Vec2<T>)
    {
        self.x = pos.x;
        self.y = pos.y;
    }

    /// Test if two rectangles intersect.
    pub fn intersect<'a>(this: &'a Rect<T>, other: &'a Rect<T>) -> bool
    where
        T: Add<Output = T> + PartialOrd + Copy,
    {
        !(this.x > other.x + other.w
            || this.x + this.w < other.x
            || this.y > other.y + other.h
            || this.y + this.h < other.y)
    }

    /// Function to calculate the bounding rectangle that is between two
    /// vectors. The order of the vectors is irrelevent for this. As long as
    /// they are diagonally opposite of each other, this function will work.
    pub fn bounding_rect(pos1: Vec2<T>, pos2: Vec2<T>) -> Self
    where
        T: PartialOrd + Sub<Output = T>,
    {
        let vertices = [pos1, pos2];

        Self::bounding_rect_n(&vertices)
    }

    /// Function to calculate the bounding rectangle of n vertices provided. The
    /// order of them is not relevant and a point that is contained by the
    /// vertices will not change the result.
    ///
    /// # Panics
    /// If there is not at least one vertex in the vertices slice, the function
    /// will panic, since it is impossible to calculate any bounds in such a
    /// case.
    pub fn bounding_rect_n(vertices: &[Vec2<T>]) -> Self
    where
        T: PartialOrd + Sub<Output = T>,
    {
        if vertices.is_empty() {
            panic!("Cannot create bounding rectangle without any vertices");
        }

        let mut min = vertices[0];
        let mut max = vertices[0];

        for vertex in vertices.iter().skip(1) {
            min.x = super::partial_min(min.x, vertex.x);
            min.y = super::partial_min(min.y, vertex.y);
            max.x = super::partial_max(max.x, vertex.x);
            max.y = super::partial_max(max.y, vertex.y);
        }

        Self {
            x: min.x,
            y: min.y,
            w: max.x - min.x,
            h: max.y - min.y,
        }
    }

    /// Get the shortest way that must be applied to this Rect to clear out of
    /// another Rect of the same type so that they would not intersect any more.
    pub fn shortest_way_out(&self, of: &Rect<T>) -> Vec2<T>
    where
        T: Add<Output = T> + Sub<Output = T> + Signed + PartialOrd,
    {
        // Check upwards
        let mut move_y = of.y - self.y - self.h;
        // Check downwards
        let move_down = of.y + of.h - self.y;
        if move_down < -move_y {
            move_y = move_down;
        }

        // Check left
        let mut move_x = of.x - self.x - self.w;
        // Check right
        let move_right = of.x + of.w - self.x;
        if move_right < -move_x {
            move_x = move_right;
        }

        if move_x.abs() < move_y.abs() {
            Vec2::new(move_x, T::zero())
        }
        else {
            Vec2::new(T::zero(), move_y)
        }
    }

    /// Calculate the area of the rectangle.
    pub fn area(&self) -> T
    where
        T: Signed,
    {
        sign::abs(self.w) * sign::abs(self.h)
    }

    fn contains_point(&self, point: &Vec2<T>) -> bool
    where
        T: Add<Output = T> + PartialOrd,
    {
        point.x >= self.x
            && point.x <= self.x + self.w
            && point.y >= self.y
            && point.y <= self.y + self.h
    }

    fn contains_rect(&self, rect: &Rect<T>) -> bool
    where
        T: Add<Output = T> + Sub<Output = T> + Zero + PartialOrd,
    {
        /* True, if the rightmost x-coordinate of the called rectangle is further
         * right or the same as the rightmost coordinate of the given rect.
         */
        let x_exceeds = self.x + self.w - rect.x - rect.w >= T::zero();
        // The same for the y-coordinates
        let y_exceeds = self.y + self.h - rect.y - rect.h >= T::zero();

        x_exceeds && y_exceeds && self.x <= rect.x && self.y <= rect.y
    }

    fn is_inside_rect(&self, rect: &Rect<T>) -> bool
    where
        T: Add<Output = T> + Sub<Output = T> + Zero + PartialOrd,
    {
        rect.contains_rect(&self)
    }
}

#[cfg(test)]
mod test
{
    use super::*;

    #[test]
    fn test_intersect()
    {
        let a = Rect::from_slice([0, 0, 4, 4]);
        let b = Rect::from_slice([-1, -1, 1, 1]);

        assert!(Rect::intersect(&a, &b));
    }
}