//! Places and sizes on the canvas.
//!
//! The canvas is a grid of terminal cells (at Normal zoom) with no edges, so
//! coordinates can be negative. `x` grows to the right and `y` downward, as in
//! the terminal.

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

/// A point on the canvas.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
pub struct CanvasPos {
    pub x: i32,
    pub y: i32,
}

impl CanvasPos {
    /// The point at `x`, `y`.
    pub const fn new(x: i32, y: i32) -> CanvasPos {
        CanvasPos { x, y }
    }
}

/// A movement on the canvas: `dx` cells to the right, `dy` cells down.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
pub struct CanvasOffset {
    pub dx: i32,
    pub dy: i32,
}

impl CanvasOffset {
    /// A movement of `dx` cells to the right and `dy` cells down.
    pub const fn new(dx: i32, dy: i32) -> CanvasOffset {
        CanvasOffset { dx, dy }
    }
}

impl Add<CanvasOffset> for CanvasPos {
    type Output = CanvasPos;

    fn add(self, offset: CanvasOffset) -> CanvasPos {
        CanvasPos::new(self.x + offset.dx, self.y + offset.dy)
    }
}

impl AddAssign<CanvasOffset> for CanvasPos {
    fn add_assign(&mut self, offset: CanvasOffset) {
        *self = *self + offset;
    }
}

impl Sub for CanvasPos {
    type Output = CanvasOffset;

    /// The movement that goes from `other` to `self`.
    fn sub(self, other: CanvasPos) -> CanvasOffset {
        CanvasOffset::new(self.x - other.x, self.y - other.y)
    }
}

impl Neg for CanvasOffset {
    type Output = CanvasOffset;

    fn neg(self) -> CanvasOffset {
        CanvasOffset::new(-self.dx, -self.dy)
    }
}

/// A width and a height on the canvas, in cells.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
pub struct CanvasSize {
    pub width: u16,
    pub height: u16,
}

impl CanvasSize {
    /// A size of `width` by `height` cells.
    pub const fn new(width: u16, height: u16) -> CanvasSize {
        CanvasSize { width, height }
    }
}

/// A rectangle on the canvas: its top-left corner and its size.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
pub struct CanvasRect {
    pub pos: CanvasPos,
    pub size: CanvasSize,
}

impl CanvasRect {
    /// The rectangle with its top-left corner at `pos`.
    pub const fn new(pos: CanvasPos, size: CanvasSize) -> CanvasRect {
        CanvasRect { pos, size }
    }

    /// The first column inside.
    pub fn left(self) -> i32 {
        self.pos.x
    }

    /// The first row inside.
    pub fn top(self) -> i32 {
        self.pos.y
    }

    /// The first column past the right edge.
    pub fn right(self) -> i32 {
        self.pos.x + i32::from(self.size.width)
    }

    /// The first row past the bottom edge.
    pub fn bottom(self) -> i32 {
        self.pos.y + i32::from(self.size.height)
    }

    /// The middle cell (rounded toward the top left).
    pub fn center(self) -> CanvasPos {
        CanvasPos::new(
            self.pos.x + i32::from(self.size.width) / 2,
            self.pos.y + i32::from(self.size.height) / 2,
        )
    }

    /// Whether the two rectangles share at least one cell.
    pub fn overlaps(self, other: CanvasRect) -> bool {
        self.left() < other.right()
            && other.left() < self.right()
            && self.top() < other.bottom()
            && other.top() < self.bottom()
    }
}

/// The four directions, on screen and on the canvas. Up is toward smaller
/// `y`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Direction {
    Up,
    Right,
    Down,
    Left,
}

impl Direction {
    /// The direction pointing the other way.
    pub fn opposite(self) -> Direction {
        match self {
            Direction::Up => Direction::Down,
            Direction::Right => Direction::Left,
            Direction::Down => Direction::Up,
            Direction::Left => Direction::Right,
        }
    }
}