//! Data structures for representing pieces and shapes.

use crate::matrix::Mat;

use core::ops::Range;

/// Represents a location for a piece, including its orientation.
#[derive(Copy, Clone, Eq, PartialEq, Hash)]
pub struct Loc {
    /// Horizontal coordinate.
    pub x: i16,
    /// Vertical coordinate.
    pub y: i16,
    /// Rotation state.
    pub r: Rot,
}

impl From<(i16, i16, Rot)> for Loc {
    #[inline]
    fn from((x, y, r): (i16, i16, Rot)) -> Self {
        Loc { x, y, r }
    }
}

impl From<(i16, i16)> for Loc {
    #[inline]
    fn from((x, y): (i16, i16)) -> Self {
        (x, y, Rot::default()).into()
    }
}

impl core::fmt::Debug for Loc {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        (self.x, self.y, self.r).fmt(f)
    }
}

/// Represents a rotation state for a piece. The initial state is "north" (`N`), and there
/// are 4 total orientations to represent each 90 degree turn possible.
#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Default, Hash)]
#[repr(i8)]
pub enum Rot {
    /// North; the initial state.
    #[default]
    N = 0,
    /// East; clockwise ("cw") from north.
    E = 1,
    /// South; two rotations in any direction from north.
    S = 2,
    /// West; counterclockwise ("ccw") from north.
    W = 3,
}

impl From<i8> for Rot {
    #[inline]
    fn from(v: i8) -> Self {
        unsafe { core::mem::transmute(v & 3) }
    }
}

/// Interface for representations of shapes in the abstract, not tied to any particular
/// position or orientation.
pub trait Shape<'c> {
    /// Returns the cell data for this shape when given a specific rotation state.
    fn cells(&self, rot: Rot) -> Cells<'c>;
}

/// Data structure representing a set of cells located somewhere on the board. Logically
/// this is like a set of (x,y) coordinates, but the implementation uses rowwise bit
/// patterns similar to [`Mat`] for more efficient [intersection
/// tests](Cells::intersects).
///
/// The cells in this representation cannot be rotated; rotations are achieved by
/// modifying the rotation state of a [`Loc`] and then determining the cells of the result
/// using [`Piece::cells`].
#[derive(Copy, Clone, Eq)]
pub struct Cells<'c> {
    data: *const u16,
    x: i16,
    y: i16,
    h: i16,
    w: i16,
    _slice: core::marker::PhantomData<&'c [u16]>,
}

impl PartialEq for Cells<'_> {
    #[inline]
    fn eq(&self, rhs: &Self) -> bool {
        // XXX(iitalics): identical 'data' should imply identical width; width is only
        // stored to make bounds tests faster but could theoretically be derived from the
        // bits in each row
        debug_assert!(self.data != rhs.data || self.w == rhs.w);
        (self.data, self.x, self.y, self.h) == (rhs.data, rhs.x, rhs.y, rhs.h)
    }
}

impl core::hash::Hash for Cells<'_> {
    #[inline]
    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
        (self.x, self.y, self.data()).hash(state)
    }
}

impl<'c> Cells<'c> {
    /// Constructs cells from the initial extents and rowwise bit representations of the
    /// occupied cells.
    #[inline]
    pub fn new(xs: Range<i16>, ys: Range<i16>, data: &'c [u16]) -> Self {
        assert!(!xs.is_empty());
        assert!(!ys.is_empty());
        assert_eq!(ys.len(), data.len());
        Self {
            x: xs.start,
            y: ys.start,
            w: xs.end - xs.start,
            h: ys.end - ys.start,
            data: data.as_ptr(),
            _slice: core::marker::PhantomData,
        }
    }

    /// Returns a pair of ranges, `(xs, ys)`, which indicates the furthest extents that
    /// may contain cells. For example, a north T piece at the origin would return
    /// `(-1..=1, 0..=1)` since it contains leftmost cell (-1,0), rightmost cell (0,1),
    /// and uppermost cell (0,1).
    #[inline]
    pub fn extents(&self) -> (Range<i16>, Range<i16>) {
        (self.x..self.x + self.w, self.y..self.y + self.h)
    }

    #[inline]
    fn data(&self) -> &'c [u16] {
        let ptr = self.data;
        let len = self.h as usize;
        unsafe { core::slice::from_raw_parts(ptr, len) }
    }

    /// Returns true if any of the cells intersect with the given matrix.
    pub fn intersects(&self, mat: &Mat) -> bool {
        if self.x < 0 || self.x + self.w > mat.cols() {
            return true;
        }
        for (dy, &row) in self.data().iter().enumerate() {
            let y = self.y + dy as i16;
            let mask = row << self.x; // should never overflow
            if !mat.test_row(y, mask, 0) {
                return true;
            }
        }
        false
    }

    /// Translates the cells by the given amount in both directions.
    #[inline]
    pub fn translate(&self, dx: i16, dy: i16) -> Self {
        let mut copy = *self;
        copy.x = self.x.checked_add(dx).expect("overflow/underflow");
        copy.y = self.y.checked_add(dy).expect("overflow/underflow");
        copy
    }

    #[cfg(test)]
    pub(crate) fn coords(&self) -> impl Iterator<Item = (i16, i16)> + 'c {
        let data = self.data();
        let (xs, ys) = self.extents();
        ys.enumerate()
            .flat_map(move |(i, y)| xs.clone().enumerate().map(move |(j, x)| (i, j, (x, y))))
            .filter_map(move |(i, j, pos)| {
                if data[i] & (1 << j) != 0 {
                    Some(pos)
                } else {
                    None
                }
            })
    }
}

impl core::fmt::Debug for Cells<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        let data = self.data();
        let (xs, ys) = self.extents();
        write!(f, "Cells{{x0={},y0={},data=[", xs.start, ys.start)?;
        for (i, &row) in data.iter().enumerate() {
            if i > 0 {
                write!(f, ",")?;
            }
            write!(f, "\"")?;
            for j in 0..xs.len() {
                let occ = row & (1 << j) != 0;
                write!(f, "{}", if occ { 'x' } else { '.' })?;
            }
            write!(f, "\"")?;
        }
        write!(f, "]}}")?;
        Ok(())
    }
}

/// Represents the current state of a piece.
#[derive(Clone, Eq, PartialEq, Debug, Hash)]
pub struct Piece<T> {
    /// The piece type (i.e. its shape).
    pub ty: T,
    /// The location of the piece.
    pub loc: Loc,
}

impl<'c, T: Shape<'c>> Piece<T> {
    /// Returns the cells occupied by this piece.
    pub fn cells(&self) -> Cells<'c> {
        self.ty.cells(self.loc.r).translate(self.loc.x, self.loc.y)
    }
}

/// Interface for piece types that have a initial spawn location.
pub trait Spawn {
    /// Returns the (x,y) coordinates where the piece should spawn.
    fn spawn_pos(&self) -> (i16, i16);
}

impl<T: Spawn> Piece<T> {
    pub fn spawn(ty: T) -> Self {
        let loc = ty.spawn_pos().into();
        Self { ty, loc }
    }
}

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

    use alloc::vec::Vec;
    use core::ops::RangeInclusive;

    #[test]
    fn test_angle_from_i8() {
        let rots = core::iter::repeat([Rot::N, Rot::E, Rot::S, Rot::W]).flatten();
        let ints = 0i8..=127;
        for (i, r) in ints.zip(rots) {
            assert_eq!(r, i.into(), "fwd,i={i}");
        }
        let rots = core::iter::repeat([Rot::W, Rot::S, Rot::E, Rot::N]).flatten();
        let ints = (-128i8..=-1).rev(); // -1,-2,...,-128
        for (i, r) in ints.zip(rots) {
            assert_eq!(r, i.into(), "bwd,i={i}");
        }
    }

    // .X.
    // .XX  origin at (1,1)
    // ...
    #[derive(Copy, Clone, Eq, PartialEq, Debug, Hash)]
    pub struct Tri;

    impl Shape<'static> for Tri {
        fn cells(&self, rot: Rot) -> Cells<'static> {
            match rot {
                Rot::N => Cells::new(0..2, 0..2, &[0b11, 0b01]),
                Rot::E => Cells::new(0..2, -1..1, &[0b01, 0b11]),
                Rot::S => Cells::new(-1..1, -1..1, &[0b10, 0b11]),
                Rot::W => Cells::new(-1..1, 0..2, &[0b11, 0b10]),
            }
        }
    }

    fn coords(x: i16, y: i16, r: Rot) -> Vec<(i16, i16)> {
        let piece = Piece {
            ty: Tri,
            loc: Loc { x, y, r },
        };
        let mut coords: Vec<_> = piece.cells().coords().collect();
        coords.sort();
        coords
    }

    #[test]
    fn test_coords() {
        assert_eq!(coords(5, 8, Rot::N), [(5, 8), (5, 9), (6, 8)]);
        assert_eq!(coords(5, 8, Rot::E), [(5, 7), (5, 8), (6, 8),]);
        assert_eq!(coords(5, 8, Rot::S), [(4, 8), (5, 7), (5, 8),]);
        assert_eq!(coords(5, 8, Rot::W), [(4, 8), (5, 8), (5, 9),]);
    }

    const MAT: &Mat = mat! {
        ".........x";
        "..x.....xx";
        "xxx.xxx.xx";
    };

    fn isects(xs: RangeInclusive<i16>, y: i16, r: Rot) -> Vec<bool> {
        xs.map(|x| {
            let piece = Piece {
                ty: Tri,
                loc: Loc { x, y, r },
            };
            piece.cells().intersects(MAT)
        })
        .collect()
    }

    #[test]
    #[allow(clippy::just_underscores_and_digits)]
    fn test_intersects() {
        use Rot::*;
        let __ = false;
        let xx = true;
        // N.
        // NN
        assert_eq!(isects(0..=8, 0, N), [xx; 9]);
        assert_eq!(isects(0..=8, 1, N), [__, xx, xx, __, __, __, __, xx, xx]);
        assert_eq!(isects(0..=8, 2, N), [__, __, __, __, __, __, __, __, xx]);
        assert_eq!(isects(0..=8, 3, N), [__; 9]);
        // EE
        // E.
        assert_eq!(isects(0..=8, 0, E), [xx; 9]);
        assert_eq!(isects(0..=8, 1, E), [xx, xx, xx, __, xx, xx, xx, xx, xx]);
        assert_eq!(isects(0..=8, 2, E), [__, __, xx, __, __, __, __, __, xx]);
        assert_eq!(isects(0..=8, 3, E), [__; 9]);
        // SS
        // .S
        assert_eq!(isects(1..=9, 0, S), [xx; 9]);
        assert_eq!(isects(1..=9, 1, S), [xx, xx, xx, xx, xx, xx, __, xx, xx]);
        assert_eq!(isects(1..=9, 2, S), [__, xx, __, __, __, __, __, xx, xx]);
        assert_eq!(isects(1..=9, 3, S), [__, __, __, __, __, __, __, __, xx]);
        // .W
        // WW
        assert_eq!(isects(1..=9, 0, W), [xx; 9]);
        assert_eq!(isects(1..=9, 1, W), [__, xx, xx, __, __, __, __, xx, xx]);
        assert_eq!(isects(1..=9, 2, W), [__, __, __, __, __, __, __, __, xx]);
        assert_eq!(isects(1..=9, 3, W), [__; 9]);
    }
}