use super::*;

/// An Offset represents the position of the left edge of some Segment.
/// Offsets must be paired with a *power* to map to quantum coordinates.
/// The absolute DhtLocation of the offset is determined by the "power" of its
/// context, and topology of the space, by:
///
///   dht_location = offset * 2^pow * quantum_size
pub trait Offset: Sized + Copy + Clone + Deref<Target = u32> + From<u32> {
    /// The type of quantum to map to, which also implies the absolute coordinates
    type Quantum: Quantum;

    /// Get the absolute coordinate for this Offset
    fn to_absolute(
        &self,
        topo: &Topology,
        power: u8,
    ) -> <<Self as Offset>::Quantum as Quantum>::Absolute;

    /// Get the quantum coordinate for this Offset
    fn to_quantum(&self, power: u8) -> Self::Quantum;

    /// Get the nearest rounded-down Offset for the given Loc
    fn from_absolute_rounded(loc: Loc, topo: &Topology, power: u8) -> Self;
}

/// An Offset in space.
#[derive(
    Copy,
    Clone,
    Debug,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
    Hash,
    derive_more::Add,
    derive_more::Sub,
    derive_more::Mul,
    derive_more::Div,
    derive_more::Deref,
    derive_more::DerefMut,
    derive_more::From,
    derive_more::Into,
    serde::Serialize,
    serde::Deserialize,
)]
#[serde(transparent)]
pub struct SpaceOffset(pub u32);

/// An Offset in time.
#[derive(
    Copy,
    Clone,
    Debug,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
    Hash,
    derive_more::Add,
    derive_more::Sub,
    derive_more::Mul,
    derive_more::Div,
    derive_more::Deref,
    derive_more::DerefMut,
    derive_more::From,
    derive_more::Into,
    serde::Serialize,
    serde::Deserialize,
)]
#[serde(transparent)]
pub struct TimeOffset(pub u32);

impl Offset for SpaceOffset {
    type Quantum = SpaceQuantum;

    /// Get the absolute coordinate for this Offset
    fn to_absolute(&self, topo: &Topology, power: u8) -> Loc {
        self.wrapping_mul(topo.space.quantum)
            .wrapping_mul(pow2(power))
            .into()
    }

    /// Get the quantum coordinate for this Offset
    fn to_quantum(&self, power: u8) -> Self::Quantum {
        self.wrapping_mul(pow2(power)).into()
    }

    /// Get the nearest rounded-down Offset for the given Loc
    fn from_absolute_rounded(loc: Loc, topo: &Topology, power: u8) -> Self {
        (loc.as_u32() / topo.space.quantum / pow2(power)).into()
    }
}

impl Offset for TimeOffset {
    type Quantum = TimeQuantum;

    /// Get the absolute coordinate for this Offset
    fn to_absolute(&self, topo: &Topology, power: u8) -> Timestamp {
        Timestamp::from_micros(
            self.wrapping_mul(topo.time.quantum)
                .wrapping_mul(pow2(power)) as i64,
        )
    }

    /// Get the quantum coordinate for this Offset
    fn to_quantum(&self, power: u8) -> Self::Quantum {
        self.wrapping_mul(pow2(power)).into()
    }

    /// Get the nearest rounded-down Offset for the given Loc
    fn from_absolute_rounded(loc: Loc, topo: &Topology, power: u8) -> Self {
        (loc.as_u32() / topo.time.quantum / pow2(power)).into()
    }
}

/// Any interval in space or time is represented by a node in a tree, so our
/// way of describing intervals uses tree coordinates as well:
/// The length of an interval is 2^(power), and the position of its left edge
/// is at (offset * length).
#[derive(
    Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, serde::Deserialize, serde::Serialize,
)]
pub struct Segment<O: Offset> {
    /// The exponent, where length = 2^power
    pub power: u8,
    /// The offset from the origin, measured in number of lengths
    pub offset: O,
}

impl<O: Offset> Segment<O> {
    /// Constructor
    pub fn new<OO: Into<O>>(power: u8, offset: OO) -> Self {
        Self {
            power,
            offset: offset.into(),
        }
    }

    /// How many quanta does this segment cover?
    pub fn num_quanta(&self) -> u64 {
        // If power is 32, this overflows a u32
        2u64.pow(self.power.into())
    }

    /// The length, in absolute terms (Location or microseconds of time)
    pub fn absolute_length(&self, topo: &Topology) -> u64 {
        let q = O::Quantum::dimension(topo).quantum as u64;
        // If power is 32, this overflows a u32
        self.num_quanta() * q
    }

    /// Get the quanta which bound this segment
    pub fn quantum_bounds(&self, topo: &Topology) -> (O::Quantum, O::Quantum) {
        let n = self.num_quanta();
        let a = (n * u64::from(*self.offset)) as u32;
        (
            O::Quantum::from(a).normalized(topo),
            O::Quantum::from(a.wrapping_add(n as u32).wrapping_sub(1)).normalized(topo),
        )
    }

    /// The segment contains the given quantum coord
    pub fn contains_quantum(&self, topo: &Topology, coord: O::Quantum) -> bool {
        let (lo, hi) = self.quantum_bounds(topo);
        let coord = coord.normalized(topo);
        if lo <= hi {
            lo <= coord && coord <= hi
        } else {
            lo <= coord || coord <= hi
        }
    }

    /// Split a segment in half
    pub fn bisect(&self) -> Option<[Self; 2]> {
        if self.power == 0 {
            // Can't split a quantum value (a leaf has no children)
            None
        } else {
            let power = self.power - 1;
            Some([
                Segment::new(power, O::from(self.offset.wrapping_mul(2))),
                Segment::new(power, O::from(self.offset.wrapping_mul(2).wrapping_add(1))),
            ])
        }
    }
}

impl SpaceSegment {
    /// Get the start and end bounds, in absolute Loc coordinates, for this segment
    pub fn loc_bounds(&self, topo: &Topology) -> (Loc, Loc) {
        let (a, b): (u32, u32) = bounds(&topo.space, self.power, self.offset, 1);
        (Loc::from(a), Loc::from(b))
    }
}

impl TimeSegment {
    /// Get the start and end bounds, in absolute Timestamp coordinates, for this segment
    pub fn timestamp_bounds(&self, topo: &Topology) -> (Timestamp, Timestamp) {
        let (a, b): (i64, i64) = bounds64(&topo.time, self.power, self.offset, 1);
        let o = topo.time_origin.as_micros();
        (Timestamp::from_micros(a + o), Timestamp::from_micros(b + o))
    }
}

/// Alias
pub type SpaceSegment = Segment<SpaceOffset>;
/// Alias
pub type TimeSegment = Segment<TimeOffset>;

pub(super) fn bounds<N: From<u32>>(
    dim: &Dimension,
    power: u8,
    offset: SpaceOffset,
    count: u32,
) -> (N, N) {
    debug_assert_ne!(dim.quantum, 0);
    debug_assert_ne!(count, 0);
    let q = dim.quantum.wrapping_mul(pow2(power));
    let start = offset.wrapping_mul(q);
    let len = count.wrapping_mul(q);
    (start.into(), start.wrapping_add(len).wrapping_sub(1).into())
}

pub(super) fn bounds64<N: From<i64>>(
    dim: &Dimension,
    power: u8,
    offset: TimeOffset,
    count: u32,
) -> (N, N) {
    debug_assert_ne!(dim.quantum, 0);
    debug_assert_ne!(count, 0);
    let q = dim.quantum as i64 * 2i64.pow(power.into());
    let start = (*offset as i64).wrapping_mul(q);
    let len = (count as i64).wrapping_mul(q);
    (start.into(), start.wrapping_add(len).wrapping_sub(1).into())
}