use crate::{
    DBData, DBWeight, Timestamp,
    algebra::{HasZero, MonoidValue, Semigroup},
    dynamic::{DataTrait, DynUnit, Erase, WeightTrait},
    operator::Aggregator,
    trace::Cursor,
    utils::Tup1,
};
use std::{cmp::min, marker::PhantomData};

/// An [aggregator](`crate::operator::Aggregator`) that returns the
/// smallest value with non-zero weight.
///
/// This is a highly efficient aggregator, as it only scans the input
/// Z-set until hitting the first non-zero weight.
#[derive(Clone)]
pub struct Min;

#[derive(Clone)]
pub struct MinSemigroup<V>(PhantomData<V>);

impl<V> Semigroup<V> for MinSemigroup<V>
where
    V: Ord + Clone,
{
    fn combine(left: &V, right: &V) -> V {
        min(left, right).clone()
    }
}

impl<V, T, R> Aggregator<V, T, R> for Min
where
    V: DBData,
    T: Timestamp,
    R: DBWeight + MonoidValue,
{
    type Accumulator = V;
    type Output = V;
    type Semigroup = MinSemigroup<V>;

    fn aggregate<VTrait, RTrait>(
        &self,
        cursor: &mut dyn Cursor<VTrait, DynUnit, T, RTrait>,
    ) -> Option<Self::Output>
    where
        VTrait: DataTrait + ?Sized,
        RTrait: WeightTrait + ?Sized,
        V: Erase<VTrait>,
        R: Erase<RTrait>,
    {
        while cursor.key_valid() {
            // FIXME: This could be more succinct if we had an `Add<&Self, Output = Self>`
            // bound on `R`
            let mut weight: R = HasZero::zero();
            cursor.map_times(&mut |_, w| {
                weight.add_assign_by_ref(unsafe { w.downcast() });
            });
            if !weight.is_zero() {
                return Some(unsafe { cursor.key().downcast::<V>().clone() });
            }

            cursor.step_key();
        }

        None
    }

    fn finalize(&self, accumulator: Self::Accumulator) -> Self::Output {
        accumulator
    }
}

/// An aggregator that returns the smallest Some() value with non-zero weight
/// or None if no such value exists.
///
/// This is useful for implementing the SQL MIN operator.
#[derive(Clone)]
pub struct MinSome1;

#[derive(Clone)]
pub struct MinSome1Semigroup<V>(PhantomData<V>);

impl<V> Semigroup<Tup1<Option<V>>> for MinSome1Semigroup<V>
where
    V: DBData,
{
    fn combine(left: &Tup1<Option<V>>, right: &Tup1<Option<V>>) -> Tup1<Option<V>> {
        Tup1(match (&left.0, &right.0) {
            (None, None) => None,
            (Some(left), None) => Some(left.clone()),
            (None, Some(right)) => Some(right.clone()),
            (Some(left), Some(right)) => Some(min(left, right).clone()),
        })
    }
}

impl<V, T, R> Aggregator<Tup1<Option<V>>, T, R> for MinSome1
where
    V: DBData,
    T: Timestamp,
    R: DBWeight + MonoidValue,
{
    type Accumulator = Tup1<Option<V>>;
    type Output = Tup1<Option<V>>;
    type Semigroup = MinSome1Semigroup<V>;

    fn aggregate<VTrait, RTrait>(
        &self,
        cursor: &mut dyn Cursor<VTrait, DynUnit, T, RTrait>,
    ) -> Option<Self::Output>
    where
        VTrait: DataTrait + ?Sized,
        RTrait: WeightTrait + ?Sized,
        Tup1<Option<V>>: Erase<VTrait>,
        R: Erase<RTrait>,
    {
        let mut result = None;

        while cursor.key_valid() {
            // FIXME: This could be more succinct if we had an `Add<&Self, Output = Self>`
            // bound on `R`
            let mut weight: R = HasZero::zero();
            cursor.map_times(&mut |_, w| {
                weight.add_assign_by_ref(unsafe { w.downcast() });
            });
            if !weight.is_zero() {
                match unsafe { &cursor.key().downcast::<Tup1<Option<V>>>().0 } {
                    Some(v) => return Some(Tup1(Some(v.clone()))),
                    None => result = Some(Tup1(None)),
                }
            }

            cursor.step_key();
        }

        result
    }

    fn finalize(&self, accumulator: Self::Accumulator) -> Self::Output {
        accumulator
    }
}

/// Given a tuple `Tup1<(Option<K>, V)>`, this aggregator that returns
/// the smallest V for the smallest value K that is not None.  This is
/// useful for implementing the SQL ARG_MIN operator.  Notice that the
/// ARG_MIN(a, b) function returns the smallest a for the smallest b
/// in the collection (it compares first on b); however, the compiler
/// swaps the arguments when using this aggregator, so type `Option<K>`
/// below is the type of b, and V is the type of A.  (This aggregator
/// is used only when b is nullable, otherwise the regular Min
/// aggregator is fine.)
#[derive(Clone)]
pub struct ArgMinSome;

#[derive(Clone)]
pub struct ArgMinSomeSemigroup<K, V>(PhantomData<(K, V)>);

impl<K, V> Semigroup<Tup1<(Option<K>, V)>> for ArgMinSomeSemigroup<K, V>
where
    K: DBData,
    V: DBData,
{
    fn combine(left: &Tup1<(Option<K>, V)>, right: &Tup1<(Option<K>, V)>) -> Tup1<(Option<K>, V)> {
        match (&left.0.0, &right.0.0) {
            (None, None) => min(left, right).clone(),
            (Some(_), None) => left.clone(),
            (None, Some(_)) => right.clone(),
            (Some(_), Some(_)) => min(left, right).clone(),
        }
    }
}

impl<V, K, T, R> Aggregator<Tup1<(Option<K>, V)>, T, R> for ArgMinSome
where
    K: DBData,
    V: DBData,
    T: Timestamp,
    R: DBWeight + MonoidValue,
{
    type Accumulator = Tup1<(Option<K>, V)>;
    type Output = Tup1<V>;
    type Semigroup = ArgMinSomeSemigroup<K, V>;

    fn aggregate<VTrait, RTrait>(
        &self,
        cursor: &mut dyn Cursor<VTrait, DynUnit, T, RTrait>,
    ) -> Option<Self::Accumulator>
    where
        VTrait: DataTrait + ?Sized,
        RTrait: WeightTrait + ?Sized,
        Tup1<(Option<K>, V)>: Erase<VTrait>,
        R: Erase<RTrait>,
    {
        // Result will be None if the cursor points to an empty collection
        let mut result = None;

        while cursor.key_valid() {
            // FIXME: This could be more succinct if we had an `Add<&Self, Output = Self>`
            // bound on `R`
            let mut weight: R = HasZero::zero();
            cursor.map_times(&mut |_, w| {
                weight.add_assign_by_ref(unsafe { w.downcast() });
            });
            if !weight.is_zero() {
                let current = unsafe { cursor.key().downcast::<Tup1<(Option<K>, V)>>() };
                match current.0 {
                    (Some(_), _) => return Some(current.clone()),
                    (None, _) => {
                        if result.is_none() {
                            // remember first value, this may be the final result if
                            // all tuples have None in the first field
                            result = Some(current.clone());
                            // skip to first non-None in the first field, if it exists
                            cursor.seek_key_with(&|key| {
                                let typed = unsafe { key.downcast::<Tup1<(Option<K>, V)>>() };
                                typed.0.0.is_some()
                            });
                        }
                    }
                }
            }
        }

        result
    }

    fn finalize(&self, accumulator: Self::Accumulator) -> Self::Output {
        Tup1::new(accumulator.0.1)
    }
}
