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use arret_runtime::binding::*;

use arret_runtime::boxed;
use arret_runtime::boxed::refs::Gc;
use arret_runtime::callback;
use arret_runtime::task::Task;

#[arret_rfi_derive::rust_fun("((List & Any) -> Int)")]
pub fn stdlib_length(input: Gc<boxed::List<boxed::Any>>) -> i64 {
    input.len() as i64
}

#[arret_rfi_derive::rust_fun("(All #{H T} H (List & T) -> (List H & T))")]
pub fn stdlib_cons(
    task: &mut Task,
    head: Gc<boxed::Any>,
    tail: Gc<boxed::List<boxed::Any>>,
) -> Gc<boxed::Pair<boxed::Any>> {
    boxed::Pair::new(task, head, tail)
}

#[arret_rfi_derive::rust_fun("(All #{I O [->_ ->!]} (I ->_ O) (List & I) ->_ (List & O))")]
pub fn stdlib_map(
    task: &mut Task,
    mapper: callback::Callback<
        extern "C" fn(&mut Task, boxed::Captures, Gc<boxed::Any>) -> Gc<boxed::Any>,
    >,
    input: Gc<boxed::List<boxed::Any>>,
) -> Gc<boxed::List<boxed::Any>> {
    let output_vec: Vec<Gc<boxed::Any>> =
        input.iter().map(|elem| mapper.apply(task, elem)).collect();

    boxed::List::new(task, output_vec.into_iter())
}

#[arret_rfi_derive::rust_fun("(All #{T [->_ ->!]} (T ->_ Bool) (List & T) ->_ (List & T))")]
pub fn stdlib_filter(
    task: &mut Task,
    filter: callback::Callback<extern "C" fn(&mut Task, boxed::Captures, Gc<boxed::Any>) -> bool>,
    input: Gc<boxed::List<boxed::Any>>,
) -> Gc<boxed::List<boxed::Any>> {
    let output_vec: Vec<Gc<boxed::Any>> = input
        .iter()
        .filter(|elem| filter.apply(task, *elem))
        .collect();

    boxed::List::new(task, output_vec.into_iter())
}

#[arret_rfi_derive::rust_fun("(All #{T [->_ ->!]} (T ->_ Bool) (List & T) ->_ Bool)")]
pub fn stdlib_some_p(
    task: &mut Task,
    pred: callback::Callback<extern "C" fn(&mut Task, boxed::Captures, Gc<boxed::Any>) -> bool>,
    input: Gc<boxed::List<boxed::Any>>,
) -> bool {
    input.iter().any(|elem| pred.apply(task, elem))
}

#[arret_rfi_derive::rust_fun("(All #{T [->_ ->!]} (T ->_ Bool) (List & T) ->_ Bool)")]
pub fn stdlib_every_p(
    task: &mut Task,
    pred: callback::Callback<extern "C" fn(&mut Task, boxed::Captures, Gc<boxed::Any>) -> bool>,
    input: Gc<boxed::List<boxed::Any>>,
) -> bool {
    input.iter().all(|elem| pred.apply(task, elem))
}

#[arret_rfi_derive::rust_fun("(All #{I O [->_ ->!]} (O I ->_ O) O (List & I) ->_ O)")]
pub fn stdlib_fold(
    task: &mut Task,
    folder: callback::Callback<
        extern "C" fn(&mut Task, boxed::Captures, Gc<boxed::Any>, Gc<boxed::Any>) -> Gc<boxed::Any>,
    >,
    initial: Gc<boxed::Any>,
    input: Gc<boxed::List<boxed::Any>>,
) -> Gc<boxed::Any> {
    input
        .iter()
        .fold(initial, |acc, elem| folder.apply(task, acc, elem))
}

#[arret_rfi_derive::rust_fun("(All #{T} & (List & T) -> (List & T))")]
pub fn stdlib_concat(
    task: &mut Task,
    lists: Gc<boxed::List<boxed::List<boxed::Any>>>,
) -> Gc<boxed::List<boxed::Any>> {
    let mut list_iter = lists.iter();

    match list_iter.len() {
        0 => boxed::List::empty(),
        1 => list_iter.next().unwrap(),
        2 => {
            // Avoid building a temporary `Vec`
            let head_list = list_iter.next().unwrap();
            let tail_list = list_iter.next().unwrap();

            boxed::List::new_with_tail(task, head_list.iter(), tail_list)
        }
        _ => {
            let mut head_values = vec![];
            while list_iter.len() > 1 {
                head_values.extend(list_iter.next().unwrap().iter());
            }

            // We can reuse our tail
            boxed::List::new_with_tail(task, head_values.into_iter(), list_iter.next().unwrap())
        }
    }
}

#[arret_rfi_derive::rust_fun("(All #{T} Int (List & T) -> (List & T))")]
pub fn stdlib_take(
    task: &mut Task,
    count: i64,
    input: Gc<boxed::List<boxed::Any>>,
) -> Gc<boxed::List<boxed::Any>> {
    let usize_count = if count < 0 { 0 } else { count as usize };
    boxed::List::new(task, input.iter().take(usize_count))
}

#[arret_rfi_derive::rust_fun("(All #{T} (List & T) -> (List & T))")]
pub fn stdlib_reverse(
    task: &mut Task,
    input: Gc<boxed::List<boxed::Any>>,
) -> Gc<boxed::List<boxed::Any>> {
    let output_vec: Vec<Gc<boxed::Any>> = input.iter().collect();
    boxed::List::new(task, output_vec.into_iter().rev())
}

#[arret_rfi_derive::rust_fun("(All #{T} Int T -> (List & T))")]
pub fn stdlib_repeat(
    task: &mut Task,
    count: i64,
    value: Gc<boxed::Any>,
) -> Gc<boxed::List<boxed::Any>> {
    struct RepeatIter<T: boxed::Boxed> {
        count: i64,
        value: Gc<T>,
    }

    impl<T: boxed::Boxed> Iterator for RepeatIter<T> {
        type Item = Gc<T>;

        fn next(&mut self) -> Option<Gc<T>> {
            if self.count > 0 {
                self.count -= 1;
                Some(self.value)
            } else {
                None
            }
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            if self.count < 0 {
                (0, Some(0))
            } else {
                (self.count as usize, Some(self.count as usize))
            }
        }
    }

    impl<T: boxed::Boxed> ExactSizeIterator for RepeatIter<T> {}

    boxed::List::new(task, RepeatIter { count, value })
}