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use std::{num::NonZeroUsize, sync::Arc};

use crate::{dataset::window::WindowDataset, DatasetIterator};

/// The dataset trait defines a basic collection of items with a predefined size.
pub trait Dataset<I>: Send + Sync {
    /// Gets the item at the given index.
    fn get(&self, index: usize) -> Option<I>;

    /// Gets the number of items in the dataset.
    fn len(&self) -> usize;

    /// Checks if the dataset is empty.
    fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Returns an iterator over the dataset.
    fn iter(&self) -> DatasetIterator<'_, I>
    where
        Self: Sized,
    {
        DatasetIterator::new(self)
    }

    /// Returns a new `Dataset` of all the windows of length `size`. The windows overlap.
    /// Is empty if the input `Dataset` is shorter than `size`.
    ///
    /// # Panics
    ///
    /// Panics if `size` is 0.    
    ///
    /// # Examples
    ///
    /// ```
    /// use crate::burn_dataset::{Dataset,InMemDataset};
    /// let items = [1, 2, 3, 4].to_vec();
    /// let dataset = InMemDataset::new(items.clone());
    ///
    /// let windows = dataset.windows(2);
    ///
    /// assert_eq!(windows.len(), 3);
    /// ```
    ///
    /// # Returns
    ///
    /// A `WindowDataset` instance.
    fn windows(&self, size: usize) -> WindowDataset<'_, I>
    where
        Self: Sized,
    {
        let size = NonZeroUsize::new(size).expect("window size must be non-zero");
        WindowDataset::new(self, size)
    }
}

impl<D, I> Dataset<I> for Arc<D>
where
    D: Dataset<I>,
{
    fn get(&self, index: usize) -> Option<I> {
        self.as_ref().get(index)
    }

    fn len(&self) -> usize {
        self.as_ref().len()
    }
}

impl<I> Dataset<I> for Arc<dyn Dataset<I>> {
    fn get(&self, index: usize) -> Option<I> {
        self.as_ref().get(index)
    }

    fn len(&self) -> usize {
        self.as_ref().len()
    }
}

impl<D, I> Dataset<I> for Box<D>
where
    D: Dataset<I>,
{
    fn get(&self, index: usize) -> Option<I> {
        self.as_ref().get(index)
    }

    fn len(&self) -> usize {
        self.as_ref().len()
    }
}

impl<I> Dataset<I> for Box<dyn Dataset<I>> {
    fn get(&self, index: usize) -> Option<I> {
        self.as_ref().get(index)
    }

    fn len(&self) -> usize {
        self.as_ref().len()
    }
}