use crate::{fragment::fragment_struct::Fragment, Doubling, Growth};
use alloc::string::String;
use alloc::vec::Vec;

/// A split vector; i.e., a vector of fragments, with the following features:
///
/// * Flexible in growth strategies; custom strategies can be defined.
/// * Growth does not cause any memory copies.
/// * Capacity of an already created fragment is never changed.
/// * The above feature allows the data to stay pinned in place. Memory location of an item added to the split vector will never change unless it is removed from the vector or the vector is dropped.
pub struct SplitVec<T, G = Doubling>
where
    G: Growth,
{
    pub(crate) len: usize,
    pub(crate) fragments: Vec<Fragment<T>>,
    pub(crate) growth: G,
}

impl<T, G> SplitVec<T, G>
where
    G: Growth,
{
    pub(crate) fn from_raw_parts(len: usize, fragments: Vec<Fragment<T>>, growth: G) -> Self {
        debug_assert_eq!(len, fragments.iter().map(|x| x.len()).sum());
        Self {
            len,
            fragments,
            growth,
        }
    }

    // get
    /// Growth strategy of the split vector.
    ///
    /// Note that allocated data of split vector is pinned and allocated in fragments.
    /// Therefore, growth does not require copying data.
    ///
    /// The growth strategy determines the capacity of each fragment
    /// that will be added to the split vector when needed.
    ///
    /// Furthermore, it has an impact on index-access to the elements.
    /// See below for the complexities:
    ///
    /// * `Linear` (`SplitVec::with_linear_growth`) -> O(1)
    /// * `Doubling` (`SplitVec::with_doubling_growth`) -> O(1)
    /// * `Recursive` (`SplitVec::with_recursive_growth`) -> O(f) where f is the number of fragments; and O(1) append time complexity
    pub fn growth(&self) -> &G {
        &self.growth
    }

    /// Returns a mutable reference to the vector of fragments.
    ///
    /// # Safety
    ///
    /// Fragments of the split vector maintain the following structure:
    /// * the fragments vector is never empty, it has at least one fragment;
    /// * all fragments have a positive capacity;
    ///     * capacity of fragment f is equal to `self.growth.get_capacity(f)`.
    /// * if there exist F fragments in the vector:
    ///     * none of the fragments with indices `0..F-2` has capacity; i.e., len==capacity,
    ///     * the last fragment at position `F-1` might or might not have capacity.
    ///
    /// Breaking this structure invalidates the `SplitVec` struct,
    /// and its methods lead to UB.
    pub unsafe fn fragments_mut(&mut self) -> &mut Vec<Fragment<T>> {
        &mut self.fragments
    }

    /// Returns the fragments of the split vector.
    ///
    /// The fragments of the split vector satisfy the following structure:
    /// * the fragments vector is never empty, it has at least one fragment;
    /// * all fragments have a positive capacity;
    ///     * capacity of fragment f is equal to `self.growth.get_capacity(f)`.
    /// * if there exist F fragments in the vector:
    ///     * none of the fragments with indices `0..F-2` has capacity; i.e., len==capacity,
    ///     * the last fragment at position `F-1` might or might not have capacity.
    ///
    /// # Examples
    ///
    /// ```
    /// use orx_split_vec::*;
    ///
    /// let mut vec = SplitVec::with_linear_growth(2);
    ///
    /// for i in 0..6 {
    ///     vec.push(i);
    /// }
    ///
    /// assert_eq!(2, vec.fragments().len());
    /// assert_eq!(&[0, 1, 2, 3], vec.fragments()[0].as_slice());
    /// assert_eq!(&[4, 5], vec.fragments()[1].as_slice());
    ///
    /// ```
    pub fn fragments(&self) -> &[Fragment<T>] {
        &self.fragments
    }

    /// Maximum capacity that can safely be reached by the vector in a concurrent program.
    /// This value is often related with the capacity of the container holding meta information about allocations.
    /// Note that the split vector can naturally grow beyond this number, this bound is only relevant when the vector is `Sync`ed among threads.
    pub fn maximum_concurrent_capacity(&self) -> usize {
        self.growth()
            .maximum_concurrent_capacity(&self.fragments, self.fragments.capacity())
    }

    /// Makes sure that the split vector can safely reach the given `maximum_capacity` in a concurrent program.
    /// * returns Ok of the new maximum capacity if the vector succeeds to reserve.
    /// * returns the corresponding error message otherwise.
    ///
    /// Note that this method does not allocate the `maximum_capacity`, it only ensures that the concurrent growth to this capacity is safe.
    /// In order to achieve this, it might need to extend allocation of the fragments collection.
    /// However, note that by definition number of fragments is insignificant in a split vector.
    pub fn concurrent_reserve(&mut self, maximum_capacity: usize) -> Result<usize, String> {
        let required_num_fragments = self
            .growth
            .required_fragments_len(&self.fragments, maximum_capacity)?;

        let additional_fragments = match required_num_fragments > self.fragments.capacity() {
            true => required_num_fragments - self.fragments.capacity(),
            false => 0,
        };

        if additional_fragments > 0 {
            let prior_fragments_capacity = self.fragments.capacity();
            let num_fragments = self.fragments.len();

            unsafe { self.fragments.set_len(prior_fragments_capacity) };

            self.fragments.reserve(additional_fragments);

            unsafe { self.fragments.set_len(num_fragments) };
        }

        Ok(self.maximum_concurrent_capacity())
    }

    /// Returns the fragment index and the index within fragment of the item with the given `index`;
    /// None if the index is out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// use orx_split_vec::*;
    ///
    /// let mut vec = SplitVec::with_linear_growth(2);
    ///
    /// for i in 0..6 {
    ///     vec.push(i);
    /// }
    ///
    /// assert_eq!(&[0, 1, 2, 3], vec.fragments()[0].as_slice());
    /// assert_eq!(&[4, 5], vec.fragments()[1].as_slice());
    ///
    /// // first fragment
    /// assert_eq!(Some((0, 0)), vec.get_fragment_and_inner_indices(0));
    /// assert_eq!(Some((0, 1)), vec.get_fragment_and_inner_indices(1));
    /// assert_eq!(Some((0, 2)), vec.get_fragment_and_inner_indices(2));
    /// assert_eq!(Some((0, 3)), vec.get_fragment_and_inner_indices(3));
    ///
    /// // second fragment
    /// assert_eq!(Some((1, 0)), vec.get_fragment_and_inner_indices(4));
    /// assert_eq!(Some((1, 1)), vec.get_fragment_and_inner_indices(5));
    ///
    /// // out of bounds
    /// assert_eq!(None, vec.get_fragment_and_inner_indices(6));
    /// ```
    #[inline(always)]
    pub fn get_fragment_and_inner_indices(&self, index: usize) -> Option<(usize, usize)> {
        self.growth
            .get_fragment_and_inner_indices(self.len, &self.fragments, index)
    }

    // helpers

    #[inline(always)]
    pub(crate) fn has_capacity_for_one(&self) -> bool {
        // TODO: below line should not fail but it does when clear or truncate is called
        // self.fragments[self.fragments.len() - 1].has_capacity_for_one()

        self.fragments
            .last()
            .map(|f| f.has_capacity_for_one())
            .unwrap_or(false)
    }

    /// Adds a new fragment to fragments of the split vector; returns the capacity of the new fragment.
    #[inline(always)]
    pub(crate) fn add_fragment(&mut self) -> usize {
        self.add_fragment_get_fragment_capacity(false)
    }

    /// Adds a new fragment and return the capacity of the added (now last) fragment.
    fn add_fragment_get_fragment_capacity(&mut self, zeroed: bool) -> usize {
        let new_fragment_capacity = self.growth.new_fragment_capacity(&self.fragments);

        let mut new_fragment = Fragment::new(new_fragment_capacity);
        if zeroed {
            // SAFETY: new_fragment empty with len=0, zeroed elements will not be read with safe api
            unsafe { new_fragment.zero() };
        }

        self.fragments.push(new_fragment);

        new_fragment_capacity
    }

    pub(crate) fn add_fragment_with_first_value(&mut self, first_value: T) {
        let capacity = self.growth.new_fragment_capacity(&self.fragments);
        let new_fragment = Fragment::new_with_first_value(capacity, first_value);
        self.fragments.push(new_fragment);
    }

    pub(crate) fn drop_last_empty_fragment(&mut self) {
        let drop_empty_last_fragment = self.fragments.last().map(|f| f.is_empty()).unwrap_or(false);
        if drop_empty_last_fragment {
            _ = self.fragments.pop();
        }
    }

    #[inline(always)]
    pub(crate) fn growth_get_ptr(&self, index: usize) -> Option<*const T> {
        self.growth.get_ptr(&self.fragments, index)
    }

    #[inline(always)]
    pub(crate) fn growth_get_ptr_mut(&mut self, index: usize) -> Option<*mut T> {
        self.growth.get_ptr_mut(&mut self.fragments, index)
    }

    /// Makes sure that the split vector can safely reach the given `maximum_capacity` in a concurrent program.
    ///
    /// Returns new maximum capacity.
    ///
    /// Note that this method does not allocate the `maximum_capacity`, it only ensures that the concurrent growth to this capacity is safe.
    /// In order to achieve this, it might need to extend allocation of the fragments collection.
    /// However, note that by definition number of fragments is insignificant in a split vector.
    pub fn reserve_maximum_concurrent_capacity(&mut self, new_maximum_capacity: usize) -> usize {
        let current_max = self.maximum_concurrent_capacity();
        match current_max < new_maximum_capacity {
            true => {
                self.concurrent_reserve(new_maximum_capacity)
                    .expect("Failed to reserve maximum capacity");
                self.maximum_concurrent_capacity()
            }
            false => self.maximum_concurrent_capacity(),
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::growth::growth_trait::GrowthWithConstantTimeAccess;
    use crate::test_all_growth_types;
    use crate::*;
    use alloc::vec;

    #[test]
    fn fragments() {
        fn test<G: Growth>(mut vec: SplitVec<usize, G>) {
            for i in 0..42 {
                vec.push(i);
            }

            let mut combined = vec![];
            let mut combined_mut = vec![];
            for fra in vec.fragments() {
                combined.extend_from_slice(fra);
            }
            for fra in unsafe { vec.fragments_mut() } {
                combined_mut.extend_from_slice(fra);
            }

            for i in 0..42 {
                assert_eq!(i, vec[i]);
                assert_eq!(i, combined[i]);
                assert_eq!(i, combined_mut[i]);
            }
        }
        test_all_growth_types!(test);
    }

    #[test]
    fn get_fragment_and_inner_indices() {
        fn test<G: Growth>(mut vec: SplitVec<usize, G>) {
            for i in 0..432 {
                vec.push(i);
                assert_eq!(None, vec.get_fragment_and_inner_indices(i + 1));
            }

            for i in 0..432 {
                let (f, ii) = vec.get_fragment_and_inner_indices(i).expect("is-some");
                assert_eq!(vec[i], vec.fragments[f][ii]);
            }
        }
        test_all_growth_types!(test);
    }

    #[test]
    fn get_ptr_mut() {
        fn test<G: GrowthWithConstantTimeAccess>(mut vec: SplitVec<usize, G>) {
            for i in 0..65 {
                vec.push(i);
            }
            for i in 0..64 {
                let p = vec.get_ptr_mut(i).expect("is-some");
                assert_eq!(i, unsafe { *p });
            }
            for i in 64..vec.capacity() {
                let p = vec.get_ptr_mut(i);
                assert!(p.is_some());
            }

            for i in vec.capacity()..(vec.capacity() * 2) {
                let p = vec.get_ptr_mut(i);
                assert!(p.is_none());
            }
        }

        test(SplitVec::with_doubling_growth());
        test(SplitVec::with_linear_growth(6));
    }

    #[test]
    fn add_fragment() {
        fn test<G: Growth>(mut vec: SplitVec<usize, G>) {
            for _ in 0..10 {
                let expected_new_fragment_cap = vec.growth.new_fragment_capacity(&vec.fragments);
                let new_fragment_cap = vec.add_fragment();
                assert_eq!(expected_new_fragment_cap, new_fragment_cap);
            }

            vec.clear();

            let mut expected_capacity = vec.capacity();
            for _ in 0..2 {
                let expected_new_fragment_cap = vec.growth.new_fragment_capacity(&vec.fragments);
                expected_capacity += expected_new_fragment_cap;
                vec.add_fragment();
            }

            assert_eq!(expected_capacity, vec.capacity());
        }

        test_all_growth_types!(test);
    }
}