#pragma once

#include "irrt_utils.hpp"
#include "irrt_typedefs.hpp"
#include "irrt_slice.hpp"

/*
    NDArray-related implementations.
`*/

// NDArray indices are always `uint32_t`.
using NDIndex = uint32_t;

namespace {
    namespace ndarray_util {
        template <typename SizeT>
        static void set_indices_by_nth(SizeT ndims, const SizeT* shape, SizeT* indices, SizeT nth) {
            for (int32_t i = 0; i < ndims; i++) {
                int32_t dim_i = ndims - i - 1;
                int32_t dim = shape[dim_i];

                indices[dim_i] = nth % dim;
                nth /= dim;
            }
        }

        // Compute the strides of an ndarray given an ndarray `shape`
        // and assuming that the ndarray is *fully C-contagious*.
        //
        // You might want to read up on https://ajcr.net/stride-guide-part-1/.
        template <typename SizeT>
        static void set_strides_by_shape(SizeT itemsize, SizeT ndims, SizeT* dst_strides, const SizeT* shape) {
            SizeT stride_product = 1;
            for (SizeT i = 0; i < ndims; i++) {
                int dim_i = ndims - i - 1;
                dst_strides[dim_i] = stride_product * itemsize;
                stride_product *= shape[dim_i];
            }
        }

        // Compute the size/# of elements of an ndarray given its shape
        template <typename SizeT>
        static SizeT calc_size_from_shape(SizeT ndims, const SizeT* shape) {
            SizeT size = 1;
            for (SizeT dim_i = 0; dim_i < ndims; dim_i++) size *= shape[dim_i];
            return size;
        }

        template <typename SizeT>
        static bool can_broadcast_shape_to(
            const SizeT target_ndims,
            const SizeT *target_shape,
            const SizeT src_ndims,
            const SizeT *src_shape
        ) {
            /*
                // See https://numpy.org/doc/stable/user/basics.broadcasting.html

                This function handles this example:
                ```
                Image  (3d array): 256 x 256 x 3
                Scale  (1d array):             3
                Result (3d array): 256 x 256 x 3
                ```

                Other interesting examples to consider:
                - `can_broadcast_shape_to([3], [1, 1, 1, 1, 3]) == true`
                - `can_broadcast_shape_to([3], [3, 1]) == false`
                - `can_broadcast_shape_to([256, 256, 3], [256, 1, 3]) == true`

                In cases when the shapes contain zero(es):
                - `can_broadcast_shape_to([0], [1]) == true`
                - `can_broadcast_shape_to([0], [2]) == false`
                - `can_broadcast_shape_to([0, 4, 0, 0], [1]) == true`
                - `can_broadcast_shape_to([0, 4, 0, 0], [1, 1, 1, 1]) == true`
                - `can_broadcast_shape_to([0, 4, 0, 0], [1, 4, 1, 1]) == true`
                - `can_broadcast_shape_to([4, 3], [0, 3]) == false`
                - `can_broadcast_shape_to([4, 3], [0, 0]) == false`
            */

            // This is essentially doing the following in Python:
            // `for target_dim, src_dim in itertools.zip_longest(target_shape[::-1], src_shape[::-1], fillvalue=1)`
            for (SizeT i = 0; i < max(target_ndims, src_ndims); i++) {
                SizeT target_dim_i = target_ndims - i - 1;
                SizeT src_dim_i = src_ndims - i - 1;

                bool target_dim_exists = target_dim_i >= 0;
                bool src_dim_exists = src_dim_i >= 0;

                SizeT target_dim = target_dim_exists ? target_shape[target_dim_i] : 1;
                SizeT src_dim = src_dim_exists ? src_shape[src_dim_i] : 1;

                bool ok = src_dim == 1 || target_dim == src_dim;
                if (!ok) return false;
            }

            return true;
        }
    }

    typedef uint8_t NDSliceType;
    extern "C" {
        const NDSliceType INPUT_SLICE_TYPE_INDEX = 0;
        const NDSliceType INPUT_SLICE_TYPE_SLICE = 1;
    }

    struct NDSlice {
        // A poor-man's `std::variant<int, UserRange>`
        NDSliceType type;

        /*
            if type == INPUT_SLICE_TYPE_INDEX => `slice` points to a single `SizeT`
            if type == INPUT_SLICE_TYPE_SLICE => `slice` points to a single `UserRange`
        */
        uint8_t *slice;
    };

    namespace ndarray_util {
        template<typename SizeT>
        SizeT deduce_ndims_after_slicing(SizeT ndims, SizeT num_slices, const NDSlice *slices) {
            irrt_assert(num_slices <= ndims);

            SizeT final_ndims = ndims;
            for (SizeT i = 0; i < num_slices; i++) {
                if (slices[i].type == INPUT_SLICE_TYPE_INDEX) {
                    final_ndims--; // An integer slice demotes the rank by 1
                }
            }
            return final_ndims;
        }
    }

    template <typename SizeT>
    struct NDArrayIndicesIter {
        SizeT ndims;
        const SizeT *shape;
        SizeT *indices;

        void set_indices_zero() {
            __builtin_memset(indices, 0, sizeof(SizeT) * ndims);
        }

        void next() {
            for (SizeT i = 0; i < ndims; i++) {
                SizeT dim_i = ndims - i - 1;

                indices[dim_i]++;
                if (indices[dim_i] < shape[dim_i]) {
                    break;
                } else {
                    indices[dim_i] = 0;
                }
            }
        }
    };

    // The NDArray object. `SizeT` is the *signed* size type of this ndarray.
    //
    // NOTE: The order of fields is IMPORTANT. DON'T TOUCH IT
    //
    // Some resources you might find helpful:
    // - The official numpy implementations:
    //   - https://github.com/numpy/numpy/blob/735a477f0bc2b5b84d0e72d92f224bde78d4e069/doc/source/reference/c-api/types-and-structures.rst
    // - On strides (about reshaping, slicing, C-contagiousness, etc)
    //   - https://ajcr.net/stride-guide-part-1/.
    //   - https://ajcr.net/stride-guide-part-2/.
    //   - https://ajcr.net/stride-guide-part-3/.
    template <typename SizeT>
    struct NDArray {
        // The underlying data this `ndarray` is pointing to.
        //
        // NOTE: Formally this should be of type `void *`, but clang
        // translates `void *` to `i8 *` when run with `-S -emit-llvm`,
        // so we will put `uint8_t *` here for clarity.
        uint8_t *data;

        // The number of bytes of a single element in `data`.
        //
        // The `SizeT` is treated as `unsigned`.
        SizeT itemsize;

        // The number of dimensions of this shape.
        //
        // The `SizeT` is treated as `unsigned`.
        SizeT ndims;

        // Array shape, with length equal to `ndims`.
        //
        // The `SizeT` is treated as `unsigned`.
        //
        // NOTE: `shape` can contain 0.
        //   (those appear when the user makes an out of bounds slice into an ndarray, e.g., `np.zeros((3, 3))[400:].shape == (0, 3)`)
        SizeT *shape;

        // Array strides (stride value is in number of bytes, NOT number of elements), with length equal to `ndims`.
        //
        // The `SizeT` is treated as `signed`.
        //
        // NOTE: `strides` can have negative numbers.
        //   (those appear when there is a slice with a negative step, e.g., `my_array[::-1]`)
        SizeT *strides;

        // Calculate the size/# of elements of an `ndarray`.
        // This function corresponds to `np.size(<ndarray>)` or `ndarray.size`
        SizeT size() {
            return ndarray_util::calc_size_from_shape(ndims, shape);
        }

        // Calculate the number of bytes of its content of an `ndarray` *in its view*.
        // This function corresponds to `ndarray.nbytes`
        SizeT nbytes() {
            return this->size() * itemsize;
        }

        void set_pelement_value(uint8_t* pelement, const uint8_t* pvalue) {
            __builtin_memcpy(pelement, pvalue, itemsize);
        }

        uint8_t* get_pelement_by_indices(const SizeT *indices) {
            uint8_t* element = data;
            for (SizeT dim_i = 0; dim_i < ndims; dim_i++)
                element += indices[dim_i] * strides[dim_i];
            return element;
        }

        uint8_t* get_nth_pelement(SizeT nth) {
            irrt_assert(0 <= nth);
            irrt_assert(nth < this->size());

            SizeT* indices = (SizeT*) __builtin_alloca(sizeof(SizeT) * this->ndims);
            ndarray_util::set_indices_by_nth(this->ndims, this->shape, indices, nth);
            return get_pelement_by_indices(indices);
        }

        // Get pointer to the first element of this ndarray, assuming
        // `this->size() > 0`, i.e., not "degenerate" due to zeroes in `this->shape`)
        //
        // This is particularly useful for when the ndarray is just containing a single scalar.
        uint8_t* get_first_pelement() {
            irrt_assert(this->size() > 0);
            return this->data; // ...It is simply `this->data`
        }

        // Is the given `indices` valid/in-bounds?
        bool in_bounds(const SizeT *indices) {
            for (SizeT dim_i = 0; dim_i < ndims; dim_i++) {
                bool dim_ok = indices[dim_i] < shape[dim_i];
                if (!dim_ok) return false;
            }
            return true;
        }

        // Fill the ndarray with a value
        void fill_generic(const uint8_t* pvalue) {
            NDArrayIndicesIter<SizeT> iter;
            iter.ndims = this->ndims;
            iter.shape = this->shape;
            iter.indices = (SizeT*) __builtin_alloca(sizeof(SizeT) * ndims);
            iter.set_indices_zero();

            for (SizeT i = 0; i < this->size(); i++, iter.next()) {
                uint8_t* pelement = get_pelement_by_indices(iter.indices);
                set_pelement_value(pelement, pvalue);
            }
        }

        // Set the strides of the ndarray with `ndarray_util::set_strides_by_shape`
        void set_strides_by_shape() {
            ndarray_util::set_strides_by_shape(itemsize, ndims, strides, shape);
        }

        // https://numpy.org/doc/stable/reference/generated/numpy.eye.html
        void set_to_eye(SizeT k, const uint8_t* zero_pvalue, const uint8_t* one_pvalue) {
            __builtin_assume(ndims == 2);

            // TODO: Better implementation

            fill_generic(zero_pvalue);
            for (SizeT i = 0; i < min(shape[0], shape[1]); i++) {
                SizeT row = i;
                SizeT col = i + k;
                SizeT indices[2] = { row, col };

                if (!in_bounds(indices)) continue;

                uint8_t* pelement = get_pelement_by_indices(indices);
                set_pelement_value(pelement, one_pvalue);
            }
        }

        // To support numpy complex slices (e.g., `my_array[:50:2,4,:2:-1]`)
        //
        // Things assumed by this function:
        // - `dst_ndarray` is allocated by the caller
        // - `dst_ndarray.ndims` has the correct value (according to `ndarray_util::deduce_ndims_after_slicing`).
        //   - ... and `dst_ndarray.shape` and `dst_ndarray.strides` have been allocated by the caller as well
        //
        // Other notes:
        // - `dst_ndarray->data` does not have to be set, it will be derived.
        // - `dst_ndarray->itemsize` does not have to be set, it will be set to `this->itemsize`
        // - `dst_ndarray->shape` and `dst_ndarray.strides` can contain empty values
        void slice(SizeT num_ndslices, NDSlice* ndslices, NDArray<SizeT>* dst_ndarray) {
            // REFERENCE CODE (check out `_index_helper` in `__getitem__`):
            //   https://github.com/wadetb/tinynumpy/blob/0d23d22e07062ffab2afa287374c7b366eebdda1/tinynumpy/tinynumpy.py#L652

            irrt_assert(dst_ndarray->ndims == ndarray_util::deduce_ndims_after_slicing(this->ndims, num_ndslices, ndslices));

            dst_ndarray->data = this->data;

            SizeT this_axis = 0;
            SizeT dst_axis = 0;

            for (SizeT i = 0; i < num_ndslices; i++) {
                NDSlice *ndslice = &ndslices[i];
                if (ndslice->type == INPUT_SLICE_TYPE_INDEX) {
                    // Handle when the ndslice is just a single (possibly negative) integer
                    // e.g., `my_array[::2, -5, ::-1]`
                    //                      ^^------ like this
                    SizeT index_user = *((SizeT*) ndslice->slice);
                    SizeT index = resolve_index_in_length(this->shape[this_axis], index_user);
                    dst_ndarray->data += index * this->strides[this_axis]; // Add offset

                    // Next
                    this_axis++;
                } else if (ndslice->type == INPUT_SLICE_TYPE_SLICE) {
                    // Handle when the ndslice is a slice (represented by UserSlice in IRRT)
                    // e.g., `my_array[::2, -5, ::-1]`
                    //                 ^^^------^^^^----- like these
                    UserSlice<SizeT>* user_slice = (UserSlice<SizeT>*) ndslice->slice;
                    Slice<SizeT> slice = user_slice->indices(this->shape[this_axis]); // To resolve negative indices and other funny stuff written by the user

                    // NOTE: There is no need to write special code to handle negative steps/strides.
                    // This simple implementation meticulously handles both positive and negative steps/strides.
                    // Check out the tinynumpy and IRRT's test cases if you are not convinced.
                    dst_ndarray->data += slice.start * this->strides[this_axis]; // Add offset (NOTE: no need to `* itemsize`, strides count in # of bytes)
                    dst_ndarray->strides[dst_axis] = slice.step * this->strides[this_axis]; // Determine stride
                    dst_ndarray->shape[dst_axis] = slice.len(); // Determine shape dimension

                    // Next
                    dst_axis++;
                    this_axis++;
                } else {
                    __builtin_unreachable();
                }
            }

            irrt_assert(dst_axis == dst_ndarray->ndims); // Sanity check on the implementation
        }

        // Similar to `np.broadcast_to(<ndarray>, <target_shape>)`
        // Assumptions:
        //   - `this` has to be fully initialized.
        //   - `dst_ndarray->ndims` has to be set.
        //   - `dst_ndarray->shape` has to be set, this determines the shape `this` broadcasts to.
        //
        // Other notes:
        //   - `dst_ndarray->data` does not have to be set, it will be set to `this->data`.
        //   - `dst_ndarray->itemsize` does not have to be set, it will be set to `this->data`.
        //   - `dst_ndarray->strides` does not have to be set, it will be overwritten.
        //
        // Cautions:
        //   ```
        //   xs = np.zeros((4,))
        //   ys = np.zero((4, 1))
        //   ys[:] = xs # ok
        // 
        //   xs = np.zeros((1, 4))
        //   ys = np.zero((4,))
        //   ys[:] = xs # allowed
        //   # However `np.broadcast_to(xs, (4,))` would fails, as per numpy's broadcasting rule.
        //   # and apparently numpy will "deprecate" this? SEE https://github.com/numpy/numpy/issues/21744
        //   # This implementation will NOT support this assignment.
        //   ```
        void broadcast_to(NDArray<SizeT>* dst_ndarray) {
            dst_ndarray->data = this->data;
            dst_ndarray->itemsize = this->itemsize;

            irrt_assert(
                ndarray_util::can_broadcast_shape_to(
                    dst_ndarray->ndims,
                    dst_ndarray->shape,
                    this->ndims,
                    this->shape
                )
            );

            SizeT stride_product = 1;
            for (SizeT i = 0; i < max(this->ndims, dst_ndarray->ndims); i++) {
                SizeT this_dim_i = this->ndims - i - 1;
                SizeT dst_dim_i = dst_ndarray->ndims - i - 1;

                bool this_dim_exists = this_dim_i >= 0;
                bool dst_dim_exists = dst_dim_i >= 0;

                // TODO: Explain how this works
                bool c1 = this_dim_exists && this->shape[this_dim_i] == 1;
                bool c2 = dst_dim_exists && dst_ndarray->shape[dst_dim_i] != 1;
                if (!this_dim_exists || (c1 && c2)) {
                    dst_ndarray->strides[dst_dim_i] = 0; // Freeze it in-place
                } else {
                    dst_ndarray->strides[dst_dim_i] = stride_product * this->itemsize;
                    stride_product *= this->shape[this_dim_i]; // NOTE: this_dim_exist must be true here.
                }
            }
        }

        // Simulates `this_ndarray[:] = src_ndarray`, with automatic broadcasting.
        // Caution on https://github.com/numpy/numpy/issues/21744
        // Also see `NDArray::broadcast_to`
        void assign_with(NDArray<SizeT>* src_ndarray) {
            irrt_assert(
                ndarray_util::can_broadcast_shape_to(
                    this->ndims,
                    this->shape,
                    src_ndarray->ndims,
                    src_ndarray->shape
                )
            );

            // Broadcast the `src_ndarray` to make the reading process *much* easier
            SizeT* broadcasted_src_ndarray_strides = __builtin_alloca(sizeof(SizeT) * this->ndims); // Remember to allocate strides beforehand
            NDArray<SizeT> broadcasted_src_ndarray = {
                .ndims = this->ndims,
                .shape = this->shape,
                .strides = broadcasted_src_ndarray_strides
            };
            src_ndarray->broadcast_to(&broadcasted_src_ndarray);

            // Using iter instead of `get_nth_pelement` because it is slightly faster
            SizeT* indices = __builtin_alloca(sizeof(SizeT) * this->ndims);
            auto iter = NDArrayIndicesIter<SizeT> {
                .ndims = this->ndims,
                .shape = this->shape,
                .indices = indices
            };
            const SizeT this_size = this->size();
            for (SizeT i = 0; i < this_size; i++, iter.next()) {
                uint8_t* src_pelement = broadcasted_src_ndarray_strides->get_pelement_by_indices(indices);
                uint8_t* this_pelement = this->get_pelement_by_indices(indices);
                this->set_pelement_value(src_pelement, src_pelement);
            }
        }
    };
}

extern "C" {
    uint32_t __nac3_ndarray_size(NDArray<int32_t>* ndarray) {
        return ndarray->size();
    }

    uint64_t __nac3_ndarray_size64(NDArray<int64_t>* ndarray) {
        return ndarray->size();
    }

    void __nac3_ndarray_fill_generic(NDArray<int32_t>* ndarray, uint8_t* pvalue) {
        ndarray->fill_generic(pvalue);
    }

    void __nac3_ndarray_fill_generic64(NDArray<int64_t>* ndarray, uint8_t* pvalue) {
        ndarray->fill_generic(pvalue);
    }

    // void __nac3_ndarray_slice(NDArray<int32_t>* ndarray, int32_t num_slices, NDSlice<int32_t> *slices, NDArray<int32_t> *dst_ndarray) {
    //     // ndarray->slice(num_slices, slices, dst_ndarray);
    // }
}