/**
* @license Apache-2.0
*
* Copyright (c) 2021 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

#include "stdlib/ndarray/base/broadcast_shapes.h"
#include <stdint.h>

/**
* Broadcasts array shapes to a single shape.
*
* ## Notes
*
* -   Two respective dimensions in two shape arrays are compatible if
*
*     1.  the dimensions are equal.
*     2.  one dimension is `1`.
*
* -   If successful, the function returns `0`; otherwise, the function returns `-1` (e.g., due to incompatible shapes).
*
* -   Even if the function is unsuccessful, the function may still overwrite elements in the output array before returning. In other words, do not assume that providing incompatible shapes is a no-op with regard to the output array.
*
* @param M        number of array shapes
* @param shapes   pointer to an array containing shape arrays
* @param ndims    array containing the number of dimensions for (i.e., length of) each respective shape array
* @param out      pointer to output array
* @return         status
*
* @example
* #include "stdlib/ndarray/base/broadcast_shapes.h"
* #include <stdint.h>
*
* int64_t N1 = 4;
* int64_t sh1[] = { 8, 1, 6, 1 };
*
* int64_t N2 = 3;
* int64_t sh2[] = { 7, 1, 5 };
*
* int64_t ndims[] = { N1, N2 };
* int64_t *shapes[] = { sh1, sh2 };
*
* int64_t out[] = { 0, 0, 0, 0 };
* int8_t status = stdlib_ndarray_broadcast_shapes( 2, shapes, ndims, out );
*/
int8_t stdlib_ndarray_broadcast_shapes( int64_t M, int64_t *shapes[], int64_t ndims[], int64_t *out ) {
	int64_t dim;
	int64_t *sh;
	int64_t n1;
	int64_t n2;
	int64_t d;
	int64_t N;
	int64_t i;
	int64_t j;

	if ( M == 0 ) {
		return 0;
	}
	sh = shapes[ 0 ];
	N = ndims[ 0 ];

	// If provided a single input shape array, then the broadcast shape is input shape...
	if ( M == 1 ) {
		for ( i = 0; i < N; i++ ) {
			out[ i ] = sh[ i ];
		}
		return 0;
	}
	// Determine the maximum dimensionality...
	for ( i = 1; i < M; i++ ) {
		if ( ndims[ i ] > N ) {
			N = ndims[ i ];
		}
	}
	// Compute the broadcast shape...
	i = N - 1;
	while ( i >= 0 ) {
		n1 = ndims[ 0 ] - N + i;
		if ( n1 >= 0 ) {
			dim = sh[ n1 ];
		} else {
			dim = 1;
		}
		for ( j = 1; j < M; j++ ) {
			n2 = ndims[ j ] - N + i;
			if ( n2 >= 0 ) {
				d = shapes[ j ][ n2 ];
			} else {
				d = 1;
			}
			if ( dim == 1 ) {
				dim = d;
				continue;
			}
			if ( d == 1 || dim == d ) {
				// When either `d` is `1` or `d` equals the current output shape dimension, the current output shape dimension remains the same...
				continue;
			}
			// The current shape cannot be broadcast against one of the other shapes...
			return -1;
		}
		out[ i ] = dim;
		i -= 1;
	}
	return 0;
}