/*
 * N-dimensional strided array
 * Copyright 2018 Anton Khirnov <anton@khirnov.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

#include "ndarray.h"

struct NDArrayInternal {
    size_t     alloc_size;
    void      *data;

    size_t    *shape;
    ptrdiff_t *stride;
};

int mg2di_ndarray_alloc(NDArray **result, unsigned int dims,
                        const size_t * const size, unsigned int flags)
{
    NDArray *a;
    int ret;

    if (!dims || dims >= INT_MAX)
        return -EINVAL;

    a = calloc(1, sizeof(*a));
    if (!a)
        return -ENOMEM;

    a->priv = calloc(1, sizeof(*a->priv));
    if (!a->priv) {
        free(a);
        return -ENOMEM;
    }

    a->priv->shape = calloc(dims, sizeof(*a->priv->shape));
    if (!a->priv->shape) {
        ret = -ENOMEM;
        goto fail;
    }
    memcpy(a->priv->shape, size, dims * sizeof(*a->priv->shape));

    a->priv->stride = calloc(dims, sizeof(*a->priv->stride));
    if (!a->priv->stride) {
        ret = -ENOMEM;
        goto fail;
    }

    a->priv->stride[dims - 1] = 1;
    for (int i = (int)dims - 2; i >= 0; i--)
        a->priv->stride[i] = size[i + 1] * a->priv->stride[i + 1];

    a->priv->alloc_size = a->priv->stride[0] * size[0] * sizeof(*a->data);
    ret = posix_memalign((void**)&a->priv->data, 64, a->priv->alloc_size);
    if (ret != 0) {
        ret = -ret;
        goto fail;
    }

    if (flags & NDARRAY_ALLOC_ZERO)
        memset(a->priv->data, 0, a->priv->alloc_size);

    a->dims   = dims;

    a->data   = a->priv->data;
    a->shape  = a->priv->shape;
    a->stride = a->priv->stride;

    *result = a;

    return 0;
fail:
    mg2di_ndarray_free(&a);
    return ret;
}

int mg2di_ndarray_slice(NDArray **result, NDArray *src,
                        const Slice * const slice)
{
    NDArray *a;
    ptrdiff_t offset;
    int ret;

    a = calloc(1, sizeof(*a));
    if (!a)
        return -ENOMEM;

    a->priv = calloc(1, sizeof(*a->priv));
    if (!a->priv) {
        free(a);
        return -ENOMEM;
    }

    a->priv->shape = calloc(src->dims, sizeof(*a->priv->shape));
    if (!a->priv->shape) {
        ret = -ENOMEM;
        goto fail;
    }
    memcpy(a->priv->shape, src->priv->shape, src->dims * sizeof(*a->priv->shape));

    a->priv->stride = calloc(src->dims, sizeof(*a->priv->stride));
    if (!a->priv->stride) {
        ret = -ENOMEM;
        goto fail;
    }
    memcpy(a->priv->stride, src->priv->stride, src->dims * sizeof(*a->priv->shape));

    offset = 0;
    for (unsigned int i = 0; i < src->dims; i++) {
        const Slice *s = &slice[i];
        ptrdiff_t start, end, step;

        if (s->start == PTRDIFF_MAX) {
            start = 0;
            end   = src->shape[i];
            step  = 1;
        } else {
            start = s->start;
            end   = s->end;
            step  = s->step;

            if (step < 1) {
                ret = step ? -ENOSYS : -EINVAL;
                goto fail;
            }

            if (start < 0)
                start = src->shape[i] + start;
            if (end <= 0)
                end = src->shape[i] + end;

            if (start >= end || end > src->shape[i]) {
                ret = -EINVAL;
                goto fail;
            }
        }

        offset += src->stride[i] * start;

        a->priv->stride[i] *= step;
        a->priv->shape[i]   = (end - start) / step;
    }

    a->dims   = src->dims;

    a->data   = src->data + offset;
    a->shape  = a->priv->shape;
    a->stride = a->priv->stride;

    *result = a;
    return 0;

fail:
    mg2di_ndarray_free(&a);
    return ret;
}

int mg2di_ndarray_wrap(NDArray **result, unsigned int dims,
                       const size_t * const size, double *data,
                       const ptrdiff_t * const stride)
{
    NDArray *a;
    int ret;

    if (!dims || dims >= INT_MAX)
        return -EINVAL;

    a = calloc(1, sizeof(*a));
    if (!a)
        return -ENOMEM;

    a->priv = calloc(1, sizeof(*a->priv));
    if (!a->priv) {
        free(a);
        return -ENOMEM;
    }

    a->priv->shape = calloc(dims, sizeof(*a->priv->shape));
    if (!a->priv->shape) {
        ret = -ENOMEM;
        goto fail;
    }
    memcpy(a->priv->shape, size, dims * sizeof(*a->priv->shape));

    a->priv->stride = calloc(dims, sizeof(*a->priv->stride));
    if (!a->priv->stride) {
        ret = -ENOMEM;
        goto fail;
    }
    memcpy(a->priv->stride, stride, dims * sizeof(*a->priv->shape));

    a->dims   = dims;

    a->data   = data;
    a->shape  = a->priv->shape;
    a->stride = a->priv->stride;

    *result = a;

    return 0;
fail:
    mg2di_ndarray_free(&a);
    return ret;
}

void mg2di_ndarray_free(NDArray **pa)
{
    NDArray *a = *pa;

    if (!a)
        return;

    if (a->priv) {
        free(a->priv->data);
        free(a->priv->shape);
        free(a->priv->stride);
    }
    free(a->priv);

    free(a);
    *pa = NULL;
}

static int copy_axis(NDArray *dst, const NDArray *src, unsigned int axis,
                     ptrdiff_t offset_dst, ptrdiff_t offset_src)
{
    if (dst->shape[axis] != src->shape[axis])
        return -EINVAL;

    if (axis == dst->dims - 1) {
        if (dst->stride[axis] == 1 && src->stride[axis] == 1)
            memcpy(dst->data + offset_dst, src->data + offset_src, sizeof(*dst->data) * dst->shape[axis]);
        else {
            for (size_t idx = 0; idx < dst->shape[axis]; idx++)
                dst->data[offset_dst + idx * dst->stride[axis]] = src->data[offset_src + idx * src->stride[axis]];
        }
        return 0;
    }

    for (size_t idx = 0; idx < dst->shape[axis]; idx++)
        copy_axis(dst, src, axis + 1, offset_dst + idx * dst->stride[axis], offset_src + idx * src->stride[axis]);

    return 0;
}

int mg2di_ndarray_copy(NDArray *dst, const NDArray *src)
{
    const unsigned int dims = src->dims;

    if (dims != dst->dims)
        return -EINVAL;

    return copy_axis(dst, src, 0, 0, 0);
}