/**

 * Copyright (C) 2025 Niklas Haas

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * FFmpeg 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

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

#include "libavutil/avassert.h"

#include "ops_backend.h"

typedef struct MemcpyPriv {

    int num_planes;

    int index[4]; /* or -1 to clear plane */

    uint8_t clear_value[4];

} MemcpyPriv;

/**

 * Switch to loop if total padding exceeds this number of bytes. Chosen to

 * align with the typical L1 cache size of modern CPUs, as this avoids the

 * risk of the implementation loading one extra unnecessary cache line.

 */

#define SWS_MAX_PADDING 64

/* Memcpy backend for trivial cases */

static void process(const SwsOpExec *exec, const void *priv,

                    int x_start, int y_start, int x_end, int y_end)

{

    const MemcpyPriv *p = priv;

    const int lines = y_end - y_start;

    const int bytes = x_end * exec->block_size_out;

    av_assert1(x_start == 0 && x_end == exec->width);

    for (int i = 0; i < p->num_planes; i++) {

        uint8_t *out = exec->out[i];

        const int idx = p->index[i];

        const int use_loop = exec->out_stride[i] > bytes + SWS_MAX_PADDING;

        if (idx < 0 && !use_loop) {

            memset(out, p->clear_value[i], exec->out_stride[i] * lines);

        } else if (idx < 0) {

            for (int y = y_start; y < y_end; y++) {

                memset(out, p->clear_value[i], bytes);

                out += exec->out_stride[i];

            }

        } else if (exec->out_stride[i] == exec->in_stride[idx] && !use_loop) {

            memcpy(out, exec->in[idx], exec->out_stride[i] * lines);

        } else {

            const uint8_t *in = exec->in[idx];

            for (int y = y_start; y < y_end; y++) {

                memcpy(out, in, bytes);

                out += exec->out_stride[i];

                in  += exec->in_stride[idx];

            }

        }

    }

}

static int compile(SwsContext *ctx, SwsOpList *ops, SwsCompiledOp *out)

{

    MemcpyPriv p = {0};

    for (int n = 0; n < ops->num_ops; n++) {

        const SwsOp *op = &ops->ops[n];

        switch (op->op) {

        case SWS_OP_READ:

            if ((op->rw.packed && op->rw.elems != 1) || op->rw.frac || op->rw.filter)

                return AVERROR(ENOTSUP);

            for (int i = 0; i < op->rw.elems; i++)

                p.index[i] = i;

            break;

        case SWS_OP_SWIZZLE: {

            const MemcpyPriv orig = p;

            for (int i = 0; i < 4; i++) {

                /* Explicitly exclude swizzle masks that contain duplicates,

                 * because these are wasteful to implement as a memcpy */

                for (int j = 0; j < i; j++) {

                    if (op->swizzle.in[i] == op->swizzle.in[j])

                        return AVERROR(ENOTSUP);

                }

                p.index[i] = orig.index[op->swizzle.in[i]];

            }

            break;

        }

        case SWS_OP_CLEAR:

            for (int i = 0; i < 4; i++) {

                if (!SWS_COMP_TEST(op->clear.mask, i))

                    continue;

                if (op->clear.value[i].den != 1)

                    return AVERROR(ENOTSUP);

                /* Ensure all bytes to be cleared are the same, because we

                 * can't memset on multi-byte sequences */

                uint8_t val = op->clear.value[i].num & 0xFF;

                uint32_t ref = val;

                switch (ff_sws_pixel_type_size(op->type)) {

                case 2: ref *= 0x101; break;

                case 4: ref *= 0x1010101; break;

                }

                if (ref != op->clear.value[i].num)

                    return AVERROR(ENOTSUP);

                p.clear_value[i] = val;

                p.index[i] = -1;

            }

            break;

        case SWS_OP_WRITE:

            if ((op->rw.packed && op->rw.elems != 1) || op->rw.frac || op->rw.filter)

                return AVERROR(ENOTSUP);

            p.num_planes = op->rw.elems;

            break;

        default:

            return AVERROR(ENOTSUP);

        }

    }

    *out = (SwsCompiledOp) {

        .slice_align = 1,

        .block_size  = 1,

        .func = process,

        .priv = av_memdup(&p, sizeof(p)),

        .free = av_free,

    };

    return out->priv ? 0 : AVERROR(ENOMEM);

}

const SwsOpBackend backend_murder = {

    .name       = "memcpy",

    .compile    = compile,

    .hw_format  = AV_PIX_FMT_NONE,

};