// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////

//

/// \file       delta_encoder.c

/// \brief      Delta filter encoder

//

//  Author:     Lasse Collin

//

///////////////////////////////////////////////////////////////////////////////

#include "delta_encoder.h"

#include "delta_private.h"

/// Copies and encodes the data at the same time. This is used when Delta

/// is the first filter in the chain (and thus the last filter in the

/// encoder's filter stack).

static void

copy_and_encode(lzma_delta_coder *coder,

    const uint8_t *restrict in, uint8_t *restrict out, size_t size)

{

  const size_t distance = coder->distance;

  for (size_t i = 0; i < size; ++i) {

    const uint8_t tmp = coder->history[

        (distance + coder->pos) & 0xFF];

    coder->history[coder->pos-- & 0xFF] = in[i];

    out[i] = in[i] - tmp;

  }

}

/// Encodes the data in place. This is used when we are the last filter

/// in the chain (and thus non-last filter in the encoder's filter stack).

static void

encode_in_place(lzma_delta_coder *coder, uint8_t *buffer, size_t size)

{

  const size_t distance = coder->distance;

  for (size_t i = 0; i < size; ++i) {

    const uint8_t tmp = coder->history[

        (distance + coder->pos) & 0xFF];

    coder->history[coder->pos-- & 0xFF] = buffer[i];

    buffer[i] -= tmp;

  }

}

static lzma_ret

delta_encode(void *coder_ptr, const lzma_allocator *allocator,

    const uint8_t *restrict in, size_t *restrict in_pos,

    size_t in_size, uint8_t *restrict out,

    size_t *restrict out_pos, size_t out_size, lzma_action action)

{

  lzma_delta_coder *coder = coder_ptr;

  lzma_ret ret;

  if (coder->next.code == NULL) {

    const size_t in_avail = in_size - *in_pos;

    const size_t out_avail = out_size - *out_pos;

    const size_t size = my_min(in_avail, out_avail);

    // in and out might be NULL. In such cases size == 0.

    // Null pointer + 0 is undefined behavior so skip

    // the call in that case as it would do nothing anyway.

    if (size > 0)

      copy_and_encode(coder, in + *in_pos, out + *out_pos,

          size);

    *in_pos += size;

    *out_pos += size;

    ret = action != LZMA_RUN && *in_pos == in_size

        ? LZMA_STREAM_END : LZMA_OK;

  } else {

    const size_t out_start = *out_pos;

    ret = coder->next.code(coder->next.coder, allocator,

        in, in_pos, in_size, out, out_pos, out_size,

        action);

    // Like above, avoid null pointer + 0.

    const size_t size = *out_pos - out_start;

    if (size > 0)

      encode_in_place(coder, out + out_start, size);

  }

  return ret;

}

static lzma_ret

delta_encoder_update(void *coder_ptr, const lzma_allocator *allocator,

    const lzma_filter *filters_null lzma_attribute((__unused__)),

    const lzma_filter *reversed_filters)

{

  lzma_delta_coder *coder = coder_ptr;

  // Delta doesn't and will never support changing the options in

  // the middle of encoding. If the app tries to change them, we

  // simply ignore them.

  return lzma_next_filter_update(

      &coder->next, allocator, reversed_filters + 1);

}

extern lzma_ret

lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,

    const lzma_filter_info *filters)

{

  next->code = &delta_encode;

  next->update = &delta_encoder_update;

  return lzma_delta_coder_init(next, allocator, filters);

}

extern lzma_ret

lzma_delta_props_encode(const void *options, uint8_t *out)

{

  // The caller must have already validated the options, so it's

  // LZMA_PROG_ERROR if they are invalid.

  if (lzma_delta_coder_memusage(options) == UINT64_MAX)

    return LZMA_PROG_ERROR;

  const lzma_options_delta *opt = options;

  out[0] = opt->dist - LZMA_DELTA_DIST_MIN;

  return LZMA_OK;

}