// SPDX-License-Identifier: 0BSD

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

//

/// \file       simple_coder.c

/// \brief      Wrapper for simple filters

///

/// Simple filters don't change the size of the data i.e. number of bytes

/// in equals the number of bytes out.

//

//  Author:     Lasse Collin

//

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

#include "simple_private.h"

/// Copied or encodes/decodes more data to out[].

static lzma_ret

copy_or_code(lzma_simple_coder *coder, 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)

{

  assert(!coder->end_was_reached);

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

    lzma_bufcpy(in, in_pos, in_size, out, out_pos, out_size);

    // Check if end of stream was reached.

    if (coder->is_encoder && action == LZMA_FINISH

        && *in_pos == in_size)

      coder->end_was_reached = true;

  } else {

    // Call the next coder in the chain to provide us some data.

    const lzma_ret ret = coder->next.code(

        coder->next.coder, allocator,

        in, in_pos, in_size,

        out, out_pos, out_size, action);

    if (ret == LZMA_STREAM_END) {

      assert(!coder->is_encoder

          || action == LZMA_FINISH);

      coder->end_was_reached = true;

    } else if (ret != LZMA_OK) {

      return ret;

    }

  }

  return LZMA_OK;

}

static size_t

call_filter(lzma_simple_coder *coder, uint8_t *buffer, size_t size)

{

  const size_t filtered = coder->filter(coder->simple,

      coder->now_pos, coder->is_encoder,

      buffer, size);

  coder->now_pos += filtered;

  return filtered;

}

static lzma_ret

simple_code(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_simple_coder *coder = coder_ptr;

  // TODO: Add partial support for LZMA_SYNC_FLUSH. We can support it

  // in cases when the filter is able to filter everything. With most

  // simple filters it can be done at offset that is a multiple of 2,

  // 4, or 16. With x86 filter, it needs good luck, and thus cannot

  // be made to work predictably.

  if (action == LZMA_SYNC_FLUSH)

    return LZMA_OPTIONS_ERROR;

  // Flush already filtered data from coder->buffer[] to out[].

  if (coder->pos < coder->filtered) {

    lzma_bufcpy(coder->buffer, &coder->pos, coder->filtered,

        out, out_pos, out_size);

    // If we couldn't flush all the filtered data, return to

    // application immediately.

    if (coder->pos < coder->filtered)

      return LZMA_OK;

    if (coder->end_was_reached) {

      assert(coder->filtered == coder->size);

      return LZMA_STREAM_END;

    }

  }

  // If we get here, there is no filtered data left in the buffer.

  coder->filtered = 0;

  assert(!coder->end_was_reached);

  // If there is more output space left than there is unfiltered data

  // in coder->buffer[], flush coder->buffer[] to out[], and copy/code

  // more data to out[] hopefully filling it completely. Then filter

  // the data in out[]. This step is where most of the data gets

  // filtered if the buffer sizes used by the application are reasonable.

  const size_t out_avail = out_size - *out_pos;

  const size_t buf_avail = coder->size - coder->pos;

  if (out_avail > buf_avail || buf_avail == 0) {

    // Store the old position so that we know from which byte

    // to start filtering.

    const size_t out_start = *out_pos;

    // Flush data from coder->buffer[] to out[], but don't reset

    // coder->pos and coder->size yet. This way the coder can be

    // restarted if the next filter in the chain returns e.g.

    // LZMA_MEM_ERROR.

    //

    // Do the memcpy() conditionally because out can be NULL

    // (in which case buf_avail is always 0). Calling memcpy()

    // with a null-pointer is undefined even if the third

    // argument is 0.

    if (buf_avail > 0)

      memcpy(out + *out_pos, coder->buffer + coder->pos,

          buf_avail);

    *out_pos += buf_avail;

    // Copy/Encode/Decode more data to out[].

    {

      const lzma_ret ret = copy_or_code(coder, allocator,

          in, in_pos, in_size,

          out, out_pos, out_size, action);

      assert(ret != LZMA_STREAM_END);

      if (ret != LZMA_OK)

        return ret;

    }

    // Filter out[] unless there is nothing to filter.

    // This way we avoid null pointer + 0 (undefined behavior)

    // when out == NULL.

    const size_t size = *out_pos - out_start;

    const size_t filtered = size == 0 ? 0 : call_filter(

        coder, out + out_start, size);

    const size_t unfiltered = size - filtered;

    assert(unfiltered <= coder->allocated / 2);

    // Now we can update coder->pos and coder->size, because

    // the next coder in the chain (if any) was successful.

    coder->pos = 0;

    coder->size = unfiltered;

    if (coder->end_was_reached) {

      // The last byte has been copied to out[] already.

      // They are left as is.

      coder->size = 0;

    } else if (unfiltered > 0) {

      // There is unfiltered data left in out[]. Copy it to

      // coder->buffer[] and rewind *out_pos appropriately.

      *out_pos -= unfiltered;

      memcpy(coder->buffer, out + *out_pos, unfiltered);

    }

  } else if (coder->pos > 0) {

    memmove(coder->buffer, coder->buffer + coder->pos, buf_avail);

    coder->size -= coder->pos;

    coder->pos = 0;

  }

  assert(coder->pos == 0);

  // If coder->buffer[] isn't empty, try to fill it by copying/decoding

  // more data. Then filter coder->buffer[] and copy the successfully

  // filtered data to out[]. It is probable, that some filtered and

  // unfiltered data will be left to coder->buffer[].

  if (coder->size > 0) {

    {

      const lzma_ret ret = copy_or_code(coder, allocator,

          in, in_pos, in_size,

          coder->buffer, &coder->size,

          coder->allocated, action);

      assert(ret != LZMA_STREAM_END);

      if (ret != LZMA_OK)

        return ret;

    }

    coder->filtered = call_filter(

        coder, coder->buffer, coder->size);

    // Everything is considered to be filtered if coder->buffer[]

    // contains the last bytes of the data.

    if (coder->end_was_reached)

      coder->filtered = coder->size;

    // Flush as much as possible.

    lzma_bufcpy(coder->buffer, &coder->pos, coder->filtered,

        out, out_pos, out_size);

  }

  // Check if we got everything done.

  if (coder->end_was_reached && coder->pos == coder->size)

    return LZMA_STREAM_END;

  return LZMA_OK;

}

static void

simple_coder_end(void *coder_ptr, const lzma_allocator *allocator)

{

  lzma_simple_coder *coder = coder_ptr;

  lzma_next_end(&coder->next, allocator);

  lzma_free(coder->simple, allocator);

  lzma_free(coder, allocator);

  return;

}

static lzma_ret

simple_coder_update(void *coder_ptr, const lzma_allocator *allocator,

    const lzma_filter *filters_null lzma_attribute((__unused__)),

    const lzma_filter *reversed_filters)

{

  lzma_simple_coder *coder = coder_ptr;

  // No update support, just call the next filter in the chain.

  return lzma_next_filter_update(

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

}

extern lzma_ret

lzma_simple_coder_init(lzma_next_coder *next, const lzma_allocator *allocator,

    const lzma_filter_info *filters,

    size_t (*filter)(void *simple, uint32_t now_pos,

      bool is_encoder, uint8_t *buffer, size_t size),

    size_t simple_size, size_t unfiltered_max,

    uint32_t alignment, bool is_encoder)

{

  // Allocate memory for the lzma_simple_coder structure if needed.

  lzma_simple_coder *coder = next->coder;

  if (coder == NULL) {

    // Here we allocate space also for the temporary buffer. We

    // need twice the size of unfiltered_max, because then it

    // is always possible to filter at least unfiltered_max bytes

    // more data in coder->buffer[] if it can be filled completely.

    coder = lzma_alloc(sizeof(lzma_simple_coder)

        + 2 * unfiltered_max, allocator);

    if (coder == NULL)

      return LZMA_MEM_ERROR;

    next->coder = coder;

    next->code = &simple_code;

    next->end = &simple_coder_end;

    next->update = &simple_coder_update;

    coder->next = LZMA_NEXT_CODER_INIT;

    coder->filter = filter;

    coder->allocated = 2 * unfiltered_max;

    // Allocate memory for filter-specific data structure.

    if (simple_size > 0) {

      coder->simple = lzma_alloc(simple_size, allocator);

      if (coder->simple == NULL)

        return LZMA_MEM_ERROR;

    } else {

      coder->simple = NULL;

    }

  }

  if (filters[0].options != NULL) {

    const lzma_options_bcj *simple = filters[0].options;

    coder->now_pos = simple->start_offset;

    if (coder->now_pos & (alignment - 1))

      return LZMA_OPTIONS_ERROR;

  } else {

    coder->now_pos = 0;

  }

  // Reset variables.

  coder->is_encoder = is_encoder;

  coder->end_was_reached = false;

  coder->pos = 0;

  coder->filtered = 0;

  coder->size = 0;

  return lzma_next_filter_init(&coder->next, allocator, filters + 1);

}