/**
 * libs/heatshrink/heatshrink_decoder.cpp
 */
#include <stdlib.h>
#include <string.h>
#include "heatshrink_decoder.h"

#pragma GCC optimize ("O3")

/* States for the polling state machine. */
typedef enum {
  HSDS_TAG_BIT,               /* tag bit */
  HSDS_YIELD_LITERAL,         /* ready to yield literal byte */
  HSDS_BACKREF_INDEX_MSB,     /* most significant byte of index */
  HSDS_BACKREF_INDEX_LSB,     /* least significant byte of index */
  HSDS_BACKREF_COUNT_MSB,     /* most significant byte of count */
  HSDS_BACKREF_COUNT_LSB,     /* least significant byte of count */
  HSDS_YIELD_BACKREF          /* ready to yield back-reference */
} HSD_state;

#if HEATSHRINK_DEBUGGING_LOGS
  #include <stdio.h>
  #include <ctype.h>
  #include <assert.h>
  #define LOG(...) fprintf(stderr, __VA_ARGS__)
  #define ASSERT(X) assert(X)
  static const char *state_names[] = {
    "tag_bit",
    "yield_literal",
    "backref_index_msb",
    "backref_index_lsb",
    "backref_count_msb",
    "backref_count_lsb",
    "yield_backref"
  };
#else
  #define LOG(...) /* no-op */
  #define ASSERT(X) /* no-op */
#endif

typedef struct {
  uint8_t *buf;               /* output buffer */
  size_t buf_size;            /* buffer size */
  size_t *output_size;        /* bytes pushed to buffer, so far */
} output_info;

#define NO_BITS ((uint16_t)-1)

/* Forward references. */
static uint16_t get_bits(heatshrink_decoder *hsd, uint8_t count);
static void push_byte(heatshrink_decoder *hsd, output_info *oi, uint8_t byte);

#if HEATSHRINK_DYNAMIC_ALLOC
heatshrink_decoder *heatshrink_decoder_alloc(uint16_t input_buffer_size, uint8_t window_sz2, uint8_t lookahead_sz2) {
  if ((window_sz2 < HEATSHRINK_MIN_WINDOW_BITS) ||
      (window_sz2 > HEATSHRINK_MAX_WINDOW_BITS) ||
      (input_buffer_size == 0) ||
      (lookahead_sz2 < HEATSHRINK_MIN_LOOKAHEAD_BITS) ||
      (lookahead_sz2 >= window_sz2)) {
      return nullptr;
  }
  size_t buffers_sz = (1 << window_sz2) + input_buffer_size;
  size_t sz = sizeof(heatshrink_decoder) + buffers_sz;
  heatshrink_decoder *hsd = HEATSHRINK_MALLOC(sz);
  if (hsd == nullptr) return nullptr;
  hsd->input_buffer_size = input_buffer_size;
  hsd->window_sz2 = window_sz2;
  hsd->lookahead_sz2 = lookahead_sz2;
  heatshrink_decoder_reset(hsd);
  LOG("-- allocated decoder with buffer size of %zu (%zu + %u + %u)\n",
      sz, sizeof(heatshrink_decoder), (1 << window_sz2), input_buffer_size);
  return hsd;
}

void heatshrink_decoder_free(heatshrink_decoder *hsd) {
  size_t buffers_sz = (1 << hsd->window_sz2) + hsd->input_buffer_size;
  size_t sz = sizeof(heatshrink_decoder) + buffers_sz;
  HEATSHRINK_FREE(hsd, sz);
  (void)sz;   /* may not be used by free */
}
#endif

void heatshrink_decoder_reset(heatshrink_decoder *hsd) {
  size_t buf_sz = 1 << HEATSHRINK_DECODER_WINDOW_BITS(hsd);
  size_t input_sz = HEATSHRINK_DECODER_INPUT_BUFFER_SIZE(hsd);
  memset(hsd->buffers, 0, buf_sz + input_sz);
  hsd->state = HSDS_TAG_BIT;
  hsd->input_size = 0;
  hsd->input_index = 0;
  hsd->bit_index = 0x00;
  hsd->current_byte = 0x00;
  hsd->output_count = 0;
  hsd->output_index = 0;
  hsd->head_index = 0;
}

/* Copy SIZE bytes into the decoder's input buffer, if it will fit. */
HSD_sink_res heatshrink_decoder_sink(heatshrink_decoder *hsd,
  uint8_t *in_buf, size_t size, size_t *input_size) {
  if (hsd == nullptr || in_buf == nullptr || input_size == nullptr)
    return HSDR_SINK_ERROR_NULL;

  size_t rem = HEATSHRINK_DECODER_INPUT_BUFFER_SIZE(hsd) - hsd->input_size;
  if (rem == 0) {
    *input_size = 0;
    return HSDR_SINK_FULL;
  }

  size = rem < size ? rem : size;
  LOG("-- sinking %zd bytes\n", size);
  /* copy into input buffer (at head of buffers) */
  memcpy(&hsd->buffers[hsd->input_size], in_buf, size);
  hsd->input_size += size;
  *input_size = size;
  return HSDR_SINK_OK;
}


/*****************
 * Decompression *
 *****************/

#define BACKREF_COUNT_BITS(HSD) (HEATSHRINK_DECODER_LOOKAHEAD_BITS(HSD))
#define BACKREF_INDEX_BITS(HSD) (HEATSHRINK_DECODER_WINDOW_BITS(HSD))

// States
static HSD_state st_tag_bit(heatshrink_decoder *hsd);
static HSD_state st_yield_literal(heatshrink_decoder *hsd, output_info *oi);
static HSD_state st_backref_index_msb(heatshrink_decoder *hsd);
static HSD_state st_backref_index_lsb(heatshrink_decoder *hsd);
static HSD_state st_backref_count_msb(heatshrink_decoder *hsd);
static HSD_state st_backref_count_lsb(heatshrink_decoder *hsd);
static HSD_state st_yield_backref(heatshrink_decoder *hsd, output_info *oi);

HSD_poll_res heatshrink_decoder_poll(heatshrink_decoder *hsd, uint8_t *out_buf, size_t out_buf_size, size_t *output_size) {
  if (hsd == nullptr || out_buf == nullptr || output_size == nullptr)
    return HSDR_POLL_ERROR_NULL;

  *output_size = 0;

  output_info oi;
  oi.buf = out_buf;
  oi.buf_size = out_buf_size;
  oi.output_size = output_size;

  while (1) {
    LOG("-- poll, state is %d (%s), input_size %d\n", hsd->state, state_names[hsd->state], hsd->input_size);
    uint8_t in_state = hsd->state;
    switch (in_state) {
      case HSDS_TAG_BIT:
        hsd->state = st_tag_bit(hsd);
        break;
      case HSDS_YIELD_LITERAL:
        hsd->state = st_yield_literal(hsd, &oi);
        break;
      case HSDS_BACKREF_INDEX_MSB:
        hsd->state = st_backref_index_msb(hsd);
        break;
      case HSDS_BACKREF_INDEX_LSB:
        hsd->state = st_backref_index_lsb(hsd);
        break;
      case HSDS_BACKREF_COUNT_MSB:
        hsd->state = st_backref_count_msb(hsd);
        break;
      case HSDS_BACKREF_COUNT_LSB:
        hsd->state = st_backref_count_lsb(hsd);
        break;
      case HSDS_YIELD_BACKREF:
        hsd->state = st_yield_backref(hsd, &oi);
        break;
      default:
        return HSDR_POLL_ERROR_UNKNOWN;
    }

    // If the current state cannot advance, check if input or output
    // buffer are exhausted.
    if (hsd->state == in_state)
      return (*output_size == out_buf_size) ? HSDR_POLL_MORE : HSDR_POLL_EMPTY;
  }
}

static HSD_state st_tag_bit(heatshrink_decoder *hsd) {
  uint32_t bits = get_bits(hsd, 1);  // get tag bit
  if (bits == NO_BITS)
    return HSDS_TAG_BIT;
  else if (bits)
    return HSDS_YIELD_LITERAL;
  else if (HEATSHRINK_DECODER_WINDOW_BITS(hsd) > 8)
    return HSDS_BACKREF_INDEX_MSB;
  else {
    hsd->output_index = 0;
    return HSDS_BACKREF_INDEX_LSB;
  }
}

static HSD_state st_yield_literal(heatshrink_decoder *hsd, output_info *oi) {
  /* Emit a repeated section from the window buffer, and add it (again)
   * to the window buffer. (Note that the repetition can include
   * itself.)*/
  if (*oi->output_size < oi->buf_size) {
    uint16_t byte = get_bits(hsd, 8);
    if (byte == NO_BITS) { return HSDS_YIELD_LITERAL; } /* out of input */
    uint8_t *buf = &hsd->buffers[HEATSHRINK_DECODER_INPUT_BUFFER_SIZE(hsd)];
    uint16_t mask = (1 << HEATSHRINK_DECODER_WINDOW_BITS(hsd))  - 1;
    uint8_t c = byte & 0xFF;
    LOG("-- emitting literal byte 0x%02x ('%c')\n", c, isprint(c) ? c : '.');
    buf[hsd->head_index++ & mask] = c;
    push_byte(hsd, oi, c);
    return HSDS_TAG_BIT;
  }
  return HSDS_YIELD_LITERAL;
}

static HSD_state st_backref_index_msb(heatshrink_decoder *hsd) {
  uint8_t bit_ct = BACKREF_INDEX_BITS(hsd);
  ASSERT(bit_ct > 8);
  uint16_t bits = get_bits(hsd, bit_ct - 8);
  LOG("-- backref index (msb), got 0x%04x (+1)\n", bits);
  if (bits == NO_BITS) { return HSDS_BACKREF_INDEX_MSB; }
  hsd->output_index = bits << 8;
  return HSDS_BACKREF_INDEX_LSB;
}

static HSD_state st_backref_index_lsb(heatshrink_decoder *hsd) {
  uint8_t bit_ct = BACKREF_INDEX_BITS(hsd);
  uint16_t bits = get_bits(hsd, bit_ct < 8 ? bit_ct : 8);
  LOG("-- backref index (lsb), got 0x%04x (+1)\n", bits);
  if (bits == NO_BITS) { return HSDS_BACKREF_INDEX_LSB; }
  hsd->output_index |= bits;
  hsd->output_index++;
  uint8_t br_bit_ct = BACKREF_COUNT_BITS(hsd);
  hsd->output_count = 0;
  return (br_bit_ct > 8) ? HSDS_BACKREF_COUNT_MSB : HSDS_BACKREF_COUNT_LSB;
}

static HSD_state st_backref_count_msb(heatshrink_decoder *hsd) {
  uint8_t br_bit_ct = BACKREF_COUNT_BITS(hsd);
  ASSERT(br_bit_ct > 8);
  uint16_t bits = get_bits(hsd, br_bit_ct - 8);
  LOG("-- backref count (msb), got 0x%04x (+1)\n", bits);
  if (bits == NO_BITS) { return HSDS_BACKREF_COUNT_MSB; }
  hsd->output_count = bits << 8;
  return HSDS_BACKREF_COUNT_LSB;
}

static HSD_state st_backref_count_lsb(heatshrink_decoder *hsd) {
  uint8_t br_bit_ct = BACKREF_COUNT_BITS(hsd);
  uint16_t bits = get_bits(hsd, br_bit_ct < 8 ? br_bit_ct : 8);
  LOG("-- backref count (lsb), got 0x%04x (+1)\n", bits);
  if (bits == NO_BITS) { return HSDS_BACKREF_COUNT_LSB; }
  hsd->output_count |= bits;
  hsd->output_count++;
  return HSDS_YIELD_BACKREF;
}

static HSD_state st_yield_backref(heatshrink_decoder *hsd, output_info *oi) {
  size_t count = oi->buf_size - *oi->output_size;
  if (count > 0) {
    size_t i = 0;
    if (hsd->output_count < count) count = hsd->output_count;
    uint8_t *buf = &hsd->buffers[HEATSHRINK_DECODER_INPUT_BUFFER_SIZE(hsd)];
    uint16_t mask = (1 << HEATSHRINK_DECODER_WINDOW_BITS(hsd)) - 1;
    uint16_t neg_offset = hsd->output_index;
    LOG("-- emitting %zu bytes from -%u bytes back\n", count, neg_offset);
    ASSERT(neg_offset <= mask + 1);
    ASSERT(count <= (size_t)(1 << BACKREF_COUNT_BITS(hsd)));

    for (i = 0; i < count; i++) {
      uint8_t c = buf[(hsd->head_index - neg_offset) & mask];
      push_byte(hsd, oi, c);
      buf[hsd->head_index & mask] = c;
      hsd->head_index++;
      LOG("  -- ++ 0x%02x\n", c);
    }
    hsd->output_count -= count;
    if (hsd->output_count == 0) { return HSDS_TAG_BIT; }
  }
  return HSDS_YIELD_BACKREF;
}

/* Get the next COUNT bits from the input buffer, saving incremental progress.
 * Returns NO_BITS on end of input, or if more than 15 bits are requested. */
static uint16_t get_bits(heatshrink_decoder *hsd, uint8_t count) {
  uint16_t accumulator = 0;
  int i = 0;
  if (count > 15) return NO_BITS;
  LOG("-- popping %u bit(s)\n", count);

  /* If we aren't able to get COUNT bits, suspend immediately, because we
   * don't track how many bits of COUNT we've accumulated before suspend. */
  if (hsd->input_size == 0 && hsd->bit_index < (1 << (count - 1))) return NO_BITS;

  for (i = 0; i < count; i++) {
    if (hsd->bit_index == 0x00) {
      if (hsd->input_size == 0) {
        LOG("  -- out of bits, suspending w/ accumulator of %u (0x%02x)\n", accumulator, accumulator);
        return NO_BITS;
      }
      hsd->current_byte = hsd->buffers[hsd->input_index++];
      LOG("  -- pulled byte 0x%02x\n", hsd->current_byte);
      if (hsd->input_index == hsd->input_size) {
        hsd->input_index = 0; /* input is exhausted */
        hsd->input_size = 0;
      }
      hsd->bit_index = 0x80;
    }
    accumulator <<= 1;
    if (hsd->current_byte & hsd->bit_index) {
      accumulator |= 0x01;
      if (0) {
        LOG("  -- got 1, accumulator 0x%04x, bit_index 0x%02x\n",
        accumulator, hsd->bit_index);
      }
    }
    else if (0) {
      LOG("  -- got 0, accumulator 0x%04x, bit_index 0x%02x\n",
      accumulator, hsd->bit_index);
    }
    hsd->bit_index >>= 1;
  }

  if (count > 1) LOG("  -- accumulated %08x\n", accumulator);
  return accumulator;
}

HSD_finish_res heatshrink_decoder_finish(heatshrink_decoder *hsd) {
  if (hsd == nullptr) { return HSDR_FINISH_ERROR_NULL; }
  switch (hsd->state) {
    case HSDS_TAG_BIT:
      return hsd->input_size == 0 ? HSDR_FINISH_DONE : HSDR_FINISH_MORE;

    /* If we want to finish with no input, but are in these states, it's
     * because the 0-bit padding to the last byte looks like a backref
     * marker bit followed by all 0s for index and count bits. */
    case HSDS_BACKREF_INDEX_LSB:
    case HSDS_BACKREF_INDEX_MSB:
    case HSDS_BACKREF_COUNT_LSB:
    case HSDS_BACKREF_COUNT_MSB:
      return hsd->input_size == 0 ? HSDR_FINISH_DONE : HSDR_FINISH_MORE;

    /* If the output stream is padded with 0xFFs (possibly due to being in
     * flash memory), also explicitly check the input size rather than
     * uselessly returning MORE but yielding 0 bytes when polling. */
    case HSDS_YIELD_LITERAL:
      return hsd->input_size == 0 ? HSDR_FINISH_DONE : HSDR_FINISH_MORE;

    default: return HSDR_FINISH_MORE;
  }
}

static void push_byte(heatshrink_decoder *hsd, output_info *oi, uint8_t byte) {
  LOG(" -- pushing byte: 0x%02x ('%c')\n", byte, isprint(byte) ? byte : '.');
  oi->buf[(*oi->output_size)++] = byte;
  (void)hsd;
}