/*
 * Copyright (c) 2018 IOTA Stiftung
 * https://github.com/iotaledger/iota_common
 *
 * Refer to the LICENSE file for licensing information
 */

#include <math.h>

#include "common/defs.h"
#include "common/trinary/tryte_long.h"

size_t min_trytes(int64_t const value) {
  // Need minimum 1 tryte to represent any number
  size_t num = 1;
  int64_t v_abs = value < 0 ? -value : value;
  // As long as value is > than (27^2)/2, need one more tryte
  while (v_abs > pow(TRYTE_SPACE_SIZE, num) / 2) {
    num++;
  }
  return num;
}

int64_t trytes_to_long(tryte_t const *const trytes, size_t const length) {
  int64_t value = 0;
  for (size_t j = 0; j < length; j++) {
    tryte_t tryte = trytes[j];
    // Trivial case, tryte value is 0
    if (tryte == '9') {
      continue;
    }
    // Get the tryte index - it's also the tryte value
    tryte = tryte - '@';
    // For indexes > 13 the value is negative
    if (tryte > TRYTE_VALUE_MAX) {
      tryte = tryte - TRYTE_SPACE_SIZE;
    }
    // Accumulate the tryte values
    value += tryte * pow(TRYTE_SPACE_SIZE, j);
  }
  return value;
}

// Return the number of trytes needed to encode the value
size_t long_to_trytes(int64_t const value, tryte_t *const trytes) {
  // Calculate number of iterations (number of trytes)
  size_t num_trytes = min_trytes(value);
  int64_t v_abs = value;
  for (int i = num_trytes - 1; i >= 0; i--) {
    // Check if the current value to convert is negative
    uint8_t negative = v_abs < 0;
    // Get its absolute value
    v_abs = negative ? -v_abs : v_abs;
    // int64_t v_abs = negative ? -value : value;
    // Precalculate the current power order (27^i)
    int64_t radix_pow = pow(TRYTE_SPACE_SIZE, i);
    // Find out the highest order tryte for this value
    int64_t tryte = (v_abs + radix_pow / 2ULL) / radix_pow;
    // Store the remainder of value minus the value of the highest order tryte
    v_abs -= radix_pow * tryte;
    // If the original value was negative, the tryte value should also be
    // negative
    if (negative) {
      tryte = tryte ? TRYTE_SPACE_SIZE - tryte : tryte;
      v_abs = -v_abs;
    }
    trytes[i] = TRYTE_ALPHABET[tryte];
  }
  return num_trytes;
}