#include "git-compat-util.h"

#include "base85.h"

static const char en85[] = {

  '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',

  'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',

  'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',

  'U', 'V', 'W', 'X', 'Y', 'Z',

  'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',

  'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',

  'u', 'v', 'w', 'x', 'y', 'z',

  '!', '#', '$', '%', '&', '(', ')', '*', '+', '-',

  ';', '<', '=', '>', '?', '@', '^', '_', '`', '{',

  '|', '}', '~'

};

static char de85[256];

static void prep_base85(void)

{

  if (de85['Z'])

    return;

  for (size_t i = 0; i < ARRAY_SIZE(en85); i++) {

    int ch = en85[i];

    de85[ch] = i + 1;

  }

}

int decode_85(char *dst, const char *buffer, int len)

{

  prep_base85();

  while (len) {

    unsigned acc = 0;

    int de, cnt = 4;

    unsigned char ch;

    do {

      ch = *buffer++;

      de = de85[ch];

      if (--de < 0)

        return error("invalid base85 alphabet %c", ch);

      acc = acc * 85 + de;

    } while (--cnt);

    ch = *buffer++;

    de = de85[ch];

    if (--de < 0)

      return error("invalid base85 alphabet %c", ch);

    /* Detect overflow. */

    if (0xffffffff / 85 < acc ||

        0xffffffff - de < (acc *= 85))

      return error("invalid base85 sequence %.5s", buffer-5);

    acc += de;

    cnt = (len < 4) ? len : 4;

    len -= cnt;

    do {

      acc = (acc << 8) | (acc >> 24);

      *dst++ = acc;

    } while (--cnt);

  }

  return 0;

}

static void encode_85(char *buf, const unsigned char *data, int bytes)

{

  while (bytes) {

    unsigned acc = 0;

    int cnt;

    for (cnt = 24; cnt >= 0; cnt -= 8) {

      unsigned ch = *data++;

      acc |= ch << cnt;

      if (--bytes == 0)

        break;

    }

    for (cnt = 4; cnt >= 0; cnt--) {

      int val = acc % 85;

      acc /= 85;

      buf[cnt] = en85[val];

    }

    buf += 5;

  }

  *buf = 0;

}

/*

 * Split the provided data into chunks of at most 52 bytes. Each chunk

 * is base85-encoded into a line with the following format:

 *  - Byte 0: encodes the chunk size (1-52) as a letter: 'A'-'Z' for

 *    1-26 bytes, 'a'-'z' for 27-52 bytes.

 *  - Bytes 1 onwards: base85-encoded data (up to 65 bytes).

 *  - Followed by a newline and NUL terminator.

 * The output callback is called once per line.

 */

void chunk_and_encode85(const unsigned char *data, unsigned long len,

      each_encoded_line_fn output, void *output_data)

{

  while (len) {

    int line_len;

    int bytes = (BASE85_CHUNK_SIZE < len) ? BASE85_CHUNK_SIZE : len;

    char line[71];

    len -= bytes;

    if (bytes <= 26)

      line[0] = bytes + 'A' - 1;

    else

      line[0] = bytes - 26 + 'a' - 1;

    encode_85(line + 1, data, bytes);

    data = data + bytes;

    line_len = strlen(line);

    line[line_len++] = '\n';

    line[line_len] = '\0';

    output(line, line_len, output_data);

  }

}