/**
 *  @file      dat2pl1.c
 *  @brief     Convert EBCDIC to ASCII for NSSDC PSPG-00472
 *  @author    Yukio Yamamoto
 *  @date      2013/04/03
 */
#include <stdio.h>
#include <stdlib.h>

#define SIZE_HEADER 2
#define SIZE_BUF 2000
#define SIZE_CODE 3
#define RECORD_LENGTH 80

/*
 * Notice:
 * It appears that CCSID EBCDIC-US was adoped.
 * See RFC 1345: Character Mnemonics & Character Sets
 */
char ebcdic[16][16][SIZE_CODE] = {
  {"NU","SH","SX","EX","ET","EQ","AK","BL","BS","HT","LF","VT","FF","CR","SO","SI"},
  {"DL","D1","D2","D3","D4","NK","SY","EB","CN","EM","SB","EC","FS","GS","RS","US"},
  {"??","??","??","??","??","??","??","??","??","??","??","??","??","??","??","??"},
  {"??","??","??","??","??","??","??","??","??","??","??","??","??","??","??","??"},
  {"  ","??","??","??","??","??","??","??","??","??","Ct",". ","< ","( ","+ ","| "},
  {"& ","??","??","??","??","??","??","??","??","??","! ","$ ","* ",") ","; ","^ "},
  {"- ","/ ","??","??","??","??","??","??","??","??","BB",", ","% ","_ ","> ","? "},
  {"??","??","??","??","??","??","??","??","??","'!",": ","# ","@ ","' ","= ","\" "},
  {"??","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 ","??","??","??","??","??","??"},
  {"0 ","1 ","2 ","3 ","4 ","5 ","6 ","7 ","8 ","9 ","??","??","??","??","??","DT"},
};

char ebcdic2ascii(unsigned char c) {
  int high = c >> 4;
  int low = c & 0x0f;
  char* code = ebcdic[high][low];
  
  if (high < 4) {
    return ' ';
  }
  if (code[1] != ' ') {
    return ' ';
  }
  return code[0];
}

int main(int argc, char** argv) {
  FILE* f;
  unsigned char header[SIZE_HEADER];
  unsigned char buf[SIZE_BUF];
  size_t r, size;
  int i;
  int ret = EXIT_SUCCESS;
  
  f = fopen(argv[1], "rb");
  if (f == NULL) {
    fprintf(stderr, "no such file: %s\n", argv[1]);
    ret = EXIT_FAILURE;
    goto finish;
  }
  
  while ((r = fread(header, sizeof(char), SIZE_HEADER, f)) > 0) {
    if (r != SIZE_HEADER) {
      fprintf(stderr, "invalid format\n");
      ret = EXIT_FAILURE;
      goto finish;
    }
    
    size = header[0];
    size = (size << 8) + header[1];
    if (size > SIZE_BUF) {
      fprintf(stderr, "data size exceeds buffer size %zd\n", size);
      ret = EXIT_FAILURE;
      goto finish;
    }
    
    if ((r = fread(buf, sizeof(char), size, f)) > 0) {
      if (size != r) {
        fprintf(stderr, "warning: data might be terminated\n");
      }
      for(i = 0; i < r; ++i) {
        putchar(ebcdic2ascii(buf[i]));
        if (i % RECORD_LENGTH == (RECORD_LENGTH - 1)) {
          putchar('\n');
        }
      }
    }
  }
  
finish:
  if (f) {
    fclose(f);
  }
  return ret;
}