// Created by Juergen Helbing in 2001 as a part of the MyNews project 

// This is a source code example for the yDecoder - see also:  http://www.yenc.org
// It is public domain - as well as the yEnc specification
//
// The progamming style is very "basic" and readable.
//
// The function is scanning the incoming file stream (fIn) for yEncoded blocks.
// The stream must be supported by the newsreader - in case of multipart
// the entire parts must be in the input stream. The newsreader should provide
// the decoder with a textfile which contains all the parts. This source
// can contain additional headers between the parts - they are simply skipped.

// This example requires the parts in correct sequence (1-2-3-4-...-n)
// Advanced decoders might be able to operate on mixed sequence - and even
// missing parts or parts from different "fill" posts

// print() and eprint() are logging displays from 'MyNews'
// Crc32 - functions are available in the yEncoder example

// ad_fgetscr() read data from the input stream into the buffer and removes CRLF.


unsigned long hex_to_ulong(char * text)  // Because strtol() does not deliver 32 bit on my C-Compiler
	{
	unsigned long res;
	unsigned char c;

	if (text==NULL) return(-1);

	res=0;
loop:
	c=*text; text++;
	if ((c>='0')&(c<='9'))
		{
		res=(res<<4)+((long)(c-48) & 0x0F);
		goto loop;
		}
	if ((c>='A')&(c<='F'))
		{
		res=(res<<4)+((long)(c-55) & 0x0F);
		goto loop;
		}
	if ((c>='a')&(c<='f'))
		{
		res=(res<<4)+((long)(c-87) & 0x0F);
		goto loop;
		}
	return(res);
	}



int yDecode(FILE * fOut, FILE * fIn, long y_line, long y_size,int y_part)
	{
	unsigned char srcbuf[4100];
	unsigned char desbuf[4100];
	unsigned char * srcp;
	unsigned char * desp;
	int deslen;
	int srclen;
	unsigned char c;
	int id;
	char * cp;
	long decolen;
	long y_begin;
	long y_end;
	long sumlen;
	int partnr;
	unsigned long crc32;
	char name[260];
	int esize;

	if (aDsp) print("yDecoder started...\r\n");

	sumlen=0; partnr=1;

part_start:
	CrcInit();  // Analyse only CRC per part
	decolen=0;
	deslen=0; desp=desbuf;

	if (y_part)  // This is a multipart message !
		{
		cp=ad_fgetscr((char*) srcbuf,4097,fIn);  // fgets especially with ad_length
		if (cp==NULL)
			{
			eprint("Unexpected eof in yEncoded file\r\n");
			return(1);
			}

		if (aDsp) print("=ypart-line:  %s\r\n",srcbuf);

		if (strncmp((char*) srcbuf,"=ypart ",7))
			{
			eprint("Missing =ypart line in yEncoded multipart message\r\n");
			return(2);
			}
		cp=strstr((char*)srcbuf,"end=");
		if (cp==NULL)
			{
			eprint("Missing end= in yEncoded multipart message\r\n");
			return(2);
			}
		y_end=atol(cp+4);

		cp=strstr((char*)srcbuf,"begin=");
		if (cp==NULL)
			{
			eprint("Missing begin= in yEncoded multipart message\r\n");
			return(2);
			}
		y_begin=atol(cp+6);

		if (aDsp) print("part-begin: %ld\r\n",y_begin);
		if (aDsp) print("part-end  : %ld\r\n",y_end);

		}


loop:

	cp=ad_fgetscr((char*) srcbuf,4097,fIn);  // fgets especially with ad_length
	if (cp==NULL)
		{
		eprint("Unexpected eof in yEncoded file\r\n");
		return(1);
		}
	if (strncmp((char*) srcbuf,"=yend ",6)==0)
		{
		if (aDsp) print("Endline (%d bytes): %s\r\n",decolen,srcbuf);
		goto end_of_file;
		}
	srclen=strlen((char*)srcbuf);
	if (srclen<y_line)
		{
		if (aDsp) print("Last line.\r\n");
		}
	srcp=srcbuf;

loop2:
	c=*srcp; srcp++;
	if (c==0)
		{
		goto loop;  // End of line reached
		}
	if (c == '=')  // The escape character comes in
		{
		c=*srcp; srcp++;
		if (c==0) return(2); // Last char cannot be escape char !
		c=(unsigned char)(c-64);
		}
	c=(unsigned char)(c-42);  // Subtract the secret number
	*desp=c; desp++; deslen++;	decolen++;

	CrcAdd(c);

	if (deslen>=4096)
		{
		id=fwrite(desbuf,deslen,1,fOut);
		if (id != 1)
			{
			eprint("Error in writing decoded file (code=%d)\r\n",errno);
			return(3);
			}
		deslen=0; desp=desbuf;
		}
	goto loop2;

end_of_file:


	if (deslen>0)  // Empty the last buffer
		{
		id=fwrite(desbuf,deslen,1,fOut);
		if (id != 1)
			{
			eprint("Error in writing decoded file (code=%d)\r\n",errno);
			return(4);
			}
		}

	cp=strstr((char*) srcbuf,"size=");  // Compare the decoded size to the =yend size
	if (cp)
		{
		esize=atoi(cp+5);
		if (esize != decolen)
			{
			sprintf(name,"%s(size=%ld)",attname,decolen);
			strcpy(attname,name);
			eprint("Corrupt yEnc binary - endsize mismatch (%s%s)\r\n",attname,attext);
			return(0);
			}
		}


	// Check the srcbuf for the CRC
	if (y_part==0)
		{
		cp=strstr((char*)srcbuf,"crc32=");
		if (cp)
			{
			crc32=hex_to_ulong((char*)(cp+6));
			ad_rescrc=crc_val ^ 0xFFFFFFFFl;
			if (aDsp) print("Included CRC: $%08lx - calculated CRC: $%08lx\r\n",crc32,ad_rescrc);
			}
		}
	else
		{
		cp=strstr((char*)srcbuf,"pcrc32=");
		if (cp)
			{
			crc32=hex_to_ulong((char*)(cp+7));
			ad_rescrc=crc_val ^ 0xFFFFFFFFl;
			if (aDsp) print("Included CRC: $%08lx - calculated CRC: $%08lx\r\n",crc32,ad_rescrc);
			}
		}

	if (cp!=NULL)
		{
		if (crc32 != ad_rescrc)
			{
			sprintf(name,"%s(crc=$%08lx)",attname,ad_rescrc);
			strcpy(attname,name);
			eprint("Corrupt yEnc binary - CRC mismatch (%s%s)\r\n",attname,attext);
			return(0);
			}
		}

	if (y_part==0)  // Single message
		{
		if ((y_part==0) & (decolen != y_size))
			{
			// eprint("Y-Decoder: Size mismatch - file corrupt.\r\n");

			sprintf(name,"%s(len=%ld)",attname,decolen);
			strcpy(attname,name);
			eprint("Corrupt yEnc binary - size mismatch (%s%s)\r\n",attname,attext);

			return(0);
			}

		ad_reslen=decolen;
		ad_rescrc=crc_val ^ 0xFFFFFFFFl;

		if (aDsp) print("yDecoder: Job done. %ld bytes written. CRC: $%08lx \r\n",decolen,ad_rescrc);
		return(0);
		}

	// Multipart message

	if ((y_part>0) & (decolen != (y_end-y_begin+1)))
		{
		eprint("yDecoder: Part size mismatch - file corrupt.\r\n");
		return(6);
		}

	sumlen=sumlen+decolen;
	if (sumlen == y_size)  // Completely decoded
		{
		if (aDsp) print("yDecoder: Multpart Job done. %ld bytes written\r\n",sumlen);

		ad_reslen=sumlen;
		ad_rescrc=crc_val ^ 0xFFFFFFFFl;

		return(0);
		}
	if (sumlen>y_size)
		{
		eprint("yDecoder: More data than expected. File corrupt.\r\n");
		return(7);
		}

	// Now scan the file for the rest !

	partnr++;  // Now scan for this part number

ploop:

	cp=ad_fgetscr((char*) srcbuf,4097,fIn);  // fgets especially with ad_length
	if (cp==NULL)
		{
		eprint("Unexpected eof in multipart yEncoded file\r\n");
		return(1);
		}
	if (strncmp((char*) srcbuf,"=ybegin ",8))
		{
		if (aDsp) print("yEnc skipped: %s\r\n",srcbuf);
		goto ploop;
		}
	cp=strstr((char*)srcbuf," part=");
	if (cp==NULL)
		{
		eprint("No part in next ybegin found - in multipart yEncoded file\r\n");
		return(1);
		}
	if (atoi(cp+6) != partnr)
		{
		eprint("Unexpected part (%d) found in yEncoded message. Expected was (%d)\r\n",atoi(cp+6),partnr);
		return(1);
		}
	if (aDsp) print("Found part # %d\r\n",partnr);

	// Additional plausi possible for name & size

	goto part_start;
	}




// ......  A part from the decoder which scans messages for attachments .......

is_yEncoded:
	if (strncmp(line,"=ybegin ",8)==0)
		{
		cp=strstr(line,"name=");
		if (cp==NULL) goto loop;  // Error - filename not found
		strcpy(attname,cp+5);  // Store the filename
		*cp=0; // throw away the filename

		cp=strstr(line,"size=");
		if (cp==NULL) goto loop;  // Error - size not found
		y_size=atol(cp+5);

		cp=strstr(line,"line=");
		if (cp==NULL) goto loop;  // Error - linelength not found
		y_line=atol(cp+5);

		y_part=0;
		cp=strstr(line,"part=");   // Check if this is a multipart message
		if (cp)
			{
			y_part=atol(cp+5);
			if (y_part != 1) goto loop;   // MUST start with the first part for proper decoding
			}

		// Now we can decode the file -- let's assume that this is a valid file

		attext[0]=0;
		cp=strrchr(attname,'.');
		if (cp)
			{
			strcpy(attext,cp); *cp=0;
			}

		sprintf(filename,"%s\\decode.tmp",datadir);
		if (aDsp) print("DesFileName = (%s%s)\r\n",attname,attext);

		// 27-03-2001: Set the filename jsut in case we cannot decode it
		sprintf(ad_desname,"%s\\%s%s",ad_despath,attname,attext);

		// filelen=0;

		if (ad_crcmode) CrcInit();
		if (ad_cleanmode)
			{
			ad_cleanmode=2;  // This will prevent us from writing more to the clean buffer
			if (aDsp) print("Begin cleaning...\r\n");
			CrcInit();
			}

		fOut=copen(filename,"wb");
		if (fOut==NULL)  // Possibly already exists
			{
			eprint("AutoDecode: Cannot create DesFile (%s)\r\n",filename);
			cclose(fIn);
			rb_picerr++;
			return(-1);
			// goto loop;
			}
		// Now decode that file !

		id=yDecode(fOut,fIn,y_line,y_size,y_part);
		if (id)
			{
			eprint("yDecode failed (reason: %d)\r\n",id);
			goto abortus;
			}
		print("yDecode successful\r\n");
		cclose(fOut);

		filelen=ad_reslen;

		goto file_ok;
		};