/************************************************************\
 **      Created originally by Jonathan Naylor, G4KLX      **
 **     Later embellished by John Magliacane, KD2BD to     **
 **     detect and handle voids found in the SRTM data     **
 ************************************************************
 **                    Compile like this:                  **
 **      cc -Wall -O3 -s -lbz2 srtm2sdf.c -o srtm2sdf      **
 **              Last modification: 18-Mar-2006            **
\************************************************************/ 

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <bzlib.h>

#define BZBUFFER 65536

char sdf_filename[25], sdf_path[255], replacement_flag, opened=0;
int srtm[1201][1201], usgs[1200][1200], max_north, max_west,
    min_north, min_west, merge=0, min_elevation, bzerror;

int ReadSRTM(char *filename)
{
	int x, y, infile, byte, bytes_read;
	unsigned char error, buffer[2];
	char north[3], west[4], *base=NULL;

	if (strstr(filename, ".zip")!=NULL)
	{
		fprintf(stderr, "*** Error: \"%s\" must be uncompressed\n",filename);
		return -1;

	}

	if (strstr(filename, ".hgt")==NULL)
	{
		fprintf(stderr, "*** Error: \"%s\" does not have the correct extension (.hgt)\n",filename);
		return -1;
	}

	base=strrchr(filename, '/');
	
	if (base==NULL)
		base=filename;
	else
		base+=1;

	north[0]=base[1];
	north[1]=base[2];
	north[2]=0;

	west[0]=base[4];
	west[1]=base[5];
	west[2]=base[6];
	west[3]=0;

	if ((base[0]!='N' && base[0]!='S') || (base[3]!='W' && base[3]!='E'))
	{
		fprintf(stderr, "*** Error: \"%s\" doesn't look like a valid SRTM filename.\n", filename);
		return -1;
	}

	max_west=atoi(west);

	if (base[3]=='E')
		max_west=360-max_west;

	min_west=max_west-1;

	if (max_west==360)
		max_west=0;

	if (base[0]=='N')
		min_north=atoi(north);
	else
		min_north=-atoi(north);

	max_north=min_north+1;

	infile=open(filename, O_RDONLY);

	if (infile==0)
	{
		fprintf(stderr, "*** Error: Cannot open \"%s\"\n", filename);
		return -1;
	}

	read(infile,&buffer,2);

	if ((buffer[0]=='P') && (buffer[1]=='K'))
	{
		fprintf(stderr, "*** Error: \"%s\" still appears to be compressed!\n",filename);
		close(infile);
		return -1;
	}

	lseek(infile,0L,SEEK_SET);

	sprintf(sdf_filename, "%d:%d:%d:%d.sdf", min_north, max_north, min_west, max_west);

	error=0;
	replacement_flag=0;

	printf("Reading %s... ", filename);
	fflush(stdout);

	for (x=0; (x<1201 && error==0); x++)
		for (y=0; (y<1201 && error==0); y++)
		{
			bytes_read=read(infile,&buffer,2);

			if (bytes_read==2)
			{
				byte=buffer[1]+(buffer[0]<<8);

				if (buffer[0]&128)
					byte-=0x10000;

				/* Flag problem elevations here */

				if (byte<=min_elevation)
					replacement_flag=1;

				srtm[x][y]=byte;
			}

			else
				error=1;
		}

	if (error)
	{
		fprintf(stderr,"\n*** Error: Premature EOF detected while reading \"%s\"!  :-(\n",filename);
		return -1;
	}

	close(infile);

	return 0;
}

int LoadSDF_SDF(char *name)
{
	/* This function reads uncompressed
	   SPLAT Data Files (.sdf) into memory. */

	int x, y, dummy;
	char sdf_file[255], path_plus_name[255];
	FILE *infile;

	for (x=0; name[x]!='.' && name[x]!=0 && x<250; x++)
		sdf_file[x]=name[x];

	sdf_file[x]='.';
	sdf_file[x+1]='s';
	sdf_file[x+2]='d';
	sdf_file[x+3]='f';
	sdf_file[x+4]=0;

	strncpy(path_plus_name,sdf_path,255);
	strncat(path_plus_name,sdf_file,255);

	infile=fopen(path_plus_name,"rb");

	if (infile==NULL)
		return 0;

	fscanf(infile,"%d", &dummy);
	fscanf(infile,"%d", &dummy);
	fscanf(infile,"%d", &dummy);
	fscanf(infile,"%d", &dummy);

	printf("\nReading %s... ",path_plus_name);
	fflush(stdout);

	for (x=0; x<1200; x++)
		for (y=0; y<1200; y++)
			fscanf(infile,"%d",&usgs[x][y]);

	fclose(infile);

	return 1;
}

char *BZfgets(BZFILE *bzfd, unsigned length)
{
	/* This function returns at most one less than 'length' number
	   of characters from a bz2 compressed file whose file descriptor
	   is pointed to by *bzfd.  In operation, a buffer is filled with
	   uncompressed data (size = BZBUFFER), which is then parsed
	   and doled out as NULL terminated character strings every time
	   this function is invoked.  A NULL string indicates an EOF
	   or error condition. */

	static int x, y, nBuf;
	static char buffer[BZBUFFER+1], output[BZBUFFER+1];
	char done=0;

	if (opened!=1 && bzerror==BZ_OK)
	{
		/* First time through.  Initialize everything! */

		x=0;
		y=0;
		nBuf=0;
		opened=1;
		output[0]=0;
	}

	do
	{
		if (x==nBuf && bzerror!=BZ_STREAM_END && bzerror==BZ_OK && opened)
		{
			/* Uncompress data into a static buffer */

			nBuf=BZ2_bzRead(&bzerror, bzfd, buffer, BZBUFFER);
			buffer[nBuf]=0;
			x=0;
		}

		/* Build a string from buffer contents */

		output[y]=buffer[x];

		if (output[y]=='\n' || output[y]==0 || y==(int)length-1)
		{
			output[y+1]=0;
			done=1;
			y=0;
		}

		else
			y++;
		x++;

	} while (done==0);

	if (output[0]==0)
		opened=0;

	return (output);
}

int LoadSDF_BZ(char *name)
{
	/* This function reads .bz2 compressed
	   SPLAT Data Files into memory. */

	int x, y, dummy;
	char sdf_file[255], path_plus_name[255];
	FILE *fd;
	BZFILE *bzfd;

	for (x=0; name[x]!='.' && name[x]!=0 && x<247; x++)
		sdf_file[x]=name[x];

	sdf_file[x]='.';
	sdf_file[x+1]='s';
	sdf_file[x+2]='d';
	sdf_file[x+3]='f';
	sdf_file[x+4]='.';
	sdf_file[x+5]='b';
	sdf_file[x+6]='z';
	sdf_file[x+7]='2';
	sdf_file[x+8]=0;

	strncpy(path_plus_name,sdf_path,255);
	strncat(path_plus_name,sdf_file,255);

	fd=fopen(path_plus_name,"rb");
	bzfd=BZ2_bzReadOpen(&bzerror,fd,0,0,NULL,0);

	if (fd!=NULL && bzerror==BZ_OK)
	{
		printf("\nReading %s... ",path_plus_name);
		fflush(stdout);

		sscanf(BZfgets(bzfd,255),"%d",&dummy);
		sscanf(BZfgets(bzfd,255),"%d",&dummy);
		sscanf(BZfgets(bzfd,255),"%d",&dummy);
		sscanf(BZfgets(bzfd,255),"%d",&dummy);
	
		for (x=0; x<1200; x++)
			for (y=0; y<1200; y++)
				sscanf(BZfgets(bzfd,20),"%d",&usgs[x][y]);

		fclose(fd);

		BZ2_bzReadClose(&bzerror,bzfd);

		return 1;
	}

	else
		return 0;
}

char LoadSDF(char *name)
{
	/* This function loads the requested SDF file from the filesystem.
	   First, it tries to invoke the LoadSDF_SDF() function to load an
	   uncompressed SDF file (since uncompressed files load slightly
	   faster).  Failing that, it tries to load a compressed SDF file
	   by invoking the LoadSDF_BZ() function. */

	int return_value=-1;

	/* Try to load an uncompressed SDF first. */

	return_value=LoadSDF_SDF(name);

	/* If that fails, try loading a compressed SDF. */

	if (return_value==0 || return_value==-1)
		return_value=LoadSDF_BZ(name);

	return return_value;
}

int ReadUSGS()
{
	char usgs_filename[15];

	/* usgs_filename is a minimal filename ("40:41:74:75").
	   Full path and extentions are added later though
	   subsequent function calls. */

	sprintf(usgs_filename, "%d:%d:%d:%d", min_north, max_north, min_west, max_west);

	return (LoadSDF(usgs_filename));
}

void average_terrain(x,y,z)
int x, y, z;
{
	long accum;
	int temp=0, count, bad_value;
	double average;

	bad_value=srtm[x][y];

	accum=0L;
	count=0;

	if (x!=0)
	{
		temp=srtm[x-1][y];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if (x!=1201)
	{
		temp=srtm[x+1][y];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if ((x!=0) && (y!=1201))
	{
		temp=srtm[x-1][y+1];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if (y!=1201)
	{
		temp=srtm[x][y+1];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if ((x!=1201) && (y!=1201))
	{
		temp=srtm[x+1][y+1];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if ((x!=0) && (y!=0))
	{
		temp=srtm[x-1][y-1];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if (y!=0)
	{
		temp=srtm[x][y-1];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if ((x!=1201) && (y!=0))
	{
		temp=srtm[x+1][y-1];

		if (temp>bad_value)
		{
			accum+=temp;
			count++;
		}
	}

	if (count!=0)
	{
		average=(((double)accum)/((double)count));
		temp=(int)(average+0.5);
	}

	if (temp>min_elevation)
		srtm[x][y]=temp;
	else
		srtm[x][y]=min_elevation;
}

void WriteSDF(char *filename)
{
	int x, y, byte, last_good_byte=0;
	FILE *outfile;

	printf("\nWriting %s... ", filename);
	fflush(stdout);

	outfile=fopen(filename,"wb");

	fprintf(outfile, "%d\n%d\n%d\n%d\n", max_west, min_north, min_west, max_north);

	for (x=1200; x>0; x--)
		for (y=1200; y>0; y--)
		{
			byte=srtm[x][y];

			if (byte>min_elevation)
				last_good_byte=byte;

			if (byte<min_elevation)
			{
				if (merge)
					fprintf(outfile,"%d\n",usgs[1200-x][1200-y]);
				else
					{
						average_terrain(x,y,last_good_byte);
						fprintf(outfile,"%d\n",srtm[x][y]);
					}
			}
			else
				fprintf(outfile,"%d\n",byte);
		}

	printf("Done!\n");

	fclose(outfile);
}

int main(int argc, char **argv)
{
	int x, y, z=0;
	char *env=NULL, string[255];
	FILE *fd;

	if (argc==1 || (argc==2 && strncmp(argv[1],"-h",2)==0))
	{
		fprintf(stderr, "\nsrtm2sdf: Generates SPLAT! elevation data files from unzipped SRTM-3\nelevation data files, and replaces SRTM data voids with elevation\ndata from existing SDF files.\n\n");
		fprintf(stderr, "\tAvailable Options...\n\n");
		fprintf(stderr, "\t-d directory path of existing .sdf files\n\t   (overrides path in ~/.splat_path file)\n\n");
		fprintf(stderr, "\t-n elevation (in meters) below which SRTM data\n\t   is replaced by existing SDF data (default=0)\n\n");

		fprintf(stderr, "Examples: srtm2sdf N40W074.hgt\n");
		fprintf(stderr, "          srtm2sdf -d /cdrom/sdf N40W074.hgt\n");
		fprintf(stderr, "          srtm2sdf -d /dev/null N40W074.hgt  (prevents data replacement)\n");
		fprintf(stderr, "          srtm2sdf -n -5 N40W074.hgt\n\n");

		return 1;
	}

	y=argc-1;

	min_elevation=0;

	for (x=1, z=0; x<=y; x++)
	{
		if (strcmp(argv[x],"-d")==0)
		{
			z=x+1;

			if (z<=y && argv[z][0] && argv[z][0]!='-')
				strncpy(sdf_path,argv[z],253);
		}

		if (strcmp(argv[x],"-n")==0)
		{
			z=x+1;

			if (z<=y && argv[z][0])
			{
				sscanf(argv[z],"%d",&min_elevation);

				if (min_elevation<-32768)
					min_elevation=0;
			}			 
		}
	}

	/* If no SDF path was specified on the command line (-d), check
	   for a path specified in the $HOME/.splat_path file.  If the
	   file is not found, then sdf_path[] remains NULL, and a data
	   merge will not be attempted if voids are found in the SRTM file. */

	if (sdf_path[0]==0)
	{
		env=getenv("HOME");

		sprintf(string,"%s/.splat_path",env);

		fd=fopen(string,"r");

		if (fd!=NULL)
		{
			fgets(string,253,fd);

			/* Remove <CR> and/or <LF> from string */

			for (x=0; string[x]!=13 && string[x]!=10 && string[x]!=0 && x<253; x++);
			string[x]=0;

			strncpy(sdf_path,string,253);

			fclose(fd);
		}
	}

	/* Ensure a trailing '/' is present in sdf_path */

	if (sdf_path[0])
	{
		x=strlen(sdf_path);

		if (sdf_path[x-1]!='/' && x!=0)
		{
			sdf_path[x]='/';
			sdf_path[x+1]=0;
		}
	}

	if (ReadSRTM(argv[z+1])==0)
	{
		if (replacement_flag && sdf_path[0])
			merge=ReadUSGS();

		WriteSDF(sdf_filename);
	}

	return 0;
}