#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <sys/stat.h>

#define UMOD_MAGIC 0x9FE3C5A3

typedef struct
{
	uint32_t sig, dir, size, ver, crc;
} umodfoot_t;

typedef struct
{
	char *fname;
	uint32_t ofs, len, flags;
} umoddir_t;

// CRC has to be done in this very specific way or shit will go wrong
// I totally did not take this from leaked Unreal Engine source code

uint32_t crctable[256];

void crcinit( void )
{
	for( uint32_t i=0; i<256; i++ ) for ( uint32_t c=(i<<24), j=8; j; j-- )
		crctable[i] = c = (c&0x80000000)?((c<<1)^0x04C11DB7):(c<<1);
}

uint32_t crc( const void *s, size_t l, uint32_t crc )
{
	uint8_t *d = (uint8_t*)s;
	crc = ~crc;
	for ( size_t i=0; i<l; i++ ) crc = (crc<<8)^crctable[(crc>>24)^d[i]];
	return ~crc;
}

// fuck you tim sweeney (or whoever else is responsible for this crime)
int32_t readindex( FILE *f )
{
	uint8_t byte[5] = {0};
	fread(&byte[0],1,1,f);
	if ( !byte[0] ) return 0;
	if ( byte[0]&0x40 )
	{
		for ( int i=1; i<5; i++ )
		{
			fread(&byte[i],1,1,f);
			if ( !(byte[i]&0x80) ) break;
		}
	}
	int32_t tf = byte[0]&0x3f;
	tf |= (int32_t)(byte[1]&0x7f)<<6;
	tf |= (int32_t)(byte[2]&0x7f)<<13;
	tf |= (int32_t)(byte[3]&0x7f)<<20;
	tf |= (int32_t)(byte[4]&0x7f)<<27;
	if ( byte[0]&0x80 ) tf *= -1;
	return tf;
}

int main( int argc, char **argv )
{
	if ( argc < 2 )
	{
		fprintf(stderr,"usage: umodextract <umod file>\n");
		return 1;
	}
	FILE *f = fopen(argv[1],"rb");
	fseek(f,-20,SEEK_END);
	umodfoot_t feet;
	fread(&feet,1,20,f);
	if ( feet.sig != UMOD_MAGIC )
	{
		fclose(f);
		return 2;
	}
	//printf("sig: %08X\ndir: &%u\nsize: %u bytes\nver: %u\ncrc: %08X\n",
	//	feet.sig,feet.dir,feet.size,feet.ver,feet.crc);
	// CRC verification
	void *dat = malloc(feet.size-20);
	fseek(f,0,SEEK_SET);
	fread(dat,1,feet.size-20,f);
	crcinit();
	uint32_t thiscrc = crc(dat,feet.size-20,0);
	free(dat);
	if ( thiscrc != feet.crc )
	{
		fprintf(stderr,"CRC mismatch! %08X != %08X\n",thiscrc,feet.crc);
		fclose(f);
		return 4;
	}
	fseek(f,feet.dir,SEEK_SET);
	int32_t ndir = readindex(f);
	//printf("ndir: %d\n",ndir);
	umoddir_t *dir = calloc(ndir,sizeof(umoddir_t));
	for ( int32_t i=0; i<ndir; i++ )
	{
		int32_t flen = readindex(f);
		dir[i].fname = malloc(flen);
		fread(dir[i].fname,1,flen,f);
		fread(&(dir[i].ofs),1,4,f);
		fread(&(dir[i].len),1,4,f);
		fread(&(dir[i].flags),1,4,f);
		//printf("fname: %.*s (%d)\nofs: &%u\nlen: %u\nflags: %08X\n",
		//	flen,dir[i].fname,flen,dir[i].ofs,dir[i].len,dir[i].flags);
		long saved = ftell(f);
		fseek(f,dir[i].ofs,SEEK_SET);
		int isini = 0;
		if ( (isini=!!strstr(dir[i].fname,"Manifest.ini")) || !!strstr(dir[i].fname,"Manifest.int") )
		{
			printf("==== BEGIN Manifest.in%c ====\n\n",isini?'i':'t');
			uint8_t *str = malloc(dir[i].len);
			fread(str,1,dir[i].len,f);
			fwrite(str,1,dir[i].len,stdout);
			free(str);
			printf("\n==== END Manifest.in%c ====\n",isini?'i':'t');
		}
		else
		{
			char *rpath = dir[i].fname;
			if ( !strchr(rpath,'\\') )
			{
				FILE *fout = fopen(rpath,"wb");
				void *dat = malloc(dir[i].len);
				fread(dat,1,dir[i].len,f);
				fwrite(dat,1,dir[i].len,fout);
				free(dat);
				fclose(fout);
			}
			else
			{
				FILE *fout;
				// subdivide folders
				char *nxt = 0;
				//int i = 0;
				do
				{
					nxt = strchr(rpath,'\\');
					if ( nxt )
					{
						*nxt = '\0';
						//printf("path%d: %s\n",i,rpath);
						mkdir(rpath,0755);
						*nxt = '/';
						rpath = nxt+1;
					}
					else
					{
						// the file itself
						//printf("fout: %s\n",dir[i].fname);
						printf("==== EXTRACTING %s (%u bytes) ====\n",dir[i].fname,dir[i].len);
						fout = fopen(dir[i].fname,"wb");
						void *dat = malloc(dir[i].len);
						fread(dat,1,dir[i].len,f);
						fwrite(dat,1,dir[i].len,fout);
						free(dat);
						fclose(fout);
					}
					//i++;
				} while ( nxt );
			}
		}
		fseek(f,saved,SEEK_SET);
	}
	for ( int32_t i=0; i<ndir; i++ ) free(dir[i].fname);
	free(dir);
	fclose(f);
	return 0;
}