#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <math.h>
#include "mytar.h"

#define BLOCK_SIZE 512
#define END_OF_ARCHIVE 1
#define TABLE_OF_CONTENTS 1
#define EXTRACT 2


/* global to keep track of current block */
static int curblock;

static int open_archive(void);
static void get_next_block(int, char *);
static int read_header(char *, headerVar *); 
static void fill_headerstruct(char *, headerVar *);
static int is_header(char *);
static void print_pathname();
static void process(const int);
static int num_blocks_to_advance(headerVar);
void extract_file(int fd, headerVar headerbuf);
static void make_dir();
static void make_link();
static void make_file();


int main(int argc, char *argv[]) {
//	headerVar headerbuf;
//	int n;
//	snprintf(headerbuf.size, 12, "%o", (unsigned int) 513);
	process(TABLE_OF_CONTENTS);
//	int num = num_blocks_to_advance(headerbuf);
//	printf("Number of blocks to advance: %i\n", num);
	return 0; 
}

static void process(const int mode) {
   int fd;
	char blockbuf[BLOCK_SIZE], zerobuf[BLOCK_SIZE];
	headerVar headerbuf;
   memset(zerobuf, 0, BLOCK_SIZE);
	int endOfArchive = 0; 
	fd = open_archive();

	while (!endOfArchive)
	{
		get_next_block(fd, blockbuf);
		printf("Done with reading block %i\n", curblock - 1);

		/* End of Archive check */
	  	if ( memcmp(blockbuf, zerobuf, BLOCK_SIZE) == 0 ) 
		{
			printf("inside end of archive\n");
			get_next_block(fd, blockbuf);
			printf("after end of archive !!!\n");
			if ( memcmp(blockbuf, zerobuf, BLOCK_SIZE) == 0)  {
				printf("Comparison");
				endOfArchive = 1;
				continue;
			}	
			else curblock--;
      }


		/* Decompose header into headerVar */
		if (read_header(blockbuf, &headerbuf) == -1) {
		   fprintf(stderr, "process: Malformed header found. Bailing.\n");
			exit(1);
		}

		if (mode == TABLE_OF_CONTENTS) {
			print_pathname();
			curblock += num_blocks_to_advance(headerbuf); /* advance the current block */
			         												  /* by the filesize in blocks */ 
			         
	   }                                             

		else if (mode == EXTRACT) {
		/*	extract_file(); */
			curblock += num_blocks_to_advance(headerbuf);  /* advance the current block */
			         												  /* by the filesize in blocks */                  
		}	                                                      
      
	}
	close(fd);
}
/* calculates the number of blocks occupied by certain filesize */
static int num_blocks_to_advance(headerVar headerbuf) {
	long double filesize = strtol(headerbuf.size, NULL, 8);
  	long double numblocks = filesize / BLOCK_SIZE; 
		
	return ( (int) ceil(numblocks) );
}

/* initializes file descriptor fd to archive name */
static int open_archive(void) {
   int fd;
	/* set current block to 0 */
	curblock = 0;
	
	if  ( (fd = open("archive", O_RDONLY)) == -1 ) 
	{
	   perror("archive");
	   exit(1);
	}
	fchmod(fd, S_IRUSR | S_IWUSR);
	printf("open_archive fd: %i\n", fd);
   return fd;
}



/* reads into buffer a block from the file */
static void get_next_block(int fd, char *blockbuf) {
   int readBytes;

	printf("get_nextblcok fd: %i\n", fd);
	printf("Current block is: %i\n", curblock);
   if ( lseek(fd, BLOCK_SIZE * curblock, SEEK_SET) == -1)
   {
      perror("lseek in get_next_block");
   }
	printf("Begin reading new header.\n");
   if  ( (readBytes = read(fd, blockbuf, BLOCK_SIZE)) == -1 )
      perror("read in get_next_block");
   else if (readBytes < BLOCK_SIZE)
      fprintf(stderr, "Unexpected end of archive.  Bailing\n");
   curblock++;       /* increment the current block */
	printf("After block is: %i\n", curblock);
}



/* read_header populates headerbuf from block.
 * returns -1 for error, 0 for sucess */
static int read_header(char *blockbuf, headerVar* headerbuf) {
	
		printf("In read_header\n");
		printf("Printed Block is '%s'\n", blockbuf);
	if ( is_header(blockbuf) ) {
		printf("Header found");
		fill_headerstruct(blockbuf, headerbuf);
	}
	else
		return -1; /* not a header */
		
   return 0;
}

static void fill_headerstruct(char *blockbuf, headerVar *headerbuf) 
{
      memmove(headerbuf->pathname, blockbuf, 100);
      memmove(headerbuf->mode, blockbuf + 100, 8);
      memmove(headerbuf->uid, blockbuf + 108, 8);
      memmove(headerbuf->gid, blockbuf + 116, 8);
      memmove(headerbuf->size, blockbuf + 124, 12);
      memmove(headerbuf->mtime, blockbuf + 136, 12);
      memmove(headerbuf->chksum, blockbuf + 148, 8);
      memmove(&headerbuf->typeflag, blockbuf + 156, 1);
      memmove(headerbuf->linkname, blockbuf + 157, 100);
      memmove(headerbuf->magic, blockbuf + 257, 6);
      memmove(headerbuf->version, blockbuf + 263, 2);
      memmove(headerbuf->uname, blockbuf + 265, 32);
      memmove(headerbuf->gname, blockbuf + 297, 32);
      memmove(headerbuf->devmajor, blockbuf + 329, 8);
      memmove(headerbuf->devminor, blockbuf + 337, 8);
      memmove(headerbuf->prefix, blockbuf + 345, 155);
      
}

/* checks if blockbuf is a header by comparing ustar and checksum.
 * returns 1 on success, 0 if not a header. ERROR: returns -1  */
static int is_header(char *blockbuf) {
   int i;                           /* counter */
   unsigned int sum = 0;
   char c;                          /* current char */
   char checksum[8];                /* store the real checksum */
   char calculatedchecksum[8];         /* to store the calculated checksum */
//   char magic[6] = "ustar";
   char tempbuf[BLOCK_SIZE];
   
	printf("in is_header\n");
   /* check to make sure ustar is present */
   if ( strncmp("ustar", &blockbuf[257], 6) != 0) {
      return 0; /* not a header */
	} 
	printf("ustar success\n");
   /* extract checksum from buffer */
   memcpy(checksum, &blockbuf[148], 8);
   printf("%c\n", blockbuf[148]); 
   printf("%c\n", blockbuf[149]); 
   printf("%c\n", blockbuf[150]); 
   printf("%c\n", blockbuf[151]); 
   printf("%c\n", blockbuf[152]); 
   printf("%c\n", blockbuf[153]); 
   printf("%c\n", blockbuf[154]); 
   printf("%c\n", blockbuf[155]); 

	/* copy buffer into a a temp buffer */
   memcpy(tempbuf, blockbuf, BLOCK_SIZE);
   /* set tempbuf checksum field to all spaces) */
   memset(&tempbuf[148], ' ', 8);
   
	/* calculate full sum of temp buffer 0 through 512 */
	for (i = 0; i < BLOCK_SIZE; i++)
	{
	   c = tempbuf[i];
	   sum += (unsigned char) c;
	}
	printf("sum is %i\n", sum);
	/* compare the checksum with the calculated checksum */
	sprintf(calculatedchecksum, "%07o", sum);
	/* return 1 if the checksum matches */
	
	printf("Checksum is %s\n", checksum);
	printf("Calculated Checksum is %s\n", calculatedchecksum);

	if ( strncmp(checksum, calculatedchecksum, 8) == 0 ) {
		printf("checksum success\n");
	   return 1; /* success */
	}
	else
		printf("Checksum failure\n");
   return 0; /* not a header */
}
static void print_pathname() {}



void extract_file(int fd, headerVar headerbuf) {

}

static void make_dir()
{
	
}

static void make_link()
{

}

static void make_file()
{

}