#include <stdio.h>
#include <stdlib.h>
#include <time.h>

/* 4 MB buffer */
#define BUFFER_SIZE (4 * 1024 * 1024)

#define MAX_UNSIGNED_CHAR_VAL 255

#define MAX_DELETE_ITERATIONS 32

/* Securely erases a file on the disc, by overwriting,
   a given number of times, its content with a random
   sequence of bytes. */
int DeleteFile(const char* const fileName, unsigned int overwriteCount)
{
	FILE* fileToErase;
	long fileSize, filePosition;
	unsigned char* buffer;
	size_t bytesToWrite;
	unsigned int i, j;

	if ((fileToErase = fopen(fileName, "rb+")) == NULL)
		return -1;

	if (overwriteCount > MAX_DELETE_ITERATIONS)
		overwriteCount = MAX_DELETE_ITERATIONS;

	/* Sets the file stream to be unbuffered */
	setbuf(fileToErase, NULL);

	/* Determines the file length */
	fseek(fileToErase, 0, SEEK_END);
	fileSize = ftell(fileToErase);

	printf("\nStarting the wipe of file \"%s\" ...\n", fileName);

	if (fileSize > 0)
	{
		/* Allocates the buffer on the heap */
		buffer = (unsigned char*)malloc(BUFFER_SIZE * sizeof(unsigned char));

		/* Data overwrite iteration */
		for (i = 0; i < overwriteCount; i++)
		{
			/* Initializes the random generator */
			srand((unsigned int)time(NULL));
			
			/* Initializes the random buffer */
			for (j = 0; j < BUFFER_SIZE; j++)
				buffer[j] = (unsigned char)(rand() % (MAX_UNSIGNED_CHAR_VAL + 1));
			
			printf("\nWipe iteration %u ... ", i + 1);
			
			/* Moves the file pointer to the beginning of the file */
			fseek(fileToErase, 0, SEEK_SET);
			filePosition = 0;

			/* Data overwriting block */
			while (filePosition < fileSize)
			{
				if (filePosition + BUFFER_SIZE <= fileSize)
					bytesToWrite = BUFFER_SIZE;
				else
					bytesToWrite = (size_t)(fileSize - filePosition);

				fwrite(buffer, sizeof(unsigned char), bytesToWrite, fileToErase);

				printf("#");

				filePosition += (long)bytesToWrite;
			}

			printf("   Done\n");
		}

		free(buffer);
	}

	fclose(fileToErase);
                          
	if (remove(fileName) < 0)
		return -2;

	return 0;
}

int main(int argc, char** argv)
{
	unsigned int iterationsCount;
	
	if ( (argc != 3) || ((iterationsCount = (unsigned int)atoi(argv[2])) == 0) )
	{
		fprintf(stderr, "\nUsage: wipeit file_path iterations_count\n");
		return -1;
	}
	
	if (DeleteFile(argv[1], iterationsCount) < 0)
	{
		fprintf(stderr, "\nCould not delete the file \"%s\".\n", argv[1]);
		return -2;
	}

	printf("\nFile \"%s\" deleted successfully.\n", argv[1]);
	return 0;
}