// ProjectThreeSourceA.c
// This program searches a binary file for a given hex pattern. Files are
//  found in the binary file via this pattern. The offsets of where the files
//  were found are output to another file, to be named by user input. Along with
//  the number of files found and their offsets, the output file will also contain
//  their sizes.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

struct FileHeader {
  unsigned long magic_number;
  unsigned long fileLength;
} header;

void performFileIO(const char *infile)
{
  FILE *FileIn, *FileOut;
  char inBuffer[BUFSIZ];
  char tempBuffer[4];
  int position = 0, len;
  // marks the header of a file found within the input file
  const unsigned char pattern[] = {0xFF, 0x57, 0x50, 0x43};

  // properly open the binary file for reading
  FileIn = fopen(infile, "rb");

  if (FileIn == NULL) {
    printf("The file could not be opened, please check your file and location before trying again.\n");
    exit(1);
  }

  printf("Enter the name and path for the output file: ");
  gets(inBuffer);
  FileOut = fopen(inBuffer, "w+b");

  // position the file marker at the beginning of file
  fseek(FileIn, 0, SEEK_SET);

  while (!feof(FileIn))
  {
    position++;

    if (fgetc(FileIn) == pattern[0]) {
      tempBuffer[0] = pattern[0];
      if (fread(tempBuffer + 1, sizeof(char), 3, FileIn) != 3) {
        printf("Error reading file.\n");
        exit(1);
      }

      if (memcmp(pattern, tempBuffer, sizeof(pattern)) == 0) {
        printf("Match Found.\n");

        // now that match is found load pattern into struct
        header.magic_number = pattern;

        fseek(FileIn, 21, SEEK_CUR); // find the file size
        // four byte size of file found
        if (fread(tempBuffer, sizeof(char), 4, FileIn) != 4) {
          printf("Match found but fatal error reading file.\n");
          exit(1);
        }

        // after finding filesize load it into struct
        header.fileLength = tempBuffer;

        // retract to the pattern header
        fseek(FileIn, -25, SEEK_CUR);

        // read the full - whole file loaded into the structure
        if (fread(&header, sizeof(struct FileHeader), 1, FileIn) != 1) {
          printf("Match found but fatal error reading of size struct.\n");
          exit(1);
        }

        // present for output to user specified file
        fwrite(&header, sizeof(struct FileHeader), 1, FileOut);
        break;
        continue;
      }

      fseek(FileIn, -3, SEEK_CUR);
    }
  }

  // close the files and at the same time flush the buffers
  fclose(FileIn);
  fclose(FileOut);
}

// program entry point
int main(int argc, char *argv[])
{
  char buffer[BUFSIZ];

  printf("Please enter the name and path of the binary file: ");
  gets(buffer);

  performFileIO(buffer);

  printf("\n Done!\n Press enter to exit\n");
  getchar();

  return 0;
}