#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "errorAndExit.h"
#include "fileReader.h"
#include "utils/fileUtilities.h"
#include "utils/min.h"

//Opens the given file at the given offset
void initFileReader(char path[], unsigned long offset) {
  file.name = path;

  file.filePointer = fopen(file.name, "r");
  if (file.filePointer == NULL) {
    fprintf(stderr, "Could not open file \"%s\" for reading: %s\n", file.name, strerror(errno));
    errorAndExit();
  }

  //get file size
  fseek(file.filePointer, 0L, SEEK_END);
  file.size = ftell(file.filePointer);

  //seek to offset
  if (offset != 0UL) {
    fseek(file.filePointer, offset, SEEK_SET);
  } else {
    rewind(file.filePointer);
  }
  file.offset = offset;
}


//Reads the given amount of bytes from the file and writes them into the given buffer. Automatically opens next file if EOF is reached.
void getBytes(uint8_t* buffer, unsigned long numBytes, bool isLast) {
  uint8_t* bufferPosition = buffer;
  unsigned long remainingBytes = numBytes;

  //As long as we still need to read bytes
  while (remainingBytes > 0) {
    //Read as many bytes as we can from the current file
    const unsigned long availableBytes = min(remainingBytes, file.size - file.offset);

    //Read bytes into buffer if we have a valid buffer, otherwise skip bytes
    if (buffer) {
      readBytesIntoBuffer(bufferPosition, availableBytes);
      bufferPosition += availableBytes;
    } else {
      skipBytes(availableBytes);
    }
    remainingBytes -= availableBytes;

    //If we've reached end of file, close file and open next file
    if (file.offset == file.size) {
      closeCurrentFile();
      //Unless we've reached the end, in that case don't open next file in case we've reached the end of the last disk
      if (!isLast) {
        openNextFile();
      } else if (remainingBytes > 0) {
        fprintf(stderr, "Reached end of last disk but have to read %lu more bytes.\n", remainingBytes);
        errorAndExit();
      }
    }
  }
}