#pragma implementation
//#define TRACE
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include "bufio.h"

bufio::bufio(int f,int size,int sect) {
  tfd = fd = f;
  bufcnt = -1;
  buf = new char[bufsize = size];
  sectsize = sect;
  bufpos = 0;
  curpos = 0;
  cursize = 0;
  tmpsize = 0;
}

bufio::~bufio() {
  close(fd);
  if (tfd != fd)
    close(tfd);
  delete [] buf;
}

void *bufio::read(long pos,int size) {
  // resize buffer if required
  long newpos = pos & ~(sectsize - 1);
  curpos = pos - newpos;
  if (curpos + size > bufsize) {
    bufsize = (size + sectsize) & ~(sectsize - 1);
    // save data already read if required
    if (newpos >= bufpos && newpos - bufpos < bufcnt) {
      char *newbuf = new char[bufsize];
      bufcnt -= newpos - bufpos;
      memcpy(newbuf,buf + newpos - bufpos,bufcnt);
      delete [] buf;
      buf = newbuf;
      bufpos = newpos;
    }
    else {
      delete [] buf;
      buf = new char[bufsize];
      bufcnt = 0;
    }
  }
  // seek to new buffer if required (we already made sure size <= bufsize)
  if (pos < bufpos || pos > bufpos + bufcnt) {
    if (seek(newpos) != newpos) return 0;
    bufpos = newpos;
    bufcnt = ::read(tfd,buf,bufsize);
#ifdef TRACE
    fprintf(stderr,"bufio::read(%ld,%d) read(%ld,%d) = %d\n",
      pos,size,bufpos,bufsize,bufcnt);
#endif
    if (bufcnt < 0) {
      bufcnt = 0;
    }
  }
  curpos = pos - bufpos;
  cursize = size;
  // read additional data from input if required
  if (curpos + size > bufcnt || curpos == bufcnt) {
    int offset = curpos & ~(sectsize - 1);
    int remsize = bufcnt - offset;
    curpos -= offset;
    bufpos += offset;
    memcpy(buf,buf + offset,remsize);
    int rfd = (pos < tmpsize) ? tfd : fd;
    bufcnt = ::read(rfd, buf + remsize, bufsize - remsize);
#ifdef TRACE
    fprintf(stderr,
    "bufio::read(%ld,%d) read(%d) = %d, fd=%d, tmpsize=%ld, offset=%d\n",
      pos,size,bufsize - remsize,bufcnt,rfd,tmpsize,offset);
#endif
    if (bufcnt <= 0) {
      bufcnt = remsize;
      return 0;
    }
    // flush buffer to backing file
    bufcnt += remsize;
    if (tfd != fd && bufpos + bufcnt > tmpsize) {
      int n = tmpsize - bufpos;
      //assert(n >= 0);
      n = ::write(tfd,buf + n,bufcnt - n);
      if (n > 0)
	tmpsize += n;
    }
  }
  if (curpos + size > bufcnt) return 0;
  return buf + curpos;
}

void bufio::setSequential() {
  if (tfd != fd) return;
  // open tmp
  char buf[] = "/tmp/bufioXXXXXX";
  const char *tmpnam = mktemp(buf);
  tfd = open(tmpnam,O_RDWR+O_CREAT+O_EXCL+O_APPEND,0600);
  unlink(tmpnam);
}

long bufio::seek(long pos) {
  curpos = cursize = 0;
  bufpos = pos;
  if (tfd == fd) {
    bufcnt = 0;
    if (lseek(fd,pos,0) == pos) return pos;
    setSequential();
    if (tfd < 0) return -1;
  }
  while (tmpsize < pos) {
    bufcnt = ::read(fd,buf,bufsize);
    if (bufcnt <= 0) break;
    int n = ::write(tfd,buf,bufcnt);
    if (n <= 0) break;
    tmpsize += n;
  }
  return lseek(tfd,pos,0);
}

void *bufio::read(int size) {
  return read(getpos(),size);
}