#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include "main.h"
#include <sys/wait.h>
#include <signal.h>

int file_exists(char *file) 
{

  struct stat foo;              /* throw away argument for stat */
  /* null files don't exist */
  if (file == NULL) {
    return 0;                
  }  
  /* on success 0 is returned */
  if (stat(file, &foo) == 0) {  /* this is you checking whether the return value of stat is 1 */
    return 1;                   /* true, happy, passed */
  }
  return 0;

}

/* find out if $PAGER is set */
char* get_pager()
{
  char *pager;  
  pager = getenv("PAGER");  /* set pager to $PAGER environment variable */  
  if (pager == NULL) {  /* if pager is NULL (the enviroment variable is unset) */ 
    /*     printf("PAGER is unset\n"); */
    if ( file_exists("/usr/bin/less") ) { /* if /usr/bin/less exists as a file */
      pager = "/usr/bin/less";  /* set pager to /usr/bin/less */
    } 
  }
  if (pager == NULL) {        /* if pager is NULL (the enviroment variable is unset) */
    if ( file_exists("/bin/more") ) { /* if /bin/more exists as a file */
      pager = "/bin/more";     
    }
  }
  if (pager == NULL) {
    pager = "cat";
  }
  return pager;
}

/* this function displays each file to the user */
int display_file(char *filename)
{
  gzFile *file_ptr;
  char *pager;
  int wait_status;       /* wait stores the exit status of the child here  */
  pid_t fork_result;
  int file_pipes[2] = {0};
  char gzbuffer[2048] = {0};
  int data_processed;
  
  /* leave curses mode to display the file */
  kill_curses();      

  /* get the $PAGER env variable */
  pager = get_pager();

  /* first we create a pipe this will pass data between two processes */
  if (pipe(file_pipes) != 0) {
    perror("pipe error");
    exit(EXIT_FAILURE);
  }  
  /* next the new process is created with fork() */
  fork_result = fork();
  /* check if fork() works */
  if (fork_result == (pid_t)-1) {
    perror("fork error");
    exit(EXIT_FAILURE);
  }

  /* now we have both parent and child processes */
  switch (fork_result) {
    case -1: {
      perror("fork failed");
      exit(1);
    }
      
    case 0: {
      /* we are in the childs thread of execution */
      /* set stdin to a copy of the readable fd of the pipe */
      close(file_pipes[1]); /* not using the write end of the pipe */
      close(0); /* redirecting standard input */
      dup(file_pipes[0]); /* duplicate the pipe, setting stdin */
	
      /* close the pipes read and write fd's because we made a copy */
      close(file_pipes[0]); /* stdin should be a copy now, so don't need */

      /* call the external program */
      (void)execlp(pager, pager, "-", (char *)NULL);
      /* DEBUG printf("should never get here...\n"); */
      break;
    }

    default: {
      /* we are in the parents thread of execution */
      close(file_pipes[0]); /* not using the read end of the pipe */
      
      /*  open the file for reading */
      if ((file_ptr = gzopen(filename, "r")) == NULL) {
	perror("Cannot open file for reading");
	return 1;
      }

      /* read the file line by line or until EOF */
      while (gzgets(file_ptr, gzbuffer, 256) != Z_NULL) {
        /* user might quit before scrolling to EOF */
        signal(SIGPIPE, SIG_IGN);
	/* send all the data to the child */
	data_processed = write(file_pipes[1], gzbuffer, strlen(gzbuffer));
	if (data_processed == -1) {
          
          perror("write error");
          exit(EXIT_FAILURE);
	}
	if (data_processed != strlen(gzbuffer)) {
          /* data_processed is short .. should be rare */
	  exit(EXIT_FAILURE);
	}
	/* make sure we're not done with the file before continuing */
	if (gzeof(file_ptr)) {
	  break;
	}
      }
      close(file_pipes[1]);  /* done with the writing end of the pipe */
      /*  close the file  */
      gzclose(file_ptr);
      /*  wait for the child to finish */
      wait(&wait_status);	/* returns the PID of child */
      /*  continue with the main program */
      break;
    } /* end default case */
  } /* end switch */
  return 0;
}