//--------------------------------------------
// NAME: Daniel Kirov
// CLASS: XI a
// NUMBER: 10
// PROBLEM: #1
// FILE NAME: tail.c
// FILE PURPOSE:
// This is my only version of the homework in which we have to
// implement tail.
//---------------------------------------------

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdbool.h>
#include <errno.h>
#define BUFF_SIZE 420

//--------------------------------------------
// FUNCTION: openFile
// a function to open a file and check for opening errors
// PARAMETERS:
// int descriptor - this is the index of the file i open
// const char* filename - this the name of the file that has to be open
//----------------------------------------------
int openFile(const char* filename)
{
    int descriptor = open(filename, O_RDONLY);
    int errsv = errno;

    const char message[100];
    strcpy(message, "tail: cannot open `");
    strcat(message, filename);
    strcat(message, "` for reading: No such file or directory");


    const char message_[100];
    strcpy(message_, "tail: cannot open ’");
    strcat(message_, filename);
    strcat(message_, "’ for reading: Permission denied");

    if(descriptor < 0)
    {
        if(errsv == ENOENT)
        {
            write(STDOUT_FILENO, message, strlen(message));
        }
        else if(errsv == EACCES)
        {
            write(STDOUT_FILENO, message_, strlen(message_));
        }
        return -1;
    }
    else
    {
        return descriptor;
    }
}
//--------------------------------------------
// FUNCTION: lineCount
// A function to count the new lines in a file
// PARAMETERS:
// int descriptor - this is the index of the file i open
//----------------------------------------------
int lineCount(int descriptor)
{
    int status_read = 1;
    char buff[BUFF_SIZE];
    int i = 0;
    int lines = 0;


    while((status_read = read(descriptor, buff, BUFF_SIZE)) > 0)
    {
        for(i = 0; i < status_read; i++)
        {
            if(buff[i] == '\n')
            {
                lines++;
            }
        }
    }
    return lines;
}
//--------------------------------------------
// FUNCTION: linesPrint
// A function to print the last 10 lines in a file
// PARAMETERS:
// int descriptor - this is the index of the file i open
// int lines - this is the number of the new lines in a file
//----------------------------------------------
void linesPrint(int descriptor,int lines)
{
    int status_read = 1;
    char buff[BUFF_SIZE];
    bool printing = false;
    int lines2 = 0;
    int i = 0;

    lseek(descriptor, 0, SEEK_SET);

    if(lines > 10)
    {
        while((status_read = read(descriptor, buff, BUFF_SIZE)) > 0)
        {
            for(i = 0; i < status_read; i++)
            {
                if(printing)
                {
                    write(STDOUT_FILENO, &buff[i], 1);
                }
                else
                {
                    if(buff[i] == '\n')
                    {
                        lines2++;
                    }
                    if(lines2 == (lines - 9))
                    {
                        printing = true;
                    }
                }
            }
        }
    }
    else
    {
        while((status_read = read(descriptor, buff, BUFF_SIZE)) > 0)
        {
            for(i = 0; i < status_read; i++)
            {
                write(STDOUT_FILENO, &buff[i], 1);
            }
        }
    }


}
//--------------------------------------------
// FUNCTION: tail
// A function to execute tail
// PARAMETERS:
// const char* filename - this the name of the file that has to be open
//----------------------------------------------
void tail(const char* filename)
{
    int lines;
    int descriptor = openFile(filename);
    lines = lineCount(descriptor);
    linesPrint(descriptor, lines);
    close(descriptor);
}

int main(int argc, char *argv[] )
{
    int i = 0;

    if(argc > 2)
    {
        for(i = 1; i < argc; i++)
        {
            if(argv[i] == '-')
            {
                int temp_file = open("temp_file.txt", O_RDONLY | O_CREAT | O_TRUNC);
                char new_buff[BUFF_SIZE];
                int status_read = 1;

                while(status_read > 0)
                {
                    status_read = read(STDIN_FILENO, new_buff, BUFF_SIZE);
                    int written = 0;
                    int status_write;
                    while(written < status_read)
                    {
                        status_write = write(temp_file, new_buff + written, status_read - written);
                        written = written + status_read;
                    }
                }
                tail(temp_file);
            }
            else
            {
                const char filename[100];
                strcpy(filename, "==> ");
                strcat(filename, argv[i]);
                strcat(filename, " <==\n");
                write(STDOUT_FILENO, filename, strlen(filename));
                tail(argv[i]);
            }
        }
    }
    else if(argc == 2)
    {
        tail(argv[1]);
    }

    return 0;
}