#include <ctype.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "args.h"
#include "libcharin.h"
#include "libstris.h"

#define DEFAULT_LENGTH 10
#define OFLOW(STR) (STR[strlen(STR)-1] != '\n')
#ifndef PAGE_SIZE
#	ifndef PAGESIZE
#		define PAGE_SIZE 1024
#	else
#		define PAGE_SIZE PAGESIZE
#	endif
#endif

/*
	TODO
	* fix limits.h stuff; if limits.h isn't on the system define
		reasonable limits in its place
	* don't use unsafe string functions
	* fix bugs
*/


void
tail(FILE *input, FILE *output, int length){
	bool loop = 1;
	char *lines[length];
	size_t ls[length];
	int i;
	int filelines = 0;
	size_t offset = 0;

	for(i = 0; i < length; i++){
		ls[i] = PAGE_SIZE;
		lines[i] = (char *)calloc(ls[i], sizeof(char));
	}

	i = 0;

	while(fgets(lines[i] + offset, ls[i], input)){
		if(OFLOW(lines[i])){
			offset += ls[i] - 1;
			ls[i] += PAGE_SIZE;
			/* should be more resilient */
			if(realloc(lines[i], ls[i]) == NULL){
				fprintf(stderr, "tail: Couldn't re-allocate memory (%d bytes)\n", ls[i] * sizeof(char));
				exit(1);
			}
			continue;
		}
		offset = 0;
		++filelines;
		i = (i + 1) % length;
	}

	for(i = filelines % length; loop || i != filelines % length; i = (i + 1) % length){
		if(loop && i == filelines % length)
			loop = 0;
		printf("%s", lines[i]);
	}

	/* glitch here when `tail`ing normal files */
	for(i = 0; i < length; i++){
		free(lines[i]);
	}
	return;
}


void
usage(char *name){
	fprintf(stderr, "Usage: %s [-ht] [-n integer] [file...]\n", name);
	exit(1);
}

int
main(int argc, char *argv[]){
	char **argsv = getargsv(argc, argv);
	char *flags = getflags(argc, argv);
	char mode[3] = "rb";
	char filepath[NAME_MAX+PATH_MAX];
	char *lengthstr;
	size_t fplen = NAME_MAX+PATH_MAX;
	FILE *input;
	FILE *output = stdout;
	int argsc = getargsc(argc, argv);
	int i;
	int length = DEFAULT_LENGTH;
	size_t s;

	if(charin(flags, 'h'))
		usage(argv[0]);

	if(charin(flags, 'n')){
		lengthstr = getflag(argc, argv, 'n');
		if(!strisint(lengthstr) || *lengthstr == '\0')
			usage(argv[0]);
		else
			length = atoi(lengthstr);
	}

	if(charin(flags, 't'))
		/* Explicitly open files as text rather than as binary.
		 * this changes "rb" to "r". Should have no effect on
		 * POSIX systems but may change CRLF to just LF with
		 * MS Windows. I don't know why anyone would need this
		 * but it's here for those that do. */
		mode[1] = '\0';

	if(argsc == 0)
		tail(stdin, output, length);
	else
		for(i = 1; i < argsc; ++i){
			if(i > 1)
				fprintf(output, "\n");

			if(!strcmp(argv[i], "-")){
				realpath(argv[i], filepath);
				input = fopen(argv[i], "r");
				if(input == NULL){
					fprintf(stderr, "%s: %s: Could not open file for reading\n", argv[0], filepath);
					exit(1);
				}
			}else{
				input = stdin;

				/* probably safe but could be vulnerable */
				/* just making filepath[] = "<stdin>" */
				s = strlen("<stdin>") + 1; /* minimum size for filepath */
				if(fplen >= s)
					strcpy(filepath, "<stdin>");
				else if(realloc(filepath, s) == NULL)
					fprintf(stderr, "%s: Failed to reallocate path string, using <stdin>\n", argv[0]);
			}

			fprintf(output, "==> %s <==\n", filepath);
			tail(input, output, length);
			if(input != stdin && fclose(input) != 0){
				fprintf(stderr, "%s: %s: Could not close file. Exiting...\n", argv[0], filepath);
				exit(1);
			}
		}

	return 0;
}