#include "command.h"
#include "lslib.h"

#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static struct {
    bool lines;
    int count;
    bool print_headers;
    bool dont_print_headers;
    bool print_as_grow;
    int grow_wait;
} flags;

static size_t tail_file_lines(FILE* file, unsigned int count, size_t skip) {

    char** ring;
    int* ring_len;
    int index, read;
    unsigned int size, i;
    size_t len;
    char* line;

    ring = xalloc(sizeof(char*) * count);
    memset(ring, 0, sizeof(char*) * count);

    ring_len = xalloc(sizeof(int) * count);
    
    index = 0;
    size = 0;

    fseek(file, skip, SEEK_SET);
    
    len = skip;
    line = NULL;
    
    while ((read = getline(&line, &len, file)) != -1) {

        if (ring[index] != NULL) free(ring[index]);
        ring[index] = line;
        ring_len[index] = read;

        index++;
        index %= count;
        if (size < count) size++;

        line = NULL;
    }

    index += count - size;
    index %= count;
   
    for (i = 0; i < size; i++) {
        fwrite(ring[index], ring_len[index], 1, stdout);
        free(ring[index]);
        index += 1;
        index %= count;
    }

    free(line);
    fclose(file);
    free(ring);
    free(ring_len);

    return len;
}

static size_t tail_file_chars(FILE* file, unsigned int count, size_t skip) {

    char* ring;
    int index;
    unsigned int size, i;
    int read, c;

    ring = xalloc(sizeof(char) * count);
    memset(ring, 0, count);

    index = 0;
    size = 0;

    fseek(file, skip, SEEK_SET);
    read = skip;
    
    while((c = getc(file)) != EOF) {
        ring[index] = c;
        index++;
        read++;
        index %= count;
        if (size < count) size++;
    }

    index += count - size;
    index %= count;

    for (i = 0; i < size; i++) {
        putchar(ring[index]);
        index += 1;
        index %= count;
    }

    fclose(file);

    return read;
}

static void help(void) {
    printf("Usage: tail [OPTIONS] [FILE]...\n\n");
    printf("Print last 10 lines of FILEs (or stdin) to.\n");
    printf("With more than one FILE, precede each with a filename header.\n\n");
    printf("\t-c [+]N[bkm]\tPrint last N bytes\n");
	printf("\t-n N[bkm]\tPrint last N lines\n");
	printf("\t\t\t(b:*512 k:*1024 m:*1024^2)\n");
	printf("\t-q\t\tNever print headers\n");
	printf("\t-v\t\tAlways print headers\n");
	printf("\t-f\t\tPrint data as file grows\n");
	printf("\t-s SECONDS\tWait SECONDS between reads with -f\n");
    exit(EXIT_SUCCESS);
}

static void print_header(char* path, bool many) {
    if (flags.dont_print_headers) return;
    if (!many && !flags.print_headers) return;
    if (streql("-", path)) {
        printf("\n==> standard input <==\n");
    } else {
        printf("\n=>> %s <==\n", path);
    }
}

static void tail_file(char* path, bool many) {

    FILE* file;
    size_t skip;

    file = get_file(path, "r");
    print_header(path, many);
    
    skip = 0;
    while (true) {
        if (flags.lines) {
            skip = tail_file_lines(file, flags.count, skip);
        } else {
            skip = tail_file_chars(file, flags.count, skip);
        }
        if (!flags.print_as_grow) break;
        sleep(flags.grow_wait);
        get_file(path, "r");
    };
}

static int short_arg(char c, char* next) {
    switch (c) {
        case 'c': {
            long int bkm;

            flags.lines = false;
            
            check_arg(next);
            bkm = get_blkm(next);
            
            if (bkm < 1) {
                error("bkm cannot be less than 1");
            }
            
            flags.count = bkm;
            return ARG_USED;
        }
        case 'n': {
            long int bkm;

            flags.lines = true;
            
            check_arg(next);
            bkm = get_blkm(next);
            
            if (bkm < 1) {
                error("bkm cannot be less than 1");
            }
            
            flags.count = bkm;
            return ARG_USED;
        }
        case 'q':
            flags.dont_print_headers = true;
            break;
        case 'v':
            flags.print_headers = true;
            break;
        case 'f':
            flags.print_as_grow = true;
            break;
        case 's': {
            long int sec;

            check_arg(next);
            sec = get_number(next);
            
            if (sec < 1) {
                error("wait seconds cannot be less than 1");
            }
            
            flags.grow_wait = sec;
            return ARG_USED;
        }
        default: 
            return ARG_INVALID;
    }
    return ARG_UNUSED;
}

COMMAND(tail_main) {

    int start, count, i;

    flags.count = 10;
    flags.dont_print_headers = false;
    flags.print_headers = false;
    flags.lines = true;
    flags.print_as_grow = false;
    flags.grow_wait = 10;

    start = parse_args(argc, argv, help, short_arg, NULL);

    count = argc - start;

    if (count < 1) {
        tail_file_lines(stdin, 10, 0);
        return EXIT_SUCCESS;
    }

    if (count == 1) {
        tail_file(argv[start], false);
        return EXIT_SUCCESS;
    }

    for (i = 0; i < count; i++) {
        tail_file(argv[start + i], true);
    }

    return EXIT_SUCCESS;
}