#include "../command.h"

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

static size_t tail_file_lines(FILE* file, unsigned int count, size_t skip) {
    char* ring[count];
    memset(ring, 0, sizeof(char*) * count);

    int ring_len[count];
    
    int index = 0;
    unsigned int size = 0;

    int read;
    fseek(file, skip, SEEK_SET);
    size_t len = skip;
    char* 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 (unsigned int i = 0; i < size; i++) {
        fwrite(ring[index], ring_len[index], 1, stdout);
        free(ring[index]);
        index += 1;
        index %= count;
    }

    free(line);
    fclose(file);

    return len;
}

static size_t tail_file_chars(FILE* file, unsigned int count, size_t skip) {
    char ring[count];
    memset(ring, 0, count);

    int index = 0;
    unsigned int size = 0;

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

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

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

    fclose(file);

    return read;
}

static void help() {
    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 char* next_arg(int argc, char** argv, int index) {
    if (index >= argc) {
        error("error: expected another argument after option");
    }
    return argv[index];
}

static void print_header(char* path, struct Flags* flags, 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, struct Flags* flags, bool many) {
    FILE* file = get_file(path, "r");
    print_header(path, flags, many);
    
    size_t 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");
    };
}

COMMAND(tail) {

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

    int start = 0;
    for (int i = 0; i < argc; i++) { 
        if (!prefix("-", argv[i])) break;
        if (streql(argv[0], "--help")) help();
        start++;
        int i_s = i;
        for (size_t j = 1; j < strlen(argv[i_s]); j++) {
            char c = argv[i_s][j];
            switch(c) {
                case 'c': {
                    start++;
                    flags.lines = false;
                    char* arg = next_arg(argc, argv, ++i);
                    long int bkm = get_blkm(arg);
                    if (bkm < 1) {
                        error("error: bkm cannot be less than 1");
                    }
                    flags.count = bkm;
                    break;
                }
                case 'n': {
                    start++;
                    flags.lines = true;
                    char* arg = next_arg(argc, argv, ++i);
                    long int bkm = get_blkm(arg);
                    if (bkm < 1) {
                        error("error: bkm cannot be less than 1");
                    }
                    flags.count = bkm;
                    break;
                }
                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': {
                    start++;
                    char* arg = next_arg(argc, argv, ++i);
                    long int sec = get_number(arg);
                    if (sec < 1) {
                        error("error: wait seconds cannot be less than 1");
                    }
                    flags.grow_wait = sec;
                    break;
                }
                default: {
                    error("error: unknown option -%c", c);
                }
            }
        }
    }

    int count = argc - start;

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

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

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

    return EXIT_SUCCESS;
}