#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/ctype.h>

#define MODULE_NAME "aoc2023d3p2"
MODULE_AUTHOR("logan2611");
MODULE_LICENSE("Dual MIT/GPL");
MODULE_DESCRIPTION("Advent of Code 2023 Day 3 Part 2 (The Linux Kernel Module)");
MODULE_VERSION("0.1");

const int length = 140; // Number of lines
//const int length = 10; // Number of lines
const int width = length + 1; // Width of lines (including newline, carriage return or null terminator)

// Parameter that specifies the input file
static char *path = "/tmp/input";
module_param(path, charp, S_IRUGO);
MODULE_PARM_DESC(path, "The path to the data input.");

static ssize_t read_input(struct file *file, loff_t pos, size_t n, char *buffer) {
    ssize_t bytes_read;

    bytes_read = kernel_read(file, buffer, n, &pos);
    if (bytes_read < 0) {
        pr_err("%s: Error reading file: %zd\n", MODULE_NAME, bytes_read);
    }

    return bytes_read;
}

static void make_num_string(char *input, char *output, int head, int tail) {
    memcpy(output, input + head, tail+1-head);
}

static int atoi(char *input) {
    int ret;
    int err = kstrtoint(input, 10, &ret);
    if (err < 0) {
        //pr_err("%s: Failed to convert string to number: \"%d\"\n", MODULE_NAME, err);
        return 0;
    }

    return ret;
}


static int find_head_number(char *input, int pos) {
    while(isdigit(input[pos]) && pos >= 0) {
        //pr_info("%s: Scanning head: %c (%d)\n", MODULE_NAME, input[pos], pos);
        pos--;
    }
    //pr_info("%s: Found head: %c (%d)\n", MODULE_NAME, input[pos], pos);
    return pos + 1;
}

static int find_tail_number(char *input, int head) {
    while(isdigit(input[head])) {
        //pr_info("%s: Scanning tail: %c (%d)\n", MODULE_NAME, input[head], head);
        head++;
    }
    //pr_info("%s: Found tail: %c (%d)\n", MODULE_NAME, input[head], head);
    return head - 1;
}

static int find_adjacent_numbers(char *top, char *middle, char *bottom, int offset) {
    int adjacent = 0;
    int prod = 1;

    int topskip = 0;
    int midskip = 0;
    int botskip = 0;

    for(int pos = offset-1; pos <= offset+1; pos++) {
        //pr_info("%s: Scanning position %d\n", MODULE_NAME, pos);
        if(isdigit(top[pos]) && pos > topskip) {
            int head = find_head_number(top, pos);
            int tail = find_tail_number(top, head);


            char numstr[8] = {0};
            make_num_string(top, numstr, head, tail);

            prod *= atoi(numstr);
            adjacent++;
            topskip = tail;
            pr_info("%s: Found adjacent number top: %d %d-%d v:%d\n", MODULE_NAME, pos, head, tail, atoi(numstr));
        }

        if(isdigit(middle[pos]) && pos > midskip) {
            int head = find_head_number(middle, pos);
            int tail = find_tail_number(middle, head);

            char numstr[8] = {0};
            make_num_string(middle, numstr, head, tail);

            prod *= atoi(numstr);
            adjacent++;
            midskip = tail;
            pr_info("%s: Found adjacent number mid: %d %d-%d v:%d\n", MODULE_NAME, pos, head, tail, atoi(numstr));
        }

        if(isdigit(bottom[pos]) && pos > botskip) {
            int head = find_head_number(bottom, pos);
            int tail = find_tail_number(bottom, head);

            char numstr[8] = {0};
            make_num_string(bottom, numstr, head, tail);

            prod *= atoi(numstr);
            adjacent++;
            botskip = tail;
            pr_info("%s: Found adjacent number bottom: %d %d-%d v:%d\n", MODULE_NAME, pos, head, tail, atoi(numstr));
        }
    }

    if(adjacent == 2) {
        return prod;
    } else {
        return 0;
    }
}


static int find_stars(char *top, char *middle, char *bottom) {
    int beginning = -1;
    int sum = 0;

    for(int i = 0; i < width; i++) {
        if(middle[i] == '*') {
            beginning = i;
            pr_info("%s: Found star: %d\n", MODULE_NAME, i);

            sum += find_adjacent_numbers(top, middle, bottom, beginning);
        }
    }
    return sum;
}



static int __init test_init(void) {
    struct file *f;

    pr_info("%s: Module loaded\n", MODULE_NAME);

    f = filp_open(path, O_RDONLY, 0);
    if(IS_ERR(f)) {
        pr_err("%s: Failed to open %s\n", MODULE_NAME, path);
        return PTR_ERR(f);
    }

    char buf[3][width+1];
    memset(buf, 0, sizeof(buf));

    read_input(f, 0, width, buf[2]);

    int sum = 0;

    for(int line = 1; line <= length; line++) {
        pr_info("%s: %s", MODULE_NAME, buf[2]);

        memcpy(buf[0], buf[1], sizeof(buf[0]));
        memcpy(buf[1], buf[2], sizeof(buf[1]));

        if(length - line > 0) {
            read_input(f, line*width, length, buf[2]);
        } else {
            memset(buf[2], 0, sizeof(buf[2]));
        }

        sum += find_stars(buf[0], buf[1], buf[2]);
    }

    filp_close(f, NULL);

    pr_info("%s: Answer: %d\n", MODULE_NAME, sum);
    return 0;
}

static void __exit test_exit(void) {
    pr_info("%s: Module unloaded\n", MODULE_NAME);
}

module_init(test_init);
module_exit(test_exit);