#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

#define STRBUF_SIZE     200
#define DEFAULT_FILE    "input.txt"
#define ISDIGIT(X)      (X >= '0' && X <= '9')

// Parses a found number.
// The provided location can be any digit of the
// number; this function will automatically
// seek the first digit before processing.
// Erases numbers as they are processed.
uint16_t parse_num_at(char *str, uint8_t idx)
{

    // Check input
    if (str[idx] < '0' || str[idx] > '9') return 0;

    // Find first digit of number
    while (ISDIGIT(str[idx]) && idx) idx--;
    if (!ISDIGIT(str[idx])) idx++;

    uint16_t num = 0;

    // Add up all digits
    while (ISDIGIT(str[idx]))
    {
        num = (num * 10) + (str[idx] - '0');
        // Erase the number to make sure we don't count it twice
        str[idx] = '.';
        idx++;
    }

    return num;
}

// Returns the sum of all numbers around a symbol,
// including diagonals.
uint16_t search_numbers_around( uint8_t idx,
                                char *above,
                                char *current,
                                char *below)
{
    uint16_t sum = 0;
    if (idx) sum += parse_num_at(above, idx - 1);
    sum += parse_num_at(above, idx);
    sum += parse_num_at(above, idx + 1);

    sum += parse_num_at(current, idx + 1);
    sum += parse_num_at(current, idx - 1);

    if (idx) sum += parse_num_at(below, idx - 1);
    sum += parse_num_at(below, idx);
    sum += parse_num_at(below, idx + 1);

    return sum;
}

// Search through a line of *current for symbols.
// returns the sum for that line (erases numbers as
// they are processed.)
uint16_t parse_line(char *above, char *current, char *below)
{
    uint16_t sum = 0;
    uint8_t idx;
    char c;

    for (idx = 0; current[idx] != 0; idx++)
    {
        c = current[idx];
        if (!ISDIGIT(c) && c != '.' && c != '\n')
        {
            // We've found a symbol,
            // add up all numbers around it
            sum += search_numbers_around(idx, above, current, below);
        }
    }
    
    return sum;
}

int main(int argc, char **argv)
{
    // Get filename as an argument, defaults to "input.txt"
    char *path = (argc > 1) ? argv[1] : DEFAULT_FILE;

    if (!path)
    {
        printf("Requires input file.\n");
        return 1;
    }

    FILE *file = fopen(path, "r");

    if (!file)
    {
        printf("Could not find file.");
        return 1;
    }

    char *above =   malloc(sizeof(char) * STRBUF_SIZE);
    char *current = malloc(sizeof(char) * STRBUF_SIZE);
    char *below =   malloc(sizeof(char) * STRBUF_SIZE);

    memset(above, '.', STRBUF_SIZE);
    fgets(current, STRBUF_SIZE, file);

    uint32_t sum = 0;

    while (fgets(below, 200, file))
    {
        sum += parse_line(above, current, below);

        free(above);
        above = current;
        current = below;
        below = malloc(sizeof(char) * STRBUF_SIZE);
        memset(below, '.', STRBUF_SIZE);
    }

    // Process the last line of the file
    sum += parse_line(above, current, below);

    printf("Sum: %d\n", sum);

    return 0;
}