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

// How much memory to allocate for each line
#define MAX_LINE_LEN 200

#define DEFAULT_FILE "input.txt"

// Returns 0 if a string is not a number (e.g. 'two')
// Otherwise, returns the equivilant ascii character digit.
// Only works for single digits.
// Only accepts lower case.
char parse_num(char *str)
{
    const char *num_strings[10] =  { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };

    // The lengths of the strings above, 
    const uint8_t num_string_lens[10] =  { 4, 3, 3, 5, 4, 4, 3, 5, 5, 4 };

    bool possible_nums[10] = { [0 ... 9] = true };
    uint8_t num_idx = 0;
    uint8_t char_incriment = 0;
    char current;
    bool result_still_possible = false;

    for (char_incriment = 0; char_incriment < 6; char_incriment++)
    {
        // Grab out next character in the string
        current = *(str + char_incriment);

        for (num_idx = 0; num_idx < 10; num_idx++)
        {
            if (!possible_nums[num_idx]) continue;

            // If we have passed the end of our number string and every character has matched,
            // then we return our valid character.
            if (char_incriment == num_string_lens[num_idx] && possible_nums[num_idx]) return (num_idx + '0');

            // If the character is not the letter it should be, disqualify this number.
            // e.g. if num_idx == 1 and char_incriment == 2, current should equal 'e'
            // because 'e' is the 3rd number in the word 'one.'
            if (current != num_strings[num_idx][char_incriment]) possible_nums[num_idx] = false;
            else result_still_possible = true;
        }
        if (!result_still_possible) return 0;
    }

    return 0;
}

// Returns a string of the next line.
// Remember to free() this after you're finished.
// Limited by MAX_LINE_LEN (I'm lazy.)
char *next_line(FILE *file)
{
    char *strbuf = malloc(sizeof(char) * MAX_LINE_LEN);
    uint8_t idx = 0;
    char current = 0;

    while (current != '\n' && current != EOF)
    {
        current = fgetc(file);
        strbuf[idx] = current;
        idx++;
    }

    return strbuf;
}

int main(int argc, char **argv) {

    // Get filename as an argument
    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;
    }

    int8_t firstdigit = -1;
    int8_t lastdigit = -1;
    int8_t parsed_num = -1;
    uint32_t sum = 0;
    char current = 0;
    char *strbuf = next_line(file);
    uint8_t strbuf_idx = 0;

    while (current != EOF)
    {
        parsed_num = parse_num(strbuf + strbuf_idx);
        current = strbuf[strbuf_idx++];

        if (current == '\n')
        {
            if (lastdigit == -1) lastdigit = firstdigit;
            sum += (firstdigit * 10) + lastdigit;
            firstdigit = -1;
            lastdigit = -1;
            strbuf_idx = 0;
            free(strbuf);
            strbuf = next_line(file);
            continue;
        }

        if (parsed_num != 0) current = parsed_num;

        if (current < '0' || current > '9') continue;

        if (firstdigit == -1)
        {
            firstdigit = current - '0';
        }
        else
        {
            lastdigit = current - '0';
        }
    }

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

    return 0;
}