#include <stdlib.h>
#include <stdio.h>
#include <err.h>
#include <stdbool.h>
#include "input.h"

#define INPUT "input/03.txt"
#define INPUT_SIZE 12

unsigned long parse_line(char* binary_line, char expected_end) {
	char* endp = NULL;
	unsigned long result = strtoul(binary_line, &endp, 2);
	if(*endp != expected_end)
		err(1, "cannot parse line: %s\n", binary_line);
	return result;
}

unsigned long compute_gamma(struct input_str* input) {
	int oneCount[INPUT_SIZE];
	// TODO is that necessary ?
	for(int k = 0; k < INPUT_SIZE; k++) {
		oneCount[k] = 0;
	}

	for(size_t i = 0; i < input->line_count; i++) {
		char* line = input->lines[i];
		for(int j = 0; j < INPUT_SIZE; j++) {
			if(line[j] == '1')
				oneCount[j]++;
		}
	}

	// null terminated string	
	char binary[INPUT_SIZE + 1];
	for(int h = 0; h < INPUT_SIZE; h++) {
		binary[h] = oneCount[h] >= input->line_count / 2.0f ? '1' : '0';
	}
	binary[INPUT_SIZE] = '\0';
	unsigned long gamma = parse_line(binary, '\0');
	return gamma; 
}

unsigned long compute_epsilon(unsigned long gamma) {
	unsigned long epsilon = gamma ^ 0xFFF;
	return epsilon;
}

void part1(struct input_str* input) {
	unsigned long gamma = compute_gamma(input);
	unsigned long epsilon = compute_epsilon(gamma);
	printf("%ld\n", gamma * epsilon);
}

unsigned long search_criteria(struct input_str* input, unsigned long criteria) {
	unsigned long match;
	bool foundLine = false;
	unsigned long mask = 1 << (INPUT_SIZE - 1); // we start by checking only the first bit
	for(int linePos = 0; linePos < INPUT_SIZE; linePos++) {
		for(size_t is = 0; is < input->line_count; is++) {
			// TODO this parsing step could be outside of this loop
			unsigned long parsedLine = parse_line(input->lines[is], '\n');
			if((parsedLine & mask) == (criteria & mask)) {
				// this line fits the criteria
				if(foundLine) {
					// more than one line fits, we need to consider another bit
					foundLine = false;
					mask = (mask >> 1) | (1 << (INPUT_SIZE - 1));
					break;
				}
				else {
					// save it for later
					foundLine = true;
					match = parsedLine;
				}
			}
		}

		// checked all lines, if we found one matching then it is the one we want
		if(foundLine)
			break;
	}

	if(!foundLine)
		err(1, "cannot find line matching mask %ld\n", mask);

	return match;
}

void part2(struct input_str* input) {
	unsigned long o2_criteria = compute_gamma(input);
	unsigned long o2_rate = search_criteria(input, o2_criteria);
	unsigned long co2_criteria = compute_epsilon(o2_criteria);
	unsigned long co2_scrub = search_criteria(input, co2_criteria);
	printf("%ld\n", o2_rate * co2_scrub);
}

int main() {
	// read input data
	struct input_str input;
	input_str_read(&input, INPUT);

	// do stuff
	part1(&input);
	part2(&input);

	// cleanup & exit
	input_str_free(&input);
	return 0;
}